共查询到20条相似文献，搜索用时 15 毫秒
1.
Requirement of heterochromatin for cohesion at centromeres 总被引：1，自引：0，他引：1
Bernard P Maure JF Partridge JF Genier S Javerzat JP Allshire RC 《Science (New York, N.Y.)》2001,294(5551):2539-2542
Centromeres are heterochromatic in many organisms, but the mitotic function of this silent chromatin remains unknown. During cell division, newly replicated sister chromatids must cohere until anaphase when Scc1/Rad21-mediated cohesion is destroyed. In metazoans, chromosome arm cohesins dissociate during prophase, leaving centromeres as the only linkage before anaphase. It is not known what distinguishes centromere cohesion from arm cohesion. Fission yeast Swi6 (a Heterochromatin protein 1 counterpart) is a component of silent heterochromatin. Here we show that this heterochromatin is specifically required for cohesion between sister centromeres. Swi6 is required for association of Rad21-cohesin with centromeres but not along chromosome arms and, thus, acts to distinguish centromere from arm cohesion. Therefore, one function of centromeric heterochromatin is to attract cohesin, thereby ensuring sister centromere cohesion and proper chromosome segregation. 相似文献
2.
Cell division depends on the separation of sister chromatids in anaphase. In yeast, sister separation is initiated by cleavage of cohesin by the protease separase. In vertebrates, most cohesin is removed from chromosome arms by a cleavage-independent mechanism. Only residual amounts of cohesin are cleaved at the onset of anaphase, coinciding with its disappearance from centromeres. We have identified two separase cleavage sites in the human cohesin subunit SCC1 and have conditionally expressed noncleavable SCC1 mutants in human cells. Our results indicate that cohesin cleavage by separase is essential for sister chromatid separation and for the completion of cytokinesis. 相似文献
3.
Chromosome alignment on the mitotic spindle is monitored by the spindle checkpoint. We identify Sgo1, a protein involved in meiotic chromosome cohesion, as a spindle checkpoint component. Budding yeast cells with mutations in SGO1 respond normally to microtubule depolymerization but not to lack of tension at the kinetochore, and they have difficulty attaching sister chromatids to opposite poles of the spindle. Sgo1 is thus required for sensing tension between sister chromatids during mitosis, and its degradation when they separate may prevent cell cycle arrest and chromosome loss in anaphase, a time when sister chromatids are no longer under tension. 相似文献
4.
The structure of sister minichromosome DNA before anaphase in Saccharomyces cerevisiae 总被引：13，自引：0，他引：13
The role of DNA topology in holding sister chromatids together before anaphase was investigated by analyzing the structure of a small circular minichromosome in cell cycle (cdc) mutants of the yeast Saccharomyces cerevisiae. In the majority of cells arrested after S phase but before anaphase, sister minichromosome molecules are not topologically interlocked with each other. The analysis of the ploidy of minichromosomes in cells that are released from arrest demonstrates that the sister molecules are properly segregated when the cell cycle block is removed. Therefore, sister minichromosome molecules need not remain topologically interlocked until anaphase in order to be properly segregated, and topological interlocking of sister DNA molecules apparently is not the primary force holding sister chromatids together. 相似文献
5.
In eukaryotic cells, sister DNA molecules remain physically connected from their production at S phase until their separation during anaphase. This cohesion is essential for the separation of sister chromatids to opposite poles of the cell at mitosis. It also permits chromosome segregation to take place long after duplication has been completed. Recent work has identified a multisubunit complex called cohesin that is essential for connecting sisters. Proteolytic cleavage of one of cohesin's subunits may trigger sister separation at the onset of anaphase. 相似文献
6.
CARLSON JG 《Science (New York, N.Y.)》1956,124(3214):203-206
My conclusions, which, I confess, are tentative and based mainly on studies of one kind of cell, the grasshopper neuroblast, may be summarized as follows. The late prophase orientation of the chromosomes is a carry-over from the late telophase orientation. It is apparently maintained by means of the centromeres, which appear to be attached within a limited region of the nucleus throughout telophase, interphase, and prophase. Metaphase orientation of the chromosomes may be explained as the resultant of two forces: a force involving the centromere and spindle, which is responsible for keeping the centromeres in the equatorial plane of the spindle, and a repulsion force involving the noncentromeric portion of the chromosomes, which results in a tendency toward uniform spacing of the chromosomes outside the spindle. Anaphase separation of sister chromatids and their subsequent movement toward the poles of the spindle involves at least four distinct phases: (i) the initial poleward movement of the centromeres, which may be due to intrinsic repulsion or to a force acting between spindle and centromeres that produces an angle of almost 90 degrees between the separated and unseparated portions of the chromatids; (ii) the autonomous separation of the noncentromeric part of the chromosome; (iii) elongation of the spindle, beginning just after the sister chromatids are separated proximally and ending when the longer chromatids are about to lose contact distally; and (iv) the later movement apart of the daughter chromosomes, probably resulting from a pushing force exerted by elongation of the interzonal fibers. 相似文献
7.
Cells from Werner syndrome patients are characterized by slow growth rates, premature senescence, accelerated telomere shortening rates, and genome instability. The syndrome is caused by the loss of the RecQ helicase WRN, but the underlying molecular mechanism is unclear. Here we report that cells lacking WRN exhibit deletion of telomeres from single sister chromatids. Only telomeres replicated by lagging strand synthesis were affected, and prevention of loss of individual telomeres was dependent on the helicase activity of WRN. Telomere loss could be counteracted by telomerase activity. We propose that WRN is necessary for efficient replication of G-rich telomeric DNA, preventing telomere dysfunction and consequent genomic instability. 相似文献
8.
Meiotic cohesin complexes at centromeres behave differently from those along chromosome arms, but the basis for these differences has remained elusive. The fission yeast cohesin molecule Rec8 largely replaces its mitotic counterpart, Rad21/Scc1, along the entire chromosome during meiosis. Here we show that Rec8 complexes along chromosome arms contain Rec11, whereas those in the vicinity of centromeres have a different partner subunit, Psc3. The arm associated Rec8-Rec11 complexes are critical for meiotic recombination. The Rec8-Psc3 complexes comprise two different types of assemblies. First, pericentromeric Rec8-Psc3 complexes depend on histone methylation-directed heterochromatin for their localization and are required for cohesion during meiosis II. Second, central core Rec8-Psc3 complexes form independently of heterochromatin and are presumably required for establishing monopolar attachment at meiosis I. These findings define distinct modes of assembly and functions for cohesin complexes at different regions along chromosomes. 相似文献
9.
Segregation of sister chromatids in mammalian cells 总被引：13，自引：0，他引：13
Segregation of sister chromatids in embryonic mouse cells in primary tissue culture is not random. In mitosis those chromatids replicated on a DNA template synthesized during the preceding division cycle are separated from those constructed on a template synthesized two division cycles previously. Segregation in cells of the Chinese hamster follows a similar, but less pronounced, pattern. 相似文献
10.
Mammalian kinetochores contain the centromere-specific histone H3 variant CENP-A, whose incorporation into limited chromosomal regions may be important for centromere function and chromosome segregation during mitosis. However, regulation of CENP-A localization and its role have not been clear. Here we report that the fission yeast homolog SpCENP-A is essential for establishing centromere chromatin associated with equal chromosome segregation. SpCENP-A binding to the nonrepetitious inner centromeres depended on Mis6, an essential centromere connector protein acting during G1-S phase of the cell cycle. Mis6 is likely required for recruiting SpCENP-A to form proper connection of sister centromeres. 相似文献
11.
Palframan WJ Meehl JB Jaspersen SL Winey M Murray AW 《Science (New York, N.Y.)》2006,313(5787):680-684
The spindle checkpoint delays cell cycle progression until microtubules attach each pair of sister chromosomes to opposite poles of the mitotic spindle. Following sister chromatid separation, however, the checkpoint ignores chromosomes whose kinetochores are attached to only one spindle pole, a state that activates the checkpoint prior to metaphase. We demonstrate that, in budding yeast, mutual inhibition between the anaphase-promoting complex (APC) and Mps1, an essential component of the checkpoint, leads to sustained inactivation of the spindle checkpoint. Mps1 protein abundance decreases in anaphase, and Mps1 is a target of the APC. Furthermore, expression of Mps1 in anaphase, or repression of the APC in anaphase, reactivates the spindle checkpoint. This APC-Mps1 feedback circuit allows cells to irreversibly inactivate the checkpoint during anaphase. 相似文献
12.
13.
During meiosis, two chromosome segregation phases follow a single round of DNA replication. We identified factors required to establish this specialized cell cycle by examining meiotic chromosome segregation in a collection of yeast strains lacking all nonessential genes. This analysis revealed Sgo1, Chl4, and Iml3 to be important for retaining centromeric cohesin until the onset of anaphase II. Consistent with this role, Sgo1 localizes to centromeric regions but dissociates at the onset of anaphase II. The screen described here provides a comprehensive analysis of the genes required for the meiotic cell cycle and identifies three factors important for the stepwise loss of sister chromatid cohesion. 相似文献
14.
Neurohr G Naegeli A Titos I Theler D Greber B Díez J Gabaldón T Mendoza M Barral Y 《Science (New York, N.Y.)》2011,332(6028):465-468
Partitioning of chromatids during mitosis requires that chromosome compaction and spindle length scale appropriately with each other. However, it is not clear whether chromosome condensation and spindle elongation are linked. Here, we find that yeast cells could cope with a 45% increase in the length of their longest chromosome arm by increasing its condensation. The spindle midzone, aurora/Ipl1 activity, and Ser10 of histone H3 mediated this response. Thus, the anaphase spindle may function as a ruler to adapt the condensation of chromatids, promoting their segregation regardless of chromosome or spindle length. 相似文献
15.
Proper chromosome segregation requires the attachment of sister kinetochores to microtubules from opposite spindle poles to form bi-oriented chromosomes on the metaphase spindle. The chromosome passenger complex containing Survivin and the kinase Aurora B regulates this process from the centromeres. We report that a de-ubiquitinating enzyme, hFAM, regulates chromosome alignment and segregation by controlling both the dynamic association of Survivin with centromeres and the proper targeting of Survivin and Aurora B to centromeres. Survivin is ubiquitinated in mitosis through both Lys(48) and Lys(63) ubiquitin linkages. Lys(63) de-ubiquitination mediated by hFAM is required for the dissociation of Survivin from centromeres, whereas Lys(63) ubiquitination mediated by the ubiquitin binding protein Ufd1 is required for the association of Survivin with centromeres. Thus, ubiquitinaton regulates dynamic protein-protein interactions and chromosome segregation independently of protein degradation. 相似文献
16.
When a cell replicates its DNA during S phase of the cell cycle, the sister chromatid pairs must stick together like glue until they are separated to opposite ends of the cell (and hence into separate daughter cells) at anaphase. How the cell achieves this is still unclear but, as Takahashi and Yanagida explain in their Perspective, new findings in yeast have identified one molecule, Trf4p, that may be involved both in DNA replication and sister chromatid cohesion (Wang et al.). 相似文献
17.
By the combination of cytological analysis and using genomic in situ hybridization technique to identify an alien chromosome in wheat-Haynaldia villosa monosomic addition lines, we studied the meiotic behavior of the alien chromosome. The results indicated that the frequency of bivalent pairing was lower than the value expected in PMCs of two monosomic addition lines, the frequency of wheat chromosomes unpairing increased, and the wheat homologous chromosome pairing was interfered with by the added chromosome 6V at metaphase I. The chromosome 6V lagged in 20.3% -29.3% of PMCs, sister chromatids 6V early divided in 29.0% - 34.1% of PMCs, the single chromosome 6V in 18.2% - 26.1% of PMCs went to a pole randomly,the breakage frequency of chromosome 6V was 1.2% - 2.9%. Meanwhile, it was also found that several wheat chromosomes showed earlier division, lagging and breakage in a few PMCs. It revealed that the added chromosome 6V influenced the behavior of wheat chromosomes at anaphase. It was also found that the translocation was produced between 6V and wheat chromosomes in 1.2% of PMCs. It offered evidence for translocation between wheat and Haynaldia villosa 6V chromosomes. 相似文献
18.
二倍体和四倍体结球甘蓝减数分裂观察 总被引：1，自引：0，他引：1
观察了二倍体和同源四倍体结球甘蓝花粉母细胞减数分裂过程。结果表明:与二倍体相比,同源四倍体终变期染色体构型复杂,有四价体、三价体、二价体和单价体出现;中期Ⅰ及中期Ⅱ有个别染色体游离于赤道板外;后期Ⅰ出现落后染色体、提前解离的姊妹染色单体及染色体的不均衡分离;后期Ⅱ每极染色体数目变化较大;花粉的整齐度和生活力明显降低;讨论了造成四倍体结球甘蓝花粉育性比二倍体低的细胞学原因。 相似文献
19.
Mutations in the yeast Saccharomyces cerevisiae PIF1 gene, which encodes a 5'-to-3' DNA helicase, cause telomere lengthening and a large increase in the formation rate of new telomeres. Here, we show that Pif1p acts by inhibiting telomerase rather than telomere-telomere recombination, and this inhibition requires the helicase activity of Pif1p. Overexpression of enzymatically active Pif1p causes telomere shortening. Thus, Pif1p is a catalytic inhibitor of telomerase-mediated telomere lengthening. Because Pif1p is associated with telomeric DNA in vivo, its effects on telomeres are likely direct. Pif1p-like helicases are found in diverse organisms, including humans. We propose that Pif1p-mediated inhibition of telomerase promotes genetic stability by suppressing telomerase-mediated healing of double-strand breaks. 相似文献
20.
In Saccharomyces cerevisiae, the telomerase components Est2p, TLC1 RNA, Est1p, and Est3p are thought to form a complex that acts late during chromosome replication (S phase) upon recruitment by Cdc13p, a telomeric DNA binding protein. Consistent with this model, we show that Est1p, Est2p, and Cdc13p are telomere-associated at this time. However, Est2p, but not Est1p, also binds telomeres before late S phase. The cdc13-2 allele has been proposed to be defective in recruitment, yet Est1p and Est2p telomere association persists in cdc13-2 cells. These findings suggest a model in which Est1p binds telomeres late in S phase and interacts with Cdc13p to convert inactive, telomere-bound Est2p to an active form. 相似文献