Deciphering the H-Ras pathway in Xenopus oocyte.
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.
Gaffré
M
M
Laboratoire de Biologie du Développement, UMR-CNRS 7622, Université Pierre et Marie Curie, Paris, France.
Dupré
A
A
Valuckaite
R
R
Suziedelis
K
K
Jessus
C
C
Haccard
O
O
D000818:Animals; D002455:Cell Division; D005260:Female; D011905:Genes, ras; D016296:Mutagenesis; D009865:Oocytes / Q000166:cytology / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D014982:Xenopus laevis / Q000235:genetics / Q000502:physiology*
D012333:RNA, Messenger