Remodeling of the plasma membrane in preparation for sperm-egg recognition: roles of acrosomal proteins

Abstract

The interaction of sperm with the egg's extracellular matrix, the zona pellucida (ZP) is the first step of the union between male and female gametes. The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing. In this article, we describe our recent work, which attempts to address two lines of questions from previous studies. First, because there are numerous ZP binding proteins reported by various researchers, how do these proteins act together in sperm–ZP interaction? Second, why do a number of acrosomal proteins have ZP affinity? Are they involved mainly in the initial sperm–ZP binding or rather in anchoring acrosome reacting/reacted spermatozoa to the ZP? Our studies reveal that a number of ZP binding proteins and chaperones, extracted from the anterior sperm head plasma membrane, coexist as high molecular weight (HMW) complexes, and that these complexes in capacitated spermatozoa have preferential ability to bind to the ZP. Zonadhesin (ZAN), known as an acrosomal protein with ZP affinity, is one of these proteins in the HMW complexes. Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes. Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm–ZP binding step.

The serine protease testisin is present on the surface of capacitated stallion spermatozoa and interacts with key zona pellucida binding proteins

“…The increase in sperm surface‐exposed testisin encountered following capacitation and induction of the acrosome reaction (Fig. ) is characteristic of proteins of the acrosomal vesicle and those involved in spermatozoa–oocyte interaction (Tanphaichitr et al ., ), and suggests that testisin may play an active role in this aspect of stallion sperm function. Such involvement has already been demonstrated in the mouse, where gene knockout mice lacking Prss21 display a reduced ability of spermatozoa to undergo capacitation‐associated tyrosine phosphorylation and reduced fertilizing ability both in vitro and in vivo (Netzel‐Arnett et al ., ).…”

Oxidation reduction potential: a new biomarker of male infertility

“…Here, the increase in rOS generation is linked to an increase in cytoplasmic droplets typically found in immature sperm. 54 The increase in biomarkers of cytoplasmic space and lipid peroxidation was correlated with abnormalities in spermatozoa. 55 ids in plasma membranes, carbohydrates in nucleic acids and amino acids in proteins.…”

“…The negative effect of OS on sperm quality and consequently the male fertility potential has repeatedly been described. 19,[30][31][32][33][34]54 recent reports indicate that higher OrP levels are closely related with poor semen quality. 96,97 Male partners of fertile couples have significantly lower values when compared with normal semen parameters 97 and the OrP value allows to differentiate between fertile and infertile men.…”

Role of Antioxidants in Assisted Reproductive Techniques

“…During spermatogenesis, defects in cytoplasmic extrusion sometimes may result in the development of immature sperm that have a surplus of residual cytoplasm [ 18 19 ]. Residual cytoplasmic droplets have been associated with excessive ROS generation mediated by the concurrent increase in glucose-6-phosphate-dehydrogenase (G6PD) activity seen in abnormal spermatozoa.…”