ESCRT complexes are involved in acrosomal membrane deformations required for regulated exocytosis in human spermatozoa.

POCOGNONI CA, MAYORGA LS, BELMONTE SA.

Puerto Varas

Congreso; XII PABMB congress; 2013

The acrosome reaction of human spermatozoa is a calcium-dependent regulated exocytosis. Fusion between the outer acrosomal and plasma membranes causes the release of the acrosomal contents. The exocytic process can be arrested at a stage where SNARE proteins are assembled in trans complexes by preventing the release of calcium from the acrosome. At this stage, acrosomes are swollen, with deep invaginations of the outer acrosomal membrane. We have proposed that these membrane deformations are part of the mechanism of vesiculation. Invaginations of the acrosomal membrane are topologically equivalent to the formation of internal vesicles in endosomes, a process that depends on the assembly of the ESCRT complexes. We are exploring the possibility that the same mechanism is involved in acrosomal exocytosis. A dominant-negative mutant of VPS4, the ATPase responsible for the disassembly of the membrane attached ESCRT proteins, and the anti-VPS4 antibody inhibited acrosomal exocytosis of permeabilized human spermatozoa. Moreover TSG101 UEV, the ESCRT I domain that bind ubiquitin, and Snf7, the most important ESCRT III protein, were also inhibitory. TEM images show abnormal bending of the acrosomal membrane when sperm were stimulated in the presence of the dominant negative VPS4 or with anti-VPS4 antibodies. These observations suggest that the deformations of the acrosomal membrane necessary for acrosomal exocytosis are shaped by an ESCRT-dependent mechanism.