Phosphorylation of sperm histone during spermiogenesis in mammals

Abstract

The condensed portion of testis chromatin obtained from various mammals (bull, guinea pig, hamster, mouse, rabbit and rat) has been separated into a light fraction, in which somatic-type histone is being replaced by sperm histone, and a heavy fraction, in which the histone change has essentially been completed. Phosphorylation of sperm histone isolated from these chromatin fractions and of the epididymal sperm histone has then been analyzed by polyacrylamide gel electrophoresis and CM-52 column chromatography. In all species studied, sperm histone in the heavy fraction of testis chromatin is phosphorylated more extensively than that in the light fraction, while epididymal sperm histone consists mainly of unmodified molecules. These results suggest that phosphorylation-dephosphorylation of sperm histone occurs on the chromatin during the packaging of DNA. Degrees of phosphorylation of sperm histones vary considerably from species to species. Tetraphospho-, triphospho-, diphospho- and monophospho-sperm histone are found in the heavy fraction of rat testis chromatin. In guinea pig, hamster and mouse the corresponding chromatin fraction contains diphospho-, monophospho- and unmodified sperm histone, while only monophospho- and unmodified sperm histone are detectable in rabbit and bull. The observed differences of sperm histone phosphorylation may be a reflection of the differences of structure of sperm histone in various mammals. Phosphorylation is probably involved in the proper condensation of spermatid chromatin during mammalian spermiogenesis.