Stimulation of Xenopus oocyte maturation by inhibition of the G-protein αs subunit, a component of the plasma membrane and yolk platelet membranes

Abstract

Oocytes of Xenopus laevis undergo maturation when injected with an affinity-purified antibody against the COOH-terminal decapeptide of the α subunit of the G-protein Gs, an antibody that inhibits Gs activity. Germinal vesicle breakdown, chromosome condensation, and polar body formation occur, with a time course similar to that for oocytes treated with progesterone. The αs antibody-injected oocytes also acquire the ability to be activated by sperm. Coinjection of the catalytic subunit of cAMP-dependent protein kinase, or incubation with cycloheximide, inhibits maturation in response to injection of the αs antibody; these experiments show that the αs antibody acts at an early point in the pathway leading to oocyte maturation, before formation of maturation promoting factor, and like progesterone, its action requires protein synthesis. Immunogold electron microscopy shows that αs is present in the yolk platelet membranes as well as the plasma membrane. These results support the hypothesis that progesterone acts by inhibiting αs, and suggest that the target of progesterone could include yolk platelet membranes as well as the plasma membrane.