Polo-like kinase confers MPF autoamplification competence to growing Xenopus oocytes.
During oogenesis, the Xenopus oocyte is blocked in prophase of meiosis I. It becomes competent to resume meiosis in response to progesterone at the end of its growing period (stage VI of oogenesis). Stage IV oocytes contain a store of inactive pre-MPF (Tyr15-phosphorylated Cdc2 bound to cyclin B2); the Cdc25 phosphatase that catalyzes Tyr15 dephosphorylation of Cdc2 is also present. However, the positive feedback loop that allows MPF autoamplification is not functional at this stage of oocyte growth. We report that when cyclin B is overexpressed in stage IV oocytes, MPF autoamplification does not occur and the newly formed cyclin B-Cdc2 complexes are inactivated by Tyr15 phosphorylation, indicating that Myt1 kinase remains active and that Cdc25 is prevented to be activated. Plx1 kinase (or polo-like kinase), which is required for Cdc25 activation and MPF autoamplification in full grown oocytes is not expressed at the protein level in small stage IV oocytes. In order to determine if Plx1 could be the missing regulator that prevents MPF autoamplification, polo kinase was overexpressed in stage IV oocytes. Under these conditions, the MPF-positive feedback loop was restored. Moreover, we show that acquisition of autoamplification competence does not require the Mos/MAPK pathway.
Laboratoire de Biologie du Développement, UMR-CNRS 7622, Equipe 'Biologie de l'ovocyte', Université Pierre et Marie Curie, boîte 24, 4 place Jussieu, 75252 Paris cedex 05, France.
Anthi
A
Karaiskou
Anne-Claire
AC
Leprêtre
Golbahar
G
Pahlavan
David
D
Du Pasquier
René
R
Ozon
Catherine
C
Jessus
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D056744:Cyclin B1; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D025461:Feedback, Physiological; D005260:Female; D006801:Humans; D016200:Maturation-Promoting Factor / Q000378:metabolism*; D008540:Meiosis / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009866:Oogenesis / Q000502:physiology; D011374:Progesterone / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000378:metabolism; D000097869:Polo-Like Kinase 1
D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D019925:Cyclin A; D019926:Cyclin B; D056744:Cyclin B1; D004791:Enzyme Inhibitors; D016200:Maturation-Promoting Factor; D020928:Mitogen-Activated Protein Kinases; D019319:Okadaic Acid; D011374:Progesterone; D017346:Protein Serine-Threonine Kinases; D017231:Proto-Oncogene Proteins c-mos; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; C534699:CCNB1 protein, human; C101085:Plk1 protein, Xenopus; D000097869:Polo-Like Kinase 1