ZINC INDUCES OOCYTE MATURATION IN CHINESE TOAD (BUFO-BUFO GARGARIZANS)

Progesterone can induce maturation (as indicated by germinal vesicle b reakdown, GVBD) of amphibian oocytes in vitro. GVBD was induced by zin c alone in place of progesterone, both in Chinese toad (Bufo bufo garg arizans) and in Xenopus. In the present study, 500 mu M ZnCl2 was foun d to induce complete GVBD only when applied for 5 h to cultured oocyte s from Chinese toad. In contrast, oocytes required only a shea period (5 min) of exposure to progesterone for GVBD to occur. Cytoplasm from oocytes matured in the presence of zinc induced GVBD when microinjecte d into immature oocytes. Such results demonstrate that completion of G VBD induced by zinc involved release of probable 'maturation promoting factor'. Furthermore, zinc itself was not able to induce GVBD when in jected into the oocytes. However, external application with progestero ne or zinc induced GVBD. We report here for the first time that zinc a cts primarily at the superficial plasma membrane sites, since external ly applied zinc induced GVBD. Zinc induced maturation presents several characteristics common to progesterone-induced maturation.