The SPB-led back-and-forth movement of the nucleus is called horse-tail nuclear movement. During meiotic prophase (E), a cytoplasmic array of microtubules is tethered by Hrs1 at SPBs, thereby shaking the nucleus. A number of kinetochore and SPB components are dissociated in this stage (slim SPBs and kinetochores). Telomeres slide on the nuclear envelope toward SPBs via interaction with meiosis-specific bouquet proteins (Bqt1 and Bqt2) and nuclear membrane proteins (Kms1/2–Sad1). In reaction to mating pheromone (D), telomeres get clustered to SPBs. In interphase (e.g., G1 phase) of mitotic cycles (C), centromeres (kinetochores red) are clustered at spindle pole bodies (SPBs blue). (C–E) Conversion of chromosome arrangement upon sexual differentiation in fission yeast.
In meiosis I, sister kinetochores are oriented in a side-by-side position. In mitosis (left), sister kinetochores are bi-oriented in a back-to-back position. Moa1 (Meikin) is a meiosis-specific kinetochore protein that protects centromeric Rec8 cohesin through the recruitment of shugoshin (Sgo1) to centromeres and regulates attachment to microtubules through the recruitment of Polo kinase (Plo1). Rad21 locates in the arm region of chromosomes in both divisions, whereas meiotic cohesin Rec8 (purple ring) locates in both the arm and centromeric regions. In meiosis I (right), homologous chromosomes are paired and crossed via chiasmata. Sister chromatids are connected by mitotic cohesin Rad21 (Scc1). During mitotic cell cycles (left), homologous chromosomes behave independently. (A) Chromosomes in mitosis and in meiosis. These studies illuminate that meiosis is strategically designed to fulfill two missions: faithful segregation of genetic materials and production of genetic diversity in descendants through elaboration by meiosis-specific factors in collaboration with general factors.Ĭhromosomes in mitosis and in meiosis. Here we focus on lessons from recent advancement in genetical and cytological studies of the fission yeast Schizosaccharomyces pombe, revealing how chromosomes, cytoskeleton, and cell cycle progression are organized and particularly how these are differentiated in mitosis and meiosis. Recently, evidence began to accumulate to draw a perspective landscape showing that chromosomes and microtubules are mutually influenced: microtubules regulate chromosomes, whereas chromosomes also regulate microtubule behaviors. Yeast substantially contributed to the understanding of the molecular mechanisms of meiosis in the past decades. A huge number of studies to date have demonstrated how chromosomes behave and how meiotic events are controlled. Meiosis is a specialized style of cell division conserved in eukaryotes, particularly designed for the production of gametes.
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