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The Yin and Yang of centromeric cohesion of sister chromatids: mitotic kinases meet protein phosphatase 2A
Wei Dai, Xiaoxing Wang
Cell Division , 2006, DOI: 10.1186/1747-1028-1-9
Abstract: Sister chromatid cohesion is established during DNA replication and maintained throughout G2 and mitotic prophase and metaphase. At the molecular level, cohesin mediates sister chromatid cohesion through formation of a proposed "ring" structure that entraps chromosomes [1]. The cohesin complex is composed of Smc1, Smc3, Scc1 (substituted by Rec8 in meiosis), and Scc3 (SA1, SA2, or SA3 as an orthologue in vertebrates). During mitosis, cohesin in animal cells is removed from chromosomes in a stepwise fashion through the action of Plk1 and separase, respectively [2,3]. Upon mitotic entry, cohesin dissociates itself along the entire length of chromosomal arms, but not at centromeres, which requires the activity of Plk1 [2]. At anaphase entry, separase activity removes centromeric cohesin [3] that is otherwise inhibited by the spindle checkpoint during prophase and metaphase. Similar temporally-regulated release of cohesin also exists during meiosis. At the first meiotic division (meiosis I), separase cleaves Rec8 along chromosome arms but not at centromeres, resulting in segregation of homologous non-sister chromosomes. During meiosis II, centromeric cohesin is cleaved through the second wave of separase activity, leading to disjunction of sister centromeres and formation of haploid gametes [4,5].During the past several years, the mechanism preventing centromeric cohesin from undergoing cleavage/dissociation during early mitosis as well as meiosis I and early meiosis II has been a subject of intensive investigation [6,7]. Through the pioneering research efforts of Orr-Weaver and Watanabe groups, a family of proteins termed shugoshins/MEI-S332, has been identified in various eukaryotic model systems [8-10]. This work led to the realization that they play a critical role in mediating protection of centromeric cohesion of sister chromatids during mitosis and meiosis (see a review [11]). Whereas vertebrate shugoshin 1 (Sgo1) functions to protect centromeric cohesin during m
SGO1 Maintains Bovine Meiotic and Mitotic Centromeric Cohesions of Sister Chromatids and Directly Affects Embryo Development  [PDF]
Feng-Xia Yin, Guang-Peng Li, Chun-Ling Bai, Yang Liu, Zhu-Ying Wei, Cheng-Guang Liang, Thomas D. Bunch, Lin-Sen Zan
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073636
Abstract: Shugoshin (SGO) is a critical factor that enforces cohesion from segregation of paired sister chromatids during mitosis and meiosis. It has been studied mainly in invertebrates. Knowledge of SGO(s) in a mammalian system has only been reported in the mouse and Hela cells. In this study, the functions of SGO1 in bovine oocytes during meiotic maturation, early embryonic development and somatic cell mitosis were investigated. The results showed that SGO1 was expressed from germinal vesicle (GV) to the metaphase II stage. SGO1 accumulated on condensed and scattered chromosomes from pre-metaphase I to metaphase II. The over-expression of SGO1 did not interfere with the process of homologous chromosome separation, although once separated they were unable to move to the opposing spindle poles. This often resulted in the formation of oocytes with 60 replicated chromosomes. Depletion of SGO1 in GV oocytes affected chromosomal separation resulting in abnormal chromosome alignment at a significantly higher proportion than in control oocytes. Knockdown of SGO1 expression significantly decreased the embryonic developmental rate and quality. To further confirm the function(s) of SGO1 during mitosis, bovine embryonic fibroblast cells were transfected with SGO1 siRNAs. SGO1 depletion induced the premature dissociation of chromosomal cohesion at the centromere and along the chromosome arm giving rise to abnormal appearing mitotic patterns. The results of this study infer that SGO1 is involved in the centromeric cohesion of sister chromatids and chromosomal movement towards the spindle poles. Depletion of SGO1 causes arrestment of cell division in meiosis and mitosis.
Centromere Architecture Breakdown Induced by the Viral E3 Ubiquitin Ligase ICP0 Protein of Herpes Simplex Virus Type 1  [PDF]
Sylvain Gross, Frédéric Catez, Hiroshi Masumoto, Patrick Lomonte
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044227
Abstract: The viral E3 ubiquitin ligase ICP0 protein has the unique property to temporarily localize at interphase and mitotic centromeres early after infection of cells by the herpes simplex virus type 1 (HSV-1). As a consequence ICP0 induces the proteasomal degradation of several centromeric proteins (CENPs), namely CENP-A, the centromeric histone H3 variant, CENP-B and CENP-C. Following ICP0-induced centromere modification cells trigger a specific response to centromeres called interphase Centromere Damage Response (iCDR). The biological significance of the iCDR is unknown; so is the degree of centromere structural damage induced by ICP0. Interphase centromeres are complex structures made of proximal and distal protein layers closely associated to CENP-A-containing centromeric chromatin. Using several cell lines constitutively expressing GFP-tagged CENPs, we investigated the extent of the centromere destabilization induced by ICP0. We show that ICP0 provokes the disappearance from centromeres, and the proteasomal degradation of several CENPs from the NAC (CENP-A nucleosome associated) and CAD (CENP-A Distal) complexes. We then investigated the nucleosomal occupancy of the centromeric chromatin in ICP0-expressing cells by micrococcal nuclease (MNase) digestion analysis. ICP0 expression either following infection or in cell lines constitutively expressing ICP0 provokes significant modifications of the centromeric chromatin structure resulting in higher MNase accessibility. Finally, using human artificial chromosomes (HACs), we established that ICP0-induced iCDR could also target exogenous centromeres. These results demonstrate that, in addition to the protein complexes, ICP0 also destabilizes the centromeric chromatin resulting in the complete breakdown of the centromere architecture, which consequently induces iCDR.
Timeless Links Replication Termination to Mitotic Kinase Activation  [PDF]
Jayaraju Dheekollu,Andreas Wiedmer,James Hayden,David Speicher,Anthony L. Gotter,Tim Yen,Paul M. Lieberman
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0019596
Abstract: The mechanisms that coordinate the termination of DNA replication with progression through mitosis are not completely understood. The human Timeless protein (Tim) associates with S phase replication checkpoint proteins Claspin and Tipin, and plays an important role in maintaining replication fork stability at physical barriers, like centromeres, telomeres and ribosomal DNA repeats, as well as at termination sites. We show here that human Tim can be isolated in a complex with mitotic entry kinases CDK1, Auroras A and B, and Polo-like kinase (Plk1). Plk1 bound Tim directly and colocalized with Tim at a subset of mitotic structures in M phase. Tim depletion caused multiple mitotic defects, including the loss of sister-chromatid cohesion, loss of mitotic spindle architecture, and a failure to exit mitosis. Tim depletion caused a delay in mitotic kinase activity in vivo and in vitro, as well as a reduction in global histone H3 S10 phosphorylation during G2/M phase. Tim was also required for the recruitment of Plk1 to centromeric DNA and formation of catenated DNA structures at human centromere alpha satellite repeats. Taken together, these findings suggest that Tim coordinates mitotic kinase activation with termination of DNA replication.
Assembly of Drosophila Centromeric Chromatin Proteins during Mitosis  [PDF]
Barbara G. Mellone ,Kathryn J. Grive equal contributor,Vladimir Shteyn equal contributor,Sarion R. Bowers,Isaac Oderberg,Gary H. Karpen
PLOS Genetics , 2011, DOI: 10.1371/journal.pgen.1002068
Abstract: Semi-conservative segregation of nucleosomes to sister chromatids during DNA replication creates gaps that must be filled by new nucleosome assembly. We analyzed the cell-cycle timing of centromeric chromatin assembly in Drosophila, which contains the H3 variant CID (CENP-A in humans), as well as CENP-C and CAL1, which are required for CID localization. Pulse-chase experiments show that CID and CENP-C levels decrease by 50% at each cell division, as predicted for semi-conservative segregation and inheritance, whereas CAL1 displays higher turnover. Quench-chase-pulse experiments demonstrate that there is a significant lag between replication and replenishment of centromeric chromatin. Surprisingly, new CID is recruited to centromeres in metaphase, by a mechanism that does not require an intact mitotic spindle, but does require proteasome activity. Interestingly, new CAL1 is recruited to centromeres before CID in prophase. Furthermore, CAL1, but not CENP-C, is found in complex with pre-nucleosomal CID. Finally, CENP-C displays yet a different pattern of incorporation, during both interphase and mitosis. The unusual timing of CID recruitment and unique dynamics of CAL1 identify a distinct centromere assembly pathway in Drosophila and suggest that CAL1 is a key regulator of centromere propagation.
Mitotic dynamics
TANG Xiaowei,
唐孝威

中国科学C辑(英文版) , 1996,
Abstract: A new model for mitotic dynamics of eukaryotic cells is proposed. In the kinetochore mo-tor-midzone motor model two kinds of motors, the kinetochore motors and the midzone motors, play important roles in chromosome movement. Using this model the chromosome congression during prometaphase, the chromosome oscillation during metaphase and the chromatid segregation during anaphase are described in a unified way.
Intergenic Locations of Rice Centromeric Chromatin  [PDF]
Huihuang Yan,Paul B. Talbert,Hye-Ran Lee,Jamie Jett,Steven Henikoff,Feng Chen,Jiming Jiang
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0060286
Abstract: Centromeres are sites for assembly of the chromosomal structures that mediate faithful segregation at mitosis and meiosis. Plant and animal centromeres are typically located in megabase-sized arrays of tandem satellite repeats, making their precise mapping difficult. However, some rice centromeres are largely embedded in nonsatellite DNA, providing an excellent model to study centromere structure and evolution. We used chromatin immunoprecipitation and 454 sequencing to define the boundaries of nine of the 12 centromeres of rice. Centromere regions from chromosomes 8 and 9 were found to share synteny, most likely reflecting an ancient genome duplication. For four centromeres, we mapped discrete subdomains of binding by the centromeric histone variant CENH3. These subdomains were depleted in both intact and nonfunctional genes relative to interspersed subdomains lacking CENH3. The intergenic location of rice centromeric chromatin resembles the situation for human neocentromeres and supports a model of the evolution of centromeres from gene-poor regions.
Intergenic Locations of Rice Centromeric Chromatin  [PDF]
Huihuang Yan,Paul B Talbert,Hye-Ran Lee,Jamie Jett,Steven Henikoff,Feng Chen ,Jiming Jiang
PLOS Biology , 2008, DOI: 10.1371/journal.pbio.0060286
Abstract: Centromeres are sites for assembly of the chromosomal structures that mediate faithful segregation at mitosis and meiosis. Plant and animal centromeres are typically located in megabase-sized arrays of tandem satellite repeats, making their precise mapping difficult. However, some rice centromeres are largely embedded in nonsatellite DNA, providing an excellent model to study centromere structure and evolution. We used chromatin immunoprecipitation and 454 sequencing to define the boundaries of nine of the 12 centromeres of rice. Centromere regions from chromosomes 8 and 9 were found to share synteny, most likely reflecting an ancient genome duplication. For four centromeres, we mapped discrete subdomains of binding by the centromeric histone variant CENH3. These subdomains were depleted in both intact and nonfunctional genes relative to interspersed subdomains lacking CENH3. The intergenic location of rice centromeric chromatin resembles the situation for human neocentromeres and supports a model of the evolution of centromeres from gene-poor regions.
Repetitive DNA is associated with centromeric domains in Trypanosoma brucei but not Trypanosoma cruzi
Samson O Obado, Christopher Bot, Daniel Nilsson, Bjorn Andersson, John M Kelly
Genome Biology , 2007, DOI: 10.1186/gb-2007-8-3-r37
Abstract: We report evidence on the location and nature of centromeric DNA in Trypanosoma cruzi and Trypanosoma brucei. In T. cruzi, we used telomere-associated chromosome fragmentation and found that GC-rich transcriptional 'strand-switch' domains composed predominantly of degenerate retrotranposons are a shared feature of regions that confer mitotic stability. Consistent with this, etoposide-mediated topoisomerase-II cleavage, a biochemical marker for active centromeres, is concentrated at these domains. In the 'megabase-sized' chromosomes of T. brucei, topoisomerase-II activity is also focused at single loci that encompass regions between directional gene clusters that contain transposable elements. Unlike T. cruzi, however, these loci also contain arrays of AT-rich repeats stretching over several kilobases. The sites of topoisomerase-II activity on T. brucei chromosome 1 and T. cruzi chromosome 3 are syntenic, suggesting that centromere location has been conserved for more than 200 million years. The T. brucei intermediate and minichromosomes, which lack housekeeping genes, do not exhibit site-specific accumulation of topoisomerase-II, suggesting that segregation of these atypical chromosomes might involve a centromere-independent mechanism.The localization of centromeric DNA in trypanosomes fills a major gap in our understanding of genome organization in these important human pathogens. These data are a significant step towards identifying and functionally characterizing other determinants of centromere function and provide a framework for dissecting the mechanisms of chromosome segregation.Centromeres are the chromosomal loci where kinetochores are assembled. The centromere/kinetochore complex is the anchor for attachment of the microtubule spindles that facilitate segregation. Two main classes of centromere have been identified. In most eukaryotes, centromeres are 'regional' and can encompass large regions of chromosomal DNA, ranging from 0.3-15 Mb in species as divers
Mitotic and meiotic chromosomes of a southern Brazilian population of Boophilus microplus (Acari, Ixodidae)
Garcia, Rosane Nunes;Garcia-Fernandez, Casemiro;Garcia, Sonia Maria Lauer;Valente, Vera Lúcia S.;
Iheringia. Série Zoologia , 2002, DOI: 10.1590/S0073-47212002000100004
Abstract: using conventional staining with acetic orcein and c-banding techniques it was investigated constitutive heterochromatin chromosomal polymorphisms and the mitotic and the meiotic behavior of male and female chromosomes of boophilus microplus (canestrini, 1887). some differences were detected in the population of southern brazil as compared to the data of other authors for populations in other latitudes. the differences being mainly concerned with the distribution of constitutive centromeric heterochromatin and variation in the length of heterochromatic blocks in the pericentromeric regions of some chromosome pairs.
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