Cytochemical localization of GalNAc and GalNAc beta 1, 4Gal beta 1,4 disaccharide in mouse zona pellucida

Carbohydrate residues contained in the zona pellucida play a key role in th e process of sperm-egg interaction. In vitro fertilization experiments have shown that a specific monoclonal antibody against GalNAc beta 1,4Gal beta 1,4 disaccharide inhibits fertilization in mice. In the present study, the ultrastructural cytochemical localization of GalNAc residues and the GalNAc beta 1,4Gal beta 1,4, disaccharide was carried out in ovarian and postovul atory oocytes by using lectin-gold cytochemistry and immunocytochemistry. P lant lectins SEA and DBA showed an affinity for the entire zona pellucida m atrix of ovarian oocytes throughout the follicular maturation; however, imm unoreactivity for GalNAc beta 1,4Gal beta 1,4 disaccharide was not detected in ovarian oocytes at the earliest stages of follicular development but wa s found to be associated with the inner region of the zona matrix at the tr ilaminar primary follicle stage. The Golgi apparatus, vesicular aggregates, and cortical granules of the oocyte were intensely labeled by SEA and DBA throughout follicular development. Immunoreactivity to GalNAc beta 1,4Gal b eta 1,4 disaccharide was first observed in the Golgi apparatus and vesicula r aggregates in trilaminar primary follicles. No immunoreactivity was obser ved in the cortical granules. In postovulatory oocytes, results were simila r to those observed in ovarian oocytes. Our results thus suggest that (1) G alNAc beta 1,4Gal beta 1,4 disaccharide residues are present only in the in ner region of the zona pellucida and, therefore, might be involved in sperm penetration through the zona pellucida, (2) the inner and outer regions of the zona pellucida contain different oligosaccharide chains, (3) the vesic ular aggregates detected in the oocyte could represent an intermediate step in the secretory pathway of zona pellucida glycoproteins and might be invo lved in the formation of cortical granules.