O-8: Molecular Mechanisms of Membrane Fusion Involved in Fertilization

Background: Assisted fertilization procedures are a currently widespread practice to regulate reproduction in humans and animals. The arising question is why the human being manipulating gametes to generate new individuals, if we do not understand yet the molecular mechanism of fertilization?. Successful completion of fertilization in mammals is dependent on three membrane fusion events: 1. the acrosomal exocytosis of sperm, named acrosome reaction, 2. the fusion of sperm and egg plasma membranes to form a zygote, and 3. the cortical granules exocytosis of fertilized eggs, named cortical reaction, to prevent polyspermy. The general aim of this project is to identify proteins involved in membrane fusion events during fertilization and study its possible involvement in oocyte maturation. Materials and Methods: To analyze acrosomal exocytosis we have performed functional assays in permeabilized and intact human sperm. To analyze cortical granules exocytosis and oocyte maturation we carry out functional assays in mouse eggs activated parthenogenetically. We also perturb protein function by microinjecting blocking antibodies and interference RNA. Results: We are characterizing the function of proteins involved in membrane fusion events during acrosome reaction, cortical reaction and oocyte maturation. We have investigated that MARCKS, a centrosome component during oocyte maturation, also plays a role in acrosomal exocytosis. Conclusion: Acrosome reaction and cortical reaction are calcium dependent processes such as neuronal exocytosis, and the concept that the molecular mechanism of membrane fusion is similar to neurons has become generalized. However, our findings show that exocytoses participating in fertilization have distinguishing qualities. In addition, sperm is a cell in interphase, while the oocyte is in meiotic division. Studying a protein in both model cells has the advantage of discovering new functions for a given protein during cell division. Our long-term goal is contribute to the understanding of the molecular mechanisms involved in fertilization, which may affect early embryonic development and implantation.