Co-operation of Gsalpha and Gbetagamma in maintaining G2 arrest in Xenopus oocytes.

Autor: Sheng Y; Ottawa Health Research Institute, Ottawa Hospital, 1053 Carling Avenue, Ottawa, Canada., Montplaisir V, Liu XJ
Jazyk: angličtina
Zdroj: Journal of cellular physiology [J Cell Physiol] 2005 Jan; Vol. 202 (1), pp. 32-40.
DOI: 10.1002/jcp.20084
Abstrakt: Progesterone-induced oocyte maturation is thought to involve the inhibition of an oocyte adenylyl cyclase and reduction of intracellular cAMP. Our previous studies demonstrated that injection of inhibitors of G protein betagamma complex induces hormone-independent oocyte maturation. In contrast, over-expression of Xenopus Gbeta1 (xGbeta1), alone or together with bovine Ggamma2, elevates oocyte cAMP and inhibits progesterone-induced oocyte maturation. To further investigate the mechanism of Gbetagamma-induced oocyte maturation, we generated a mutant xGbeta1, substituting Asp-228 for Gly (D228G). An equivalent mutation in the mammalian Gbeta1 results in the loss of its ability to activate adenylyl cyclases. Indeed, co-injection of xGbeta1D228G with Ggamma2 failed to increase oocyte cAMP or inhibit progesterone-induced oocyte maturation. To directly demonstrate that oocytes contained a Gbetagamma-regulated adenylyl cyclase, we analyzed cAMP formation in vitro by using oocyte membrane preparations. Purified brain Gbetagamma complexes significantly activated membrane-bound adenylyl cyclase activities. Multiple adenylyl cyclase isoforms were identified in frog oocytes by PCR using degenerate primers corresponding to highly conserved catalytic amino acid sequences. Among these we identified a partial Xenopus adenylyl cyclase 7 (xAC7) that was 65% identical in amino acid sequence to human AC7. A dominant-negative mutant of xAC7 induced hormone-independent oocyte maturation and accelerated progesterone-induced oocyte maturation. Theses findings suggest that xAC7 is a major component of the G2 arrest mechanism in Xenopus oocytes.
(2005 Wiley-Liss, Inc.)
Databáze: MEDLINE
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