Evidence for a pertussis toxin-sensitive G protein involved in the control of meiotic reinitiation of Xenopus laevis oocytes

Meiotic reinitiation of Xenopus laevis oocytes is induced in vitro by progesterone or insulin. The hormonal effect is inhibited in a dose-dependent manner by the injection of the A protomer of pertussis toxin (islet-activating protein, IAP) into the oocytes. This inhibition occurs only before the appearance of a maturation-promoting activity in the cytoplasm. Furthermore, injection of the toxin A protomer into recipient oocytes does not inhibit the induction of maturation obtained through injection of cytoplasm containing the maturation-promoting factor. The inhibition effect of the toxin A protomer is reversible with time. These results suggest that a pertussis-sensitive G protein is involved in intracellular signaling systems leading to the induction of MPF activity.