Because the expression of the Cathepsin L gene by rat Sertoli cells is precisely regulated by developing spermatogenic cells, we study this gene to define how germ cells aregulate gene expression by Sertoli cells, and to determine the biological consequences of this altered gene expression. We have cloned the gene from the rat, have identified Sertoli cell-specific regulatory regions and have proven that germ cells regulate transcription of this gene. The first interaction of a sperm with an egg is the binding of the sperm to the zona pellucida, a glycoprotein matrix which surrounds the egg. The structures of the carbohydrate ligands are controversial, however. To gain insight into their structures we synthesized a series of related oligosaccharides with defined structures and used these as competitive inhibitors for in vitro sperm-zona binding.
Current experiments are characterizing receptors for oligosaccharides on the sperm plasma membrane.
Additionally, we are testing whether specific oligosaccharides, when clustered on a polypeptide backbone, can trigger the acrosome reaction, an event which, in vivo, is required for fertilization. Additionally, we are determining whether oligosaccharides which inhibit sperm zona binding and trigger the acrosome reaction are present in murine ZP3. The gene encoding murine alpha 1,3-galactosyltransferase is expressed in female germ cells but not in male germ cells. Murine sperm-zona binding, a fucosyl residue is required for a high affinity sperm binding ligand.