Molecules that initiate or help stimulate the acrosome reaction by their interaction with the mammalian sperm surface

Abstract

This review deals with exogenous molecules that stimulate the acrosome reaction (AR) of mammalian sperm in vitro, presumably by acting at the sperm surface. Such molecules may exert their effect(s) by stimulating capacitation and/or by stimulation or initiation of the AR, and they are probably present at one of three putative in vivo sites (also discussed here) for the AR of a fertilizing sperm: the oviductal fluid, the cumulus oophorus matrix, and the zona pellucida. The molecules discussed include serum albumin, hydrolytic enzymes (particularly proteases); hormones including biogenic amines, estradiol, and arachidonic acid metabolites; sulfur-containing beta-amino acids; glycosaminoglycans such as hyaluronic acid; and a zona pellucida glycoprotein. Possible mechanisms to explain the effects of these molecules are also discussed. Several conclusions and suggestions are offered in this review: There is more than one site for the AR of a fertilizing sperm in vitro, depending on experimental conditions and species, but the site(s) at which the AR of a fertilizing sperm occur(s) in vivo is/are still a matter of disagreement; there are a number of molecules that can stimulate or initiate the AR in vitro, and such molecular duplication may also exist in vivo to ensure fertility; and synergistic interaction between some of those exogenous molecules may occur in the stimulation of capacitation and the stimulation or initiation of the AR.

Nongenomic activation of spermatozoa by steroid hormones: Facts and fictions

“…However, the use of protein-conjugated steroids has been criticized because they can release the free compound in unknown amounts. Moreover, big proteins, such as BSA, can have effects on sperm per se (Meizel, 1985).…”

Metabolic and surface events in fertilization

“…The exact nature and location of sperm hydrolases and other enzymes and how they might be involved in regulating sperm-zona interactions is beyond the scope of this chapter. More details on this topic can be found elsewhere [Meizel, 1985;Talbot, 19851. Considerable interest has focused recently on sperm glycoprotein-synthesizing enzymes, particularly galactosyltransferase (GalTase) of mouse sperm, which has been purified to homogeneity by affinity chromatography. Egg receptor activity has been attributed to this enzyme because: 1) it is unmasked at the end of capacitation; 2) it is probably present exclusively in the acrosomal region; 3) it inhibits sperm-egg adhesion in a concentration-dependent manner; and 4) it can galactosylate the N-acetyl glucosamine terminals on mouse zonae in the presence of UDP-galactose [Lopez et al, 19851. According to this hypothesis, interactions between sperm surface GalTase and N-acetylglucosamine residues on the zona result in the formation of enzyme-substrate complexes that initiate binding between the two cells.…”

“…While it is generally agreed that the fertilizing sperm probably undergoes the acrosome reaction in the immediate vicinity of the egg, there is at present no consensus on the exact site. Evidence obtained both in vivo and in vitro suggests that it is either in the cumulus cell mass (possibly due to interaction with components of the intercellular matrix glycosaminoglycans) or at the zona pellucida, following an initial binding phase and inductive interactions with specific molecular components of the zona [discussed by Bedford, 1983;Meizel, 1985;Myles et al, 19871. After the acrosome reaction and interaction with the external surface of the zona, the sperm penetrates this acellular structure by a combination of enzymatic and mechanical forces, the latter supplied by the hyperactivated motility of the flagellum and the rigid nature of the sperm nucleus [Yanagimachi, 1981;Harrison, 1982;Bedford, 19831.…”

Evidence that anandamide‐signaling regulates human sperm functions required for fertilization

“…Sperm acquire the capacity to fertilize eggs following removal from seminal plasma and exposure for several hours to female reproductive tract fluids in vivo, or by incubation in appropriate culture medium in vitro (Meizel, 1985;Burkman, 1990Burkman, , 1995Yanagimachi, 1994;Meizel, 1997;Kopf et al, 1999). ''Capacitated'' sperm exhibit vigorous hyperactivated motility required for fertilization, and can undergo physiological acrosome reactions at the egg's surface (Wassarman, 1987;Burkman, 1990Burkman, , 1995Yanagimachi, 1994;Kang-Decker et al, 2001).…”