Protein kinase C and meiotic regulation in isolated mouse oocytes

In this study, the possible role of protein kinase C (PKC) in mediating bot h positive and negative actions on meiotic maturation in isolated mouse ooc ytes has been examined. When cumulus cell-enclosed oocytes (CEO) were cultu red 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 an tagonists of PKC stimulated germinal vesicle breakdown (GVB) in a dose-depe ndent fashion. One of the activators, phorbol-12-myristate 13-acetate (PMA) , also triggered GVB in CEO arrested with isobutylmethylxanthine or guanosi ne, but not in those arrested with dibutyryl cyclic AMP. When denuded oocyt es (DO) were cultured for 3 hr in inhibitor-free medium, all PKC activators suppressed maturation (<10% GVB compared to 94% in controls), while the ef fect of PKC antagonists was negligible. Four of the five antagonists revers ed the meiosis-arresting action of HX in DO. PMA transiently arrested the s pontaneous maturation of both CEO and DO, with greater potency in DO. The s timulatory action of PMA in HX-arrested oocytes was dependent on cumulus ce lls, because meiotic induction occurred in CEO but not DO. PKC activators a lso preferentially stimulated cumulus expansion when compared to antagonist s. A cell-cell coupling assay determined that the action of PMA on oocyte m aturation was not due to a loss of metabolic coupling between the oocyte an d cumulus oophorus. Finally, Western analysis demonstrated the presence of PKCs <alpha>, beta1, delta, and zeta in both cumulus cells and oocytes, but only PKC epsilon was detected in the cumulus cells. It is concluded that d irect activation of PKC in the oocyte suppresses maturation, while stimulat ion within cumulus cells generates a positive trigger that leads to meiotic resumption. (C) 2001 Wiley-Liss, Inc.