Protein kinase C and meiotic regulation in isolated mouse oocytes

Abstract

In this study, the possible role of protein kinase C (PKC) in mediating both positive and negative actions on meiotic maturation in isolated mouse oocytes has been examined. When cumulus cell–enclosed oocytes (CEO) were cultured for 17–18 hr in a medium containing 4 mM hypoxanthine (HX) to maintain meiotic arrest, each of the five different activators and five different antagonists of PKC stimulated germinal vesicle breakdown (GVB) in a dose-dependent fashion. One of the activators, phorbol-12-myristate 13-acetate (PMA), also triggered GVB in CEO arrested with isobutylmethylxanthine or guanosine, but not in those arrested with dibutyryl cyclic AMP. When denuded oocytes (DO) were cultured for 3 hr in inhibitor-free medium, all PKC activators suppressed maturation (< 10% GVB compared to 94% in controls), while the effect of PKC antagonists was negligible. Four of the five antagonists reversed the meiosis-arresting action of HX in DO. PMA transiently arrested the spontaneous maturation of both CEO and DO, with greater potency in DO. The stimulatory action of PMA in HX-arrested oocytes was dependent on cumulus cells, because meiotic induction occurred in CEO but not DO. PKC activators also preferentially stimulated cumulus expansion when compared to antagonists. A cell–cell coupling assay determined that the action of PMA on oocyte maturation was not due to a loss of metabolic coupling between the oocyte and cumulus oophorus. Finally, Western analysis demonstrated the presence of PKCs α, β1, δ, and ζ in both cumulus cells and oocytes, but only PKC ϵ was detected in the cumulus cells. It is concluded that direct activation of PKC in the oocyte suppresses maturation, while stimulation within cumulus cells generates a positive trigger that leads to meiotic resumption. Mol. Reprod. Dev. 58:101–115, 2001.