Regulation of Xenopus oocyte meiosis arrest by G protein betagamma subunits.
BACKGROUND
Progesterone induces the resumption of meiosis (maturation) in Xenopus oocytes through a nongenomic mechanism involving inhibition of an oocyte adenylyl cyclase and reduction of intracellular cAMP. However, progesterone action in Xenopus oocytes is not blocked by pertussis toxin, and this finding indicates that the inhibition of the oocyte adenylyl cyclase is not mediated by the alpha subunits of classical G(i)-type G proteins.


RESULTS
To investigate the possibility that G protein betagamma subunits, rather than alpha subunits, play a key role in regulating oocyte maturation, we have employed two structurally distinct G protein betagamma scavengers (G(t)alpha and betaARK-C(CAAX)) to sequester free Gbetagamma dimers. We demonstrated that the injection of mRNA encoding either of these Gbetagamma scavengers induced oocyte maturation. The Gbetagamma scavengers bound an endogenous, membrane-associated Gbeta subunit, indistinguishable from Xenopus Gbeta1 derived from mRNA injection. The injection of Xenopus Gbeta1 mRNA, together with bovine Ggamma2 mRNA, elevated oocyte cAMP levels and inhibited progesterone-induced oocyte maturation.


CONCLUSIONS
An endogenous G protein betagamma dimer, likely including Xenopus Gbeta1, is responsible for maintaining oocyte meiosis arrest. Resumption of meiosis is induced by Gbetagamma scavengers in vitro or, naturally, by progesterone via a mechanism that suppresses the release of Gbetagamma.
Sheng
Y
Y
Loeb Research Institute, Ottawa Hospital, K1Y 4E9, Ottawa, Canada.
Tiberi
M
M
Booth
R A
RA
Ma
C
C
Liu
X J
XJ
D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D015870:Gene Expression; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008540:Meiosis / Q000502:physiology*; D009865:Oocytes / Q000187:drug effects / Q000254:growth & development*; D009866:Oogenesis / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology; D018343:Receptors, Adrenergic, beta-2 / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D018343:Receptors, Adrenergic, beta-2; D011374:Progesterone; D000242:Cyclic AMP; D020962:Heterotrimeric GTP-Binding Proteins