title: Activated polo-like kinase Plx1 is required at multiple points during mitosis in Xenopus laevis.
abstract: Entry into mitosis depends upon activation of the dual-specificity phosphatase Cdc25C, which dephosphorylates and activates the cyclin B-Cdc2 complex. Previous work has shown that the Xenopus polo-like kinase Plx1 can phosphorylate and activate Cdc25C in vitro. In the work presented here, we demonstrate that Plx1 is activated in vivo during oocyte maturation with the same kinetics as Cdc25C. Microinjection of wild-type Plx1 into Xenopus oocytes accelerated the rate of activation of Cdc25C and cyclin B-Cdc2. Conversely, microinjection of either an antibody against Plx1 or kinase-dead Plx1 significantly inhibited the activation of Cdc25C and cyclin B-Cdc2. This effect could be reversed by injection of active Cdc25C, indicating that Plx1 is upstream of Cdc25C. However, injection of Cdc25C, which directly activates cyclin B-Cdc2, also caused activation of Plx1, suggesting that a positive feedback loop exists in the Plx1 activation pathway. Other experiments show that injection of Plx1 antibody into early embryos, which do not require Cdc25C for the activation of cyclin B-Cdc2, resulted in an arrest of cleavage that was associated with monopolar spindles. These results demonstrate that in Xenopus laevis, Plx1 plays important roles both in the activation of Cdc25C at the initiation of mitosis and in spindle assembly at late stages of mitosis.
authors.affiliation: Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262, USA.
authors.forename: Y W
authors.initials: YW
authors.lastname: Qian
authors.forename: E
authors.initials: E
authors.lastname: Erikson
authors.forename: C
authors.initials: C
authors.lastname: Li
authors.forename: J L
authors.initials: JL
authors.lastname: Maller
mesh_terms: D000818:Animals; D000906:Antibodies / Q000378:metabolism / Q000494:pharmacology; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D019926:Cyclin B / Q000378:metabolism; D004789:Enzyme Activation; D005260:Female; D008938:Mitosis / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D011374:Progesterone / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011817:Rabbits; D008941:Spindle Apparatus / Q000502:physiology; D029867:Xenopus Proteins; D014982:Xenopus laevis; D020687:cdc25 Phosphatases; D000097869:Polo-Like Kinase 1
chemical_list: D000906:Antibodies; D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D019926:Cyclin B; D011374:Progesterone; D017346:Protein Serine-Threonine Kinases; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; C101085:Plk1 protein, Xenopus; D000097869:Polo-Like Kinase 1