Glycoconjugates of the rat ciliary body epithelium: A lectin histochemical and protein blotting study

The present study sought to identify and partially characterize the glycoconjugates specific to the double-layered ciliary body epithelium of the rat eye by lectin histochemistry and lectin blottings. Hydrated paraffin sections of Carnoy-fixed Sprague-Dawley rat eyes were stained with a panel of 21 different biotinylated lectins, followed by streptavidin-peroxidase and the glucose oxidase-diaminobenzidine-nickel staining procedure. The results of lectin histochemistry revealed that the inner epithelial layer was rich in GlcNAc(beta 1,4)GlcNAc, alpha-Gal, Gal(beta 1,3)GalNAc, GalNAc(alpha 1,3)GalNAc/Gal, GalNAc(alpha 1,6)Gal, Fuc(alpha 1,2)Gal(beta 1,4)GlcNAc and Gal(beta 1,4)GlcNAc(beta 1,2)Man(alpha 1,6) sugar residues as shown by its positive reactivities with S-WGA, PWA, DSA, GS-I-B4, PNA, DBA, SBA, WFA, UEA-I, LTA and PHA-E. The reactivities of GS-I-B4, PNA, DBA and SBA were restricted to the inner layer at the tips of the ciliary processes. On the other hand, the outer epithelial layer was stained evenly by DSA and Jacalin, and partly by MAA, showing that this epithelial layer was rich in GlcNAc(beta 1,4)GlcNAc, Gal(beta 1,3)GalNAc and NeuAc(alpha 2,3)Gal disaccharides. These lectin binding patterns of the ciliary body epithelium suggest a topographical and functional difference in this double cell-layered epithelium. Their possible roles in the secretion of aqueous humour and production of ciliary zonule are discussed. Some identified lectin markers specific to these two cell layers may be useful for further experimental studies. Glycoproteins extracted from the dissected ciliary body were separated by SDS-PAGE electrophoresis and analyzed by protein blottings with 8 different lectins. The results showed that at least 10 major membrane-bound glycoproteins, with molecular weights ranging from 30 to 150 kD, rich in beta-GlcNAc, beta-Gal, alpha/beta-GalNAc and NeuAc(alpha 2,6)Gal residues, were present in the microsomal fraction.