Expression of Syntaxin-2 in Bovine Sperm

Syntaxins are membrane integrated Q-SNARE proteins known to participate in exocytosis. Vesicle docking involves the binding of two plasma membrane proteins, syntaxin and SNAP-25, to the vesicle membrane protein VAMP to form a stable trimeric core complex; synaptophysin is thought to regulate the formation of this complex. Although the members of Q-SNARE proteins are characterized in somatic cells, it is not known whether related proteins function in the sperm acrosome reaction. The objective of the present study is to identify and localize syntaxin in bovine epididymal spermatozoa and to determine the fate of syntaxin 2 during the acrosome reaction. Western blots of caput and cauda sperm lysates and plasma membrane fractions, stained with anti-syntaxin 2, revealed the presence of a 31kDa band in both sperm lysates and plasma membrane fractions, respectively. Indirect immunofluorescence localized syntaxin to the anterior but not the equatorial regions of the acrosomal segment. Several biochemical analyses demonstrated that syntaxin 2 is an integral component of bovine cauda sperm plasma membranes. Our immunoblot data reveals that syntaxin 2 of bovine cauda sperm is released after lysophosphatidylcholine (LPC)-induced acrosomal exocytosis. It is assumed that syntaxin 2 may be involved in triggering the acrosome reaction through a ligand-receptor mediated signal transduction pathway.