Roles of protein kinase A and C in spontaneous maturation and in forskolin or 3-isobutyl-1-methylxanthine maintained meiotic arrest of bovine oocytes

Abstract

Four hypotheses were tested using isolated bovine oocytes. (1) Cumulus oocyte complexes (COCs) or denuded oocytes (DOs) were cultured with the protein kinase A (PKA) inhibitor, H-89, to test if meiotic arrest induced by forskolin or IBMX was due to cAMP-stimulated PKA activity or nonspecific effects of these cAMP elevators. (2) COCs were cultured with a protein kinase C (PKC) stimulator (PDD beta) or inhibitor (GF109203x) to test if PKC modulation altered oocyte maturation. (3) COCs were prestimulated for 15 min with (a) PDD beta followed by cotreatment with forskolin, or (b) with H-89 or H-7 followed by cotreatment with GF109203x, to test for interaction between the PKA and PKC signal transduction pathways. (4) H-89 was added to spontaneously maturing COCs at intervals of 0-18 hr to test if H-89 interfered with the transition between meiosis I and II. The results were as follows: H-89 interfered with forskolin or IBMX arrested oocytes in dose-response manner (IBMX ED50 = 41 microM for COCs; forskolin ED50 = 9 microM for denuded oocytes). Prestimulation with PKC induced meiotic resumption in COCs in spite of the presence of forskolin [PDD beta followed by PDD beta + forskolin: 41-47% germinal vesicle (GV) oocytes; forskolin alone: 90-95% GV], while PKC inhibition induced meiotic arrest to a similar extent as forskolin (GF109203x, 85% GV; forskolin, 67-80% GV). Additionally, pretreatment of COCs with H-89 interfered with GF109203x induced arrest (41% vs. 90% GV, respectively). Finally, H-89 interfered with the timely progression of COCs from meiosis I and II. These results indicate that the PKA and PKC pathways can modulate the maturation of bovine oocytes in vitro.