Mos activates MAP kinase in mouse oocytes through two opposite pathways

EMBO J. 2000 Nov 15;19(22):6065-74. doi: 10.1093/emboj/19.22.6065.


Activation of mitogen-activated protein kinase (MAPK) in maturing mouse oocytes occurs after synthesis of Mos, a MAPKKK. To investigate whether Mos acts only through MEK1, we microinjected constitutively active forms of MEK1 (MEK1S218D/S222D referred herein as MEK*) and Raf (DeltaRaf) into mouse oocytes. In mos(-/-) oocytes, which do not activate MAPK during meiosis and do not arrest in metaphase II, MEK* and DeltaRaf did not rescue MAPK activation and metaphase II arrest, whereas Mos induced a complete rescue. MEK* and DeltaRaf induced cleavage arrest of two-cell blastomeres. They induced MAPK activation when protein phosphatases were inhibited by okadaic acid, suggesting that Mos may inhibit protein phosphatases. Finally, in mos(-/-) oocytes, MEK* induced the phosphorylation of Xp42(mapk)D324N, a mutant less sensitive to dephosphorylation, showing that a MAPK phosphatase activity is present in mouse oocytes. We demonstrate that active MAPKK or MAPKKK cannot substitute for Mos to activate MAPK in mouse oocytes. We also show that a phosphatase activity inactivates MAPK, and that Mos can overcome this inhibitory activity. Thus Mos activates MAPK through two opposite pathways: activation of MEK1 and inhibition of a phosphatase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Enzyme Activation
  • Female
  • Gene Expression
  • In Vitro Techniques
  • MAP Kinase Kinase 1
  • Meiosis
  • Metaphase
  • Mice
  • Mice, Knockout
  • Microinjections
  • Mitogen-Activated Protein Kinase Kinases / genetics
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Mitogen-Activated Protein Kinases / metabolism*
  • Mutation
  • Okadaic Acid / pharmacology
  • Oocytes / cytology
  • Oocytes / drug effects
  • Oocytes / enzymology*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins c-mos / genetics*
  • Proto-Oncogene Proteins c-mos / metabolism*
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism
  • Puromycin / pharmacology
  • RNA, Messenger / administration & dosage
  • RNA, Messenger / genetics


  • RNA, Messenger
  • Okadaic Acid
  • Puromycin
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-mos
  • Proto-Oncogene Proteins c-raf
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 1
  • Map2k1 protein, mouse
  • Mitogen-Activated Protein Kinase Kinases