ESCRT (Endosomal Sorting Complex Required for Transport) Machinery Is Essential for Acrosomal Exocytosis in Human Sperm.
The sperm acrosome reaction is a unique, regulated exocytosis characterized by the secretion of the acrosomal content and the release of hybrid vesicles formed by patches of the outer acrosomal and plasma membranes. In previous reports, we have shown that inward invaginations of the acrosomal 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. 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, intra-acrosomal vesicles are also formed during acrosomal exocytosis. Endosomal sorting complex required for transport (ESCRT) participates in the organization of membrane microdomains that are invaginated and released as intraluminal vesicles in endosomes. We report here that members of ESCRT I (TSG101), ESCRT III (CHMP4), and the AAA ATPase VPS4 are present in the acrosomal region of the human sperm. Perturbing the function of these factors with antibodies or recombinant proteins inhibited acrosomal exocytosis in permeabilized cells. A similar effect was observed with a dominant-negative mutant of VPS4A cross-linked to a cell-penetrating peptide in nonpermeabilized sperm stimulated with a calcium ionophore. When the function of ESCRTs was inhibited, acrosomes showed abnormal deformation of the acrosomal membrane, and SNARE proteins that participate in acrosomal exocytosis failed to be stabilized in neurotoxin-resistant complexes. However, the growing of membrane invaginations was not blocked, and numerous intra-acrosomal vesicles were observed. These observations indicate that ESCRT-mediated processes are essential for acrosomal secretion, implicating these multifunctional complexes in an exocytic event crucial for sperm-egg fusion.
Instituto de Histología y Embriología de Mendoza/Consejo Nacional de Investigaciones Científicas y Técnicas, School of Medicine, National University of Cuyo, Mendoza, Argentina.
Cristian A
CA
Pocognoni
Instituto de Histología y Embriología de Mendoza/Consejo Nacional de Investigaciones Científicas y Técnicas, School of Medicine, National University of Cuyo, Mendoza, Argentina.
María Victoria
MV
Berberián
Instituto de Histología y Embriología de Mendoza/Consejo Nacional de Investigaciones Científicas y Técnicas, School of Medicine, National University of Cuyo, Mendoza, Argentina lmayorga@fcm.uncu.edu.ar.
Luis S
LS
Mayorga
D000074183:ATPases Associated with Diverse Cellular Activities; D000177:Acrosome / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism / Q000502:physiology*; D005089:Exocytosis; D006801:Humans; D008297:Male; D050600:SNARE Proteins / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism
D056827:Endosomal Sorting Complexes Required for Transport; D050600:SNARE Proteins; D000251:Adenosine Triphosphatases; D025262:Vacuolar Proton-Translocating ATPases; D000074183:ATPases Associated with Diverse Cellular Activities; C490305:VPS4A protein, human; C490304:VPS4B protein, human
ESCRTs; acrosomal swelling; acrosome reaction; human sperm; multivesicular bodies; regulated exocytosis