Sulphated glycoconjugates are powerful inhibitors of spermatozoa binding to the vitelline envelope in amphibian eggs.

Background Information: In amphibians, the role of sulphated glycans has not been determined in spermatozoa-egg interaction, although they are known to be involved in other systems. In previous studies, it was found that, in Discoglossus pictus, a VE (vitelline envelope) glycoprotein of 63 kDa exhibits high homology to Xenopus laevis gp69/gp64 and to ZP2 of mammals. gp63 and a glycoprotein of 75 kDa are both capable of binding the spermatozoa in in vitro assays and, having similar peptide maps and different glycosylation, are probably two glycoforms of the same protein.

Vitelline envelope gps 63 and 75 specifically bind sperm in "in vitro" assays in Discoglossus pictus.

In Xenopus, conflicting data related to sperm-vitelline envelope (VE) binding suggest that further experiments should be performed to study the role of VE glycoproteins in sperm binding. In this article, we studied the VE of Discoglossus pictus, where gp63, the product of the Dp ZP2 gene, has high molecular identity to Xenopus gp69/64 and to mouse ZP2 and only A23187-treated sperm bind to VE. Sperm bind to VE all over the egg, yet a sperm tuft was found only in the animal half of the egg, where the dimple, the site of fertilization, is located and an intense immunostain was detected in VE by an antiserum directed against gp69/64.