Chromosome Cohesion and Segregation
Eukaryotic cells have multiple chromosomes as carts for the genetic information. In order to ensure faithful reproduction for proliferation in mitosis, or providing an opportunity for genetic reassortment in meiosis, cells must have the ability to deliver
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Chromosome Cohesion and Segregation KOHTA TAKAHASHI, MITSUHIRO YANAGIDA
11.1 Introduction
Eukaryotic cells have multiple chromosomes as carts for the genetic information. In order to ensure faithful reproduction for proliferation in mitosis, or providing an opportunity for genetic reassortment in meiosis, cells must have the ability to deliver their chromosomes properly and in good order to the daughter cells. Chromosome missegregation leads to aneuploidy, the most common genetic aberrations causing birth defects or cancer. During the cell cycle, therefore, the order and timing of dynamic changes in chromosomal morphology and behavior must be tightly controlled to coincide with the cytoskeletal changes that coordinately participate in the processes of genome redistribution. Molecular mechanisms governing three major transitions in the morphological state of sister chromatids will be reviewed in this chapter - cohesion, condensation and separation. Other relevant topics are the establishment of the mitotic spindle (Chap. 13), the organization of kinetochores (Chap. 10) and the septation process (Chap. 15), as well as the regulation of cell cycle-controlling protein kinases in general (Chap. 3). Chromosome cohesion is holding the sister chromatids together from S to M phase, ensuring proper spindle attachment of sister centromeres before anaphase. Also, in meiosis this key device enables a cell to distinguish between homologous chromosomes and sister chromatids, which is important in strand selection for meiotic crossing-over. Chromosome condensation is a compacting process that initiates at the onset of M phase, a prerequisite for the mitotic spindles to capture the chromosomes effectively and separate them without entanglement. At the onset of anaphase, cohesion between the sisters is finally dissolved and chromosome separation takes place, each pair of the sisters being equally distributed along the kinetochore micro tubules to the opposite poles. To maintain euploidy with high fidelity, several evolutionarily conserved protein complexes, such as anaphase-promoting complex or cyclosome (APC/C), securin-separase complex, cohesin and condensin, play fundamental roles in chromosome segregation. Recent genetic and biochemical studies using several model organisms have uncovered the control mechanisms of these large complexes and their functional interrelationships. In the following sections, we introduce the fission yeast gene products involved in these processes and discuss their contributions to our current understanding of the field. R. Egel (ed.), The Molecular Biology of Schizosaccharomyces pombe © Springer-Verlag Berlin Heidelberg 2004
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Kohta Takahashi, Mitsuhiro Yanagida
In brief, cohesin and condensin are structural components periodically loaded onto the chromosomes at discrete foci for sister-chromatid cohesion and condensation, respectively. In turn, the separation of sister chromatids at the onset of anaphase is triggered by a quick-release cascade of highly regulated proteases. The loaded spr
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