MedWorm.com provides a medical RSS filtering service. Over 6000 RSS medical sources are combined and output via different filters. This feed contains the latest items from the 'Chromosoma' source. Mon, 06 Feb 2012 09:32:03 +0100 http://www.medworm.com/index.php?rid=5654694&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Far8h71722k4l474g%2F Abstract  In many organisms, telomere DNA consists of simple sequence repeat tracts that are required to protect the chromosome end. In the yeast Saccharomyces cerevisiae, tract maintenance requires two checkpoint kinases of the ATM family, Tel1p and Mec1p. Previous work has shown that Tel1p is recruited to functional telomeres with shorter repeat tracts to promote telomerase-mediated repeat addition, but the role of Mec1p is unknown. We found that Mec1p telomere association was detected as cells senesced when telomere function was compromised by extreme shortening due to either the loss of telomerase or the double-strand break binding protein Ku. Exonuclease I effects the removal of the 5' telomeric strand, and eliminating it prevented both senescence and Mec1p telomere ass... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5654694 Mon, 30 Jan 2012 16:05:33 +0100 5654694 http://www.medworm.com/index.php?rid=5615645&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fw43n865742728225%2F Abstract  Inefficient and inaccurate repair of DNA damage is the principal cause of DNA mutations, chromosomal aberrations, and carcinogenesis. Numerous multiple-step DNA repair pathways exist whose deployment depends on the nature of the DNA lesion. Common to all eukaryotic DNA repair pathways is the need to unravel the compacted chromatin structure to facilitate access of the repair machinery to the DNA and restoration of the original chromatin state afterward. Accordingly, our cells utilize a plethora of coordinated mechanisms to locally open up the chromatin structure to reveal the underlying DNA sequence and to orchestrate the efficient and accurate repair of DNA lesions. Here we review changes to the chromatin structure that are intrinsic to the DNA damage response an... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5615645 Tue, 17 Jan 2012 07:09:59 +0100 5615645 http://www.medworm.com/index.php?rid=5556121&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F47l1n31r157t8084%2F Abstract  Telomeric DNA is present at the ends of eukaryotic chromosomes and is bound by telomere “capping” proteins, which are the (Cdc13–Stn1–Ten1) CST complex, Ku (Yku70–Yku80), and Rap1–Rif1–Rif2 in budding yeast. Inactivation of any of these complexes causes telomere “uncapping,” stimulating a DNA damage response (DDR) that frequently involves resection of telomeric DNA and stimulates cell cycle arrest. This is presumed to occur because telomeres resemble one half of a DNA double-strand break (DSB). In this review, we outline the DDR that occurs at DSBs and compare it to the DDR occurring at uncapped telomeres, in both budding yeast and metazoans. We give particular attention to the resection of DSBs in budding yeast by Mre11–Xrs2–Rad50 (MRX), Sgs... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5556121 Tue, 27 Dec 2011 16:50:13 +0100 5556121 http://www.medworm.com/index.php?rid=5556120&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fln301605156766u6%2F In this study, we show that the NTD domain of Chromator is required for proper localization to chromatin during interphase and that chromosome morphology defects observed in Chromator hypomorphic mutant backgrounds can be largely rescued by expression of this domain. Furthermore, we show that the ChD domain can interact with histone H1 and that this interaction is necessary for correct chromatin targeting. Nonetheless, that localization to chromatin still occurs in the absence of the ChD indicates that Chromator possesses a second mechanism for chromatin association and we provide evidence that this association is mediated by other sequences residing in the NTD. Taken together these findings suggest that Chromator's chromatin functions are largely governed by the NH2-terminal domain ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5556120 Tue, 27 Dec 2011 16:50:13 +0100 5556120 http://www.medworm.com/index.php?rid=5541606&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F5204131332281467%2F Abstract  It has been more than two decades since the original chromosome transmission fidelity (Ctf) screen of Saccharomyces cerevisiae was published. Since that time the spectrum of mutations known to cause Ctf and, more generally, chromosome instability (CIN) has expanded dramatically as a result of systematic screens across yeast mutant arrays. Here we describe a comprehensive summary of the original Ctf genetic screen and the cloning of the remaining complementation groups as efforts to expand our knowledge of the CIN gene repertoire and its mutability in a model eukaryote. At the time of the original screen, it was impossible to predict either the genes and processes that would be overrepresented in a pool of random mutants displaying a Ctf phenotype or what the entire... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5541606 Fri, 23 Dec 2011 16:54:52 +0100 5541606 http://www.medworm.com/index.php?rid=5519558&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk6957hv033575820%2F Abstract  Condensin complexes are essential for chromosome condensation and segregation in mitosis, while condensin dysfunction, among other pathways leading to chromosomal bridging in mitosis, may play a role in tumor genomic instability, including recently discovered chromotripsis. To characterize potential double-strand breaks specifically occurring in late anaphase, human chromosomes depleted of condensin were analyzed by γ-H2AX ChIP followed by high-throughput sequencing (ChIP-seq). In condensin-depleted cells, the nonrepeated parts of the genome were shown to contain distinct γ-H2AX enrichment zones 75% of which overlapped with known hemizygous deletions in cancers. Furthermore, some tandemly repeated DNA sequences, analyzed separately from the rest of the genome, s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5519558 Fri, 16 Dec 2011 16:55:16 +0100 5519558 http://www.medworm.com/index.php?rid=5472827&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fq3676l225615m357%2F Abstract  In many species, including wheat, crossing over is distal, and the proximal regions of chromosome arms contribute little to genetic maps. This was thought to be a consequence of terminal initiation of synapsis favoring distal crossing over. However, in an inverted rye chromosome arm, the pattern of metaphase I chiasmata was also inverted, suggesting that crossover frequencies were specific to chromosome segments. Here, wheat chromosome arms 2BS and 4AL, with essentially entire arms inverted in reverse tandem duplications (rtd), were studied in the MI of meiosis. Inversion–duplication placed the recombining segments in the middle of the arms. While the overall pairing frequencies of the inverted–duplicated arms were considerably reduced relative to normal arms,... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5472827 Thu, 01 Dec 2011 19:20:44 +0100 5472827 http://www.medworm.com/index.php?rid=5436140&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ff7l1j2646775h747%2F Abstract  The functional output of the genome is closely dependent on its organization within the nucleus, which ranges from the 10-nm chromatin fiber to the three-dimensional arrangement of this fiber in the nuclear space. Recent observations suggest that intra- and inter-chromosomal interactions between distant sequences underlie several aspects of transcription regulatory processes. These contacts can bring enhancers close to their target genes or prevent inappropriate interactions between regulatory sequences via insulators. In addition, intra- and inter-chromosomal interactions can bring co-activated or co-repressed genes to the same nuclear location. Recent technological advances have made it possible to map long-range cis and trans interactions at relatively high reso... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5436140 Fri, 18 Nov 2011 06:57:49 +0100 5436140 http://www.medworm.com/index.php?rid=5415598&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fh4373285v0257458%2F Abstract  Engineered minichromosomes offer an enormous opportunity to plant biotechnology as they have the potential to simultaneously transfer and stably express multiple genes. Following a top-down approach, we truncated endogenous chromosomes in barley (Hordeum vulgare) by Agrobacterium-mediated transfer of T-DNA constructs containing telomere sequences. Blocks of Arabidopsis-like telomeric repeats were inserted into a binary vector suitable for stable transformation. After transfer of these constructs into immature embryos of diploid and tetraploid barley, chromosome truncation by T-DNA-induced de novo formation of telomeres could be confirmed by fluorescent in situ hybridisation, primer extension telomere repeat amplification and DNA gel blot analysis in regenerated plants... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5415598 Sat, 12 Nov 2011 16:53:16 +0100 5415598 http://www.medworm.com/index.php?rid=5415599&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fq81t233200524377%2F Abstract  Although centromere protein B (CENP-B) is a highly conserved mammalian centromere protein, its function remains unknown. The presence of the protein is required to form artificial satellite DNA-based centromeres de novo, yet cenpb knockout mice are viable for multiple generations with no mitotic or meiotic defects, and the protein is not present at fully functional neocentromeres. Previous studies have suggested that the presence of functionally redundant paralogues of CENP-B may explain the lack of a phenotype in knockout mice, and the related Tigger-derived (TIGD) family of proteins has been implicated as the most likely candidate for such paralogues. Here, we describe an investigation of the centromere-binding properties of the three TIGD proteins most highly re... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5415599 Sat, 12 Nov 2011 16:53:15 +0100 5415599 http://www.medworm.com/index.php?rid=5415601&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fpvrl079372085x40%2F Content Type Journal ArticleCategory ErratumPages 1-2DOI 10.1007/s00412-011-0350-9Authors Subhash C. Lakhotia, Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221005 IndiaMoushami Mallik, Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221005 IndiaAnand K. Singh, Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221005 IndiaMukulika Ray, Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi, 221005 India Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=5415601 Wed, 09 Nov 2011 17:51:22 +0100 5415601 http://www.medworm.com/index.php?rid=5415600&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F0j7541h3118828t7%2F We report that Drosophila mof mutations in males and females, as well as mof knockdown in SL-2 cells, reduce post-irradiation survival. MOF depletion in SL-2 cells also results in an elevated frequency of metaphases with chromosomal aberrations, suggesting that MOF is involved in DDR. Mutation in Drosophila mof also results in a defective mitotic checkpoint, enhanced apoptosis, and a defective p53 response post-irradiation. In addition, IR exposure enhanced H4K16ac levels in Drosophila as it also does in mammals. These results are the first to demonstrate a requirement for MOF in the whole animal IR response and suggest that the role of MOF in the response to IR is conserved between Drosophila and mammals. Content Type Journal ArticleCategory Research ArticlePages 1-12DOI 10.1007/s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5415600 Wed, 09 Nov 2011 17:51:22 +0100 5415600 http://www.medworm.com/index.php?rid=5394481&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fc3671412l6041324%2F Abstract  Chromosomal aberrations are often associated with incomplete genome duplication, for instance at common fragile sites, or as a consequence of chemical alterations in the DNA template that block replication forks. Studies of the cancer-prone disease Fanconi anaemia (FA) have provided important insights into the resolution of replication problems. The repair of interstrand DNA crosslinks induced by chemotherapy drugs is coupled with DNA replication and controlled by FA proteins. We discuss here the recent discovery of new FA-associated proteins and the development of new tractable repair systems that have dramatically improved our understanding of crosslink repair. We focus also on how FA proteins protect against replication failure in the context of fragile sites a... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5394481 Sat, 05 Nov 2011 17:09:50 +0100 5394481 http://www.medworm.com/index.php?rid=5394482&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fh516204218321267%2F Abstract  The assembly of the transcription machinery is a key step in gene activation, but even basic details of this process remain unclear. Here we discuss the apparent discrepancy between the classic sequential assembly model based mostly on biochemistry and an emerging dynamic assembly model based mostly on fluorescence microscopy. The former model favors a stable transcription complex with subunits that cooperatively assemble in order, whereas the latter model favors an unstable complex with subunits that may assemble more randomly. To confront this apparent discrepancy, we review the merits and drawbacks of the different experimental approaches and list potential biasing factors that could be responsible for the different interpretations of assembly. We then discuss ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5394482 Wed, 02 Nov 2011 16:55:47 +0100 5394482 http://www.medworm.com/index.php?rid=5394483&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F10457814u2782451%2F Abstract  The base excision repair machinery protects DNA in cells from the damaging effects of oxidation, alkylation, and deamination; it is specialized to fix single-base damage in the form of small chemical modifications. Base modifications can be mutagenic and/or cytotoxic, depending on how they interfere with the template function of the DNA during replication and transcription. DNA glycosylases play a key role in the elimination of such DNA lesions; they recognize and excise damaged bases, thereby initiating a repair process that restores the regular DNA structure with high accuracy. All glycosylases share a common mode of action for damage recognition; they flip bases out of the DNA helix into a selective active site pocket, the architecture of which permits a sensit... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5394483 Wed, 02 Nov 2011 16:55:45 +0100 5394483 http://www.medworm.com/index.php?rid=5342116&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fe63617pw4l42k0g6%2F Abstract  The P elements of Drosophila melanogaster are well-studied transposons with both mobilizing and repressor functions. P elements can also variably silence the expression of certain other transgenes through a phenomenon known as P element-dependent silencing (PDS). To examine the role of the P repressor in PDS, we have induced, isolated, and characterized 22 point mutations in an archetype P element called P[SalI]89D. All mutations showed a loss in the ability to silence one or more assays for the PDS phenotype. These mutants also lost the ability to induce the suppression of variegation in P[hsp26-pt-T]39C-12, another P element-dependent phenotype. A subgroup of 11 mutations was further assayed for their ability to act as a P repressor and silence the P element promoter... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5342116 Tue, 18 Oct 2011 15:58:32 +0100 5342116 http://www.medworm.com/index.php?rid=5342117&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk028u5050tl37m14%2F Content Type Journal ArticleCategory Editorial NotePages 1-1DOI 10.1007/s00412-011-0345-6Authors Erich A. Nigg, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=5342117 Mon, 17 Oct 2011 15:49:05 +0100 5342117 http://www.medworm.com/index.php?rid=5329098&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj12151341v112453%2F Abstract  During meiosis, pairing of homologous chromosomes and their synapsis are essential prerequisites for normal male gametogenesis. Even limited autosomal asynapsis often leads to spermatogenic impairment, the mechanism of which is not fully understood. The present study was aimed at deliberately increasing the size of partial autosomal asynapsis and analysis of its impact on male meiosis. For this purpose, we studied the effect of t 12 haplotype encompassing four inversions on chromosome 17 on mouse autosomal translocation T(16;17)43H (abbreviated T43H). The T43H/T43H homozygotes were fully fertile in both sexes, while +/T43H heterozygous males, but not females, were sterile with meiotic arrest at late pachynema. Inclusion of the t 12 haplotype in trans to the... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5329098 Sat, 15 Oct 2011 15:46:28 +0100 5329098 http://www.medworm.com/index.php?rid=5280065&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fjn1552l524r653n2%2F Abstract  Sex chromosome dosage compensation in both eutherian and marsupial mammals is achieved by X chromosome inactivation (XCI)—transcriptional repression that silences one of the two X chromosomes in the somatic cells of females. We recently used RNA fluorescent in situ hybridization (FISH) to show, in individual nuclei, that marsupial X inactivation (in the absence of XIST) occurs on a gene-by-gene basis, and that escape from inactivation is stochastic and independent of gene location. In the absence of similar data from fibroblast cell lines of eutherian representatives, a meaningful comparison is lacking. We therefore used RNA-FISH to examine XCI in fibroblast cell lines obtained from three distantly related eutherian model species: African savannah elephant (Loxod... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5280065 Tue, 27 Sep 2011 05:52:37 +0100 5280065 http://www.medworm.com/index.php?rid=5231305&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F6u737x1008833603%2F Abstract  Eukaryotic cells employ a plethora of conserved proteins and mechanisms to ensure genome integrity. In metazoa, these mechanisms must operate in the context of organism development. This mini-review highlights two emerging features of DNA damage responses in Drosophila: a crosstalk between DNA damage responses and components of the spindle assembly checkpoint, and increasing evidence for the effect of DNA damage on the developmental program at multiple points during the Drosophila life cycle. Content Type Journal ArticleCategory Mini-ReviewPages 1-9DOI 10.1007/s00412-011-0342-9Authors Tin Tin Su, MCD Biology, University of Colorado, Boulder, CO 80309-0347, USA Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=5231305 Fri, 16 Sep 2011 16:43:01 +0100 5231305 http://www.medworm.com/index.php?rid=5231306&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj44u629407516186%2F Abstract  The hs-GAL4 t -driven expression of the hsrω-RNAi transgene or EP93D allele of the noncoding hsrω resulted in global down- or upregulation, respectively, of the large hsrω-n transcripts following heat shock. Subsequent to temperature shock, hsrω-null or those expressing hsrω-RNAi or the EP93D allele displayed delayed lethality of most embryos, first or third instar larvae. Three-day-old hsrω-null flies mostly died immediately or within a day after heat shock. Heat-shock-induced RNAi or EP expression in flies caused only a marginal lethality but severely affected oogenesis. EP allele or hsrω-RNAi expression after heat shock did not affect heat shock puffs and Hsp70 synthesis. Both down- and upregulation of hsrω-n transcripts suppressed reappearance of the h... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5231306 Mon, 12 Sep 2011 15:53:01 +0100 5231306 http://www.medworm.com/index.php?rid=5216624&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj3476177853x1124%2F Abstract  In microsporocytes of the European larch, we demonstrated the presence of several mRNAs in spherical nuclear bodies. In the nuclei of microsporocytes, we observed up to 12 bodies, ranging from 0.5 to 6 μm in diameter, during the prophase of the first meiotic division. Our previous studies revealed the presence of polyadenylated RNA (poly(A) RNA) in these bodies, but did not confirm the presence of nascent transcripts or splicing factors of the SR family. The lack of these molecules precludes the bodies from being the sites of synthesis and early maturation of primary transcripts (Kołowerzo et al., Protoplasma 236:13–19, 2009). However, the bodies serve as sites for the accumulation of splicing machinery, including the Sm proteins and small nuclear RNAs. C... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5216624 Fri, 09 Sep 2011 16:46:44 +0100 5216624 http://www.medworm.com/index.php?rid=5136755&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F322134436l6u4734%2F Abstract  The kinetochore is a complex multiprotein structure located at centromeres and required for the proper segregation of chromosomes during mitosis and meiosis. An important role in kinetochore assembly and function plays the centromeric histone H3 variant (CENH3). Cell cycle stage of CENH3 deposition to centromeres varies between different organisms. We confirmed by in vivo studies that deposition of Arabidopsis CENH3 takes place at centromeres during G2 and demonstrated that additionally a low turnover of CENH3 occurs along the cell cycle, apparently for replacement of damaged protein. Furthermore, enhanced yellow fluorescent protein (EYFP)-CENH3 of photobleached chromocenters is not replaced by EYFP-CENH3 molecules from unbleached centromeres of the same nucleus, i... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5136755 Sat, 13 Aug 2011 06:05:27 +0100 5136755 http://www.medworm.com/index.php?rid=5123655&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fw61x26514k487811%2F Abstract  Fluorescent chromatin tagging by the lacO operator/lac repressor system in Arabidopsis thaliana is useful to trace distinct chromatin domains in living cells. Nevertheless, the tandem repeats of the tagging system may alter the spatial organisation of chromatin within nuclei by increasing homologous pairing as well as association with heterochromatin. Efficient homologous pairing occurs if lacO repeat arrays of ∼10 kb are present at two loci, either on the same chromosome or on different chromosomes. DNA hypomethylation of lacO repeats results in reduced homologous pairing. Because, in plants, DNA methylation can serve as a signal for H3-lysine9-dimethylation (H3K9me2), and subsequently for non-CG-context DNA methylation, SET-domain histone methyltransferase ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5123655 Wed, 10 Aug 2011 15:44:20 +0100 5123655 http://www.medworm.com/index.php?rid=5123657&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F3r46518846775532%2F In this study, we present molecular cytogenetic and CENP-A chromatin immunoprecipitation (ChIP) on CHIP analyses of two neocentromeres that have formed in chromosome band 8q21 each with a unique DNA and CENP-A chromatin configuration. The first neocentromere was found on a neodicentric chromosome 8 with an inactivated endogenous centromere, where the centromeric activity and CENP-A domain were repositioned to band 8q21 on a large tandemly repeated DNA. This is the first example of a neocentromere forming on repetitive DNA, as all other mapped neocentromeres have formed on single copy DNA. Quantitative fluorescent in situ hybridization (FISH) analysis showed a 60% reduction in the alpha satellite array size at the inactive centromere compared to the active centromere on the normal chr... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5123657 Mon, 08 Aug 2011 19:51:36 +0100 5123657 http://www.medworm.com/index.php?rid=5123656&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fb154tq6364851535%2F Abstract  Recombination between homologous chromosomes is crucial to ensure their proper segregation during meiosis. This is achieved by regulating the choice of recombination template. In mitotic cells, double-strand break repair with the sister chromatid appears to be preferred, whereas interhomolog recombination is favoured during meiosis. However, in the last year, several studies in yeast have shown the importance of the meiotic recombination between sister chromatids. Although this thinking seems to be new, evidences for sister chromatid exchange during meiosis were obtained more than 50 years ago in non-model organisms. In this mini-review, we comment briefly on the most recent advances in this hot topic and also describe observations which suggest the existence... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5123656 Mon, 08 Aug 2011 19:51:36 +0100 5123656 http://www.medworm.com/index.php?rid=5075061&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fl257276648x46900%2F Abstract  The male hypermethylated (MHM) region of the chicken Z chromosome encodes a non-coding RNA that is expressed only in females. The MHM sequence is found only in galliform birds, and Z genes near this region show an unusual degree of dosage compensation between males and females despite the overall low level of dosage compensation in Z chromosome gene expression in birds. Here we report that the MHM locus shows a dramatic sex difference in the configuration of chromatin, open in females and condensed in males, based on DNA fluorescent in situ hybridization of an MHM probe in interphase nuclei. The demethylating agent 5-aza-cytidine causes an asymmetric effect on the two Z chromosomes of males, altering the chromatin configuration, MHM RNA expression, and H4K16Ac mod... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5075061 Tue, 26 Jul 2011 15:50:06 +0100 5075061 http://www.medworm.com/index.php?rid=5067577&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk1ww5g47324j3033%2F Abstract  Efficient spindle assembly involves the generation of spatial cues around chromosomes that locally stabilize microtubule (MT) plus-ends. In addition to the small GTPase Ran, there is evidence that Aurora B kinase might also generate a spatial cue around chromosomes but direct proof for this is still lacking. Here, we find that the Aurora B substrate MCAK localizes to MT plus-ends throughout the mitotic spindle, but its accumulation is strongly reduced on MT plus-ends near chromatin, suggesting that a signal emanating from chromosomes negatively regulates MCAK plus-end binding. Indeed, we show that Aurora B is the kinase responsible for producing this chromosome-derived signal. These results are the first to visualize spatially restricted Aurora B kinase activity a... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5067577 Sat, 23 Jul 2011 15:46:17 +0100 5067577 http://www.medworm.com/index.php?rid=5067578&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy524247300427187%2F Abstract  The dynamics of genome modification that occurred from the initial hybridization event to the stabilization of allopolyploid species remains largely unexplored. Here, we studied inheritance and expression of rDNA loci in the initial generations of Brassica napus allotetraploids (2n = 38, AACC) resynthesized from Brassica oleracea (2n = 18, CC) and B. rapa (2n = 20, AA) and compared the patterns to natural forms. Starting already from F1 generation, there was a strong uniparental silencing of B. oleracea genes. The epigenetic reprogramming was accompanied with immediate condensation of C-genome nucleolar organizer region (NOR) and progressive transgeneration hypermethylation of polymerase I promoters, mainly at CG sites. No such changes were observed in ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5067578 Fri, 22 Jul 2011 17:05:12 +0100 5067578 http://www.medworm.com/index.php?rid=5034567&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F4188q57153443056%2F Abstract  Equal distribution of DNA in mitosis requires the assembly of a large proteinaceous ensemble onto the centromeric DNA, called the kinetochore. With few exceptions, kinetochore specification is independent of the DNA sequence and is determined epigenetically by deposition at the centromeric chromatin of special nucleosomes containing an H3-related histone, CENP-A. Onto centromeric CENP-A chromatin is assembled the so-called constitutive centromere-associated network (CCAN) of 16 proteins distributed in several functional groups as follows: CENP-C, CENP-H/CENP-I/CENP-K/, CENP-L/CENP-M/CENP-N, CENP-O/CENP-P/CENP-Q/CENP-R/CENP-U(50), CENP-T/CENP-W, and CENP-S/CENP-X. One role of the CCAN is to recruit outer kinetochore components further, such as KNL1, the Mis12 compl... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5034567 Wed, 13 Jul 2011 06:11:45 +0100 5034567 http://www.medworm.com/index.php?rid=5015989&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fg0570u2613112611%2F Abstract  Homologous chromosomes exchange genetic information through recombination during meiotic synapsis, a process that increases genetic diversity and is fundamental to sexual reproduction. Meiotic studies in mammalian species are scarce and mainly focused on human and mouse. Here, the meiotic recombination events were determined in three species of Platyrrhini monkeys (Cebus libidinosus, Cebus nigritus and Alouatta caraya) by analysing the distribution of MLH1 foci at the stage of pachytene. Moreover, the combination of immunofluorescence and fluorescent in situ hybridisation has enabled us to construct recombination maps of primate chromosomes that are homologous to human chromosomes 13 and 21. Our results show that (a) the overall number of MLH1 foci varies among all ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=5015989 Thu, 07 Jul 2011 05:43:40 +0100 5015989 http://www.medworm.com/index.php?rid=4996758&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fe0547622531k47q6%2F Abstract  The divergence of lineages leading to extant squamate reptiles (lizards, snakes, and amphisbaenians) and birds occurred about 275 million years ago. Birds, unlike squamates, have karyotypes that are typified by the presence of a number of very small chromosomes. Hence, a number of chromosome rearrangements might be expected between bird and squamate genomes. We used chromosome-specific DNA from flow-sorted chicken (Gallus gallus) Z sex chromosomes as a probe in cross-species hybridization to metaphase spreads of 28 species from 17 families representing most main squamate lineages and single species of crocodiles and turtles. In all but one case, the Z chromosome was conserved intact despite very ancient divergence of sauropsid lineages. Furthermore, the probe paint... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4996758 Fri, 01 Jul 2011 17:43:16 +0100 4996758 http://www.medworm.com/index.php?rid=4966378&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fl4n21u741x42410l%2F Abstract  The nucleolus is the subnuclear organelle responsible for ribosome subunit biogenesis and can also act as a stress sensor. It forms around clusters of ribosomal DNA (rDNA) and is mainly organised in three subcompartments, i.e. fibrillar centre, dense fibrillar component and granular component. Here, we describe the localisation of 21 protein factors to an intranucleolar region different to these main subcompartments, called the intranucleolar body (INB). These factors include proteins involved in DNA maintenance, protein turnover, RNA metabolism, chromatin organisation and the post-translational modifiers SUMO1 and SUMO2/3. Increase in the size and number of INBs is promoted by specific types of DNA damage and depends on the functional integrity of the nucleolus. ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4966378 Wed, 22 Jun 2011 15:59:12 +0100 4966378 http://www.medworm.com/index.php?rid=4966379&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F12m11478q2u68435%2F We examined whether changes in gene expression due to LPS activation imply that genes have repositioned in the nuclear space. We first performed a transcriptomic analysis to identify the differentially expressed genes and then analysed the networks involved during lypopolysaccharide/interferon gamma activation in monocyte-derived macrophages. This allowed us to select four up-regulated (IL1β, IL8, CXCL10 and TNFα) and four down-regulated (VIM, LGALS3, TUBA3 and IGF2) genes. Their expression statuses were verified by quantitative real-time RT-PCR before studying their behaviour in the nuclear space during macrophage activation by means of 3D fluorescence in situ hybridization. No global correlation was found between gene activity and radial positioning. Only TNFα belonging to the h... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4966379 Wed, 22 Jun 2011 06:08:01 +0100 4966379 http://www.medworm.com/index.php?rid=4930489&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F6q8535136t357257%2F Abstract  Chromosome painting is one of the most powerful and spectacular tools of modern molecular cytogenetics, enabling complex analyses of nuclear genome structure and evolution. For many years, this technique was restricted to the study of mammalian chromosomes, as it failed to work in plant genomes due mainly to the presence of large amounts of repetitive DNA common to all the chromosomes of the complement. The availability of ordered, chromosome-specific BAC clones of Arabidopsis thaliana containing relatively little repetitive genomic DNA enabled the first chromosome painting in dicotyledonous plants. Here, we show for the first time chromosome painting in three different cytotypes of a monocotyledonous plant—the model grass, Brachypodium distachyon. Possible direct... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4930489 Sat, 11 Jun 2011 06:05:58 +0100 4930489 http://www.medworm.com/index.php?rid=4851679&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fp865200333xk0755%2F Content Type Journal ArticlePages 1-2DOI 10.1007/s00412-011-0323-zAuthors Erin K. Schwartz, Department of Microbiology, University of California–Davis, Davis, CA 95616–8665, USAWolf-Dietrich Heyer, Department of Microbiology, University of California–Davis, Davis, CA 95616–8665, USA Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=4851679 Thu, 19 May 2011 16:33:32 +0100 4851679 http://www.medworm.com/index.php?rid=4851680&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy01473t88235r463%2F Abstract  Sugar beet (Beta vulgaris) chromosomes consist of large heterochromatic blocks in pericentromeric, centromeric, and intercalary regions comprised of two different highly abundant DNA satellite families. To investigate DNA methylation at single base resolution at heterochromatic regions, we applied a method for strand-specific bisulfite sequencing of more than 1,000 satellite monomers followed by statistical analyses. As a result, we uncovered diversity in the distribution of different methylation patterns in both satellite families. Heavily methylated CG and CHG (H=A, T, or C) sites occur more frequently in intercalary heterochromatin, while CHH sites, with the exception of CAA, are only sparsely methylated, in both intercalary and pericentromeric/centromeric heter... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4851680 Wed, 18 May 2011 18:19:09 +0100 4851680 http://www.medworm.com/index.php?rid=4838143&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F836832x032076647%2F Abstract  Virtually all processes of the genome biology affect or are affected by the torsional state of DNA. Torsional energy associated with an altered twist facilitates or hinders the melting of the double helix, its molecular interactions, and its spatial folding in the form of supercoils. Yet, understanding how the torsional state of DNA is modulated remains a challenging task due to the multiplicity of cellular factors involved in the generation, transmission, and dissipation of DNA twisting forces. Here, an overview of the implication of DNA topoisomerases, DNA revolving motors, and other DNA interactions that determine local levels of torsional stress in bacterial and eukaryotic chromosomes is provided. Particular emphasis is made on the experimental approaches bein... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4838143 Thu, 12 May 2011 16:44:41 +0100 4838143 http://www.medworm.com/index.php?rid=4818632&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fb7312737654045w2%2F Abstract  The Y loops of Drosophila spermatocytes are formed by the expression of huge individual transcription units on the Y chromosome and their large size provides a unique system for the investigation of the organisation of transcription in intact nuclei. By labelling ribonucleo-protein (RNP) components, the loop chromatin and nascent transcripts in Y loop C, we reveal a highly structured organisation of RNP domains associated with nascent transcripts. We distinguish two types of RNP domain, a proximal domain that runs alongside the chromatin of loop C and a distal RNP domain that wraps around the proximal domain and the loop chromatin. The proximal domain is marked by the Pasilla protein, and separate distal subdomains are marked by the S5 antigen and Boule. We discuss... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4818632 Tue, 10 May 2011 06:02:50 +0100 4818632 http://www.medworm.com/index.php?rid=4810925&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv667q34u6l820745%2F Abstract  Studies carried out in cultured cells have implicated modifiers of epigenetic reprogramming in the regulation of telomere length, reporting elongation in cells that were null for DNA methyltransferase DNA methyltransferase 1 (Dnmt1), both de novo DNA methyltransferases, Dnmt3a and Dnmt3b or various histone methyltransferases. To investigate this further, we assayed telomere length in whole embryos or adult tissue from mice carrying mutations in four different modifiers of epigenetic reprogramming: Dnmt1, DNA methyltransferase 3-like, structural maintenance of chromosomes hinge domain containing 1, and forkhead box O3a. Terminal restriction fragment analysis was used to compare telomere length in homozygous mutants, heterozygous mutants and wild-type littermates. Co... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4810925 Fri, 06 May 2011 16:20:40 +0100 4810925 http://www.medworm.com/index.php?rid=4787143&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F193t2877523x7255%2F Abstract   Sciara coprophila (Diptera, Nematocera) constitutes a classic model to analyze unusual chromosome behavior such as the somatic elimination of paternal X chromosomes, the elimination of the whole paternal, plus non-disjunction of the maternal X chromosome at male meiosis. The molecular organization of the heterochromatin in S. coprophila is mostly unknown except for the ribosomal DNA located in the X chromosome pericentromeric heterochromatin. The characterization of the centromeric regions, thus, is an essential and required step for the establishment of S. coprophila as a model system to study fundamental mechanisms of chromosome segregation. To accomplish such a study, heterochromatic sections of the X chromosome centromeric region from salivary glands polytene ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4787143 Mon, 02 May 2011 05:43:20 +0100 4787143 http://www.medworm.com/index.php?rid=4744511&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F95177gjqjl805p73%2F Abstract  Copy number variation (CNV) in terms of aneuploidies of both entire chromosomes and chromosomal segments is an important evolutionary driving force, but it is inevitably accompanied by potentially problematic variations in gene doses and genomic instability. Thus, a delicate balance must be maintained between mechanisms that compensate for variations in gene doses (and thus allow such genomic variability) and selection against destabilizing CNVs. In Drosophila, three known compensatory mechanisms have evolved: a general segmental aneuploidy-buffering system and two chromosome-specific systems. The two chromosome-specific systems are the male-specific lethal complex, which is important for dosage compensation of the male X chromosome, and Painting of fourth, which s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4744511 Wed, 20 Apr 2011 06:05:33 +0100 4744511 http://www.medworm.com/index.php?rid=4730825&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F25817341n87n6479%2F Abstract  The TTAGG repeat, the only determined telomerase-dependent sequence in the Insecta, is generally reputed to be the canonical telomeric motif within the class. By studying the distribution of telomeric DNAs in 30 coleopteran beetles using Southern hybridization, BAL 31 DNA end-degradation assay and fluorescence in situ hybridization, we showed that arrays built of a TCAGG repeat substitute for (TTAGG)n sequences in all tested species within the superfamily Tenebrionoidea. We also provided the experimental evidence that (TCAGG)n repeats represent the terminal sequences on all chromosomes of the model species Tribolium castaneum. (TCAGG)n repeats are therefore promoted as the first sequence-motif alternative to TTAGG-type chromosome ends in insects. Detection of speci... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4730825 Fri, 15 Apr 2011 15:50:09 +0100 4730825 http://www.medworm.com/index.php?rid=4730826&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fb2n062g6x1608400%2F Content Type Journal ArticlePages 1-1DOI 10.1007/s00412-011-0316-yAuthors Bennie B. L. G. Lemmens, Department of Toxicogenetics, Leids Universitair Medisch, Centrum Gebouw 2, Postzone S-4 Postbus 9600, Einthovenweg 20, 2333 ZC, Leiden, The NetherlandsMarcel Tijsterman, Department of Toxicogenetics, Leids Universitair Medisch, Centrum Gebouw 2, Postzone S-4 Postbus 9600, Einthovenweg 20, 2333 ZC, Leiden, The Netherlands Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=4730826 Tue, 12 Apr 2011 06:56:00 +0100 4730826 http://www.medworm.com/index.php?rid=4577603&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F855vu50737kk6063%2F In this study, up to four distinct CENH3 (BrCENH3) cDNAs were identified in individuals of each of three diploid species of Brassica. Comparison of the BrCENH3 cDNAs implied three related gene families: BrCENH3-A in Brassica rapa (AA), BrCENH3-B in B. nigra (BB), and BrCENH3-C in B. oleracea (CC). Each family encoded a histone fold domain and N-terminal histone tails that vary in length in all three families. The BrCENH3-B cDNAs have a deletion of two exons relative to BrCENH3-A and BrCENH3-C, consistent with the more ancient divergence of the BB genome. Chromatin immunoprecipitation and immunolabeling tests with anti-BrCENH3 antibodies indicated that both centromeric tandem repeats and the centromere-specific retrotransposons of Brassica are directly associated with BrCENH3 proteins. In... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4577603 Thu, 10 Mar 2011 17:12:39 +0100 4577603 http://www.medworm.com/index.php?rid=4564640&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Flk3j474wr113587v%2F Abstract   Drosophila males undergo meiosis without recombination or chiasmata but homologous chromosomes pair and disjoin regularly. The X–Y pair utilizes a specific repeated sequence within the heterochromatic ribosomal DNA blocks as a pairing site. No pairing sites have yet been identified for the autosomes. To search for such sites, we utilized probes targeting specific heterochromatic regions to assay heterochromatin pairing sequences and behavior in meiosis by fluorescence in situ hybridization (FISH). We found that the small fourth chromosome pairs at heterochromatic region 61 and associates with the X chromosome throughout prophase I. Homolog pairing of the fourth chromosome is disrupted when the homolog conjunction complex is perturbed by mutations in SNM or MNM... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4564640 Mon, 07 Mar 2011 17:02:34 +0100 4564640 http://www.medworm.com/index.php?rid=4539598&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fc747156k43474nm0%2F Abstract  Interstitial telomeric sequences (ITSs) in hamster cells are hot spots for spontaneous and induced chromosome aberrations (CAs). Most data on ITS instability to date have been obtained in DNA repair-proficient cells. The classical non-homologous end joining repair pathway (C-NHEJ), which is the principal double strand break (DSB) repair mechanism in mammalian cells, is thought to restore the morphologically correct chromosome structure. The production of CAs thus involves DNA-PKcs-independent repair pathways. In our current study, we investigated the participation of DNA-PKcs from the C-NHEJ pathway in the repair of spontaneous or radiation-induced DSBs in ITSs using wild-type and DNA-PKcs mutant Chinese hamster ovary cells. Our data demonstrate that DNA-PKcs stab... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4539598 Fri, 25 Feb 2011 17:05:05 +0100 4539598 http://www.medworm.com/index.php?rid=4511017&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fg8m32554hq7u2626%2F Abstract  CRAMPED (CRM), conserved from plants to animals, was previously characterized genetically as a repressive factor involved in the formation of facultative and constitutive heterochromatin (Polycomb silencing, position effect variegation). We show that crm is dynamically regulated during replication and identify the Histone gene cluster (His-C) as a major CRM target. Surprisingly, CRM is specifically required for the expression of the Histone H1 gene, like the promoter-bound transcription factor TRF2. Consistently with this, CRM genetically interacts and co-immunoprecipitates with TRF2. However, the Polycomb phenotypes observed in crm mutants are not observed in TRF2 hypomorphic mutants, suggesting that they correspond to independent roles of CRM. CRM is thus a highly ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4511017 Sat, 19 Feb 2011 06:55:26 +0100 4511017 http://www.medworm.com/index.php?rid=4500777&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fhm12601004v214w5%2F Abstract  Dioecious Silene latifolia evolved heteromorphic sex chromosomes within the last ten million years, making it a species of choice for studies of the early stages of sex chromosome evolution in plants. About a dozen genes have been isolated from its sex chromosomes and basic genetic and deletion maps exist for the X and Y chromosomes. However, discrepancies between Y chromosome maps led to the proposal that individual Y chromosomes may differ in gene order. Here, we use an alternative approach, with fluorescence in situ hybridization (FISH), to locate individual genes on S. latifolia sex chromosomes. We demonstrate that gene order on the Y chromosome differs between plants from two populations. We suggest that dynamic gene order may be a general property of Y chromo... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4500777 Thu, 17 Feb 2011 07:00:57 +0100 4500777 http://www.medworm.com/index.php?rid=4441544&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fn070j203506jj406%2F Abstract  Megakaryopoiesis is largely disturbed in myelodysplastic syndromes (MDS), and megakaryocytes (MKs) frequently show multinucleation. Here, we investigated dysplastic mono-, bi-, and multinuclear MKs (n = 169) of seven patients with MDS and one patient with myelodysplastic/myeloproliferative neoplasm by sequential multilocus FISH. Analysis of binuclear MKs with a combined DNA content of 4 N (n = 46) indicated a significantly even (symmetric) chromosome distribution between the two separate nuclei (p = 0.0223), which suggests bipolar spindle orientation and symmetric chromosome segregation during the first endomitotic cell cycle. In contrast, multinuclear MKs of higher ploidy (>4 N, n = 108) demonstrated a significantly uneven (asymmetric) c... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4441544 Tue, 01 Feb 2011 09:25:16 +0100 4441544 http://www.medworm.com/index.php?rid=4427948&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ff603w1216p73k77l%2F In this study, we demonstrate that in contrast to all eutherian species studied to date, partial synapsis of the heterologous sex chromosomes during pachytene stage in the horse is not associated with the formation of a typical macrochromatin domain at the XY body. While phosphorylated histone H2AX (γH2AX) and macroH2A1.2 are present as a diffuse signal over the entire macrochromatin domain in mouse pachytene spermatocytes, γH2AX, macroH2A1.2, and the cohesin subunit SMC3 are preferentially enriched at meiotic sex chromosome cores in equine spermatocytes. Moreover, although several histone modifications associated with this nuclear domain in the mouse such as H3K4me2 and ubH2A are conspicuously absent in the equine XY body, prominent RNA polymerase II foci persist at the sex chromo... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4427948 Thu, 27 Jan 2011 17:36:52 +0100 4427948 http://www.medworm.com/index.php?rid=4427947&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ff43811044627614k%2F We report the discovery of H3.5, a novel non-CenH3 histone H3 variant. H3.5 is encoded on human chromosome 12p11.21 and probably evolved in a common ancestor of all recent great apes (Hominidae) as a consequence of H3F3B gene duplication by retrotransposition. H3.5 mRNA is specifically expressed in seminiferous tubules of human testis. Interestingly, H3.5 has two exact copies of ARKST motifs adjacent to lysine-9 or lysine-27, and lysine-79 is replaced by asparagine. In the Hek293 cell line, ectopically expressed H3.5 is assembled into chromatin and targeted by PTM. H3.5 preferentially colocalizes with euchromatin, and it is associated with actively transcribed genes and can replace an essential function of RNAi-depleted H3.3 in cell growth. Content Type Journal ArticlePages 1-11... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4427947 Thu, 27 Jan 2011 17:36:52 +0100 4427947 http://www.medworm.com/index.php?rid=4341771&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy0h15j58u6873467%2F We describe a method for preparing chromatin assembled in extracts for atomic force microscopy (AFM) utilizing restriction enzyme digestion followed by transferring to a mica surface. Using this method, we find that buffer dilution of the chromatin assembly extract or incubation of chromatin in solutions of low ionic strength results in loosely compacted chromatin fibers that are prone to unraveling into naked DNA. We also describe a method for direct AFM imaging of chromatin which does not utilize restriction enzymes and reveals higher-order fibers of varying widths. Due to the capability of controlling chromatin assembly conditions, we believe these methods have broad potential for studying physiologically relevant chromatin structures. Content Type Journal ArticlePages 1-10DO... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4341771 Mon, 10 Jan 2011 16:10:00 +0100 4341771 http://www.medworm.com/index.php?rid=4341770&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F001r72r09k61836j%2F We describe a karyotypic polymorphism on the zebra finch Z chromosome. This polymorphism was discovered because of a difference in the position of the centromere and because it occurs at varying frequencies in domesticated colonies in the USA and Germany and among two zebra finch subspecies. Using DNA fluorescent in situ hybridization to map specific Z genes and measurements of DNA replication, we show that this polymorphism is the result of a large pericentric inversion involving the majority of the chromosome. We sequenced a likely breakpoint for the inversion and found many repetitive sequences. Around the breakpoint, there are numerous repetitive sequences and several copies of PAK3 (p21-activated kinase 3)-related sequences (PAK3Z) which showed testes-specific expression by RT-PC... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4341770 Mon, 10 Jan 2011 16:10:00 +0100 4341770 http://www.medworm.com/index.php?rid=4341772&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F750ul44128m03712%2F Abstract  Homologous recombination is required for maintaining genomic integrity by functioning in high-fidelity repair of DNA double-strand breaks and other complex lesions, replication fork support, and meiotic chromosome segregation. Joint DNA molecules are key intermediates in recombination and their differential processing determines whether the genetic outcome is a crossover or non-crossover event. The Holliday model of recombination highlights the resolution of four-way DNA joint molecules, termed Holliday junctions, and the bacterial Holliday junction resolvase RuvC set the paradigm for the mechanism of crossover formation. In eukaryotes, much effort has been invested in identifying the eukaryotic equivalent of bacterial RuvC, leading to the discovery of a number of... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4341772 Mon, 10 Jan 2011 16:09:59 +0100 4341772 http://www.medworm.com/index.php?rid=4301700&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F7v37232w77870808%2F Abstract  The temperate annual grass Brachypodium distachyon is a diploid species with a chromosome base number of 5. It is strikingly different from other Eurasian species of the genus, which are perennial and often polyploid, with the diploids typically having base numbers of 8 or 9. Previously, phylogenies indicated that B. distachyon split from the other species early in the evolution of the genus, while its genome sequence revealed that extensive synteny on a chromosomal scale had been maintained with rice, a tropical grass with a base number of 12. Here we show evidence that B. distachyon may have a homoploid origin, involving ancestral interspecific hybridisation, although it does not appear to be a component of any of the perennial Eurasian allopolyploids. Using a cy... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4301700 Wed, 29 Dec 2010 17:09:31 +0100 4301700 http://www.medworm.com/index.php?rid=4283999&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fn47n3ql3hx666644%2F Abstract  Double-strand breaks represent an extremely cytolethal form of DNA damage and thus pose a serious threat to the preservation of genetic and epigenetic information. Though it is well-known that double-strand breaks such as those generated by ionising radiation are among the principal causative factors behind mutations, chromosomal aberrations, genetic instability and carcinogenesis, significantly less is known about the epigenetic consequences of double-strand break formation and repair for carcinogenesis. Double-strand break repair is a highly coordinated process that requires the unravelling of the compacted chromatin structure to facilitate repair machinery access and then restoration of the original undamaged chromatin state. Recent experimental findings have p... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4283999 Mon, 20 Dec 2010 22:01:54 +0100 4283999 http://www.medworm.com/index.php?rid=4270700&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fc48153v8q617q4n5%2F Abstract  In bread wheat (Triticum aestivum L.), initial studies using deletion lines indicated that crossover (CO) events occur mainly in the telomeric regions of the chromosomes with a possible correlation with the presence of genes. However, little is known about the distribution of COs at the sequence level. To investigate this, we studied in detail the pattern of COs along a contig of 3.110 Mb using two F2 segregating populations (Chinese Spring × Renan (F2-CsRe) and Chinese Spring × Courtot (F2-CsCt)) each containing ~2,000 individuals. The availability of the sequence of the contig from Cs enabled the development of 318 markers among which 23 co-dominant polymorphic markers (11 SSRs and 12 SNPs) were selected for CO distribution analyses. The distribution of CO... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4270700 Wed, 15 Dec 2010 19:11:53 +0100 4270700 http://www.medworm.com/index.php?rid=4207011&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fm125524313187574%2F Abstract  In somatic cells of female marsupial and eutherian mammals, X chromosome inactivation (XCI) occurs. XCI results in the transcriptional silencing of one of the two X chromosomes and is accompanied by specific covalent histone modifications attributable to the inactive chromatin state. Because data about repressed chromatin of the inactive X chromosome (Xi) in marsupials are sparse, we examined in more detail the distribution of active and inactive chromatin markers on metaphase X chromosomes of an American marsupial, Monodelphis domestica. Consistent with data reported previously both for eutherian and marsupial mammals, we found that the Xi of M. domestica lacks active histone markers—H3K4 dimethylation and H3K9 acetylation. We did not observe on metaphase spreads... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4207011 Thu, 25 Nov 2010 20:06:21 +0100 4207011 http://www.medworm.com/index.php?rid=4188762&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy06n50u37810t74k%2F Abstract  We confirmed the occurrence of the insect TTAGG telomeric repeats in the mealybug Planococcus lilacinus, a radiation-resistant coccid, by single primer polymerase chain reaction (PCR) and Southern hybridization. Analysis of Bal31 nuclease-digested DNA by Southern hybridization and chromosomes by FISH suggests that these repeats occur mainly at the ends of the chromosomes. However, sequence analysis of the PCR products of TTAGG-associated sequences from genomic DNA showed their interstitial occurrence and association with certain unrelated low-copy repeats. Because of their shorter length, the interstitial TTAGG sequences were detectable by primed in situ hybridizations but not by FISH. Analysis of chromosomes recovered after irradiation by fluorescent in situ hybrid... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4188762 Thu, 18 Nov 2010 17:53:10 +0100 4188762 http://www.medworm.com/index.php?rid=4188763&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F61631u103t014r62%2F We describe a method to construct ring-X chromosomes in Drosophila via I-CreI-mediated exchange in rDNA, and then rapidly diagnose the recovery of ring chromosomes via FLP-mediated sister chromatid exchange within the ring. The method we describe provides a ready means to tailor the genetic content of ring-X chromosomes, making it suited to produce ring-X chromosomes for a variety of experimental purposes. Content Type Journal ArticleDOI 10.1007/s00412-010-0297-2Authors Mary M. Golic, Department of Biology, University of Utah, Salt Lake City, UT 84112, USAKent G. Golic, Department of Biology, University of Utah, Salt Lake City, UT 84112, USA Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=4188763 Wed, 17 Nov 2010 21:03:47 +0100 4188763 http://www.medworm.com/index.php?rid=4178063&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F2264827l32v20771%2F Abstract  Nucleocytoplasmic export and biogenesis of mRNPs are closely coupled. At the gene, concomitant with synthesis of the pre-mRNA, the transcription machinery, hnRNP proteins, processing, quality control and export machineries cooperate to release processed and export competent mRNPs. After diffusion through the interchromatin space, the mRNPs are translocated through the nuclear pore complex and released into the cytoplasm. At the nuclear pore complex, defined compositional and conformational changes are triggered, but specific cotranscriptionally added components are retained in the mRNP and subsequently influence the cytoplasmic fate of the mRNP. Processes taking place at the gene locus and at the nuclear pore complex are crucial for integrating export as an essent... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4178063 Mon, 15 Nov 2010 18:14:24 +0100 4178063 http://www.medworm.com/index.php?rid=4142138&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fm34917h16w747v18%2F Abstract  Faithful repair of DNA double-strand breaks (DSBs) is vital for animal development, as inappropriate repair can cause gross chromosomal alterations that result in cellular dysfunction, ultimately leading to cancer, or cell death. Correct processing of DSBs is not only essential for maintaining genomic integrity, but is also required in developmental programs, such as gametogenesis, in which DSBs are deliberately generated. Accordingly, DSB repair deficiencies are associated with various developmental disorders including cancer predisposition and infertility. To avoid this threat, cells are equipped with an elaborate and evolutionarily well-conserved network of DSB repair pathways. In recent years, Caenorhabditis elegans has become a successful model system in which... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4142138 Fri, 05 Nov 2010 10:51:57 +0100 4142138 http://www.medworm.com/index.php?rid=4043748&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk377727x03l47883%2F Abstract  Attachment of telomeres to the nuclear envelope (NE) and their clustering in a chromosomal bouquet during meiotic prophase I is an evolutionary conserved event that promotes chromosome pairing and recombination. In fission yeast, bouquet formation fails when the telomeric protein Rap1 is absent or when the telomeric protein Taz1 fails to recruit Rap1 to telomeres. The mammalian Rap1 orthologue is a component of the shelterin complex and localises to telomeres through an interaction with a Taz1-like telomeric DNA binding factor, TRF2. Here, we investigated the role of mammalian Rap1 in meiotic telomere attachment and clustering by analysing spermatogenesis in Rap1-deficient mice. The results establish that the meiotic three-dimensional nuclear architecture and reco... Chromosoma journals http://www.medworm.com/rss/comments.php?id=4043748 Wed, 06 Oct 2010 16:44:06 +0100 4043748 http://www.medworm.com/index.php?rid=3997039&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fh871l72542853k62%2F Abstract  Centromeres are specialized chromosomal domains that direct mitotic kinetochore assembly and are defined by the presence of CENP-A (CID in Drosophila) and CENP-C. While the role of CENP-A appears to be highly conserved, functional studies in different organisms suggest that the precise role of CENP-C in kinetochore assembly is still under debate. Previous studies in vertebrate cells have shown that CENP-C inactivation causes mitotic delay, chromosome missegregation, and apoptosis; however, in Drosophila, the role of CENP-C is not well-defined. We have used RNA interference depletion in S2 cells to address this question and we find that depletion of CENP-C causes a kinetochore null phenotype, and consequently, the spindle checkpoint, kinetochore–microtubule intera... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3997039 Wed, 22 Sep 2010 16:42:35 +0100 3997039 http://www.medworm.com/index.php?rid=3997040&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fp63047363n658786%2F Abstract  The condensed heterochromatic domains are known to be associated with transcriptional repression and cell differentiation. Here, we investigate the function of heterochromatin protein HP1b, a member of the HP1 family in Drosophila melanogaster, in transcription and development. Both knockdown and overexpression of HP1b resulted in partial lethality, indicating that HP1b is essential for the normal development. In contrast to the positive role of HP1a in heterochromatin formation, overexpression of HP1b decondensed the pericentromeric heterochromatin and reduced the association of HP1a and H3K9me2 with it, both known markers of pericentric heterochromatin. Interestingly, the structure of the heterochromatic fourth chromosome appeared not to be affected. Further expe... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3997040 Mon, 20 Sep 2010 19:41:50 +0100 3997040 http://www.medworm.com/index.php?rid=3950043&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F01667761g38083qr%2F In this study, we explore which factors in replication-compromised cells promote abnormal chromosome ploidy. We expressed mutant forms of either polymerase α (Polα) or polymerase δ (Polδ) in normal human fibroblasts to compromise DNA replication. Cells expressing the mutant Polα-protein failed to sustain mitotic arrest and, when propagated progressively, down-regulated Mad2 and BubR1 and accumulated 4N-DNA from the 2N-DNA cells. Significantly, a population of these cells became tetraploids. The Polα mutant expressing cells also exhibited elevated cellular senescence markers, suggesting as a mechanism to limit proliferation of the tetraploids. Expression of the Polδ mutant also caused cells to accumulate 4N-DNA. In contrast to the Polα mutant expressing cells, the Polδ mutant... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3950043 Wed, 08 Sep 2010 16:02:52 +0100 3950043 http://www.medworm.com/index.php?rid=3884220&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Feq70105567j76381%2F Abstract  Nuclear pore complexes (NPCs) serve as transport channels across the nuclear membrane, a double lipid bilayer that physically separates the nucleoplasm and cytoplasm of eukaryotic cells. New evidence suggests that the multiprotein nuclear pores also play a role in chromatin organization and gene expression. Given the importance of NPC function, it is not surprising that a growing list of human diseases and developmental defects have been linked to its malfunction. In order to fully understand the functional repertoire of NPCs and their essential role for nuclear organization, it is critical to determine the sequence of events that lead to the formation of nuclear pores. This is particularly relevant since NPC number, and possibly composition, are tightly linked to... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3884220 Wed, 18 Aug 2010 17:40:01 +0100 3884220 http://www.medworm.com/index.php?rid=3866576&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F855w2213w743142n%2F Abstract  While many studies have provided significant insight into homolog pairing during meiosis, information on non-homologous pairing is much less abundant. In the present study, fluorescence in situ hybridization (FISH) was used to investigate non-homologous pairing in haploid rice during meiosis. At pachytene, non-homologous chromosomes paired and formed synaptonemal complexes. FISH analysis data indicated that chromosome pairing could be grouped into three major types: (1) single chromosome paired fold-back as the univalent structure, (2) two non-homologous chromosomes paired as the bivalent structure, and (3) three or more non-homologous chromosomes paired as the multivalent structure. In the survey of 70 cells, 65 contained univalents, 45 contained bivalents, and 49... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3866576 Thu, 12 Aug 2010 18:33:56 +0100 3866576 http://www.medworm.com/index.php?rid=3866577&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F08m1k24086766n12%2F We examined mouse progenitor B cell lymphomas with a common translocation, der(12)t(12;15), which fuses a gene-rich region of mouse chromosome12 (Mmu12) with a gene-poor region of mouse chromosome15 (Mmu15). We found that sequences 2.3 Mb proximal and 2.7 Mb distal to the der(12)t(12;15) breakpoint had different nuclear positions measured relative to the nuclear radius. However, their positions were similar on unrearranged chromosomes in the same tumor cells and normal progenitor B cells. In addition, higher-order chromatin folding marked by three-dimensional gene clustering was not significantly altered for the 7 Mb of Mmu15 sequence distal to this translocation breakpoint. Translocation also did not correspond to significant changes in gene expression in this region.... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3866577 Wed, 11 Aug 2010 21:22:37 +0100 3866577 http://www.medworm.com/index.php?rid=3830425&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fh6u532399w51l740%2F Abstract  Cyclin-dependent kinases (CDKs) play a central role in the regulation of cell cycle progression in eukaryotes. The onset of S phase, the initiation of chromosomal DNA replication, is a major cell cycle event that is regulated by CDKs. Eukaryotic chromosomal DNA replication is highly regulated and occurs as a two-step reaction. The first reaction, known as licensing, is essential for DNA replication by making cell replication competent and occurs in G1 phase. Once cells enter S phase, licensed chromosomes initiate DNA replication through the action of two conserved protein kinases, S phase-specific CDK and Cdc7-Dbf4 (or Dbf4-dependent kinase). Our understanding of the regulatory mechanisms of DNA replication in model eukaryotes has advanced considerably in the past... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3830425 Wed, 04 Aug 2010 20:32:05 +0100 3830425 http://www.medworm.com/index.php?rid=3819953&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy05825rw542p5pt0%2F Abstract  The initiation of DNA replication and the elongation of DNA strands take place in chromatin, a huge compound DNA–protein complex. Although the factors involved in the process of DNA replication have been largely elucidated, the underlying mechanisms that determine their behavior in the context of chromatin have only recently begun to be understood. It has been known that transcription is tightly regulated by the state of chromatin compaction, which governs the accessibility of DNA to trans-acting factors. This process is influenced by several determinants of chromatin structure, including intrinsic nucleosome positioning, the nucleosome remodeling complex, histone post-translational modifiers, and histone- and DNA-binding proteins. Growing evidence indicates tha... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3819953 Mon, 02 Aug 2010 19:20:09 +0100 3819953 http://www.medworm.com/index.php?rid=3807144&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F2539h278vq188345%2F Abstract  FANCJ/BRIP1 encodes a helicase that has been implicated in the maintenance of genomic stability. Here, to better understand FANCJ function in DNA damage responses, we have examined the regulation of its cellular localization. FANCJ nuclear foci assemble spontaneously during S phase and are induced by various stresses. FANCJ foci colocalize with the replication fork following treatment with hydroxyurea, but not spontaneously. Using FANCJ mutants, we find that FANCJ helicase activity and the capacity to bind BRCA1 are both involved in FANCJ recruitment. Given similarities to the recruitment of another Fanconi anemia protein, FANCD2, we tested for colocalization of FANCJ and FANCD2. Importantly, these proteins show substantial colocalization, and FANCJ promotes the a... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3807144 Fri, 30 Jul 2010 16:55:25 +0100 3807144 http://www.medworm.com/index.php?rid=3793604&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fgq01853301u6p401%2F Abstract  The GTPase Ran regulates nucleocytoplasmic transport in interphase and spindle organisation in mitosis via effectors of the importin beta superfamily. Ran-binding protein 1 (RanBP1) regulates guanine nucleotide turnover on Ran, as well as its interactions with effectors. Unlike other Ran network members that are steadily expressed, RanBP1 abundance is modulated during the mammalian cell cycle, peaking in mitosis and declining at mitotic exit. Here, we show that RanBP1 downregulation takes place in mid to late telophase, concomitant with the reformation of nuclei. Mild RanBP1 overexpression in murine cells causes RanBP1 to persist in late mitosis and hinders a set of events underlying the telophase to interphase transition, including chromatin decondensation, nucle... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3793604 Sat, 24 Jul 2010 13:27:57 +0100 3793604 http://www.medworm.com/index.php?rid=3756830&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj2006v724r43731n%2F Abstract  Spo11 is a homolog of a subunit of archaebacterial topoisomerase, which catalyzes DNA double-strand breaks and initiates homologous chromosome recombination. In the present study, we silenced the SPO11-1 gene in rice (Oryza sativa) using RNAi. Rice plants with loss-of-function of OsSPO11-1 have no apparent growth defects during vegetative development, but homologous chromosome pairing and recombination are significantly obstructed. Telomeres can be assembled as bouquet during the zygotene stage of the OsSPO11-1-deficient plants, just as that in wild type. Although the two axial-associated proteins, REC8 and PAIR2, are loaded onto the chromosomes, the depletion of PAIR2 from the chromosomes is much later than in wild type. The central element of the synaptonemal com... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3756830 Tue, 13 Jul 2010 14:55:28 +0100 3756830 http://www.medworm.com/index.php?rid=3756831&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F2035144714w0m0l1%2F Abstract  Ligand-regulated nuclear receptors, such as estrogen receptors, glucocorticoid receptor, vitamin D receptor, and peroxisome proliferator-activated receptors, belong to the most widely studied and best understood transcription factors. Therefore, the dynamic nature of transcriptional regulation was observed first with different members of the nuclear receptor superfamily, but is now also extended to other transcription factors, such as nuclear factor κB. Dynamic and in part cyclical processes were observed on the level of translocation into the nucleus, association with genomic binding sites, exchange of co-regulators and chromatin modifiers, occurrence of chromatin marks, and activities of RNA polymerase II resulting in mRNA synthesis. In this review, we summariz... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3756831 Tue, 13 Jul 2010 14:55:26 +0100 3756831 http://www.medworm.com/index.php?rid=3736097&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fr4081v10631632ju%2F Abstract  The characterisation of sequences at chromosome ends of Rhynchosciara americana was continued with the screening of a genomic library using as a probe a short repeat identified in a previous report (M-22, 22 bp) which was found to be specific for noncentromeric termini of this species. Simple repeats, complex tandem and apparently dispersed repeats were present in the genomic clones analysed. Repetitive sequences do not define individual chromosome tips as they were found in all noncentromeric ends. A novel and unusually short tandem repeat type for dipteran chromosome ends (named M-16) composed of 16 nucleotides and frequently associated with M-22 arrays was characterised in this work. Islands of M-16 and M-22 tandem repeats were found in all the genomic clon... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3736097 Wed, 07 Jul 2010 16:33:13 +0100 3736097 http://www.medworm.com/index.php?rid=3736098&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ffhl25264m3217767%2F Abstract  Transient four stranded joint DNA molecules bridging sister chromatids constitute an intriguing feature of replicating genomes. Here, we studied their structure and frequency of formation in Physarum polycephalum. By “3D gels”, we evidenced that they are not made of four continuous DNA strands. Discontinuities, which do not interfere with the unique propensity of the joint DNA molecules to branch migrate in vitro, are linked to the crossover, enhanced by RNaseA, and affect at most half of the DNA strands. We propose a structural model of joint DNA molecules containing ribonucleotides inserted within one strand, a gapped strand, and two continuous DNA strands. We further show that spontaneous joint DNA molecules are short-lived and are as abundant as replication... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3736098 Wed, 07 Jul 2010 06:48:53 +0100 3736098 http://www.medworm.com/index.php?rid=3728926&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk0jn3p423438612p%2F In this study, we examined the organization of late underreplicated regions (URs) of the Drosophila melanogaster genome. When compared with their flanks, these regions showed decreased gene density. A detailed view revealed that these regions originate from unusual combination of short genes and long intergenic spacers. Furthermore, gene expression study showed that this pattern is mostly contributed by short testis-specific genes abundant in the URs. Based on these observations, we developed a genome scanning algorithm and identified 110 regions possessing similar gene density and transcriptional profiles. According to the published data, replication of these regions has been significantly shifted towards late S-phase in two Drosophila cell lines and in polytene chromosomes. Our resu... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3728926 Sun, 04 Jul 2010 22:42:10 +0100 3728926 http://www.medworm.com/index.php?rid=3709472&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fp13340m320617m21%2F Abstract  The replication dynamics at common fragile site FRA6E has been evaluated by molecular combing and interphase fluorescent in situ hybridisation (FISH) in primary human lymphocytes cultured under normal or aphidicolin-induced stress conditions. FRA6E is one of the most frequently expressed common fragile sites of the human genome. It harbours several genes, PARK2 being regarded as the most relevant one. According to the results obtained from interphase FISH analysis, FRA6E can be considered a mid-late-replicating sequence characterised by heterogeneous replication timing. Molecular combing did not reveal specific replication parameters at the fragile site: fork rates were highly comparable to those detected at an early replicating locus (LMNB2) used as control and in v... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3709472 Mon, 28 Jun 2010 16:58:07 +0100 3709472 http://www.medworm.com/index.php?rid=3602383&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fdu37x4113uw02164%2F Abstract  A chromosome with two functional centromeres is cytologically unstable and can only be stabilized when one of the two centromeres becomes inactivated via poorly understood mechanisms. Here, we report a transmissible chromosome with multiple centromeres in wheat. This chromosome encompassed one large and two small domains containing the centromeric histone CENH3. The two small centromeres are in a close vicinity and often fused as a single centromere on metaphase chromosomes. This fused centromere contained approximately 30% of the CENH3 compared to the large centromere. An intact tricentric chromosome was transmitted to about 70% of the progenies, which was likely a consequence of the dominating pulling capacity of the large centromere during anaphases of meiosis.... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3602383 Mon, 24 May 2010 16:18:34 +0100 3602383 http://www.medworm.com/index.php?rid=3572558&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F5v12774647771h34%2F Abstract  During early development in female mammals, most genes on one of the two X-chromosomes undergo transcriptional silencing. In the extraembryonic lineages of some eutherian species, imprinted X-inactivation of the paternal X-chromosome occurs. In the cells of the embryo proper, the choice of the future inactive X-chromosome is random. We mapped several genes on the X-chromosomes of five common vole species and compared their expression and methylation patterns in somatic and extraembryonic tissues, where random and imprinted X-inactivation occurs, respectively. In extraembryonic tissues, more genes were expressed on the inactive X-chromosome than in somatic tissues. We also found that the methylation status of the X-linked genes was always in accordance with their e... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3572558 Sat, 15 May 2010 08:02:39 +0100 3572558 http://www.medworm.com/index.php?rid=3546643&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy7r61556p0w27270%2F Abstract  Coilin, a molecular marker for Cajal bodies (CBs), is a phosphoprotein that contains a cryptic nucleolar localization signal and multiple interacting domains, such as the RG-box. Post-translational symmetrical dimethylation of arginines on the coilin RG-box is required for the recruitment of the survival motor neuron (SMN) protein and splicing small ribonucleoproteins (snRNPs) to CBs. Here, we analyze the role of the methylation state of coilin in the regulation of its localization to the nucleolus. We use the MCF7 MTAP−/− cell line, which lacks the gene encoding 5′-methylthioadenosine phosphorylase (MTAP). This is a key enzyme of the methionine salvage pathway. The reduction of the levels of coilin methylation causes disruption of the canonical CBs and coili... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3546643 Fri, 07 May 2010 08:16:29 +0100 3546643 http://www.medworm.com/index.php?rid=3541353&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F7441r3r04q7p4051%2F Abstract  The Ryukyu spiny rat, Tokudaia osimensis, has an XO/XO sex chromosome constitution, lacking a Y chromosome and the mammalian sex-determining gene SRY. To investigate the Y-loss event, we traced three proto-Y-linked genes, RBMY1A1, EIF2S3Y, and KDM5D, in the genome. The original Y-linked RBMY1A1 was lost as well as SRY, and the remaining RBMY1A1 was a processed pseudogene on autosome. In contrast, EIF2S3Y and KDM5D were conserved in genomes of both sexes as a result of their translocation from the Y chromosome to the X chromosome and/or autosomes. Furthermore, these genes were expressed in gonads and brains of both sexes. Our study indicated a loss of Y-linked genes with important male functions to be necessary for the Y chromosome to disappear. These functions might h... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3541353 Wed, 05 May 2010 08:11:50 +0100 3541353 http://www.medworm.com/index.php?rid=3514273&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv532112704861002%2F Abstract  Programmed DNA double-strand breaks (DSBs) are generated during meiosis to initiate homologous recombination. Various aspects of DSB formation, signaling, and repair are accomplished or governed by Mre11, a component of the MRN/MRX complex, partially in cooperation with Com1/Sae2/CtIP. We used Tetrahymena to study evolutionarily conserved and changed functions of Mre11 and Com1. There is a difference between organisms with respect to the dependency of meiotic DSB formation on Mre11. By cytology and an electrophoresis-based assay for DSBs, we found that in Tetrahymena Mre11p is not required for the formation and ATR-dependent signaling of DSBs. Its dispensability is also reflected by wild-type-like DSB-dependent reorganization of the meiotic nucleus and by the phosp... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3514273 Tue, 27 Apr 2010 06:47:47 +0100 3514273 http://www.medworm.com/index.php?rid=3482228&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fl256788375682lt9%2F Abstract  Simple Sequence Repeats (SSRs) are known to be scattered and present in high number in eukaryotic genomes. We demonstrate that dye-labeled oligodeoxyribonucleotides with repeated mono-, di-, tri, or tetranucleotide motifs (15-20 nucleotides in length) have an unexpected ability to recognize SSR target sequences in non-denatured chromosomes. The results show that all these probes are able to invade chromosomes, independent of the size of the repeat motif, their nucleotide sequence, or their ability to form alternative B-DNA structures such as triplex DNA. This novel and remarkable property of binding SSR oligonucleotides to duplex DNA targets permitted the development of a non-denaturing fluorescence in situ hybridization method that quickly and efficiently de... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3482228 Wed, 14 Apr 2010 16:50:41 +0100 3482228 http://www.medworm.com/index.php?rid=3452577&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk317v6u32v32672v%2F Abstract  The organisation of dinoflagellate chromosomes is exceptional among eukaryotes. Their genomes are the largest in the Eukarya domain, chromosomes lack histones and may exist in liquid crystalline state. Therefore, the study of the structural and functional properties of dinoflagellate chromosomes is of high interest. In this work, we have analysed the telomeres and telomerase in two Dinoflagellata species, Karenia papilionacea and Crypthecodinium cohnii. Active telomerase, synthesising exclusively Arabidopsis-type telomere sequences, was detected in cell extracts. The terminal position of TTTAGGG repeats was determined by in situ hybridisation and BAL31 digestion methods and provides evidence for the linear characteristic of dinoflagellate chromosomes. The length of... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3452577 Mon, 05 Apr 2010 21:33:36 +0100 3452577 http://www.medworm.com/index.php?rid=3432051&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F68k02q346836x361%2F Abstract  A cytological comparative analysis of male meiocytes was performed for Arabidopsis wild type and the ahp2 (hop2) mutant with emphasis on ahp2’s largely uncharacterized prophase I. Leptotene progression appeared normal in ahp2 meiocytes; chromosomes exhibited regular axis formation and assumed a typical polarized nuclear organization. In contrast, 4′,6′-diamidino-2-phenylindole-stained ahp2 pachytene chromosome spreads demonstrated a severe reduction in stabilized pairing. However, transmission electron microscopy (TEM) analysis of sections from meiocytes revealed that ahp2 chromosome axes underwent significant amounts of close alignment (44% of total axis). This apparent paradox strongly suggests that the Ahp2 protein is involved in the stabilization of homolog... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3432051 Wed, 31 Mar 2010 16:59:53 +0100 3432051 http://www.medworm.com/index.php?rid=3432053&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fa704u385j85k0u72%2F Abstract  Error-free chromosome segregation requires that all chromosomes biorient on the mitotic spindle. The motor protein Centromere-associated protein E (CENP-E) facilitates chromosome congression by mediating the lateral sliding of sister chromatids along existing K-fibers, while the mitotic kinase Aurora B detaches kinetochore–microtubule interactions that are not bioriented. Whether these activities cooperate to promote efficient chromosome biorientation and timely anaphase onset is not known. We here show that the chromosomes that fail to congress after CENP-E depletion displayed high centromeric Aurora B kinase activity. This activity destabilized spindle pole proximal kinetochore–microtubule interactions resulting in a checkpoint-dependent mitotic delay that a... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3432053 Wed, 31 Mar 2010 06:44:58 +0100 3432053 http://www.medworm.com/index.php?rid=3432052&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ftpk808320x1423v6%2F Abstract  Chromatin insulators block the action of transcriptional enhancers when interposed between an enhancer and a promoter. An Flp technology was used to examine interactions between Drosophila gypsy and Wari insulators in somatic and germ cells. The gypsy insulator consists of 12 binding sites for the Su(Hw) protein, while the endogenous Wari insulator, located on the 3′ side of the white gene, is independent from the Su(Hw) protein. Insertion of the gypsy but not Wari insulator between FRT sites strongly blocks recombination between Flp dimers bound to FRT sites located on the same chromatid (recombination in cis) or in sister chromatids (unequal recombination in trans). At the same time, the interaction between Wari and gypsy insulators regulates the efficiency of Fl... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3432052 Wed, 31 Mar 2010 06:44:58 +0100 3432052 http://www.medworm.com/index.php?rid=3423692&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fe1760u80t3211v31%2F Abstract  Comparative genetic linkage mapping using a common set of DNA markers in related species is an important methodology in plant genome research. Here, we demonstrate a comparative fluorescence in situ hybridization (FISH) mapping strategy in plants. A set of 13 bacterial artificial chromosome clones spanning the entire length of potato chromosome 6 was used for pachytene chromosome-based FISH mapping in seven distantly related Solanum species including potato, tomato, and eggplant. We discovered one paracentric inversion and one pericentric inversion within specific lineages of these species. The comparative FISH mapping data revealed the ancestral structure of this chromosome. We demonstrate that comparative FISH mapping is an efficient and powerful methodology to s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3423692 Mon, 29 Mar 2010 17:09:52 +0100 3423692 http://www.medworm.com/index.php?rid=3423693&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fw734t7vh087u71g8%2F Abstract  When chromosomes start to assemble in mitotic prophase, duplicated chromatids are not discernible within each chromosome. As condensation proceeds, they gradually show up, culminating in two rod-shaped structures apposed along their entire length within a metaphase chromosome. This process, known as sister chromatid resolution, is thought to be a prerequisite for rapid and synchronous separation of sister chromatids in anaphase. From a mechanistic point of view, the resolution process can be dissected into three distinct steps: (1) release of cohesin from chromosome arms; (2) formation of chromatid axes mediated by condensins; and (3) untanglement of inter-sister catenation catalyzed by topoisomerase II (topo II). In this review article, we summarize recent progre... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3423693 Mon, 29 Mar 2010 17:09:51 +0100 3423693 http://www.medworm.com/index.php?rid=3377274&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fvmg2736228237r33%2F Abstract  During mitosis, all chromosomes must attach to microtubules of the mitotic spindle to ensure correct chromosome segregation. Microtubule attachment occurs at specialized structures at the centromeric region of chromosomes, called kinetochores. These kinetochores can generate microtubule attachments through capture of centrosome-derived microtubules, but in addition, they can generate microtubules themselves, which are subsequently integrated with centrosome-derived microtubules to form the mitotic spindle. Here, we have performed a large scale RNAi screen and identify cyclin G-associated kinase (GAK) as a novel regulator of microtubule generation at kinetochores/chromatin. This function of GAK requires its C-terminal J-domain, which is essential for clathrin recyc... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3377274 Tue, 16 Mar 2010 14:49:18 +0100 3377274 http://www.medworm.com/index.php?rid=3361722&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F2027175265xw3212%2F Abstract  Although nucleosome remodeling is essential to transcriptional regulation in eukaryotes, little is known about its genome-wide behavior. Since a number of nucleosome positioning maps in vivo have been recently determined, we examined if their comparisons might be used for obtaining a genome-wide profile of nucleosome remodeling. Using seven yeast maps, the local variability of nucleosomes, measured by the entropy, was significantly higher in a set of reported unstable nucleosomes. The binding sites of four transcription factors, known as the remodeling factors, were distinctively high both in entropy and linker ratio, whereas those of Yhp1, their potential inhibitor, showed the lowest values in both of them. Taken together, our map shows the general information of... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3361722 Thu, 11 Mar 2010 18:12:23 +0100 3361722 http://www.medworm.com/index.php?rid=3361721&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fa5401p23382128l8%2F Abstract  The chromatin structure is important for recognition and repair of DNA damage. Many DNA damage response proteins accumulate in large chromatin domains flanking sites of DNA double-strand breaks. The assembly of these structures—usually termed DNA damage foci—is primarily regulated by MDC1, a large nuclear mediator/adaptor protein that is composed of several distinct structural and functional domains. Here, we are summarizing the latest discoveries about the mechanisms by which MDC1 mediates DNA damage foci formation, and we are reviewing the considerable efforts taken to understand the functional implication of these structures. Content Type Journal ArticleCategory REVIEWDOI 10.1007/s00412-010-0266-9Authors Stephanie Jungmichel, University of Zürich Ins... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3361721 Thu, 11 Mar 2010 18:12:23 +0100 3361721 http://www.medworm.com/index.php?rid=3357684&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fb2226p287h1u3649%2F Abstract  In the zebra finch (Taeniopygia guttata) a germline-restricted chromosome (GRC) is regularly present in males and females. While the GRC is euchromatic in oocytes, in spermatocytes this chromosome is cytologically seen as entirely heterochromatic and presumably inactive. At the end of male meiosis, the GRC is eliminated from the nucleus. By immunofluorescence on microspreads, we investigated HP1 proteins and histone modifications throughout male meiotic prophase, as well as in young spermatid stages after the GRC elimination. We found that in prophase spermatocytes the GRC chromatin differs from that of the regular chromosome complement. The GRC is highly enriched in HP1β and exhibits high levels of di- and tri-methylated histone H3 at lysine 9 and tri- and di-met... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3357684 Wed, 10 Mar 2010 16:14:36 +0100 3357684 http://www.medworm.com/index.php?rid=3325897&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fl33784853329h121%2F Abstract  Over the last several years, the sea lamprey (Petromyzon marinus) has grown substantially as a model for understanding the evolutionary fundaments and capacity of vertebrate developmental and genome biology. Recent work on the lamprey genome has resulted in a preliminary assembly of the lamprey genome and led to the realization that nearly all somatic cell lineages undergo extensive programmed rearrangements. Here we describe the development of a bacterial artificial chromosome (BAC) resource for lamprey germline DNA and use sequence information from this resource to probe the subchromosomal structure of the lamprey genome. The arrayed germline BAC library represents ∼10× coverage of the lamprey genome. Analyses of BAC-end sequences reveal that the lamprey genom... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3325897 Mon, 01 Mar 2010 18:07:55 +0100 3325897 http://www.medworm.com/index.php?rid=3297494&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ffh784k0828h732j7%2F Abstract  More than 109 base pairs of the genome in higher eucaryotes are positioned in the interphase nucleus such that gene activation, gene repression, remote gene regulation by enhancer elements, and reading as well as adjusting epigenetic marks are possible. One important structural and functional component of chromatin organization is the zinc finger factor CTCF. Two decades of research has advanced the understanding of the fundamental role that CTCF plays in regulating such a vast expanse of DNA. Content Type Journal ArticleCategory REVIEWDOI 10.1007/s00412-010-0262-0Authors Rolf Ohlsson, Karolinska Institute Institute for Microbiology, Tumor- and Cellbiology (MTC) Stockholm SwedenMarek Bartkuhn, Justus-Liebig-University Institute for Genetics 35392 Giessen Germa... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3297494 Sat, 20 Feb 2010 06:50:17 +0100 3297494 http://www.medworm.com/index.php?rid=3282717&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fe11532x5101k5301%2F Abstract  During male meiotic prophase in mammals, X and Y are in a largely unsynapsed configuration, which is thought to trigger meiotic sex chromosome inactivation (MSCI). In avian species, females are ZW, and males ZZ. Although Z and W in chicken oocytes show complete, largely heterologous synapsis, they too undergo MSCI, albeit only transiently. The W chromosome is already inactive in early meiotic prophase, and inactive chromatin marks may spread on to the Z upon synapsis. Mammalian MSCI is considered as a specialised form of the general meiotic silencing mechanism, named meiotic silencing of unsynapsed chromatin (MSUC). Herein, we studied the avian form of MSUC, by analysing the behaviour of the peculiar germline restricted chromosome (GRC) that is present as a single... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3282717 Tue, 16 Feb 2010 18:06:04 +0100 3282717 http://www.medworm.com/index.php?rid=3282718&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F5230476172434271%2F Abstract  The spindle checkpoint restrains anaphase onset and mitotic exit until all chromosomes are stably attached to the mitotic spindle via their kinetochores. The Tao1 protein kinase was recently reported as a novel spindle checkpoint component. When an siRNA was used to repress Tao1, the essential spindle checkpoint component Mad2 failed to localise to kinetochores, and cells rapidly exited mitosis. Tao1 was also shown to interact with BubR1, another essential checkpoint component, and be rapidly degraded after mitosis, a feature typical of many mitotic regulators. Here, we identify four different siRNAs that repress Tao1 protein levels as efficiently as the previously reported siRNA. However, these siRNAs do not override the spindle checkpoint. We also present data i... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3282718 Tue, 16 Feb 2010 18:06:00 +0100 3282718 http://www.medworm.com/index.php?rid=3270859&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ffh0hr11587231u62%2F Abstract  Two partially reconstructed karyotypes (RK1 and RK2) of Arabidopsis thaliana have been established from a transformant, in which four structurally changed chromosomes (α, β, γ, and δ) were involved. Both karyotypes are composed of 12 chromosomes, 2n = 1¢¢+ 3¢¢+ 4¢¢+ 5¢¢+ a¢¢+ g¢¢ = 12 for RK1 and 2n = 3¢¢+ 4¢¢+ 5¢¢+ a¢¢+ b¢¢+ g¢¢ = 12 for RK2, and these chromosome constitutions were relatively stable at least for three generations. Pairing at meiosis was limited to the homologues (1, 3, 4, 5, α, β, or γ), and no pairing occurred among non-homologous chromosomes in both karyotypes. For minichromosome α (mini α), precocious separation at metaphase I was frequently observed in RK2, as found for other minichromosomes, but was rare... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3270859 Fri, 12 Feb 2010 07:08:13 +0100 3270859 http://www.medworm.com/index.php?rid=3242721&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F6177u43k8ju14384%2F Abstract  Eukaryotic genomes function in the context of chromatin, but the roles of most nonhistone chromosomal proteins are far from understood. The D1 protein of Drosophila is an example of a chromosomal protein that has been fairly well characterized biochemically, but has nevertheless eluded functional description. To this end, we have undertaken a gain-of-function genetical analysis of D1, utilizing the GAL4-UAS system. We determined that ubiquitous overexpression of D1 using the Act5C- or tubP-GAL4 drivers was lethal to the organism during larval growth. We also ectopically expressed D1 in a tissue-limited manner using other GAL4 drivers. In general, ectopic D1 was observed to inhibit differentiation and/or development. We observed effects on pattern formation of the adu... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3242721 Tue, 02 Feb 2010 17:47:25 +0100 3242721 http://www.medworm.com/index.php?rid=3234639&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv6k43684v660844q%2F Abstract  Cotton is a model system for studying polyploidization, genomic organization, and genome-size variation because the allotetraploid was formed 1-2 million years ago, which is old enough for sequence divergence but relatively recent to maintain genome stability. In spite of characterizing random genomic sequences in many polyploidy plants, the cytogenetic and sequence data that decipher homoeologous chromosomes are very limited in allopolyploid species. Here, we reported comprehensive analyses of integrated cytogenetic and linkage maps of homoeologous chromosomes 12A and 12D in allotetraploid cotton using fluorescence in situ hybridization and a large number of bacterial artificial chromosomes that were anchored by simple sequence repeat markers in the correspon... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3234639 Mon, 01 Feb 2010 18:02:39 +0100 3234639 http://www.medworm.com/index.php?rid=3234640&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F4rr027r13010j5p1%2F Abstract  Unreductional meiotic cell division (UMCD) generates unreduced gametes and leads to polyploidy. The tetraploid wheat “Langdon” (LDN) undergoes normal meiosis, but its polyhaploid undergoes UMCD. Here, we found that sister kinetochores oriented syntelically at meiosis I in LDN, but amphitelically in LDN polyhaploid and the interspecific hybrid of LDN with Aegilops tauschii. We also observed that sister centromere cohesion persisted until anaphase II in LDN, LDN polyhaploid, and the interspecific hybrid. Meiocytes with all chromosomes oriented amphitelically underwent UMCD in LDN polyhaploid, and the interspecific hybrid, suggesting the tension created by the amphitelic orientation of sister kinetochores and persistence of centromeric cohesion between sister chro... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3234640 Mon, 01 Feb 2010 18:02:37 +0100 3234640 http://www.medworm.com/index.php?rid=3207491&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fe52604v313vr74w5%2F Abstract  Calpains form a family of Ca2+-dependent cysteine proteases involved in diverse cellular processes. However, the specific functions of each calpain isoform remain unknown. Recent reports have shown that calpain 2 (Capn2) is essential for cell viability. We have recently shown that Capn2 is a nuclear protease associated with chromosomes during mitosis in mammalian embryonic cells. We now report that Capn2 depletion impairs mitosis and induces apoptosis in murine cells. Low Capn2 levels induce chromosome alignment defects, the loss of histone H3 threonine 3 phosphorylation at centromeres, and premature sister chromatid separation. Thus, Capn2 may play a role in fundamental mitotic functions, such as the maintenance of sister chromatid cohesion. Content Type Journa... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3207491 Fri, 22 Jan 2010 10:08:52 +0100 3207491 http://www.medworm.com/index.php?rid=3192550&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj38668616n8207p7%2F Abstract  Chromatin insulators affect interactions between promoters and enhancers/silencers and function as barriers to the spread of repressive chromatin. Recently, we have found an insulator, named Wari, located on the 3′ side of the white gene. Here, we show that the previously identified 368-bp core of this insulator is sufficient for blocking Polycomb response element-mediated silencing. Although Wari does not contain binding sites for known insulator proteins, the E(y)2 and CP190 proteins bind to Wari as well as to the Su(Hw)-containing insulators in vivo. It may well be that these proteins are recruited to the insulator by as yet unidentified DNA-binding protein. Partial inactivation of E(y)2 in a weak e(y)2 u1 mutation impairs only the anti-silencing but not t... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3192550 Fri, 15 Jan 2010 17:59:09 +0100 3192550 http://www.medworm.com/index.php?rid=3121852&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F03353h53h300j70k%2F Abstract  Heterochromatin protein 1 (HP1), which binds to sites of histone H3 lysine 9 (H3K9) methylation, is primarily responsible for gene silencing and the formation of heterochromatin. We observed that HP1β is located in both the chromocenters and fibrillarin-positive nucleoli interiors. However, HP1α and HP1γ occupied fibrillarin-positive compartments to a lesser extent, corresponding to the distinct levels of HP1 subtypes at the promoter of rDNA genes. Deficiency of histone methyltransferases SUV39h and/or inhibition of histone deacetylases (HDACi) decreased HP1β and H3K9 trimethylation at chromocenters, but not in fibrillarin-positive regions that co-localized with RNA polymerase I. Similarly, SUV39h- and HDACi-dependent nucleolar rearrangement and inhibition of ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3121852 Wed, 23 Dec 2009 22:22:23 +0100 3121852 http://www.medworm.com/index.php?rid=3121853&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fpg52448206047278%2F Abstract  Chromatin insulators are required for proper temporal and spatial expression of genes in metazoans. Here, we have analyzed the distribution of insulator proteins on the 56F–58A region of chromosome 2R in Drosophila polytene chromosomes to assess the role of chromatin insulators in shaping genome architecture. Data show that the suppressor of Hairy-wing protein [Su(Hw)] is found in three structures differentially associated with insulator proteins: bands, interbands, and multi-gene domains of coexpressed genes. Results show that bands are generally formed by condensation of chromatin that belongs to genes containing one or more Su(Hw) binding sites, whereas, in interbands, Su(Hw) sites appear associated with open chromatin. In addition, clusters of coexpressed gen... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3121853 Wed, 23 Dec 2009 22:22:21 +0100 3121853 http://www.medworm.com/index.php?rid=3106551&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F544q5163q5r273h5%2F Abstract  In addition to the standard set of chromosomes (A), about 15% of eukaryote genomes carry B chromosomes. In most cases, B chromosomes behave as genomic parasites being detrimental for the individuals carrying them and prospering in natural populations because of transmission advantages (drive). B chromosomes are mostly made up of repetitive DNA sequences, especially ribosomal DNA (rDNA), satellite DNA and mobile elements. In only two cases have B chromosomes been shown to carry protein-coding genes. Although some B chromosomes seem to have derived from interspecific hybridisation, the most likely source of B chromosomes is the host genome itself, but the specific A chromosome being the B ancestor has not been identified in any B-containing species. Here, we provide... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3106551 Thu, 17 Dec 2009 07:03:37 +0100 3106551 http://www.medworm.com/index.php?rid=3081662&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F9237h35814334452%2F Abstract  NMCP1 is a plant protein that has a long coiled-coil domain within the molecule. Newly identified NMCP2 of Daucus carota and Apium graveolens showed similar peripheral localization in the interphase nucleus, and the sequence spanning the coiled-coil domain exhibited significant similarity with the corresponding region of NMCP1. To better understand disassembly and assembly of the nuclear envelope (NE) during mitosis, subcellular distribution of NMCP1 and NMCP2 was examined using A. graveolens cells. AgNMCP1 (NMCP1 in Apium) disassembled at prometaphase, dispersed mainly within the spindle, and accumulated on segregating chromosomes, while AgNMCP2 (NMCP2 in Apium), following disassembly at prometaphase with timing similar to that of AgNMCP1, dispersed throughout the m... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3081662 Tue, 08 Dec 2009 19:47:22 +0100 3081662 http://www.medworm.com/index.php?rid=3078163&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fbr7163xw8q320125%2F Abstract  The haspins are divergent members of the eukaryotic protein kinase family that are conserved in many eukaryotic lineages including animals, fungi, and plants. Recently-solved crystal structures confirm that the kinase domain of human haspin has unusual structural features that stabilize a catalytically active conformation and create a distinctive substrate binding site. Haspin localizes predominantly to chromosomes and phosphorylates histone H3 at threonine-3 during mitosis, particularly at inner centromeres. This suggests that haspin directly regulates chromosome behavior by modifying histones, although it is likely that additional substrates will be identified in the future. Depletion of haspin by RNA interference in human cell lines causes premature loss of cen... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3078163 Tue, 08 Dec 2009 06:45:21 +0100 3078163 http://www.medworm.com/index.php?rid=3078164&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F4776p64k6p3k62u0%2F Abstract  Cajal bodies (CBs) are subnuclear domains that participate in spliceosomal small nuclear ribonucleoprotein (snRNP) biogenesis and play a part in the assembly of the spliceosomal complex. The CB marker protein, coilin, interacts with survival of motor neuron (SMN) and Sm proteins. Several coilin phosphoresidues have been identified by mass spectrometric analysis. Phosphorylation of coilin affects its self-interaction and localization in the nucleus. We hypothesize that coilin phosphorylation also impacts its binding to SMN and Sm proteins. In vitro binding studies with a C-terminal fragment of coilin and corresponding phosphomimics show that SMN binds preferentially to dephosphorylated analogs and that SmB′ binds preferentially to phosphomimetic constructs. Bacte... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3078164 Mon, 07 Dec 2009 19:35:24 +0100 3078164 http://www.medworm.com/index.php?rid=3055408&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F6h60564544758766%2F Abstract  The MYST histone acetyltransferase (HAT) dTip60 is part of a multimeric protein complex that unites both HAT and chromatin remodeling activities. Here, we sought to gain insight into the biological functions of dTip60. Strong ubiquitous dTip60 knock-down in flies was lethal, whereas knock-down in the wing imaginal disk led to developmental defects in the wing. dTip60 localized to the nucleus in early embryos and was present in a large number of interbands on polytene chromosomes. Genome-wide expression analysis upon depletion of dTip60 in cell culture showed that it regulated a large number of genes in Drosophila, among which those with chromatin-related functions were highly enriched. Surprisingly, a significant portion of these genes were upregulated upon dTip60 ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=3055408 Tue, 01 Dec 2009 08:30:00 +0100 3055408 http://www.medworm.com/index.php?rid=2987910&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv9821150lk023723%2F Abstract  Chromosomal and telomeric reprogramming was assessed in intraspecies hybrids obtained by fusion of embryonic stem (ES) cells and mouse embryonic fibroblasts. Evaluation of the ploidy of ES-somatic hybrids revealed that 21 of 59 clones had a tetraploid DNA profile while the remaining clones showed deviations from the expected profile of fusion between two diploid cells. Microsatellite polymerase chain reaction analysis of four of these clones demonstrated no random loss of somatic chromosome pairs in the ES-somatic cell hybrids. Pluripotential of ES-somatic hybrids was assessed by gene expression analysis, antibody staining for Oct4 and SSEA-1 and teratoma formation containing derivatives of the three germ layers. Reprogramming of telomeric maintenance was observed... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2987910 Wed, 11 Nov 2009 07:05:39 +0100 2987910 http://www.medworm.com/index.php?rid=2987911&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F292xl556r480671m%2F Abstract  The DNA-dependent adenosine triphosphatase (ATPase) Plk1-interacting checkpoint helicase (PICH) has recently been implicated in spindle checkpoint (SAC) signaling (Baumann et al., Cell 128(1):101–114, 2007). Depletion of PICH by siRNA abolished the SAC and resulted in an apparently selective loss of Mad2 from kinetochores, suggesting a role for PICH in the regulation of the Mad1–Mad2 interaction. An apparent rescue of SAC functionality by overexpression of PICH in PICH-depleted cells initially seemed to confirm a role for PICH in the SAC. However, we have subsequently discovered that all PICH-directed siRNA oligonucleotides that abolish the SAC also reduce Mad2 mRNA and protein expression. This reduction is functionally significant, as PICH siRNA does not aboli... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2987911 Tue, 10 Nov 2009 18:45:07 +0100 2987911 http://www.medworm.com/index.php?rid=2937818&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fdh2jqp2t2886r2p3%2F Abstract  In all living cells, DNA is constantly threatened by both endogenous and exogenous agents. In order to protect genetic information, all cells have developed a sophisticated network of proteins, which constantly monitor genomic integrity. This network, termed the DNA damage response, senses and signals the presence of DNA damage to effect numerous biological responses, including DNA repair, transient cell cycle arrests (“checkpoints”) and apoptosis. The MRN complex (MRX in yeast), composed of Mre11, Rad50 and Nbs1 (Xrs2), is a key component of the immediate early response to DNA damage, involved in a cross-talk between the repair and checkpoint machinery. Using its ability to bind DNA ends, it is ideally placed to sense and signal the presence of double strand ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2937818 Tue, 27 Oct 2009 17:59:31 +0100 2937818 http://www.medworm.com/index.php?rid=2881042&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F3247744j7403937x%2F Abstract  The synaptonemal complex (SC) is the central key structure for meiosis in organisms undergoing sexual reproduction. During meiotic prophase I, homologous chromosomes exchange genetic information at the time they are attached to the lateral elements by specific DNA sequences. Most of these sequences, so far identified, consist of repeat DNA, which are subject to chromatin structural changes during meiotic prophase I. In this work, we addressed the effect of altering the chromatin structure of repeat DNA sequences mediating anchorage to the lateral elements of the SC. Administration of the histone deacetylase inhibitor trichostatin A into live rats caused death of cells in the pachytene stage as well as changes in histone marks along the synaptonemal complex. The mo... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2881042 Fri, 09 Oct 2009 06:06:50 +0100 2881042 http://www.medworm.com/index.php?rid=2812009&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fal81823nq251v365%2F Abstract  In the fission yeast, Schizosaccharomyces pombe, synaptonemal complexes (SCs) are not formed during meiotic prophase. However, structures resembling the axial elements of SCs, the so-called linear elements (LinEs) appear. By in situ immunostaining, we found Pmt3 (S. pombe's SUMO protein) transiently along LinEs, suggesting that SUMOylation of some component(s) of LinEs occurs during meiosis. Mutation of the SUMO ligase Pli1 caused aberrant LinE formation and reduced genetic recombination indicating a role for SUMOylation of LinEs for the regulation of meiotic recombination. Western blot analysis of TAP-tagged Rec10 demonstrated that there is a Pli1-dependent posttranslational modification of this protein, which is a major LinE component and a distant homolog of the... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2812009 Wed, 16 Sep 2009 18:49:44 +0100 2812009 http://www.medworm.com/index.php?rid=2812008&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fa202pn7t3203206k%2F Abstract  Knowledge about the composition and structure of centromeres is critical for understanding how centromeres perform their functional roles. Here, we report the sequences of one centromere-associated bacterial artificial chromosome clone from a Coix lacryma-jobi library. Two Ty3/gypsy-class retrotransposons, centromeric retrotransposon of C. lacryma-jobi (CRC) and peri-centromeric retrotransposon of C. lacryma-jobi, and a (peri)centromere-specific tandem repeat with a unit length of 153 bp were identified. The CRC is highly homologous to centromere-specific retrotransposons reported in grass species. An 80-bp DNA region in the 153-bp satellite repeat was found to be conserved to centromeric satellite repeats from maize, rice, and pearl millet. Fluorescence in situ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2812008 Wed, 16 Sep 2009 18:49:44 +0100 2812008 http://www.medworm.com/index.php?rid=2812010&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fr543qu673n481810%2F Abstract  Dnmt2 is a member of the animal DNA methyltransferase family of enzymes. While the role of other Dnmt proteins has been extensively characterized, comparably little is known about Dnmt2. This is surprising because Dnmt2 is the most widely conserved Dnmt protein, with homologues in protists, plants, fungi, and animals. In this review, we discuss the evidence supporting the seemingly contradictory roles of Dnmt2 in both DNA and RNA methylation. New studies are uncovering the enzymatic mechanisms that mediate these activities and also provide first insights into the biological functions of Dnmt2. Lastly, we also discuss observations that suggest a possible role for Dnmt2 in human health and disease, which further emphasizes the importance of defining Dnmt2-modulated ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2812010 Wed, 16 Sep 2009 18:49:42 +0100 2812010 http://www.medworm.com/index.php?rid=2768095&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F9685562762225472%2F Abstract  The DNA of living cells is highly compacted. Inherent in this spatial constraint is the need for cells to organize individual genetic loci so as to facilitate orderly retrieval of information. Complex genetic regulatory mechanisms are crucial to all organisms, and it is becoming increasingly evident that spatial organization of genes is one very important mode of regulation for many groups of genes. In eukaryotic nuclei, it appears not only that DNA is organized in three-dimensional space but also that this organization is dynamic and interactive with the transcriptional state of the genes. Spatial organization occurs throughout evolution and with genes transcribed by all classes of RNA polymerases in all eukaryotic nuclei, from yeast to human. There is an increas... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2768095 Thu, 03 Sep 2009 06:25:27 +0100 2768095 http://www.medworm.com/index.php?rid=2745359&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F3n4p23v47025p7n4%2F Abstract  The retinoblastoma (pRb) family of proteins are well known for their tumor suppressor properties and for their ability to regulate transcription. The action of pRb family members correlates with the appearance of repressive chromatin marks at promoter regions of genes encoding key regulators of cell proliferation. Recent studies raise the possibility that pRb family members do not simply act by controlling the activity of individual promoters but that they may also function by promoting the more general organization of chromatin. In several contexts, pRb family members stimulate the compaction or condensation of chromatin and promote the formation of heterochromatin. In this review, we summarize studies that link pRb family members to the condensation or compactio... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2745359 Fri, 28 Aug 2009 16:58:44 +0100 2745359 http://www.medworm.com/index.php?rid=2736853&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ft02h80wv134g2507%2F Abstract  Upon DNA double-strand break (DSB) induction in mammals, the histone H2A variant, H2AX, becomes rapidly phosphorylated at serine 139. This modified form, termed γ-H2AX, is easily identified with antibodies and serves as a sensitive indicator of DNA DSB formation. This review focuses on the potential clinical applications of γ-H2AX detection in cancer and in response to other cellular stresses. In addition, the role of H2AX in homeostasis and disease will be discussed. Recent work indicates that γ-H2AX detection may become a powerful tool for monitoring genotoxic events associated with cancer development and tumor progression. Content Type Journal ArticleCategory Mini-ReviewDOI 10.1007/s00412-009-0234-4Authors Jennifer S. Dickey, National Institutes of Healt... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2736853 Tue, 25 Aug 2009 16:45:57 +0100 2736853 http://www.medworm.com/index.php?rid=2736854&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fr0gw044155823242%2F Abstract  We have characterized two post-translational histone modifications in Caenorhabditis elegans on a genomic scale. Micrococcal nuclease digestion and immunoprecipitation were used to obtain distinct populations of single nucleosome cores, which were analyzed using massively parallel DNA sequencing to obtain positional and coverage maps. Two methylated histone H3 populations were chosen for comparison: H3K4 histone methylation (associated with active chromosomal regions) and H3K9 histone methylation (associated with inactivity). From analysis of the sequence data, we found nucleosome cores with these modifications to be enriched in two distinct partitions of the genome; H3K4 methylation was particularly prevalent in promoter regions of widely expressed genes, while H3... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2736854 Tue, 25 Aug 2009 06:54:16 +0100 2736854 http://www.medworm.com/index.php?rid=2729138&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fj46764538m277885%2F Abstract  Regulation of chromatin activity by covalent histone modifications has been long recognized. Histones that constitute the nucleosome are encoded by large families of genes and display a strong degree of conservation. However, histone variants exist and it is becoming clear that they play important roles in genome regulation. While most studies of the role of histone3 (H3) variants in transcriptional control comes from animal models, emerging data in plants suggest functional conservation, although plant-specific roles are likely. We review these data and speculate on the biological significance of H3 variants in plants. Content Type Journal ArticleCategory ReviewDOI 10.1007/s00412-009-0237-1Authors Mathieu Ingouff, National University of Singapore Department of... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2729138 Sun, 23 Aug 2009 05:45:05 +0100 2729138 http://www.medworm.com/index.php?rid=2718756&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fm01576p4205327jh%2F Abstract  Almost half of the human genome consists of repetitive DNA. Understanding what role these elements have in setting up chromatin states that underlie gene and chromosome function in complex genomes is paramount. The function of some types of repetitive DNA is obvious by virtue of their location, such as the alphoid arrays that define active centromeres. However, there are many other types of repetitive DNA whose evolutionary origins and current roles in genome biology remain unknown. One type of repetitive DNA that falls into this class is the macrosatellites. The relevance of these sequences to disease is clearly demonstrated by the 4q macrosatellite (D4Z4), whereupon contraction in the size of the array is associated with the onset of facioscapulohumeral muscular... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2718756 Wed, 19 Aug 2009 08:29:23 +0100 2718756 http://www.medworm.com/index.php?rid=2707989&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fqt0022g4k1pw3580%2F Abstract  In Drosophila polytene chromosomes, regions of intercalary heterochromatin are scattered throughout the euchromatic arms. Here, we present data on the first fine analysis of the individual intercalary heterochromatin region, 75C1-2, located in the 3L chromosome. By using electron microscopy, we demonstrated that this region appears as three closely adjacent condensed bands. Mapping of the region on the physical map by means of the chromosomal rearrangements with known breakpoints showed that the length of the region is about 445 kb. Although it seems that the SUUR protein binds to the whole 75C1-2 region, the proximal part of the region is fully polytenized, so the DNA underreplication zone is asymmetric and located in the distal half of the region. Finally, ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2707989 Fri, 14 Aug 2009 17:47:29 +0100 2707989 http://www.medworm.com/index.php?rid=2666400&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fc98701v66m148834%2F Abstract  Eukaryotic genomes are highly organized within the cell nucleus. Genome organization not only implies the preferential positioning of genetic elements in the interphase nucleus but also the topographic distribution of biological processes. We have investigated the relationship between spatial organization and genome function in single cells. Myc, c-Met, Igf2r, Asb4, and Zac1 genes have the same radial distribution, but they are not positioned in close proximity with respect to each other. Three-dimensional mapping of their transcription sites uncovered a gene-specific pattern of relative positioning with respect to the nucleolus. We found that the Zac1 gene transcription preferentially occurs juxtaposed to the nucleolus, and that its mRNA accumulates at this site of... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2666400 Fri, 31 Jul 2009 19:47:56 +0100 2666400 http://www.medworm.com/index.php?rid=2662229&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fp352u36226606013%2F Abstract  Aneuploidy, which leads to unpaired chromosomal axes during meiosis, is frequently accompanied by infertility. We previously showed, using three mouse models of Down syndrome, that it is an extra chromosome, but not extra gene dose, that is associated with male infertility and virtual absence of post-meiotic gem cells. Here, we test the hypothesis that aneuploid segments are differentially modified and expressed during meiosis, depending on whether they are present as an extra chromosome or not. In all three models examined, the trisomic region lacks a pairing partner, but in one case, spermatocytes have an extra (and unpaired) chromosome, while the two other models involve translocation of the trisomic region rather than an extra chromosome. An extra unpaired chr... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2662229 Wed, 29 Jul 2009 07:16:43 +0100 2662229 http://www.medworm.com/index.php?rid=2652699&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv6160m011n872746%2F We report here that egg cells of aged females show larger amounts of HP1 and Su(Var)3–9 than egg cells of young females. These data suggest that a determinant of sex may be the amount of maternally derived heterochromatic proteins. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s00412-009-0231-7Authors Giovanni Luigi Buglia, University of Rome “La Sapienza” Department of Genetics and Molecular Biology P.le A. Moro 5 00185 Rome ItalyDaniela Dionisi, University of Rome “La Sapienza” Department of Genetics and Molecular Biology P.le A. Moro 5 00185 Rome ItalyMarina Ferraro, University of Rome “La Sapienza” Department of Genetics and Molecular Biology P.le A. Moro 5 00185 Rome Italy Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Sourc... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2652699 Mon, 27 Jul 2009 21:50:09 +0100 2652699 http://www.medworm.com/index.php?rid=2639411&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F471w7u712158n627%2F Abstract  In budding yeast, we have found that sister rDNA arrays marked with fluorescent probes can be visualized as two distinguishable strands during metaphase. Upon anaphase, these arm loci are drawn into the spindle, where they adopt a cruciform-like structure and stretch 2.5-fold as they migrate to the poles. Therefore, while sister rDNA arrays appear separated in metaphase, mechanical linkages between sister arm loci persist throughout anaphase in yeast, as shown in grasshopper spermatocytes (Paliulis and Nicklas 2004). These linkages are partially dependent on the protector of cohesin, SGO1. In anaphase, the spatially regulated dissolution of these mechanical linkages serves to prevent premature sister separation and restrain the rate of spindle elongation. Thus, si... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2639411 Thu, 23 Jul 2009 09:00:33 +0100 2639411 http://www.medworm.com/index.php?rid=2633263&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fq35447735r324251%2F Abstract  The cell cycle-associated phosphorylation of histone H1.5 is manifested as three discrete phosphorylated forms, occurring exclusively on Ser17, Ser172, and Ser188 during interphase. During late G2 and mitosis the up-phosphorylation occurs exclusively on threonine at either Thr137 or Thr154 to build the tetraphosphorylated forms of H1.5, whereas the pentaphosphorylated forms result from phosphorylation at Thr10. To determine the kinetic and spatial distribution of histone H1 phosphorylation within the nucleus of synchronized Hela cells we localized three distinct phosphorylation sites of histone subtype H1.5 using affinity-purified polyclonal antibodies generated against phosphorylated Ser17, Ser172, and Thr10. Immunofluorescence labeling of synchronized HeLa cells us... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2633263 Sat, 18 Jul 2009 08:27:33 +0100 2633263 http://www.medworm.com/index.php?rid=2592847&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fq4kx184v53774748%2F Abstract  Centromeres, the chromosomal loci that form the sites of attachment for spindle microtubules during mitosis, are identified by a unique chromatin structure generated by nucleosomes containing the histone H3 variant CENP-A. The apparent epigenetic mode of centromere inheritance across mitotic and meiotic divisions has generated much interest in how CENP-A assembly occurs and how structurally divergent centromeric nucleosomes can specify the centromere complex. Although a substantial number of proteins have been implicated in centromere assembly, factors that can bind CENP-A specifically and deliver nascent protein to the centromere were, thus far, lacking. Several recent reports on experiments in fission yeast and human cells have now shown significant progress on ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2592847 Fri, 10 Jul 2009 08:10:19 +0100 2592847 http://www.medworm.com/index.php?rid=2592848&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fnu8582q215g73681%2F In this study, we have examined the genome organization in interphase nuclei during adipogenesis, using the pig as a model organism. We hypothesized that changes in the gene expression profile and chromatin remodeling which occur during cellular differentiation would elicit repositioning of whole chromosomes, moving specific genes on them to different regions of the nucleus. We established an in vitro adipogenesis differentiation system using mesenchymal stem cells, derived from porcine bone marrow. The nuclear position of seven adipogenesis genes (PPARG, SREBF1, FABP4, CEBPA, CEBPB, CREB, and GATA2), two control genes (SOX9 and MYL1), and six chromosomes carrying these gene loci (SSC4, SSC6, SSC12, SSC13, SSC15, and SSC17) was determined. We found that during adipogenesis, using the... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2592848 Thu, 09 Jul 2009 12:11:57 +0100 2592848 http://www.medworm.com/index.php?rid=2590478&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fwp722p29m75g4x70%2F Abstract  The looping model of enhancer–promoter interactions predicts that these specific long-range interactions are supported by a certain class of proteins. In particular, the Drosophila transcription factor Zeste was hypothesized to facilitate long-distance associations between enhancers and promoters. We have re-examined the role of Zeste in supporting long-range interactions between an enhancer and a promoter using the white gene as a model system. The results show that Zeste binds to the upstream white promoter region and the enhancer that is responsible for white activation in the eyes. We have confirmed the previous finding that Zeste is not required for the activity of the eye enhancer and the promoter when they are located in close proximity to each other. Howeve... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2590478 Mon, 06 Jul 2009 20:15:11 +0100 2590478 http://www.medworm.com/index.php?rid=2579224&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fh5u725723u400167%2F Abstract  B chromosomes (Bs) are dispensable components of the genomes of numerous species. To test whether the transcriptome of a host is influenced by Bs, we looked for differences in expression in response to additional Bs. Comparative complementary DNA amplified fragment length polymorphism experiments resulted in the identification of 16 putative B-chromosome-associated transcripts. This comprises 0.7% of the total transcript number and indicates a low activity of Bs. We also provide evidence that B chromosome influences in trans the transcription of A chromosome sequences. The B-specific transcribed sequences B1334, B8149, and B2465 belong to high-copy families with similarity to mobile elements. For all analyzed B-chromosome-derived transcripts, similar A chromosome-e... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2579224 Mon, 06 Jul 2009 16:51:04 +0100 2579224 http://www.medworm.com/index.php?rid=2550004&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F65426n0472754718%2F Abstract  Synapsis of homologous chromosomes is a key meiotic event, mediated by a large proteinaceous structure termed the synaptonemal complex. Here, we describe a role in meiosis for the murine death-inducer obliterator (Dido) gene. The Dido gene codes for three proteins that recognize trimethylated histone H3 lysine 4 through their amino-terminal plant homeodomain domain. DIDO3, the largest of the three isoforms, localizes to the central region of the synaptonemal complex in germ cells. DIDO3 follows the distribution of the central region protein SYCP1 in Sycp3−/− spermatocytes, which lack the axial elements of the synaptonemal complex. This indicates that synapsis is a requirement for DIDO3 incorporation. Interestingly, DIDO3 is missing from the synaptonemal complex ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2550004 Fri, 26 Jun 2009 07:12:48 +0100 2550004 http://www.medworm.com/index.php?rid=2500641&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fajl3208n74308833%2F Abstract  In contrast to yeast, plant interphase nuclei often display incomplete alignment (cohesion) along sister chromatid arms. Sister chromatid cohesion mediated by the multi-subunit cohesin complex is essential for correct chromosome segregation during nuclear divisions and for DNA recombination repair. The cohesin complex consists of the conserved proteins SMC1, SMC3, SCC3, and an α-kleisin subunit. Viable homozygous mutants could be selected for the Arabidopsis thaliana α-kleisins SYN1, SYN2, and SYN4, which can partially compensate each other. For the kleisin SYN3 and for the single-copy genes SMC1, SMC3, and SCC3, only heterozygous mutants were obtained that displayed between 77% and 97% of the wild-type transcript level. Compared to wild-type nuclei, sister chroma... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2500641 Wed, 17 Jun 2009 07:05:37 +0100 2500641 http://www.medworm.com/index.php?rid=2500642&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F651145wur2378246%2F Abstract  The interphase nucleus and nuclear envelope can acquire a myriad of shapes in normal or pathological cell states. There exist a wide variety of indentations and invaginations, of protrusions and evaginations. It has been difficult to classify and name all of these nuclear shapes and, consequently, a barrier to understanding the biochemical and biophysical causes. This review focuses upon one type of nuclear envelope shape change, named “nuclear envelope-limited chromatin sheets” (ELCS), which appears to involve exaggerated nuclear envelope growth, carrying with it one or more layers of ∼30 nm diameter heterochromatin. A hypothesis on the formation of ELCS is proposed, relating higher order heterochromatin structure in an interphase nucleus, nuclear enve... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2500642 Fri, 12 Jun 2009 10:43:57 +0100 2500642 http://www.medworm.com/index.php?rid=2500643&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fr072181747625001%2F Abstract  DNA methylation is a major epigenetic modification in the genomes of higher eukaryotes. In vertebrates, DNA methylation occurs predominantly on the CpG dinucleotide, and approximately 60% to 90% of these dinucleotides are modified. Distinct DNA methylation patterns, which can vary between different tissues and developmental stages, exist on specific loci. Sites of DNA methylation are occupied by various proteins, including methyl-CpG binding domain (MBD) proteins which recruit the enzymatic machinery to establish silent chromatin. Mutations in the MBD family member MeCP2 are the cause of Rett syndrome, a severe neurodevelopmental disorder, whereas other MBDs are known to bind sites of hypermethylation in human cancer cell lines. Here, we review the advances in our... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2500643 Tue, 09 Jun 2009 12:43:30 +0100 2500643 http://www.medworm.com/index.php?rid=2462381&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy734t77024074676%2F Abstract  We have analyzed in a true bug, Graphosoma italicum (Pentatomidae, Hemiptera), the temporal and functional relationships between recombination events, synapsis progression, and SMC1α and SMC3 cohesin axis maturation throughout the male first meiotic prophase. The localization of the histone variant histone H3 trimethylated at lysine 9 at chromosome ends has allowed us to determine the association of these heterochromatic domains through prophase I stages. Results highlighted that cohesins provide to be good markers for synapsis progression since the formation, morphology, and development of the SMC1α and SMC3 cohesin axes resemble the synaptonemal complex dynamics and, also, that in this species the initiation of recombination precedes synapsis. In addition, we h... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2462381 Thu, 04 Jun 2009 10:05:40 +0100 2462381 http://www.medworm.com/index.php?rid=2445628&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F0775w54473162421%2F Content Type Journal ArticleCategory ObituaryDOI 10.1007/s00412-009-0217-5Authors Eduardo Gorab, Universidade de São Paulo Departamento de Genética e Biologia Evolutiva, Instituto de Biociências Rua do Matão 277, Cidade Universitária São Paulo São Paulo 05508-090 Brazil Journal ChromosomaOnline ISSN 1432-0886Print ISSN 0009-5915 (Source: Chromosoma) Chromosoma journals http://www.medworm.com/rss/comments.php?id=2445628 Fri, 29 May 2009 08:16:28 +0100 2445628 http://www.medworm.com/index.php?rid=2431435&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fm3h8071041h5056p%2F Abstract  The establishment of sex-specific epigenetic marks during gametogenesis is one of the key feature of genomic imprinting. By immunocytological analysis, we thoroughly characterized the chromatin remodeling events that take place during gametogenesis in the mealybug Planococcus citri, in which an entire haploid set of (imprinted) chromosomes undergoes facultative heterochromatinization in male embryos. Building on our previous work, we have investigated the interplay of several epigenetic marks in the regulation of this genome-wide phenomenon. We characterized the germline patterns of histone modifications, Me(3)K9H3, Me(2)K9H3, and Me(3)K20H4, and of heterochromatic proteins, PCHET2 (HP1-like) and HP2-like during male and female gametogenesis. We found that at all s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2431435 Thu, 21 May 2009 06:15:54 +0100 2431435 http://www.medworm.com/index.php?rid=2426456&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fv8803jx203r24577%2F Abstract  The zebra finch (Taeniopygia guttata) germline-restricted chromosome (GRC) is the largest chromosome and has a unique system of transmission in germ cells. In the male, the GRC exists as a single heterochromatic chromosome in the germline and is eliminated from nuclei in late spermatogenesis. In the female, the GRC is bivalent and euchromatic and experiences recombination. These characteristics suggest a female-specific or female-beneficial function of the GRC. To shed light on the function of GRC, we cloned a portion of the GRC using random amplified polymorphic DNA–polymerase chain reaction and analyzed it using molecular genetic and cytogenetic methods. The GRC clone hybridized strongly to testis but not blood DNA in genomic Southern blots. In fluorescent in s... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2426456 Tue, 19 May 2009 05:54:48 +0100 2426456 http://www.medworm.com/index.php?rid=2395713&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fk33512w631767766%2F Abstract  The organization of chromosomes into euchromatin and heterochromatin is amongst the most important and enigmatic aspects of genome evolution. Constitutive heterochromatin is a basic yet still poorly understood component of eukaryotic chromosomes, and its molecular characterization by means of standard genomic approaches is intrinsically difficult. Although recent evidence indicates that the presence of transcribed genes in constitutive heterochromatin is a conserved trait that accompanies the evolution of eukaryotic genomes, the term heterochromatin is still considered by many as synonymous of gene silencing. In this paper, we comprehensively review data that provide a clearer picture of transcribed sequences within constitutive heterochromatin, with a special emp... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2395713 Sat, 02 May 2009 06:24:59 +0100 2395713 http://www.medworm.com/index.php?rid=2395712&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fu357057481167476%2F Abstract  Puffs in the polytene chromosome of Drosophila melanogaster are characteristic of sites of high-level active transcription which can be observed directly under the microscope. We studied the dependence of puff formation on chromatin modifications at a site where a GAL4-inducible transgene is located in the 61C7 cytological region. Immunostaining of salivary gland polytene chromosomes indicated no increase of either dSAGA-specific histone H3 lysine 14, or ATAC-specific histone H4 lysine 5 and 12 acetylation in the puffed region. Nor did we observe increased levels of H4K8ac, H3K18ac, or H4K16ac in the puff. In accordance with the above, puff formation as well as localization of Pol II and GAL4 was detectable at the 61C region in dAda2b and dAda2a null homozygotes, w... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2395712 Sat, 02 May 2009 06:24:59 +0100 2395712 http://www.medworm.com/index.php?rid=2385775&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fn57667t10476x2m2%2F Abstract  In 1906, the Spanish neurobiologist Santiago Ramón y Cajal was awarded the Nobel Prize in Physiology or Medicine in recognition of his work on the structure of neurons and their connections. Cajal is commonly regarded as the father of modern neuroscience. What is less well known is that Cajal also had a great interest in intracellular neuronal structures and developed the reduced silver nitrate method for the study of neurofibrils (neurofilaments) and nuclear subcompartments. It was in 1903 that Cajal discovered the “accessory body” (“Cajal body”) and seven years later, published an article on the organization of the cell nucleus in mammalian neurons that represents a masterpiece of nuclear structure at the light microscopy level. In addition to the acces... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2385775 Thu, 30 Apr 2009 06:03:18 +0100 2385775 http://www.medworm.com/index.php?rid=2373486&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Ff18054278l575477%2F Abstract  Histones of trypanosomes are quite divergent when compared to histones of most eukaryotes. Nevertheless, the histone H4 of Trypanosoma cruzi, the protozoan that causes Chagas’ disease, is acetylated in the N terminus at lysines 4, 10, and 14. Here, we investigated the cellular distribution of histone H4 containing each one of these posttranslational modifications by using specific antibodies. Histone H4 acetylated at lysine 4 (H4-K4ac) is found in the entire nuclear space preferentially at dense chromatin regions, excluding the nucleolus of replicating epimastigote forms of the parasite. In contrast, histone H4 acetylated either at K10 or K14 is found at dispersed foci all over the nuclei and at the interface between dense and nondense chromatin areas as observed... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2373486 Sat, 25 Apr 2009 07:28:07 +0100 2373486 http://www.medworm.com/index.php?rid=2373487&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2F710230t10314r625%2F Abstract  The Mre11-Rad50-Nbs1 (MRN) complex is required for numerous cellular processes that involve interactions with DNA double-strand breaks. For the majority of these processes, the MRN complex is thought to act as a unit, with each protein aiding the activity of the others. We have examined the relationship between Mre11 and Rad50 during meiosis in the basidiomycete Coprinus cinereus (Coprinopsis cinerea), investigating to what extent activities of Mre11 and Rad50 are interdependent. We showed that mre11-1 is epistatic to rad50-1 with respect to the time of meiotic arrest, indicating that Mre11 activity facilitates the diffuse diplotene arrest of rad50 mutants. Anti-Mre11 and anti-Rad50 antibodies were used to examine MRN complex localization in a wild-type strain and in ... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2373487 Sat, 25 Apr 2009 07:28:06 +0100 2373487 http://www.medworm.com/index.php?rid=2321229&cid=s_33449_50_f&fid=33449&url=http%3A%2F%2Fwww.springerlink.com%2Fcontent%2Fy38376216137p471%2F Abstract  MicroRNAs (miRNAs) were first discovered in genetic screens for regulators of developmental timing in the stem-cell-like seam cell lineage in Caenorhabditis elegans. As members of the heterochronic pathway, the lin-4 and let-7 miRNAs are required in the seam cells for the correct progression of stage-specific events and to ensure that cell cycle exit and terminal differentiation occur at the correct time. Other heterochronic genes such as lin-28 and lin-41 are direct targets of the lin-4 and let-7 miRNAs. Recent findings on the functions of the let-7 and lin-4/mir-125 miRNA families and lin-28 and lin-41 orthologs from a variety of organisms suggest that core elements of the heterochronic pathway are retained in mammalian stem cells and development. In particular, th... Chromosoma journals http://www.medworm.com/rss/comments.php?id=2321229 Thu, 02 Apr 2009 05:51:20 +0100 2321229