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

Oocyte germinal Vesicle breakdown (GVBD) was induced in striped bass ovaria n fragments when tissues were incubated with 100-nM recombinant human insul in-like growth factor-I (rhIGF-I), 25-IU human chorionic gonadotropin (hCG) ml(-1), or 290 nM of the maturation-inducing steroid (MIS), 17,20 beta ,21 -trihydroxy-4-pregnen-3-one (20 beta -S). Inhibitors of phosphatidylinosito l 3-kinase (PI 3-K), wortmannin (100 nM) and LY 294002 (50 muM), inhibited GVBD induced by these hormones. Furthermore, the inhibitors attenuated hCG- induced steroid hormone synthesis. Previous studies report that gap junctio n uncouplers inhibit GVBD induced by hCG, but not by rhIGF-I, in striped ba ss. We show that 20 beta -S-induced GVBD is also attenuated by 1 mM 1-hepta nol or 1-octanol without being affected by incubation with 3 mM ethanol. Th us, the effects of inhibiting PI 3-K activity on GtH and MIS actions are si milar 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 regu lates PI 3-K activity, possibly an IGF, participates in maintenance of gap junctional communication required for maximal GtH and MIS action. (C) 2001 Elsevier Science Inc. All rights reserved.