Role of phospholipases during sperm acrosomal exocytosis.

During fertilization the spermatozoon undergoes a process of regulated exocytosis triggered by oocyte-associated agonists. An early response generated by agonist-receptor interaction in spermatozoa is the activation of mechanisms leading to Ca2+ influx, this ion being essential for the activation of phospholipases and for the fusion of the plasma membrane with the outer acrosomal membrane. Both a phosphoinositide-specific, and a phosphatidylcholine-specific phospholipase C are involved in the generation of a variety of diacylglycerol molecular species. Phospholipase D, on the other hand, does not seem to contribute (together with a phosphatidate phosphohydrolase) to a significant generation of diacylglycerol. Phospholipase A2 action serves to release fatty acids and to generate lysophospholipids that, either directly or serving as substrates for the generation of other metabolites, have and essential role in the final stages of membrane fusion. Additional work needs to be carried out in the future to characterize which phospholipase isoenzymes are present in mammalian spermatozoa and mechanisms regulating these enzymes