Characterization of MPF and MAPK activities during meiotic maturation of Xenopus tropicalis oocytes

Dev Biol. 2002 May 15;245(2):348-61. doi: 10.1006/dbio.2002.0647.


Resumption of meiosis in oocytes of Xenopus tropicalis required translation but not transcription, and was marked by the appearance of a white spot and a dark ring, coincident with entry into metaphase I and the onset of anaphase I, respectively. Cyclin B(2)/p34(cdc2) activity increased prior to the first meiotic division, declined at the onset of anaphase I, and subsequently increased again. The capacity of egg cytoplasm to induce germinal vesicle breakdown (GVBD) was inhibited by cycloheximide, despite the fact that these oocytes contained cyclin B(2)/p34(cdc2) complexes. However, cycloheximide-treated oocytes underwent GVBD following injection of constitutively active mitogen-activated protein kinase (MAPK) kinase 2 (MEK2), p33(Ringo), or Delta 90 cyclin B. MAPK activity increased just prior to the first meiotic division and remained stable thereafter. Although injection of constitutively active MEK2 induced GVBD, treatment with the MEK inhibitors U0126 or anthrax lethal factor delayed GVBD and prevented spindle formation. Interestingly, the ability of egg cytoplasm to induce GVBD was unaffected by the inhibition of MEK activity. Our results indicate that the synthesis of a novel or short-lived protein(s) which acts in a MEK-independent fashion is required in order for egg cytoplasm to induce GVBD in X. tropicalis oocytes.

MeSH terms

  • Animals
  • CDC2 Protein Kinase / metabolism
  • Cyclin B / genetics
  • Cyclin B / metabolism
  • Cyclin B / pharmacology
  • Cytoplasm / metabolism
  • Enzyme Activation / drug effects
  • MAP Kinase Kinase 2
  • Maturation-Promoting Factor / metabolism*
  • Meiosis*
  • Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Mitogen-Activated Protein Kinases / metabolism*
  • Oocytes / cytology*
  • Oocytes / drug effects
  • Oocytes / enzymology
  • Oocytes / metabolism*
  • Progesterone / pharmacology
  • Protein Biosynthesis
  • Protein-Tyrosine Kinases / antagonists & inhibitors
  • Protein-Tyrosine Kinases / metabolism
  • Time Factors
  • Transcription, Genetic
  • Xenopus laevis
  • Xenopus*


  • Cyclin B
  • Progesterone
  • Protein-Tyrosine Kinases
  • CDC2 Protein Kinase
  • Maturation-Promoting Factor
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 2
  • Mitogen-Activated Protein Kinase Kinases