What makes centromeric cohesion resistant to separase cleavage during meiosis I but not during meiosis II?

Abstract

Segregation of chromosomes during meiosis I is triggered by separase cleavage of the cohesin's Rec8 subunit along chromosome arms. Centromeric cohesin is protected from separase cleavage during meiosis I by Sgo1/MEI-S332 proteins in complex with protein phosphatase 2A (PP2A). This retention of centromeric sister chromatid cohesion is essential for faithful segregation of chromatids during the second meiotic division. While Sgo1/PP2A complex is required for protecting centromeric sister chromatid cohesion during meiosis I, it is not known what renders the centromeric cohesion sensitive to separase cleavage during meiosis II. Our data suggest that the absence of Sgo1 and PP2A from meiosis II centromeres is not sufficient to render centromeric cohesion sensitive to cleavage by separase and additional factors are required to ensure the removal of centromeric cohesion during meiosis II.

Figure 1

The presence of Sgo1 and Par1 at centromeres during meiosis II does not interfere with chromosome segregation. Schizosaccharomyces pombe pat1-114 homozygous diploid cells expressing Sgo1-GFP from sgo1-GFP and Par1-PK9 (JG14859) and cells expressing Sgo1-GFP from sgo1-GFP-3′UTR and Par1-PK9 (JG14857) were arrested by nitrogen starvation and released into meiosis at 34°C by inactivation of pat1. Cells were harvested at the indicated time points (hours) after meiosis induction. (A) Flow cytometry profiles showing the DNA content at the indicated timepoints. (B) Cells were stained with DAPI and nuclei were counted in 100 cells per time point. Shown are the fraction of cells that contained one nucleus (diamonds), two nuclei (squares) or more than two nuclei (triangles) at the indicated time points. (C) Chromatin binding (DgII—outer centromere, top1—chromosome arm) of epitope-tagged proteins was analyzed by chromatin immunoprecipitation (ChIP) followed by quantitative real-time PCR.