Doctoral Dissertations

Orcid ID

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Biochemistry and Cellular and Molecular Biology

Major Professor

Joshua N. Bembnek

Committee Members

Andreas Nebenfuehr, Bruce McKee, Jae Park, Jianbin Wang, Tarek Hewezi


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-1DM) was generated. GFP::IFY-1DM is stably expressed during anaphase I and causes embryonic lethality. GFP::IFY-1DM causes chromosome segregation defects, polar body extrusion failure and inhibits cortical granule exocytosis. Importantly, expression of GFP::IFY-1DM 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.

Available for download on Monday, December 15, 2025

Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Included in

Cell Biology Commons