Carbohydrate-based interactions on the route of a spermatozoon to fertilization.

Male and female intercommunication along the route which the spermatozoon takes to fertilization utilizes the information potential of carbohydrates. A hierarchy of carbohydrate-based binding events exists ranging from spermatozoa-oviduct interaction to primary and secondary binding between spermatozoon and oocyte. Before in-vivo fertilization can occur, spermatozoa are stored in the caudal part of the isthmus, in tight contact with the epithelium cells lining the oviduct. The sperm reservoir seems to be created by surface-associated sperm lectins recognizing epithelial glycoconjugates. With the changing conditions in the oviduct at the time of ovulation, spermatozoa may shed those sperm lectins, creating new surfaces which allow spermatozoa to be released from the epithelium, complete capacitation and interact with the oocyte in the appropriate manner. The first contact between both gametes occurs at the spermatozoa-zona pellucida interface. The 'primary' binding initiates the acrosomal exocytosis of the spermatozoa, followed by the 'secondary' binding of the acrosome-reacted spermatozoon that in consequence leads to sperm penetration through the zona pellucida. Primary and secondary binding events are directed by the cooperative interactions of multiple carbohydrate-recognition systems that may act in a hierarchical and redundant manner. The current perspective will focus on the role of carbohydrate-binding sperm proteins in the sequence of binding events during fertilization in the pig.