Xenopus prophase oocytes reenter meiotic division in response to progesterone. The signaling pathway leading to Cdc2 activation depends on neosynthesized proteins and a decrease in PKA

Abstract

In the Xenopus ovary, oocytes are arrested at the G2/M boundary of the first meiotic division. This G2/M block is released by progesterone that triggers after a lag period of 4 to 6 hours the activation of the Cdc2/cyclin B2 complex or MPF (M-phase promoting factor), the universal inducer of the G2/M transition (reviewed by Jessus and Ozon, 1993). The progesterone-transduction pathway leading to MPF activation is not yet elucidated, as well as the majority of the Cdc2 targets required for the completion of meiotic divisions. Cdc2 is activated through the dephosphorylation of its two inhibitory residues, Thr14 and Tyr15. The Cdc25 phosphatase, which is itself activated by complex phosphorylation reactions involving the Plx1 kinase, catalyzes this activation reaction (Jessus and Ozon, 1995; Karaiskou et al., 1999; Kumagai and Dunphy, 1996; Qian et al., 1998). Two controls involved in the pathway leading to Cdc2/Cdc25 activation are known. The first one depends on the synthesis of new proteins (Wasserman and Masui, 1975), among them is c-Mos (Sagata et al., 1988), which indirectly leads to the activation of MAP kinase (reviewed by Sagata, 1997). However, it is not yet clear how the MAP kinase pathway and the MPF activation pathway are linked. The second control is achieved through the inhibition of the cAMPdependent protein kinase, PKA (Maller, 1990; Maller and Krebs, 1977). However, the in vivo targets of PKA remain unknown. The possibility that PKA could regulate the neosynthesis and/or the stabilization of proteins needed for MPF activation is an attractive hypothesis. A major objective is therefore to look for proteins whose synthesis and/or stability are needed for MPF activation and that are controlled by PKA. Cdc2 activation in Xenopus oocytes correlates with a burst in protein phosphorylation, resulting from the activation of multiple Ser/Thr kinases (Jessus and Ozon, 1993; Maller et al., 1977). Whether the kinase activation represents an upstream or downstream event of Cdc2 activation remains to be determined. A kinase that is activated before Cdc2 might be involved in the transduction pathway that leads to Cdc2 activation whereas a kinase whose activation depends on Cdc2 activity might represent a component of the phosphorylation cascade required for meiotic divisions. Eg2 is an attractive candidate as a protein whose translation is controlled during maturation and as a kinase playing a role in meiotic divisions. Eg2 protein is a member of the Eg family, whose mRNAs are adenylated during meiotic maturation (Paris et al., 1991). Eg2 also belongs to the Aurora/AIRK emerging family of protein kinases (Giet and Prigent, 1999; Roghi et al., 1998). The highest levels of expression of the various members of this family are found in the gonads (Gopalan et al., 1997; Kimura et 1127 Journal of Cell Science 113, 1127-1138 (2000) Printed in Great Britain © The Company of Biologists Limited 2000 JCS1139

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Cite this paper

@inproceedings{Vaillant2000XenopusPO, title={Xenopus prophase oocytes reenter meiotic division in response to progesterone. The signaling pathway leading to Cdc2 activation depends on neosynthesized proteins and a decrease in PKA}, author={Marie Frank - Vaillant and Olivier Haccard and Catherine Thibier and Ren{\'e} Ozon and Yannick Arlot - Bonnemains and Claude Prigent and Catherine Jessus}, year={2000} }