Meiosis-activating sterol-mediated resumption of meiosis in mouse oocytes in vitro is influenced by protein synthesis inhibition and cholera toxin

To explore the possible signaling pathways of meiosis-activating sterol (MA S)-induced oocyte maturation and to elucidate whether the MAS pathway invol ves transcription or translation, arrested immature mouse oocytes were cult ured with either the protein synthesis inhibitor cycloheximide or the heter onuclear RNA inhibitors alpha-amanitin or actinomycin D, respectively. More over, the possible involvement of a G protein-coupled receptor mechanism in MAS-mediated oocyte maturation was explored by influencing oocyte maturati on with cholera toxin (CT). MAS-induced oocyte maturation was completely blocked by the addition of 50 mu g/ml cycloheximide 4 h before the addition of MAS. Simultaneous addition of MAS and the protein synthesis inhibitor also significantly reduced the meiotic resumption compared to that in MAS-treated controls. In contrast, neither of the treatment regimens to inhibit transcription of DNA to RNA was observed to have any effect on the MAS-induced resumption of meiosis. CT was observed to inhibit MAS-induced, but not spontaneous, oocyte maturat ion in vitro, suggesting a putative involvement of G protein-coupled recept or mechanism in the MAS mode of action. In conclusion, protein synthesis was found to be an essential requirement f or maintaining the oocytes' responsiveness to MAS-induced resumption of mei osis, in contrast to transcription.