MAYORGA Luis Segundo
congresos y reuniones científicas
Membrane deformations and ion fluxes during the acrosome reaction in human sperm (conferencia)
BERBERIAN MV; SOSA CM; POCOGNONI CA; DE BLAS GA; MAYORGA, LS
Simposio; II International Symposium Translational Medicine; 2019
UNCuyo, UBA, Freiburg University Germany
Only sperm that have completed the acrosome reaction can successfully fuse with the oocyte. Therefore, the acrosomal reaction is an essential secretory process that must occur at the appropriate time and location for a productive sperm-egg interaction. The acrosome reaction relies on the same highly conserved molecules that drive intracellular membrane fusion and exocytosis in most cells; however, the change in membrane topology during secretion is unique. Hundreds of fusion pores are opened connecting the acrosomal lumen with the external medium leading to the secretion of the acrosomal content and the release of hybrid vesicles formed by patches of the outer acrosomal and plasma membranes. We have shown that the acrosomal granule swells upon stimulation and that inward invaginations of the limiting membrane delineate ring-shaped membrane microdomains that contact the plasma membrane. We have postulated that the opening and expansion of fusion pores along these rings trigger acrosomal exocytosis. Our observations indicate that swelling is a slow and asynchronic process which is uncoupled from the initial increase of cytsosolic calcium. In contrast, fusion pore opening is much faster and requires the release of calcium from the acrosome. The functional connection between these two ion fluxes is still unclear. The invaginations of the acrosomal membrane topologically resemble the deformations of the endosomal membrane leading to the assembly of luminal vesicles in multivesicular bodies. In fact, intraacrosomal vesicles are also form during acrosomal exocytosis. We have reported that perturbing the function of members of Endosomal Sorting Complex Required for Transport (ESCRT) with antibodies in permeabilized cells and membrane permeant recombinant proteins in living spermatozoa inhibited acrosomal exocytosis. These observations indicate that ESCRT-mediated processes are essential for acrosomal secretion, implicating these multifunctional complexes in an exocytic event crucial for sperm-egg interactions.