In vitro hormone induction of final oocyte maturation in striped bass (Morone saxatilis) follicles is inhibited by blockers of phosphatidylinositol 3-kinase activity

Abstract

Oocyte germinal vesicle breakdown (GVBD) was induced in striped bass ovarian fragments when tissues were incubated with 100-nM recombinant human insulin-like growth factor-I (rhIGF-I), 25-IU human chorionic gonadotropin (hCG) ml−1, or 290 nM of the maturation-inducing steroid (MIS), 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S). Inhibitors of phosphatidylinositol 3-kinase (PI 3-K), wortmannin (100 nM) and LY 294002 (50 μM), inhibited GVBD induced by these hormones. Furthermore, the inhibitors attenuated hCG-induced steroid hormone synthesis. Previous studies report that gap junction uncouplers inhibit GVBD induced by hCG, but not by rhIGF-I, in striped bass. We show that 20β-S-induced GVBD is also attenuated by 1 mM 1-heptanol or 1-octanol without being affected by incubation with 3 mM ethanol. Thus, the effects of inhibiting PI 3-K activity on GtH and MIS actions are similar to effects of uncoupling gap junctions. These data suggest that PI 3-K activity is required for GtH- MIS- and IGF-I induction of GVBD in striped bass. Our data are also consistent with the notion that a ligand that regulates PI 3-K activity, possibly an IGF, participates in maintenance of gap junctional communication required for maximal GtH and MIS action.