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J. Biol. Chem., Vol. 278, Issue 50, 49714-49720, December 12, 2003

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Xp42^Mpk1 Activation Is Not Required for Germinal Vescicle Breakdown but for Raf Complete Phosphorylation in Insulin-stimulated Xenopus Oocytes^*

Frédéric Baert, Jean-François Bodart, Béatrice Bocquet-Muchembled, Arlette Lescuyer-Rousseau, and Jean-Pierre Vilain

From the Laboratoire de Biologie du Développement UPRES-EA1033, Bâtiment SN3, IFR118, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq CEDEX, France

Fully grown G₂-arrested Xenopus oocytes resume meiosis in vitro upon exposure to hormonal stimulation. Progesterone triggers oocyte meiosis resumption through a Ras-independent pathway that involves a p39^Mos-dependent activation of the mitogen-activated protein (MAP) kinases. Insulin also triggers meiosis resumption through a tyrosine kinase receptor that activates a Ras-dependent pathway leading to the MAP kinases activation. Antisense phosphorothioate oligonucleotides were used to prevent p39^Mos accumulation and Erk-like Xp42^Mpk1 activation during insulin-induced Xenopus oocytes maturation. In contrast to previous works, prevention of p39^Mos-induced activation of Xp42^Mpk1 in insulin-treated oocytes did not inhibit but delayed meiotic resumption, like in progesterone-stimulated oocytes. Activations of Xp42^Mpk1, the unique Erk of the oocyte, and of its downstream target p90^Rsk, were impaired and phosphorylation of the MAPKK kinase Raf was partially inhibited. Similarly, oocytes treated with the MEK inhibitor U0126, stimulated by insulin exhibited delayed germinal vesicle breakdown, absence of Xp42^Mpk1 activation, and partial phosphorylation of Raf. To summarize, whereas p39^Mos-induced activation of MEK/MAPK pathway is dispensable for insulin-induced germinal vesicle breakdown, Xp42^Mpk1 activation induced by insulin is dependent upon p39^Mos synthesis. Raf complete phosphorylation appears to require the MEK/MAPK pathway activation both in progesterone and insulin-stimulated oocytes.

Received for publication, July 24, 2003 , and in revised form, September 22, 2003.

^* This work was supported by grants from the French "Ministère de l'Education Nationale" (UPRES-EA 1033). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Present address: Laboratoire de Neuroimmunologie des annélides, CNRS UMR 8017, IFR118, Bâtiment SN3, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq CEDEX, France.

To whom correspondence should be addressed. Tel.: 33-3-20-33-61-16; Fax: 33-3-20-43-40-38; E-mail: Jean-Francois.Bodart{at}univ-lille1.fr.

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