Investigating the role of Kif2c in transforming the microtubule cytoskeleton at the oocyte-to-embryo transition - Project Summary The oocyte-to-embryo transition encompasses several key developmental events that coincide with changes to the microtubule (MT) cytoskeleton. Two such events are oocyte maturation, when the prophase-arrested oocyte completes the first meiosis and arrests in metaphase II, and egg activation, when the egg initiates processes that are crucial for early embryogenesis. We have identified a zebrafish maternal-effect mutant that reveals maternal-specific control of MT organization in the oocyte and egg. Offspring of mutant females fail to complete the first cell division and contain numerous ectopic aster-like MTs throughout the cytoplasm. Chromosomes of unactivated eggs are scattered, suggesting MT dysregulation interferes with meiotic chromosome movements. The mutated gene kif2c encodes a kinesin-13 family MT depolymerase also known as mitotic centromere- associated kinesin (MCAK). Previous in vitro and in vivo model systems have shown chromosome alignment defects and ectopic MT assembly upon loss of kinesin-13. Our model is unique in that the asters seen in mutant embryos arise during oocyte maturation, coinciding with the recently discovered phenomenon of cortical maturation asters (CMAs) in zebrafish. This suggests that Kif2c regulates CMA formation during maturation. Our mutant indicates there is a second period of Kif2c function at egg activation. In wild-type eggs, cortical MTs depolymerize at egg activation, but in mutant eggs, MTs rapidly polymerize at egg activation. This suggests that Kif2c drives MT depolymerization at egg activation. As eggs are translationally silent, the same pool of Kif2c protein functions at oocyte maturation and egg activation. Thus, I hypothesize that Kif2c is precisely regulated to control CMAs during oocyte maturation before depolymerizing MTs at egg activation. In Aim 1, I will determine the nature of Kif2c MT regulation during oocyte maturation by live imaging and identifying at which MT end Kif2c functions. In Aim 2, I will investigate the regulation of Kif2c activity throughout oocyte maturation and egg activation by linking periods of Kif2c function with Kif2c phosphorylation status. In total, these experiments will identify the dynamic function and regulation of a maternal factor that modulates the MT cytoskeleton to promote chromosome integrity and developmental competence. As proper MT organization is required to protect against aneuploidy and MTOC number is often increased in cancer cells, understanding the nature of maternal MT regulation has implications in several biological processes. The institutional environment of this proposed fellowship will support the applicant in the pursuit of successful research and professional development. The applicant’s sponsor has an excellent track record in mentorship, and the applicant’s thesis committee will ensure the studies proposed here are rigorous. The proposed studies will provide insight into maternal MT regulation and are highly significant to female fertility, embryo competence, and reproductive health.
