Exocytosis and fertilization

MICHAUT, MARCELA A.

Woods Hole, MA

Simposio; 17th Annual Frontiers in Reproduction Symposium; 2014

Marine Biological Laboratory

Fertilization is a central issue in reproduction for all species. The haploid gametes fuse to generate adiploid zygote with unique characteristics. Both the male and female gametes undergo regulatedexocytosis - termed the acrosome reaction and the cortical reaction respectively - at different times duringtheir encounter. The success of fertilization depends on these exocytoses. However, the molecularmechanisms of fertilization, including the acrosome and cortical reaction, are only partially understood.The acrosome reaction is a specialized type of regulated secretion leading to a massive fusion betweenthe outer acrosomal and the plasma membranes. In the last few years, our group hasidentified several factors involved in acrosomal exocytosis in human sperm and has characterized several stages in thesecretion process. Following fusion of the acrosome-reacted spermatozoon and the egg, the contents of cortical granules are released into the perivitelline space, causing the zona pellucida to become refractory to sperm binding and penetration. The exocytic machinery responsible for this calcium regulated secretion has been only partially characterized and mostly in sea urchin eggs. In mouse only four proteins have been involved in cortical granules exocytosis. However, other proteins implicated in this particular exocytosis remain to be identified and the molecular mechanism of the membrane fusion during the cortical reaction is still unknown. We have identified new proteins involved in cortical granule exocytosis in mouse eggs and we are characterizing their participation in this process. Both acrosome exocytosis and cortical granules exocytosis are calcium dependent processes such as neuronal exocytosis. Because of this, the concept that themolecular mechanism of membrane fusion is similar to neurons has become generalized. However, our findings show that exocytoses participating in fertilization have distinguishing qualities.