Carbohydrate determinants involved in mammalian fertilization

During fertilization in mammals, the male and female gametes undergo a form of highly complex cell-cell recognition whereby a nonspecific initial binding is followed by a species-specific penetration of the zona pellucida. Recent data from many species have demonstrated the involvement of surface carbohydrates in regulating fertilization at both these stages. The potential benefits as well as drawbacks of three major techniques used so far are discussed, and the need for a cautious interpretation of the data is emphasized. During capacitation, the carbohydrate components of the entire surface of spermatozoa undergo striking changes which may be linked to the concurrent metabolic events within motile spermatozoa, leading to the appearance of egg-specific glycoconjugates in a time-dependent manner. A multiple set of glycoproteins on the sperm surface, possessing oligosaccharides synthesized by the lipid-linked pathway, are probably required during different stages of fertilization, including sperm-oocyte fusion. The oviductal glycosaminoglycans may also be involved in regulating the timing and species specificity of mammalian fertilization by masking the sperm receptor sites on the zona and triggering the physiological acrosome reaction. Future biochemical and high-resolution localization studies involving specific probes for surface glycoconjugates, glycosyltransferases, and hydrolytic enzymes should greatly aid our understanding not only of the role of the individual surface macromolecules but also of the surface domains to which they are localized.