Localization of fluorescence-labeled lectin binding sites on photoreceptor cells of the monkey retina

Abstract

The binding of eight fluorescence-labeled lectins to the photoreceptors of the monkey retina was investigated using a post-embedding staining method. Concanavalin A (specific for mannosyl and glucosyl residues) bound to the outer and inner segments of both rods and cones, while the degree of staining was more intense in the rods. The rod outer segments showed patchy fluorescence and the proximal portions of the inner segments were diffusely stained. Wheat germ agglutinin (specific for sialyl and N-acetylglucosaminyl residues) bound preferentially to the surface of the outer and inner segments of both rods and cones. Ricinum communis agglutinin-1 (specific for galactosyl residues) stained the rod outer segments in patches, particularly strongly in the region dividing the outer and inner segments. The cones were also stained, although faintly, in the same pattern as the rods. The distal halves of the rods and cones showed diffuse weak staining and their proximal halves stained spotty. Peanut agglutinin (specific for Galβ1 → 3GalNAc sequence) bound preferentially to the cones and only scarcely to the rods. The external surface of both outer and inner segments of cones were uniformly stained; the interior of the cone outer segments was also stained, while the interior of the inner segments was not. Two lectins specific for fucosyl residues, namely, Ulexeuropaeus agglutinin-1 and Lotustetragonolobus agglutinin, bound diffusely to the distal halves of the inner segments of both rods and cones. Lectins reacting with N-acetyl-galactosamine residue, i.e. Dolichos biflorus agglutinin and soybean agglutinin, bound weakly to the distal portions of rods and cones.