A novel role for glycogen synthase kinase-3 in Xenopus development: maintenance of oocyte cell cycle arrest by a β-catenin-independent mechanism

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Abstract
We have examined the expression of glycogen synthase kinase-3β in oocytes and early embryos of Xenopus and found that the protein is developmentally regulated. In resting oocytes, GSK-3β is active and it is inactivated on maturation in response to progesterone. GSK-3β inactivation is necessary and rate limiting for the cell cycle response to this hormone and the subsequent accumulation of β-catenin. Overexpression of a dominant negative form of the kinase accelerates maturation, as does inactivation by expression of Xenopus Dishevelled or microinjection of an inactivating antibody. Cell cycle inhibition by GSK- 3β is not mediated by the level of β-catenin or by a direct effect on either the MAP kinase pathway or translation of mos and cyclin B1. These data indicate a novel role for GSK-3β in Xenopus development: in addition to controlling specification of the dorsoventral axis in embryos, it mediates cell cycle arrest in oocytes.