Protein kinase C, rather than protein kinase A is involved in follicle-stimulating hormone-mediated meiotic resumption of mouse cumulus cell-enclosed oocytes 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 maturation in vitro. In the present study, the activators and inhibitors of protein kinase A (PKA) (forskolin, CDPKI and MDL-12230A) or PKC (PMA, staurosporine and sphingosine) were used to investigate the in vitro effect of PKA or PKC on spontaneous murine oocyte maturation, oocyte resumption of meiosis from HX inhibiting medium (medium+HX), and follicle stimulating hormone (FSH)-induced oocyte maturation. The results showed that when cumulus cell enclosed oocytes (CEOs) or denuded oocytes (DOs) were cultured for 24 h in the medium supplemented with forskolin (5 μM), an activator of adenylate cyclase, the spontaneous oocyte maturation were inhibited. A transient exposure (2 h) to forskolin (2–10 μM) in the medium+HX, and then transferred to a new medium+HX for the further culture, stimulated CEO resumption of meiosis. 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 promote oocyte maturation in HX arrested CEO. CDPKI (10−10–10−6 M) or MDL-12230A (10−12–10−9 M) had no effect on FSH-stimulated oocyte meiotic resumption, 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 (PB1). An activator of PKC, PMA (10−11–10−7 M) dose-dependently inhibited spontaneous oocyte maturation of CEO or DO. Inhibitors of PKC, staurosporine (10−9–10−6 M) or sphingosine (10−8–10−5 M) induced oocytes in CEOs to resume meiosis in the presence of HX in a dose dependent manner, but had no effect on DOs. FSH (50IU/L) stimulated mouse oocytes in CEOs to override 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 results indicate that PKC or PKA may be implicated in the regulation of mouse oocyte maturation. Thus while sustained high level of cAMP or PKA inhibit the resumption of meiosis, a transient rise in cAMP or PKA levels promotes oocyte maturation. The activation of PKC can also block oocyte meiotic resumption. Thus the inactivation of PKC, instead of the transient rise of PKA activity, appears to be involved in the process of FSH-mediated oocyte meiotic maturation.