CORNEAL GLYCOCONJUGATES - AN ULTRASTRUCTURAL LECTIN-GOLD STUDY

The oligosaccharide chains of cell surface and extracellular matrix gl ycoconjugates are essential for the biological properties of these mol ecules. We have, therefore, investigated carbohydrate residues in the rat cornea using biotinylated lectin-gold probes. Fixed corneas were r emoved and embedded in Lowicryl HM20 or LR White. Ultrathin sections w ere incubated in one of the lectins: Triticum vulgare (WGA), Canavalia ensiformis (Con A), Griffonia simplicifolia (GS-1), Limax flavus (LFA ) and Allomyrina dichotoma (Allo A), followed by streptavidin-gold, or the sections were incubated in cationic colloidal gold. Semi-quantifi cation of gold labelling was determined for corneal endothelium, Desce met's membrane, stroma and epithelium from electron micrographs. WGA a nd Con A binding sites were expressed either moderately or strongly th roughout the cornea, suggesting a preponderance of alpha-mannose and N -acetylglucosamine residues. A particular concentration of these sugar s was found in Descemet's membrane. In contrast, GS-1 (specific for al pha-galactose) and Allo A (specific for beta-galactose) labelled all r egions weakly. Sialic acid residues, as defined by LFA labelling and t he expression of neuraminidase-sensitive cationic colloidal gold bindi ng sites, were sparsely distributed throughout the stroma, Descemet's membrane and endothelium. In contrast, sialoglycoconjugates were found in significant concentrations in the epithelium. Electron microscopy proved useful in providing new information on the cellular and subcell ular localization of these lectin binding sites. (C) 1998 Chapman & Ha ll.