Protein kinase C is required for the disappearance of MPF upon artificial activation in mouse eggs

Abstract

The aim of the present study was to investigate the implication of protein 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 specific PKC inhibitor, and the calcium ionophore A23187 as a standard parthenogenetic agent. The exposure of zona‐free eggs to 150 μM or 50 μM OAG for 10 min resulted in meiosis II completion in ∼80% of instances. By contrast, at a lower concentration (25 μM), the PKC stimulator was ineffective as parthenogenetic agent. Shortly after the application of 150 μM OAG, the cytosolic Ca2+ concentration ([Ca2+]i) increased transiently in all the eggs examined, whereas after the addition of 50 μM OAG, [Ca2+]i remained unchanged for at least 20 min. During this period, the activity of M‐phase promoting factor (MPF) dramatically decreased and most of the eggs entered anaphase except when the PKC was inhibited by calphostin C. Similarly, MPF inactivation and meiosis resumption were prevented in calphostin C‐loaded eggs following treatment with A23187, even though the ionophore‐induced Ca2+ signalling was not affected. Taken together, our results indicate that stimulation of PKC is a sufficient and necessary event to induce 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. Mol. Reprod. Dev. 48:292–299, 1997. © 1997 Wiley‐Liss, Inc.

Profile of protein kinase C isozymes and their possible role in mammalian egg activation

“…PKC Q was also detected by immunohistochemistry (data not shown). The presence of many PKC isozymes in the egg, including PKC Q, as already demonstrated in Xenopus [17], is not surprising, since the egg is a totipotential cell which may contain various PKC isozymes involved in di¡erent developmental processes. However, since PKC Q is known to be brain-speci¢c in the adult, its role in this early stage of development should be further elaborated.…”

“…However, PKC inhibitors failed to block fertilization‐induced cortical reaction [13]. Other studies demonstrated cell cycle resumption in eggs treated with PKC [14–17]. Very few studies have actually analyzed the presence of different PKC isozymes and their biological activity in eggs.…”

Endoplasmic reticulum distribution during bovine oocyte activation is regulated by protein kinase C via actin filaments

“…It has been suggested that PKC is involved in cell cycle resumption and progression during oocyte activation. PKC pharmacological inhibitors or activators respectively blocked or induced meiotic resumption MII oocyte (Colonna et al, 1997; Eliyahu & Shalgi, 2002; Gallicano et al, 1997; Gallicano, Schwarz, McGaughey, & Capco, 1993). However, in the present work, PKC inhibition with 10 µM BIM was not enough to suppress meiotic resumption after bovine oocyte parthenogenetic activation.…”

Calmodulin-dependent protein kinase II, and not protein kinase C, is sufficient for triggering cell-cycle resumption in mammalian eggs

“…Thus PKC activity rises during egg activation when measured directly (Gallicano et al, 1997a), or indirectly by redistribution of various isoforms to the plasma membrane (Eliyahu and Shalgi, 2002;Luria et al, 2000). Furthermore inhibitors of PKC have been reported to prevent mammalian eggs exiting MetII arrest (Gallicano et al, 1997a), and conversely PKC activators are reported to induce completion of meiosis (Colonna et al, 1997;Gallicano et al, 1993;Luria et al, 2000).…”