title: Inhibiting MAP kinase activity prevents calcium transients and mitosis entry in early sea urchin embryos.
abstract: A transient calcium increase triggers nuclear envelope breakdown (mitosis entry) in sea urchin embryos. Cdk1/cyclin B kinase activation is also known to be required for mitosis entry. More recently, MAP kinase activity has also been shown to increase during mitosis. In sea urchin embryos, both kinases show a similar activation profile, peaking at the time of mitosis entry. We tested whether the activity of both kinases is required for mitosis entry and whether either kinase controls mitotic calcium signals. We found that reducing the activity of either mitotic kinase prevents nuclear envelope breakdown, despite the presence of a calcium transient, when cdk1/cyclin B kinase activity is alone inhibited. When MAP kinase activity alone was inhibited, the calcium signal was absent, suggesting that MAP kinase activity is required to generate the calcium transient that triggers nuclear envelope breakdown. However, increasing intracellular free calcium by microinjection of calcium buffers or InsP(3) while MAP kinase was inhibited did not itself induce nuclear envelope breakdown, indicating that additional MAP kinase-regulated events are necessary. After MAP kinase inhibition early in the cell cycle, the early events of the cell cycle (pronuclear migration/fusion and DNA synthesis) were unaffected, but chromosome condensation and spindle assembly are prevented. These data indicate that in sea urchin embryos, MAP kinase activity is part of a signaling complex alongside two components previously shown to be essential for entry into mitosis: the calcium transient and the increase in cdk1/cyclinB kinase activity.
authors.affiliation: Institute of Cell and Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle upon Tyne, NE2 4HH, United Kingdom.
authors.forename: Rada
authors.initials: R
authors.lastname: Philipova
authors.forename: Mark G
authors.initials: MG
authors.lastname: Larman
authors.forename: Calum P
authors.initials: CP
authors.lastname: Leckie
authors.forename: Patrick K
authors.initials: PK
authors.lastname: Harrison
authors.forename: Laurence
authors.initials: L
authors.lastname: Groigno
authors.forename: Michael
authors.initials: M
authors.lastname: Whitaker
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D016203:CDC2 Protein Kinase / Q000378:metabolism; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000737:chemistry; D002875:Chromosomes / Q000648:ultrastructure; D019926:Cyclin B / Q000378:metabolism; D003911:Dextrans / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005306:Fertilization; D047468:Immunoprecipitation; D047331:Lytechinus; D020935:MAP Kinase Signaling System; D054639:Mitogen-Activated Protein Kinase Phosphatases; D008938:Mitosis; D009570:Nitriles / Q000494:pharmacology; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011687:Purines / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D000077546:Roscovitine; D013997:Time Factors; D029867:Xenopus Proteins / Q000378:metabolism
chemical_list: D002070:Butadienes; D002843:Chromatin; D019926:Cyclin B; D003911:Dextrans; D004791:Enzyme Inhibitors; D009570:Nitriles; D011687:Purines; D011993:Recombinant Fusion Proteins; C113580:U 0126; D029867:Xenopus Proteins; D000077546:Roscovitine; D004533:Egtazic Acid; D016203:CDC2 Protein Kinase; C096688:DUSP1 protein, Xenopus; D054639:Mitogen-Activated Protein Kinase Phosphatases; D017027:Protein Tyrosine Phosphatases; D002118:Calcium