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Differential roles of p39Mos-Xp42Mpk1 cascade proteins on Raf1 phosphorylation and spindle morphogenesis in Xenopus

J-F L Bodart1, F Y Baert, C Sellier

  • 1Laboratoire de Biologie du Développement, UPRES EA 1033, Université des Sciences et Technologies de Lille, SN3, Villeneuve d'Ascq, France. Jean-Francois.bodart@univ-lille1.fr

Developmental Biology
|May 26, 2005
PubMed

Insights

Hormonal stimulation triggers Xenopus oocytes to resume meiosis, involving germinal vesicle breakdown and spindle formation. The p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) pathway is crucial for meiotic spindle organization.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Developmental Biology

Background:

  • Xenopus oocytes arrest at G2 phase and resume meiosis upon hormonal stimulation.
  • Meiosis resumption involves germinal vesicle breakdown, chromosome condensation, and bipolar spindle formation.
  • The p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) signaling cascade is activated during meiosis resumption.

Purpose of the Study:

  • To investigate the role of the p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) pathway in meiotic spindle morphogenesis.
  • To determine the specific contributions of pathway components to spindle organization.

Main Methods:

  • Inhibition of p39(Mos) accumulation using antisense morpholino and phosphorothioate oligonucleotides.
  • MEK1 inhibition using U0126.
  • Analysis of Raf1 phosphorylation.
  • Spindle morphogenesis rescue experiments with constitutively active Rsk and murine Mos protein.

Main Results:

  • Prevention of p39(Mos) accumulation impaired MEK1 phosphorylation, even in insulin-stimulated pathways.
  • Raf1 phosphorylation depended on MEK1 or Xp42(Mpk1) activity, but not p90(Rsk).
  • Inhibition of p39(Mos) or MEK1 resulted in cytoplasmic asters with condensed chromosomes, and neither p39(Mos) nor p90(Rsk) alone could rescue spindle organization.

Conclusions:

  • The p39(Mos)-MEK1-Xp42(Mpk1)-p90(Rsk) pathway is essential for the bipolar organization of the meiotic spindle in Xenopus oocytes.
  • Specific components of the pathway have distinct roles in spindle assembly.

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