CONICET | Buscador de Institutos y Recursos Humanos

Mammalian sperm must undergo a process termed capacitation to become competent to fertilize an egg. Capacitation renders the sperm competent by priming the cells to undergo a rapid exocytotic event called acrosomal exocytosis that is stimulated by the zona pellucida (ZP) of the egg or progesterone. Over the years, several biochemical events have been associated with the capacitation process; however, the question that has remained unanswered in investigations of capacitation is: What is the underlying reaction or set of reactions that transform the sperm cell from a state unresponsive to ZP or progesterone-stimulated acrosomal exocytosis to the state primed to respond to these stimuli? Our preliminary results demonstrate that the actin cytoskeleton plays a role in this process. The aim of this research was to understand how mammalian sperm acquire the competence to undergo acrosomal exocytosis during capacitation. We evaluated the establishment and stabilization of the primed state of acrosomal exocytosis that develops during the course of sperm capacitation through the formation of intermediate stages of exocytosis. To monitor the formation of intermediate stages of exocytosis, we used sperm from transgenic mouse GFP-Acr (green acrosomes) and the exposure of sp56 (monitored by flow cytometry and immunocytochemistry). We found that the actin polymerization that takes place during capacitation is essential in this process. Additionally, using Blue native gel electrophoresis and purified hybrid vesicles (generated by the fusion of the plasma membrane and the outer acrosomal membrane after exocytosis), we found that actin and several actin-related proteins participate in the formation of these intermediate stages of exocytosis.