Differential regulation of oocyte maturation and cumulus expansion in the mouse oocyte-cumulus cell complex by site-selective analogs of cyclic adenosine monophosphate.

In the present study, we have examined how differential distribution of cyclic adenosine 5'-monophosphate (cAMP)-dependent protein kinase isozymes within the mouse oocyte-cumulus cell complex might influence the physiological response of the complex to cAMP, by determining the actions of site-selective cAMP analogs on oocyte maturation and cumulus expansion. Five different analogs of cAMP were utilized: 8-thiomethyl-cAMP and 8-bromo-cAMP, which bind to site 1 on the type II regulatory subunit (RII) of cAMP-dependent protein kinase A (PKA); 8-aminohexylamino-cAMP, which binds to site 1 on the type I regulatory subunit (RI) of PKA; N6-monobutyryl cAMP, which binds to site 2 on either RI or RII; and 8-piperidino-cAMP, which binds to either site 1 on RII or site 2 on RI. These analogs were tested alone or in paired combinations that synergistically activate either the type I or type II PKA isozyme. When tested alone, analogs that can bind to, and presumably activate, type I PKA were the most potent inhibitors of germinal vesicle breakdown (GVB) in both cumulus cell-enclosed and denuded oocytes. Consistent with this result was the finding that paired combinations of analogs that selectively activate type I PKA were also most effective in preventing GVB. On the other hand, pulsing meiotically arrested cumulus cell-enclosed oocytes with high concentrations of analogs that bind to PKA II, or with paired combinations of analogs that selectively activate type II PKA, led to induction of GVB; stimulation with analogs or combinations thereof that presumably stimulate type I PKA was less effective. Cumulus expansion in response to PKA stimulation showed similar selectivity in that type II PKA-stimulating treatments were considerably more effective in provoking expansion than type I PKA-stimulating treatments. 8-N3-[32P]cAMP photoaffinity labeling of PKA regulatory subunits revealed that only RI was present in oocyte extracts, while extracts from oocyte-cumulus cell complexes contained both RI and RII. These results support the hypothesis that type II PKA mediates cAMP-stimulated cumulus expansion and resumption of meiotic maturation, while direct elevation of type I PKA within the oocyte is instrumental in maintaining meiotic arrest.