Hyperphosphorylation of Nucleoplasmin Facilitates Xenopus Sperm Decondensation at Fertilization

doi:10.1074/jbc.271.13.7253

Hyperphosphorylation of Nucleoplasmin Facilitates Xenopus Sperm Decondensation at Fertilization (*)

From the (1)Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216 and the
(2)Wellcome/CRC Institute of Cancer and Developmental Biology, Tennis Court Road, Cambridge CB2 1QR and Department of Zoology, University of Cambridge, Cambridge CB2 1QR, United Kingdom

^§To whom correspondence should be addressed:
Dept. of Biochemistry, University of Mississippi Medical Center, 2500 North State St., Jackson, MS 39216.
Tel.: 601-984-1510; Fax: 601-984-1501; leno{at}fiona.umsmed.edu.

↵^¶ Recipient of a Wellcome Trust Prize Studentship. Present address: Dept. of Cell Biology, Harvard Medical School, 25 Shattuck St., Boston, MA 02115.

Abstract

Previous studies showed that the nuclear phosphoprotein nucleoplasmin performs the first stage of chromatin decondensation of Xenopus sperm at fertilization. It binds and removes sperm basic proteins replacing them with histones. We now show that this activity depends upon the massive hyperphosphorylation of nucleoplasmin that occurs when oocytes mature into eggs. Egg extracts or purified hyperphosphorylated egg nucleoplasmin decondense sperm chromatin and remove sperm basic proteins much faster than oocyte extracts or hypophosphorylated oocyte nucleoplasmin. Furthermore, dephosphorylation of egg nucleoplasmin slows sperm decondensation and prevents basic protein removal from sperm chromatin. We conclude that hyperphosphorylation of nucleoplasmin is used to modulate the rapid changes in chromatin structure that accompany early development in Xenopus.

Footnotes

↵* This work was supported in part by an Oak Ridge Associated Universities Junior Faculty Enhancement Award (to G. H. L.), by Grant MCB-9506280 from the National Science Foundation (to G. H. L.), and by the Cancer Research Campaign (Program Grant SP1961 to R. A. L., A. D. M., and A. P.). 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.
↵¹ The abbreviations used are:

HSS

high speed supernatant

TAU

Triton/acid/urea

PAGE

polyacrylamide gel electrophoresis.
- Received January 4, 1996.
- Revision received February 7, 1996.