Reproduction Abstracts

Introduction: ROCK (Rho kinase) is a Rho-GTPase effector that is involved in various cellular functions, such as stress fiber formation, cell migration, tumor cell invasion, and cell motility. In this study, we investigated possible roles for ROCK in mouse oocyte meiosis and embryo development.

Materials and methods: Time lapse microscopy, immunofluorescence staining, western blotting, RNAi and inhibitor treatment were adopted to analyze the roles of ROCK in mouse oocytes and embryos.

Results and discussion: ROCK was localized around spindles after germinal vesicle breakdown (GVBD) and was co-localized with cytoplasmic actin and mitochondria. Disrupting ROCK activity by RNAi or an inhibitor resulted in oocyte polar body extrusion and embryo development failure. Time lapse microscopy showed that this may have been due to spindle migration and cytokinesis defects, as chromosomes segregated, but failed to extrude a polar body, and then re-aligned. Actin expression at oocyte and embryo was significantly decreased after these treatments. Actin caps of oocytes were also disrupted, which was confirmed by a failure to form cortical granule-free domains (CGFDs). In addition, the phosphorylation levels of LIMK1/2 and Cofilin, two downstream molecules of ROCK, decreased after disrupting ROCK activity in both oocytes and embryos. Thus, our results indicated that a ROCK-LIMK1/2-Cofilin-actin pathway regulated cytokinesis during mouse oocyte maturation and embryo development.