Hyperphosphorylation of nucleoplasmin facilitates Xenopus sperm decondensation at fertilization.
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.
Leno
G H
GH
Department of Biochemistry, University of Mississippi Medical Center, Jackson, 39216, USA.
Mills
A D
AD
Philpott
A
A
Laskey
R A
RA
D000818:Animals; D002467:Cell Nucleus / Q000502:physiology*; D002843:Chromatin / Q000502:physiology*; D005306:Fertilization; D008297:Male; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology*; D056489:Nucleoplasmins; D009865:Oocytes / Q000502:physiology*; D010063:Ovum / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D013094:Spermatozoa / Q000502:physiology*; D014020:Tissue Extracts / Q000494:pharmacology; D014981:Xenopus
D002843:Chromatin; D009687:Nuclear Proteins; D056489:Nucleoplasmins; D010750:Phosphoproteins; D014020:Tissue Extracts