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Mol Cell Biol, July 1998, p. 4262-4271, Vol. 18, No. 7
Howard Hughes Medical Institute and
Department of Pharmacology, University of Colorado School of
Medicine, Denver, Colorado 80262
Received 26 January 1998/Returned for modification 10 March
1998/Accepted 21 April 1998
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.
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Activated Polo-Like Kinase Plx1 Is Required at
Multiple Points during Mitosis in Xenopus laevis
*
Corresponding author. Mailing address: Howard Hughes
Medical Institute and Department of Pharmacology, University of
Colorado School of Medicine, Biomedical Research Bldg., Room 433, 4200 Ninth Ave., Box C-236, Denver, CO 80262-0236. Phone: (303) 315-7075. Fax: (303) 315-7160. E-mail: mallerj{at}essex.uchsc.edu.
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