Simposio-Biochemical and topological membrane alterations during the sperm acrosomal exocytosis.

MAYORGA, L.S.; CASTILLO BENNETT, J; ZANETTI, MN; ROGGERO, CM; TOMES, C.N.

Tucumán

Congreso; SAIB XLV; 2009

SAIB

Sperm have a single opportunity to fertilize an egg; hence they must release the content of their secretory granule (the acrosome) at the right time and place.  In resting sperm, the factors that participate in exocytosis are maintained in an inactive state.  SNAREs are assembled in cis complexes whereas NSF and synaptotagmin are inactivated by phosphorylation.  The sperm/egg interaction triggers a calcium influx from the extracellular medium that initiates several processes, including the activation of PTP1B and calcineurin, two phosphatases required for the desphosphorylation of NSF and synaptotagmin, respectively.  At the same time, the acrosome swells and forms deep invaginations in the outer acrosomal membrane.  The protruding edges of these invaginations contact the plasma membrane and these appositions are stabilized by the assembly of trans SNARE complexes. For the opening of fusion pores, calcium must be released from inside the acrosome to activate a synaptotagmin/complexin interplay that is necessary for the final steps of the exocytosis.  Fusion pore opening and expansion in the ring of apposed membranes generates hybrid vesicles that, together with the acrosomal contents, are released during the acrosomal exocytosis.  This complex process is absolutely necessary for fertilization in human and animals