Activation of Cdc2 kinase during meiotic maturation of axolotl oocyte.
Activity of Cdc2, the universal inducer of mitosis, is regulated by phosphorylation and binding to cyclin B. Comparative studies using oocytes from several amphibian species have shown that different mechanisms allow Cdc2 activation and entry into first meiotic division. In Xenopus, immature oocytes stockpile pre-M-phase promoting factor (MPF) composed of Cdc2-cyclin B complexes maintained inactive by Thr14 and Tyr15 phosphorylation of Cdc2. Activation of MPF relies on the conversion of pre-MPF into MPF by Cdc2 dephosphorylation, implying a positive feedback loop known as MPF auto-amplification. On the contrary, it has been proposed that pre-MPF is absent in immature oocyte and that MPF activation depends on cyclin synthesis in some fishes and other amphibians. We demonstrate here that MPF activation in the axolotl oocyte, an urodele amphibian, is achieved through mechanisms resembling partly those found in Xenopus oocyte. Pre-MPF is present in axolotl immature oocyte and is activated during meiotic maturation. However, monomeric Cdc2 is expressed in large excess over pre-MPF, and pre-MPF activation by Cdc2 dephosphorylation takes place progressively and not abruptly as in Xenopus oocyte. The intracellular compartmentalization as well as the low level of pre-MPF in axolotl oocyte could account for the differences in oocyte MPF activation in both species.
Vaur
Sabine
S
Equipe Régulations post-transcriptionnelles et développement précoce, Laboratoire de Biologie du Développement, UMR-CNRS 7622, Université Pierre et Marie Curie, 75252 Paris cedex 05, France.
Poulhe
Robert
R
Maton
Gilliane
G
Andéol
Yannick
Y
Jessus
Catherine
C
D000558:Ambystoma mexicanum / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D002850:Chromatography, Gel; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D006657:Histones / Q000378:metabolism; D015151:Immunoblotting; D020935:MAP Kinase Signaling System / Q000502:physiology; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism / Q000502:physiology*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011498:Protein Precursors / Q000378:metabolism*; D020687:cdc25 Phosphatases / Q000378:metabolism
D019925:Cyclin A; D019926:Cyclin B; D006657:Histones; D011498:Protein Precursors; C067034:maturation-promoting factor precursor; D016203:CDC2 Protein Kinase; D016200:Maturation-Promoting Factor; D010749:Phosphoprotein Phosphatases; D020687:cdc25 Phosphatases