Meiotic cell cycle in Xenopus oocytes is independent of cdk2 kinase.
In vertebrates, M phase-promoting factor (MPF), a universal G2/M regulator in eukaryotic cells, drives meiotic maturation of oocytes, while cytostatic factor (CSF) arrests mature oocytes at metaphase II until fertilization. Cdk2 kinase, a G1/S regulator in higher eukaryotic cells, is activated during meiotic maturation of Xenopus oocytes and, like Mos (an essential component of CSF), is proposed to be involved in metaphase II arrest in mature oocytes. In addition, cdk2 kinase has been shown recently to be essential for MPF activation in Xenopus embryonic mitosis. Here we report injection of Xenopus oocytes with the cdk2 kinase inhibitor p21Cip in order to (re)evaluate the role of cdk2 kinase in oocyte meiosis. Immature oocytes injected with p21Cip can enter both meiosis I and meiosis II normally, as evidenced by the typical fluctuations in MPF activity. Moreover, mature oocytes injected with p21Cip are retained normally in metaphase II for a prolonged period, whereas those injected with neutralizing anti-Mos antibody are released readily from metaphase II arrest. These results argue strongly against a role for cdk2 kinase in MPF activation and its proposed role in metaphase II arrest, in Xenopus oocyte meiosis. We discuss the possibility that cdk2 kinase stored in oocytes may function, as a maternal protein, solely for early embryonic cell cycles.
Furuno
N
N
Department of Biology, Faculty of Science, Kyushu University, Fukuoka, Japan.
Ogawa
Y
Y
Iwashita
J
J
Nakajo
N
N
Sagata
N
N
D000595:Amino Acid Sequence; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D016200:Maturation-Promoting Factor / Q000378:metabolism; D008540:Meiosis; D008677:Metaphase; D008969:Molecular Sequence Data; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D015398:Signal Transduction; D014981:Xenopus; D029867:Xenopus Proteins
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D017346:Protein Serine-Threonine Kinases; D017231:Proto-Oncogene Proteins c-mos; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D016200:Maturation-Promoting Factor