ACYLPHOSPHATASE SYNERGIZES WITH PROGESTERONE DURING MATURATION OF XENOPUS-LAEVIS OOCYTES

Xenopus laevis oocytes are physiologically arrested in the G2/M phase border of the first meiotic division. A number of different stimuli ca n trigger off the re-entry into the cell cycle as a consequence of act ivation of either membrane-dependent or -independent intracellular sig nals. This system has been widely used to study signal transduction me chanisms induced by hormones. Among those more intensively researched, special attention has been devoted to elucidate the mechanism of acti vation induced by progesterone. However, despite intense efforts to un derstand the intracellular signalling mechanism of progesterone, a cle ar notion of the most relevant events involved in this process has not yet been elucidated. We provide evidence that acylphosphatase, an enz yme responsible for the regulation of membrane pumps in eukaryotic cel ls, synergizes with progesterone for induction of oocyte maturation. W e deduced that this synergism may be related to the regulation of intr acellular Ca2+ levels for several reasons: (1) maturation of oocytes b y extracellular Ca2+ is blocked by acylphosphatase; (2) both progester one and acylphosphatase drastically reduced Ca2+ uptake; (3) progester one-induced maturation does not depend on a rise in intracellular Ca2, since microinjection of EGTA, a calcium chelator, does not affect ma turation induced by progesterone.