Xenopus Cdc6 confers sperm binding competence to oocytes without inducing their maturation

Xenopus Cdc6 confers sperm binding competence to oocytes without inducing their maturation

Department of Biochemistry and Cell Biology and the Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, NY 11794-5215

Contributed by William J. Lennarz

Abstract

Amphibian eggs normally require meiotic maturation to be competent for fertilization. A necessary prerequisite for this event is sperm binding, and we show that under normal physiological conditions this property is acquired at, but not before, meiotic maturation. Immature oocytes do not bind sperm, but injection of total egg poly(A)⁺ mRNA into immature oocytes confers sperm binding in the absence of meiotic maturation. Using an expression cloning approach we have isolated a single cDNA from egg poly(A)⁺ mRNA that can induce sperm binding in immature oocytes. The cDNA was found to encode Xenopus Cdc6, a protein that previously has been shown to function in initiation of DNA replication and cell cycle control. This unanticipated finding provides evidence of a link between a regulator of the cell cycle and alterations in cell surface properties that affect gamete binding.

Footnotes

↵ * To whom reprint requests should be addressed. e-mail: wlennarz{at}life.bio.sunysb.edu.
Data deposition: The sequence reported in this paper has been deposited in the GenBank database (accession no. U76834).
ABBREVIATIONS:

GVBD,

germinal vesicle breakdown;

CE,

coelomic egg envelope;

VE,

vitelline envelope;

CPE,

cytoplasmic polyadenylation element;

UTR,

untranslated region