Requirement for the MAP kinase kinase/MAP kinase cascade in Xenopus oocyte maturation.

Abstract
MAP kinase kinase (MAPKK) has been identified as a protein factor that can induce phosphorylation and activation of inactive MAP kinase in vitro. In this study, we produced an anti‐Xenopus MAPKK antibody that can specifically inhibit Xenopus MAPKK activity in vitro. Microinjection of this antibody into immature oocytes prevented progesterone‐induced MAP kinase activation. Moreover, progesterone‐induced histone H1 kinase activation and germinal vesicle breakdown (GVBD) were inhibited in the oocytes injected previously with this antibody. Furthermore, when a bacterially expressed Mos was introduced into immature oocytes, Mos‐induced MAP kinase activation and GVBD were blocked in the oocytes injected with the anti‐MAPKK antibody. These results show that MAPKK is responsible for the activation of MAP kinase in vivo and that the MAPKK/MAP kinase cascade plays a pivotal role in the MPF activation during the oocyte maturation process.