Separase Biosensor Reveals that Cohesin Cleavage Timing Depends on Phosphatase PP2ACdc55 Regulation

SummaryIn anaphase, sister chromatids separate abruptly and are then segregated by the mitotic spindle. The protease separase triggers sister separation by cleaving the Scc1/Mcd1 subunit of the cohesin ring that holds sisters together. Polo-kinase phosphorylation of Scc1 promotes its cleavage, but the underlying regulatory circuits are unclear. We developed a separase biosensor in Saccharomyces cerevisiae that provides a quantitative indicator of cohesin cleavage in single cells. Separase is abruptly activated and cleaves most cohesin within 1 min, after which anaphase begins. Cohesin near centromeres and telomeres is cleaved at the same rate and time. Protein phosphatase PP2ACdc55 inhibits cohesin cleavage by counteracting polo-kinase phosphorylation of Scc1. In early anaphase, the previously described separase inhibition of PP2ACdc55 promotes cohesin cleavage. Thus, separase acts directly on Scc1 and also indirectly, through inhibition of PP2ACdc55, to stimulate cohesin cleavage, providing a feedforward loop that may contribute to a robust and timely anaphase.

► Cohesin is cleaved abruptly in 1 min, just before sister-chromatid separation
► Cohesin is cleaved near centromeres and telomeres with the same rate and timing
► PP2ACdc55 counteracts polo-phosphorylation of cohesin to inhibit cleavage
► Separase inhibition of PP2ACdc55 may promote cleavage via a feedforward loop