Antipain microinjection prevents progesterone to inhibit adenyl cyclase in Xenopus oocytes

Abstract

Microinjection of antipain, an inhibitor of thiol and Ca 2+-dependent proteases, in immature Xenopus oocytes inhibited meiotic maturation induced by progesterone, but not by transfer of cytoplasm taken from maturing oocytes. Oocytes could be released from antipain inhibition by increasing progesterone concentration. α - 32P -ATP was microinjected to study adenylcyclase in ovo . As already reported, neosynthesis of cAMP was decreased following progesterone application. This decrease was not observed, or it was considerably reduced, in oocytes previously injected with antipain. In amphibian, full-grown ovarian oocytes are arrested at first meiotic prophase, and have a large nucleus known as the germinal vesicle. Progesterone induces the production of a cytoplasmic maturation-promoting factor (MPF), which itself triggers germinal vesicle breakdown (GVBD), and subsequent events of meiotic maturation ( Masui and Markert, 1971; Gerhart et al., 1984). A considerable body of evidences support the view that release from prophase block is due to inactivation of a cAMP-dependent protein kinase (reviewed by Maller, 1983). On the other hand, progesterone has been shown to induce a transient decrease in cAMP level ( Speaker and Butcher, 1977; Schorderet-Slatkine et al., 1982; Cicirelli et al., 1985), and this initial drop of cAMP, along with a number of studies indicating a decrease in adenylate cyclase activity ( Mulner et al., 1979; Baltus et al., 1981; Sadler and Maller, 1981; Finidori-Lepicard et al., 1981; Jordana et al., 1981), provided key support to the theory that an early drop in cAMP led to the dephosphorylation of a hypothetical protein which initiates maturation. It has been reported that several antiproteases of microbial origin, including antipain, could inhibit meiotic maturation induced by progesterone but not by the direct transfer of MPF into prophase-arrested oocytes ( Guerrier et al., 1977). Since the exact mechanism according to which progesterone inhibits adenylate cyclase activity remains unknown, this finding led us to investigate whether inhibition of adenylate cyclase following progesterone addition was also observed in antipain-injected oocytes. This communication presents the results of this study.