New insights into sperm-zona pellucida interaction: involvement of sperm lipid rafts

Abstract

Sperm-zona pellucida (ZP) binding is the first step of gamete interaction. This binding occurs in two sequential steps, starting with the primary binding of acrosome-intact sperm to the ZP followed by the secondary ZP binding of acrosome reacting/reacted sperm. While there are only a few ZP sulfoglycoproteins involved in these binding events, a large number of sperm surface molecules have been shown to possess ZP affinity. In this review, we have given explanations to the existence of these many ZP binding molecules. We have also summarized their origin and the mechanisms of how they are targeted to the sperm surface and acrosome. Recently, we have shown that sperm lipid rafts have affinity for the ZP. A number of ZP binding molecules are also present in sperm lipid rafts. In this review, we have provided an argument that sperm lipid rafts may be the platforms on the sperm surface for ZP interaction.

Comparative Analysis of Testis Protein Evolution in Rodents

“…Targets of selection at various levels of divergence: A large number of proteins participate in the processes of mammalian fertilization, and there is considerable functional redundancy between proteins, particularly in males (Tanphaichitr et al 2007). Even in the unlikely case that there is one predominant form of selection acting on one particular step of fertilization, it is very possible that the individual proteins targeted by selection differ between species.…”

“…This approach has identified positive selection (mainly on the basis of relative rates of nonsynonymous vs. synonymous change) acting on genes involved in sperm motility, semen coagulation, sperm-egg binding, and sperm-egg fusion (Clark et al 2006). The functions of numerous proteins involved in fertilization, however, are unknown ( Jansen et al 2001;Tanphaichitr et al 2007); therefore, candidate gene approaches are likely to miss important targets of selection. In contrast, a genomewide analysis of reproductive proteins can characterize general patterns of evolution as well as identify rapidly evolving genes.…”

Recombinant Mouse Sperm ZP3-binding Protein (ZP3R/sp56) Forms a High Order Oligomer That Binds Eggs and Inhibits Mouse Fertilization in Vitro

“…We did expect to see a reduction in the fertilization rate but not a complete inhibition, because the binding to the zona pellucida seems to be a very redundant process, i.e. sperm proteins other than ZP3R/sp56 are also involved in sperm-ZP binding (2). For example, the targeted deletion of three proteins involved in the binding to the ZP such as SED-1 (6), galactosyltransferase (40), and proacrosin (41) generated some level of subfertility or disregulation of acrosomal exocytosis.…”

“…The actual mechanism of binding is still unresolved. For mammals, some researchers favor a two-step process whereby primary binding with the ZP occurs through a plasma membrane receptor(s) of sperm with intact acrosomes, and secondary binding utilizes intraacrosomal proteins that are exposed during the course of or following acrosomal exocytosis ("Acrosome Reaction Model") (1,2). We and others feel that is difficult to ascertain the definitive acrosomal status at the time of binding to the zona pellucida.…”

“…While there are only a few ZP sulfoglycoproteins involved in these binding events, a large number of sperm molecules have been shown to possess ZP binding activity (2). The list includes ␤-1,4 galactosyltransferase (4), zonadhesin (5), SED-1 (6), spermadhesins (7), and ZP3R/sp56 (formerly sp56) (8).…”