Abstract
Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.
Highlights
Mammalian fertilization is a species-specific event that involves a series of interactions between sperm protein molecules and zona pellucida (ZP) glycoproteins of the oocyte
To gain the ability to bind to the ZP of an oocyte, spermatozoa undergo a sequence of post-testicular maturation events resulting in changes in the sperm protein composition, especially those localized to the sperm plasma membrane
It has been generally accepted that the interaction between the spermatozoa and the oocyte ZP during fertilization is a multi-step process, including the initial sperm attachment to the ZP surface glycoproteins, known as the primary sperm-ZP binding, resulting in the induction of acrosomal exocytosis (AE), reinforced binding to ZP known as the secondary sperm-ZP binding, sperm penetration through the ZP, and the adhesion and fusion of the sperm plasma membrane with the oolemma [72,73,74,75]
Summary
Mammalian fertilization is a species-specific event that involves a series of interactions between sperm protein molecules and zona pellucida (ZP) glycoproteins of the oocyte. The initial gamete interaction, known as the primary binding of the spermatozoa to the ZP of the oocytes, is facilitated by the complementary sperm and zona surface molecules. Spermatozoa bind the ZP carbohydrate moieties via their membrane protein receptors resulting in, for most, part species-specific gamete recognition (reviewed by Clark [7]). The differences in ZP carbohydrate moieties and sperm surface proteins are considered the main factor in the species specificity of sperm-ZP recognition and binding. This review updates current knowledge about proteins and glycans involved in spermZP interactions and proposed candidate receptors in thoroughly-investigated mammalian species, including mice, humans, porcine, and bovine. Determinants involved in the spermZP binding regulate signal transduction resulting in subsequent acrosomal exocytosis (AE), sperm-ZP penetration, and gamete fusion during successful fertilization
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