Oocyte Maturation and G Beta and Gamma Subunits

Abstract

The molecular details of progesterone-dependent Xenopus oocyte maturation are not well defined, but adenylyl cyclase activity is inhibited and cyclic AMP (cAMP) concentrations decrease. Maturation does not appear to involve Gα i activity; however, Sheng et al. found that Gβγ subunits are involved in arresting oocyte meiosis. maturation was induced by overexpressing in oocytes Gβγ scavengers, such as the α subunit of bovine transducin (Gα t ) or a membrane-localized COOH-terminal bovine β-adrenergic receptor kinase (βARK-C CAAX ) fragment, both of which sequester Gβγ subunits. βARK-C CAAX coprecipitated with Gβ in oocyte lysates, suggesting that Gβ-dependent inhibition was perturbed by direct association. Xenopus mitogen-activated protein kinase (xMAPK) was activated, an essential step in maturation, as a consequence of Gβ sequestration. Finally, overexpression of Gβγ in oocytes expressing βARK-C CAAX inhibited maturation and resulted in increased production of cAMP. These data suggest that Gβγ may influence oocyte maturation arrest and that progesterone may prevent the activation of a heterotrimeric G protein and the consequent release of Gβγ. Y. Sheng, M. Tiberi, R. A. Booth, C. Ma, X. J. Liu, Regulation of Xenopus oocyte meiosis arrest by G protein βγ subunits. Curr. Biol. 11 , 405-416 (2001). [Online Journal]