Activated α subunit of G_o protein induces oocyte maturation

The capability of various activated guanine nucleotide binding regulatory protein (G protein) α subunits to induce meiotic maturation was studied. Activated G_o protein α subunit (α*_o) but not the three inhibitory G protein α subunits triggered meiotic maturation in Xenopus oocytes. The effect was concentration dependent with a half-maximal effect in the 100-200 pM range. Injection of α*_o stimulated protein kinase C activity. Coinjection of the peptide containing residues 19-36 of protein kinase C [PKC-(19-36)], a specific protein kinase C inhibitor, blocked the α*_o- but not progesterone-induced maturation. Cycloheximide and the injection of antisense oligonucleotides specific to the c-mos transcript blocked α_o-induced maturation. Immunoprecipitation with a mos protein-specific monoclonal antibody showed that α_o-injected oocytes had phosphorylated mos protein. When PKC-(19-36) was coinjected with α*_o, phosphorylated mos protein was not observed. These observations indicate that α*_o, through protein kinase C and the translation of c-mos, can trigger meiotic division of Xenopus oocytes. Our results raise the possibility that persistently activated G proteins through cellular protooncogenes may regulate cell-cycle resumption.