Lectin histochemical detection of sulfoglycans in the zona pellucida of mammalian antral oocytes

Sulphated esters are important to increase effectiveness of specific biological activities of carbohydrates. Biochemical studies revealed the presence of distinct sulphated glycoproteins in mammal zona pellucida (ZP) that bind proacrosin and thus participate in the sperm-egg fusion processes. In the present study, 6 lectin-horseradish peroxidase conjugates (SBA, PNA, RCA-I, GSA-IB4, GSA-II and DBA) were used in combination with desulphation and sialidase digestion to identify sulphocarbohydrates in the terminal and/or subterminal position of oligosaccharide side chains of glycoproteins in the ZP of bovine, ovine, caprine and porcine antral oocytes. In particular, we identified the following terminal sulphoglycans located in the outer layer of the ZP only: SO4-GalNAc in bovine ZP; SO4-Galbeta1,3GalNAc in bovine and ovine ZP; SO4-Galbeta1,4GlcNAc in bovine, ovine and caprine ZP; SO4-alpha-Gal in bovine, caprine and porcine ZP. Subterminal sulphoglycans linked to sialic acid residues were evenly distributed throughout the entire thickness of the ZP: Neu5Ac-SO4-Galbeta1,3GalNAc in bovine and porcine ZP; Neu5Ac-SO4-Galbeta1,4GlcNAc in caprine ZP; Neu5Ac-SO4-alpha-Gal in porcine ZP; Neu5AcSO4-GlcNAc in bovine ZP. The results demonstrate that the chemical composition of the ZP differs among species determining the species-specificity of gamete interactions.