Protein kinase C, rather than protein kinase A is involved in follicle-stimulating hormone-mediated meiotic resumption of mouse cumulus cell-enclosedoocytes in hypoxanthine-supplemented medium

It has been reported that protein kinase C (PKC) activation participated in the porcine and bovine oocyte maturation, but not in mouse oocyte maturati on in vitro. In the present study, the activators and inhibitors of protein kinase A (PKA) (forskolin, CDPKI and MDL-12230A) or PKC (PMA, staurosporin e and sphingosine) were used to investigate the in vitro effect of PKA or P KC on spontaneous murine oocyte maturation, oocyte resumption of meiosis fr om HX inhibiting medium (medium + HX), and follicle stimulating hormone (FS H)-induced oocyte maturation. The results showed that when cumulus cell enc losed oocytes (CEOs) or denuded oocytes (DOs) were cultured for 24 h in the medium supplemented with forskolin (5 muM), an activator of adenylate cycl ase, the spontaneous oocyte maturation were inhibited. A transient exposure (2 h) to forskolin (2-10 muM) in the medium + HX, and then transferred to a new medium + HX for the further culture, stimulated CEO resumption of mei osis. CDPKI (10(-10)-10(-6) M), an inhibitor of PKA, also stimulated oocyte meiotic maturation of CEO in the medium + HX, but not on DO. However, MDL- 12230A (10(-12)-10(-9) M), an inhibitor of adenylate cyclase, did not promo te oocyte maturation in HX arrested CEO. CDPKI (10(-10)-10(-6) M) or MDL-12 230A (10(-12)-10(-9) M) had no effect on FSH-stimulated oocyte meiotic resu mption, except at high doses of CDPKI (10(-7)-10(-6) M) or MDL-12230A (10(- 9) M) which inhibited the FSH-induced formation of the first polar body (PB 1). An activator of PKC, PMA (10(-11)-10(-7) M) dose-dependently inhibited spontaneous oocyte maturation of CEO or DO. Inhibitors of PKC, staurosporin e (10(-9)-10(-6) M) or sphingosine (10(-8)-10(-5) M) induced oocytes in CEO s to resume meiosis in the presence of FIX in a dose dependent manner, but had no effect on DOs. FSH (50IU/L) stimulated mouse oocytes in CEOs to over ride the arrest of HX and resume meiosis, while PMA, at the level of 10(-8) -10(-6) M, dramatically inhibited the stimulatory effect of FSH. These resu lts indicate that PKC or PKA may be implicated in the regulation of mouse o ocyte maturation. Thus while sustained high level of cAMP or PKA inhibit th e resumption of meiosis, a transient rise in cAMP or PKA levels promotes oo cyte maturation. The activation of PKC can also block oocyte meiotic resump tion. Thus the inactivation of PKC, instead of the transient rise of PKA ac tivity, appears to be involved in the process of FSH-mediated oocyte meioti c maturation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.