Sperm-Egg Binding Mediated by Sperm α-l-Fucosidase in the Ascidian

What is it about?

Spermatozoa bind to the vitelline coat in the ascidians and many other animals. The binding of sperm in Halocynthia roretzi is mediated by a sperm α-l-fucosidase and complementary-l-fucosyl residues of glycoproteins in the vitelline coat. cDNA clones for α-l-fucosidase were isolated from growing testis mRNA. It contained a 1398 bp full-length cDNA insert (HrFuc'ase) that encoded the 466 amino acid residues of H. roretzi sperm α-l-fucosidase. A putative signal peptide of 21 amino acid residues proceeded the sequence for the mature protein (M.W. 52.4 kDa). The coding sequence for HrFuc'ase showed 47.7% sequence identity to the human liver fucosidase sequence. The polyclonal antibody was prepared against a lacZ-HrFuc'ase fusion protein expressed in E. coli. The antibody crossed to a 54 kDa protein in sperm on western blotting and inhibited fertilization in a dose dependent manner. These data suggest that sperm-egg binding is mediated by the sperm α-l-fucosidase, HrFuc'ase in the ascidian, H. roretzi.

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