Interaction of chromosome migration inducing proteins with meiotic maturation regulating factors during oocyte maturation

Objective: During oocyte maturation chromosome migration driven by actin nucleation give rise to asymmetric division of oocytes. The aim of this study was to determine the effects of MAPK/ERK kinase (MEK) inhibition and "maturation promoting factor" (MPF) activation on the amount and localizations of actin nucleators Formin-2 (FMN2), Spire-1 and Spire-2 and also to determine whether the relation of mitogen-activated protein kinases (MAPK) with these proteins is through MPF during in vitro maturation (IVM) of mouse oocytes. Method: MEK inhibitor PD98059 and PKA inhibitor H89 for MPF activation was applied during IVM to the germinal vesicle (GV) oocytes retrieved from preovulatory ovarian follicles of 3-5 weeks old female BalbC mice after follicle activation. Germinal vesicle breakdown (GVBD) and polar body extrusion (PBE) rates were determined. The localization of Formin-2 (FMN2), Spire-1 and Spire-2 were determined through immunofluorescence, protein levels were determined via Western blot for oocytes at different stages. Results: Though GVBD rates were similar in different groups, PBE rates were lower in MEK inhibition group. FMN2 was localized around spindle and cortex, while only cortical localizations of Spire-1 and Spire-2 were determined. MEK inhibition resulted in a decrease in FMN2, cortical Spire-1 and Spire-2 levels in PBE oocytes. MPF activation lead to decrease in FMN2 and increase in cortical Spire-1 levels in spindle migration stage oocytes, while it resulted in increase of cortical and total Spire-2 levels in PBE oocytes. Application of MEK inhibition and MPF activation at the same time resulted in compensation of the decrease in FMN2 and Spire-1, while Spire-2 levels remained low with no compensation of MPF activation. Conclusion: This study shows that MAPK and MPF affects actin nucleators FMN2, Spire-1 and Spire-2 at particular stages of oocyte maturation. According to the results of this study, MAPK directly affects Spire-2, while it affects FMN2 and Spire-1 indirectly through MPF activation. Key words: mapk, mpf, fmn2, spire-1, spire-2