Maternal Xenopus Cdk2-Cyclin E Complexes Function during Meiotic and Early Embryonic Cell Cycles That Lack a G Phase

doi:10.1074/jbc.270.12.6843

Maternal Xenopus Cdk2-Cyclin E Complexes Function during Meiotic and Early Embryonic Cell Cycles That Lack a G Phase (*)

From the Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, Colorado 80262

^¶ Investigator of the Howard Hughes Medical Institute. To whom correspondence should be addressed.

Abstract

Earlier work demonstrated that cyclins A1, B1, and B2 are not associated with Cdk2 from unfertilized Xenopus eggs. As a potential Cdk2 partner during meiosis, a cyclin E homolog was cloned from a Xenopus oocyte cDNA library and found to be 60% identical at the amino acid level to human cyclin E. Cyclin E1 protein was detected in resting oocytes, and the level increased severalfold in meiosis II, concomitant with the appearance of forms with decreased electrophoretic mobility. During oocyte maturation, the patterns of cyclin E1-associated kinase activity and Cdk2 activity were identical, with activity low until after germinal vesicle breakdown, peaking during meiosis II. Cyclin E1 complexes immunoprecipitated from unfertilized Xenopus eggs contained Cdk2 but not Cdc2. In cycling egg extracts Cdk2-cyclin E1-associated kinase activity oscillated, but the level of cyclin E1 protein and its association with Cdk2 did not vary appreciably; complex activity appeared to be regulated neither by the synthesis and destruction of the cyclin subunit nor by association/disassociation of the two subunits. During the early cleavage divisions in embryos, cyclin E1 and Cdk2 remained associated. The data indicate that the Cdk2-cyclin E complex functions during meiotic and embryonic cell cycles in addition to performing its established role during G₁ in somatic cells.

Footnotes

↵^§ Associate of the Howard Hughes Medical Institute.
↵* This work was supported by Grant GM26743 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) L23857[GenBank].
↵¹ The abbreviations used are:

MPF

maturation-promoting factor

CSF

cytostatic factor

EB

extraction buffer

Pipes

1,4-piperazinediethanesulfonic acid

DTT

dithiothreitol

PBS

phosphate-buffered saline

GVBD

germinal vesicle breakdown.
↵²Dr. T. Kishimoto, Tokyo Institute of Technology, Tokyo, personal communication.
↵³Dr. M. J. Cockerill and Dr. T. Hunt, Imperial Cancer Research Fund, South Mimms, United Kingdom, personal communication.
↵⁴Dr. J. Blow, Imperial Cancer Research Fund, South Mimms, United Kingdom, personal communication.
↵⁵R. Hartley, R. Rempel, and J. Maller, manuscript in preparation.
↵⁶Dr. T. Hunt, Imperial Cancer Research Fund, South Mimms, United Kingdom, personal communication.
↵⁷J. Su, E. Erikson, and J. Maller, unpublished results.
- Received August 16, 1994.
- Revision received January 13, 1995.