Induction of a G2-phase arrest in Xenopus egg extracts by activation of p42 mitogen-activated protein kinase.
Previous work has established that activation of Mos, Mek, and p42 mitogen-activated protein (MAP) kinase can trigger release from G2-phase arrest in Xenopus oocytes and oocyte extracts and can cause Xenopus embryos and extracts to arrest in mitosis. Herein we have found that activation of the MAP kinase cascade can also bring about an interphase arrest in cycling extracts. Activation of the cascade early in the cycle was found to bring about the interphase arrest, which was characterized by an intact nuclear envelope, partially condensed chromatin, and interphase levels of H1 kinase activity, whereas activation of the cascade just before mitosis brought about the mitotic arrest, with a dissolved nuclear envelope, condensed chromatin, and high levels of H1 kinase activity. Early MAP kinase activation did not interfere significantly with DNA replication, cyclin synthesis, or association of cyclins with Cdc2, but it did prevent hyperphosphorylation of Cdc25 and Wee1 and activation of Cdc2/cyclin complexes. Thus, the extracts were arrested in a G2-like state, unable to activate Cdc2/cyclin complexes. The MAP kinase-induced G2 arrest appeared not to be related to the DNA replication checkpoint and not to be mediated through inhibition of Cdk2/cyclin E; evidently a novel mechanism underlies this arrest. Finally, we found that by delaying the inactivation of MAP kinase during release of a cytostatic factor-arrested extract from its arrest state, we could delay the subsequent entry into mitosis. This finding suggests that it is the persistence of activated MAP kinase after fertilization that allows the occurrence of a G2-phase during the first mitotic cell cycle.
Walter
S A
SA
Department of Molecular Pharmacology, Stanford University School of Medicine, California 94305-5332, USA.
Guadagno
T M
TM
Ferrell
J E
JE
D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins / Q000378:metabolism; D002457:Cell Extracts; D002843:Chromatin / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism / Q000494:pharmacology; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology; D004789:Enzyme Activation; D016195:G2 Phase / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D009685:Nuclear Envelope / Q000378:metabolism; D009687:Nuclear Proteins; D009865:Oocytes; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D006656:Protamine Kinase / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017231:Proto-Oncogene Proteins c-mos / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors; D014981:Xenopus; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases
D018797:Cell Cycle Proteins; D002457:Cell Extracts; D002843:Chromatin; D016213:Cyclins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D029867:Xenopus Proteins; C530005:WEE1 protein, Xenopus; D011505:Protein-Tyrosine Kinases; D006656:Protamine Kinase; D017346:Protein Serine-Threonine Kinases; D017231:Proto-Oncogene Proteins c-mos; D016203:CDC2 Protein Kinase; D042846:CDC2-CDC28 Kinases; C495891:Cdk2 protein, Xenopus; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D019950:Mitogen-Activated Protein Kinase 1; D010749:Phosphoprotein Phosphatases; D020687:cdc25 Phosphatases