PROTEIN-KINASE-C IS REQUIRED FOR THE DISAPPEARANCE OF MPF UPON ARTIFICIAL ACTIVATION IN MOUSE EGGS

The aim of the present study was to investigate the implication of pro tein kinase C (PKC) in the mouse egg activation process. We used OAG ( 1-oleoyl-2-acetyl-sn-glycerol) as a PKC activator, calphostin C as a s pecific PKC inhibitor, and the calcium ionophore A23187 as a standard parthenogenetic agent. The exposure of zona-free eggs to 150 mu M or 5 0 mu M OAG for 10 min resulted in meiosis II completion in similar to 80% of instances. By contrast, at a lower concentration (25 mu M), the PKC stimulator was ineffective as parthenogenetic agent. Shortly afte r the application of 150 mu M OAG, the cylosolic Ca2+ concentration ([ Ca2+](i)) increased transiently in all the eggs examined, whereas afte r the addition of 50 mu M OAG, [Ca2+](i) remained unchanged for at lea st 20 min. During this period, the activity of M-phase promoting facto r (MPF) dramatically decreased and most of the eggs entered anaphase e xcept when the PKC was inhibited by calphostin C. Similarly, MPF inact ivation and meiosis resumption were prevented in calphostin C-loaded e ggs following treatment with A23187, even though the ionophore induced Ca2+ signalling was not affected. Taken together, our results indicat e that stimulation of PKC is a sufficient and necessary event to induc e meiosis resumption in mouse eggs and strongly suggest that, in this species, the mechanism by which a transient calcium burst triggers MPF inactivation involves a PKC-dependent pathway. (C) 1997 Wiley-Liss In c.