Expression and tyrosine phosphorylation of sp32 regulate the activation of the boar proacrosin/acrosin system.

The current study investigated the relationship between the level of expression and tyrosine phosphorylation of the sperm protein 32 (sp32) and the activation of the boar proacrosin/acrosin system. The acrosomal membrane proteins of boar sperm for use in different treatment experiments (i.e., fresh sperm, freezing and thawing, capacitation, and acrosome reaction) were separated, stained by Coomassie brilliant blue, and analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blot. The results showed that there were differences in the expression level of sp32 among capacitated, frozen-thawed, and post acrosomal reaction sperms. sp32 expression was higher and significantly higher in capacitated and post-acrosomal reaction sperms than in frozen-thawed sperms and fresh semen, respectively. The level of sp32 tyrosine phosphorylation was significantly different between the frozen-thawed sperms and sperms in the other experimental groups. However, bands with molecular masses of 38 to 170 ku in the fresh semen group were more noticeable, indicating that large acrosomal membrane proteins underwent modification and degradation during capacitation and the acrosomal reaction. As a proacrosin binding protein, sp32 shows upregulated expression and increase in tyrosine phosphorylation levels during the activation of the boar proacrosin/acrosin system.