137. ELUCIDATION OF THE MOLECULAR MECHANISMS THAT UNDERPIN CAPACITATION-ASSOCIATED SPERM SURFACE REMODELLING

Abstract

Recent research from our laboratory has provided evidence that sperm-egg interaction is mediated by a multimeric sperm receptor complex. Furthermore, we have demonstrated that this complex is assembled on the sperm surface during the final phase of their maturation, a process known as capacitation. The mechanisms underpinning this capacitation-associated surface remodelling remain poorly understood and are the subject of our current investigation. Specifically we have focused on whether this process is driven by vesicle mediated, intracellular trafficking of proteins. For this purpose we have examined the presence and physiological significance of a key part of the molecular machinery necessary for this form of trafficking, namely the enzyme dynamin. Our studies revealed that sperm are endowed with at least two isoforms of dynamin (1 and 2) both of which reside within the peri-acrosomal region of the sperm head, a location compatible with a role in sperm membrane remodelling. Consistent with this putative role, it was demonstrated that dynamin 1 was phosphorylated during capacitation, a post-translational modification that has been causally linked to both its activation and to the capacitation-associated surface remodelling of mouse spermatozoa. Furthermore, it was demonstrated that pharmacological inhibition of dynamin activity led to a concomitant reduction in the ability of spermatozoa to bind to the zona pellucida of homologous oocytes. This suppression was also correlated with reduced surface expression of a number of proteins including a subset of putative sperm-zona pellucida receptors. Collectively these data support the novel hypothesis that dynamin does participate indirectly in sperm membrane remodelling events by virtue of its ability to mediate intracellular trafficking.