Analysis of fission yeast chromosome architecture in meiotic prophase

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During the mitotic cell cycle the regulated cohesion and segregation of sister chromatids is achieved by the mitotic cohesin complex, and upon entering meiosis, this mitotic cohesin complex is replaced by the meiotic cohesin complex which choreographs the meiosis-specific chromosomal events. The meiotic cohesin, Rec8, is required for sister chromatid cohesion and homologous recombination. By directly measuring chromosome compaction in living cells of the fission yeast Schizosaccharomyces pombe, we found an additional role for cohesin in the compaction of chromosomes during meiotic prophase. In the absence of Rec8, chromosomes were loosened 2 fold when compared with wild-type cells, while the loss of the cohesin-associated protein, Pds5, resulted in Rec8-dependent over-compaction. Both homologous pairing and recombination were defective in the absence of either Rec8 or Pds5. Pds5 also demonstrated a role in maintaining sister chromatid cohesion and in reductional chromosome segregation. In the absence of Pds5, the Rec8 binding on chromosome was decreased, indicating that Pds5 modulate the association of Rec8 with meiotic chromosomes. Thus, the cohesins mediate fundamental changes in global chromatin structure that promote correct meiotic progression.