Investigating the Regulation of Separase during Meiosis I in Caenorhabditis elegans

Meiosis is a tightly regulated series of events leading to gamete formation. A key player in this process is the protease Separase (SEP-1). Known for its role in chromosome segregation, we have defined a role for SEP-1 in vesicular trafficking during cell division. Securin (IFY-1) is an inhibitory chaperone of SEP-1 that is degraded at anaphase onset after ubiquitination by the Anaphase Promoting Complex/Cyclosome (APC/C). After IFY-1 degradation, activated SEP-1 cleaves a subunit of cohesion to allow chromosome segregation. SEP-1 also displays dynamic localization during the cell cycle. In prometaphase I, IFY-1 localizes to kinetochores and mysterious cortical filaments. During anaphase I, SEP-1 transfers to the midbivalent, the region between homologous chromosomes where Cohesin localizes, and concurrently appears on vesicles, called cortical granules, in the cortex. How the dynamic localization of SEP-1 is regulated is currently unknown. Here, I investigated how the APC/C and IFY-1 regulate Separase during meiosis I. First, I observed that IFY-1 is degraded by anaphase I and is not present on vesicles. Second, APC/C activity is required for SEP-1 to localize to vesicles. apc/c RNAi results in arrested embryos with SEP-1 and IFY-1 remaining colocalized on cortical filaments. Third, partial ify-1 RNAi causes precocious SEP-1 vesicle localization. These observations suggest that IFY-1 degradation is required for SEP-1 to localize to vesicles during anaphase I. To further test this, Non-Degradable Securin fused to GFP (GFP::IFY-1^DM) was generated. GFP::IFY-1^DM is stably expressed during anaphase I and causes embryonic lethality. GFP::IFY-1^DM causes chromosome segregation defects, polar body extrusion failure and inhibits cortical granule exocytosis. Importantly, expression of GFP::IFY-1^DM causes a reduced and delayed localization of SEP-1 to vesicles during anaphase I. I conclude that degradation of IFY-1 regulates the localization of SEP-1 to vesicles to coordinate exocytosis with chromosome segregation. My findings suggest a novel role for the APC/C and IFY-1 in controlling the localization of SEP-1, in addition to regulating its protease activity for chromosome segregation and cortical granule exocytosis during anaphase I.