Intracellular acidification delays hormonal G2/M transition and inhibits G2/M transition triggered by thiophosphorylated MAPK in Xenopus oocytes.

Xenopus oocyte maturation is analogous to G2/M transition and characterized by germinal vesicle breakdown (GVBD), spindle formation, activation of MPF and Mos-Xp42(Mpk1) pathways. It is accompanied prior to GVBD by a transient increase in intracellular pH. We determined that a well known acidifying compound, NH(4)Cl, delayed progesterone-induced GVBD in a dose-dependent manner. GVBD(50) was delayed up to 2.3-fold by 10 mM NH(4)Cl. Cyclin B2 phosphorylation, Cdk1 Tyr15 dephosphorylation as well as p39(Mos) accumulation, Xp42(Mpk1) and p90(Rsk) phosphorylation induced by progesterone were also delayed by incubation of oocyte in NH(4)Cl. The delay induced by NH(4)Cl was prevented by injection of MOPS buffer pH 7.7. In contrast to acidifying medium, alkalyzing treatment such as Tris buffer pH 9 injections, accelerated GVBD, MPF and Xp42(Mpk1) activation, indicating that pHi changes control early steps of G2/M dynamics. When injected in an immature recipient oocyte, egg cytoplasm triggers GVBD through MPF auto-amplification, independently of protein synthesis. In these conditions, GVBD and Xp42(Mpk1) activation were delayed by high concentration of NH(4)Cl, which never prevented or delayed MPF activation. Strickingly, NH(4)Cl strongly inhibited thiophosphorylated active MAPK-induced GVBD and MPF activation. Nevertheless, Tris pH 9 did not have any effects on egg cytoplasm- or active MAPK-induced GVBD. Taken together, our results suggest that dynamic of early events driving Xp42(Mpk1) and MPF activation induced by progesterone may be negatively or positively regulated by pH(i) changes. However Xp42(Mpk1) pathway was inhibited by acidification alone. Finally, MPF auto-amplification loop was not sensitive to pH(i) changes.

Sellier C ，Bodart JF ，Flament S ，Baert F ，Gannon J ，Vilain JP ... -  《JOURNAL OF CELLULAR BIOCHEMISTRY》

Differential roles of p39Mos-Xp42Mpk1 cascade proteins on Raf1 phosphorylation and spindle morphogenesis in Xenopus oocytes.

Bodart JF ，Baert FY ，Sellier C ，Duesbery NS ，Flament S ，Vilain JP ... -  《DEVELOPMENTAL BIOLOGY》

Function of the Mos/MAPK pathway during oocyte maturation in the Japanese brown frog Rana japonica.

:Fully grown immature oocytes acquire the ability to be fertilized with sperm after meiotic maturation, which is finally accomplished by the formation and activation of the maturation-promoting factor (MPF). MPF is the complex of Cdc2 and cyclin B, and its function in promoting metaphase is common among species. The Mos/mitogen-activated protein kinase (MAPK) pathway is also commonly activated during vertebrate oocyte maturation, but its function seems to be different among species. We investigated the function of the Mos/MAPK pathway during oocyte maturation of the frog Rana japonica. Although MAPK was activated in accordance with MPF activation during oocyte maturation, MPF activation and germinal vesicle breakdown (GVBD) was not initiated when the Mos/MAPK pathway was activated in immature oocytes by the injection of c-mos mRNA. Inhibition of Mos synthesis by c-mos antisense RNA and inactivation of MAPK by CL100 phosphatase did not prevent progesterone-induced MPF activation and GVBD. However, continuous MAPK activation and MAPK inhibition through oocyte maturation accelerated and delayed MPF activation, respectively. Furthermore, Mos induced a low level of cyclin B protein synthesis in immature oocytes without the aid of MAPK. These results suggest that the general function of the Mos/MAPK pathway, which is not essential for MPF activation and GVBD in Rana oocytes, is to enhance cyclin B translation by Mos itself and to stabilize cyclin B protein by MAPK during oocyte maturation.

Yoshida N ，Mita K ，Yamashita M 《MOLECULAR REPRODUCTION AND DEVELOPMENT》

Xp42(Mpk1) activation is not required for germinal vesicle breakdown but for Raf complete phosphorylation in insulin-stimulated Xenopus oocytes.

Baert F ，Bodart JF ，Bocquet-Muchembled B ，Lescuyer-Rousseau A ，Vilain JP ... -  《JOURNAL OF BIOLOGICAL CHEMISTRY》

Characterization of MPF and MAPK activities during meiotic maturation of Xenopus tropicalis oocytes.

Bodart JF ，Gutierrez DV ，Nebreda AR ，Buckner BD ，Resau JR ，Duesbery NS ... -  《DEVELOPMENTAL BIOLOGY》