Glycoconjugates are likely to be of fundamental importance in the complex interactions between photoreceptors and the retinal pigment epithelium, but few have been characterized, especially in human tissue. As a preliminary step towards determining their biological functions in health and disease, a lectin-based histochemical study of the glycan expression of human outer retina was performed on glutaraldehyde-fixed, semi-thin, resin-embedded sections. The interphotoreceptor matrix and photoreceptor plasma-lemmata expressed complex bisected and non-bisected biantennary and/or triantennary N-glycans. In addition, both the rod and cone outer segments bound strongly Galanthus nivalis agglutinin (which binds terminal Manα1, 3Man-) and the rod outer segments bound selectively the isolectin II of Bandeiraea simplicifolia (which binds terminal GlcNAc-). The cilia of the rods and cones were labelled selectively with Glycine max agglutinin after sialidase pretreatment. Four putative glycan outer sequences were identified within the interphotoreceptor matrix: (i) sialylated glycans with subterminal GaINAcα1, 3GaINAc-sequences; (ii) a sialylated type with subterminal N-acetyl-lactosamine residues; (iii) Galβ1, 3GalNAcα1- residues which were substituted with sialic acid except in the cone matrix sheath; (iv) GalNAcα1, 6Galβ1- residues which were substituted in part with sialic acid. The sialic acid expression throughout was predominantly of the 2, 3-linked form with lesser amounts of 2, 6-linkage, and rod-associated structures (including the surrounding interphotoreceptor matrix) were labelled more strongly with the sialic acid-binding lectins than cone-associated structures (including the cone matrix sheath).
- Interphotoreceptor matrix
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