Abstract
The mitogen-activated protein kinase (MAPK) kinase kinase (MEKK or MAPKKK) Mos and the downstream kinase MAPK are important for metaphase II arrest in Xenopus eggs. Verlhac et al. investigated whether other kinases could substitute for Mos and its effectors. Constitutively activated forms of Raf (another MEKK) or MEK (the kinase immediately downstream of Mos that is responsible for directly phosphorylating MAPK) were unable to activate MAPK in Mos-/- eggs, unless in the presence of okadaic acid, a serine-threonine phosphatase inhibitor. Coexpression of constitutively activated MEK and a MAPK mutant that is resistant to dephosphorylation led to demonstrable MAPK activation and restored metaphase II arrest in Mos-/- eggs. These results suggest that in addition to activating MAPK through MEK, Mos is able to sustain MAPK activation by inhibiting protein serine-threonine phosphatase activity.Verlhac, M.-H., Lefebvre, C., Kubiak, J.Z., Umbhauer, M., Rassinier, P., Colledge, W., and Maro, B. (2000) Mos activates MAP kinase in mouse oocytes through two opposite pathways. EMBO J. 19: 6065-6074. [Abstract] [Full Text]
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