title: Analysis of the early embryonic cell cycles of Xenopus; regulation of cell cycle length by Xe-wee1 and Mos.
abstract: In Xenopus, cdc2 tyrosine phosphorylation is detected in the first 60-75 minute cell cycle but not in the next eleven cell cycles (cycles 2-12) which are only 30 minutes long. Here we report that the wee1/cdc25 ratio increases before the first mitotic interphase. We show that the Xe-wee1 protein is absent in stage VI oocytes and is expressed from meiosis II until gastrulation. A dominant negative form of Xe-wee1 (KM wee1) reduced the level cdc2 tyrosine phosphorylation and length of the first cycle. However, the ratio of wee1/cdc25 did not decrease after the first cycle and therefore did not explain the lack of cdc2 tyrosine phosphorylation in, nor the rapidity of, cycles 2-12. Furthermore, there was no evidence for a wee1/myt1 inhibitor in cycles 2-12. We examined the role of Mos in the first cycle because it is present during the first 20 minutes of this cycle. We arrested the rapid embryonic cell cycle (cycle 2 or 3) with Mos and restarted the cell cycle with calcium ionophore; the 30 minute cycle was converted into a 60 minute cycle, with cdc2 tyrosine phosphorylation. In addition, the injection of a non-degradable Mos (MBP-Mos) into the first cycle resulted in a dramatic elongation of this cycle (to 140 minutes). MBP-Mos did not delay DNA replication or the translation of cyclins A or B; it did, however, result in the marked accumulation of tyrosine phosphorylated cdc2. Thus, while the wee1/cdc25 ratio changes during development, these changes may not be responsible for the variety of cell cycles observed during early Xenopus embryogenesis. Our experiments indicate that Mos/MAPK can also contribute to cell cycle length.
authors.affiliation: ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, MD 21702, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Murakami
authors.forename: G F
authors.initials: GF
authors.lastname: Vande Woude
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005775:Gastrula / Q000378:metabolism; D008938:Mitosis; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D009865:Oocytes / Q000378:metabolism; D009928:Organ Specificity; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D016372:RNA, Antisense / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D011993:Recombinant Fusion Proteins; D014443:Tyrosine / Q000378:metabolism; D014981:Xenopus / Q000196:embryology*; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases
chemical_list: D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D016372:RNA, Antisense; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D014443:Tyrosine; C530005:WEE1 protein, Xenopus; D011505:Protein-Tyrosine Kinases; D017231:Proto-Oncogene Proteins c-mos; D016203:CDC2 Protein Kinase; D010749:Phosphoprotein Phosphatases; D020687:cdc25 Phosphatases