Oncogene 2006 Aug 24;2537:5155-62. doi: 10.1038/sj.onc.1209523.

Deciphering the H-Ras pathway in Xenopus oocyte.

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Xenopus oocytes are arrested in prophase of the first meiotic division. In response to progesterone, they re-enter meiosis and arrest again in metaphase of the second meiotic division. This process, called meiotic maturation, is under the control of the Cyclin B-Cdc2 complex, M phase promoting factor (MPF). Injection of a constitutively active Xenopus H-Ras protein activates MPF, suggesting that Ras proteins could be implicated in the progesterone transduction pathway. The aim of this study was (1) to elucidate the pathway triggered by H-Ras leading to MPF activation in Xenopus oocytes and (2) to investigate whether endogenous H-Ras is involved in the physiological process of meiotic maturation. We generated three constitutively active double mutants, each of them recruiting a single effector in mammalian cells, mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K) or RalGDS. Our results show that the activation of a PI3K-related enzyme is crucial for H-Ras-induced MPF activation, whereas the recruitment of either MAPK or RalGDS is not. However, although the H-Ras/PI3K pathway is functional in Xenopus oocytes, it is not the physiological transducer of progesterone responsible for meiotic resumption.

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Species referenced: Xenopus laevis
Genes referenced: cdk1 hras mapk1 pik3ca ralgds
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