Abstract
A high cyclic adenosine monophosphate (cAMP) level in fully-grown immature oocytes prevents meiotic resumption. In Xenopus, inhibitory cAMP is synthesized within oocytes depending on a stimulatory α-subunit of G-protein (Gsα). In the present study, we examined whether ooplasmic Gsα is involved in meiotic arrest of porcine oocytes. First, we studied the presence of Gsα molecules in porcine oocytes by immunoblotting, and this suggested the presence of reported isoforms (45 and 48 kDa) not only in cumulus cells but also in porcine oocytes. Then we injected an anti-Gsα antibody into porcine immature oocytes and found that inhibition of ooplasmic Gsα functions significantly promoted germinal vesicle breakdown of the oocytes, whose spontaneous meiotic resumption was prevented by 3-isobutyl-l-methylxanthine (IBMX) treatment. Although cyclin B synthesis and M-phase promoting factor (MPF) activation were largely prevented until 30 h of culture in IBMX-treated oocytes, injection of anti-Gsα antibody into these oocytes partially recovered cyclin B synthesis and activated MPF activity at 30 h. These results suggest that meiotic resumption of porcine oocytes is prevented by ooplasmic Gsα, which may stimulate cAMP synthesis within porcine oocytes, and that synthesized cAMP prevents meiotic resumption of oocytes through the signaling pathways involved in MPF activation.
