IMMUNOHISTOCHEMICAL LOCALIZATION OF CYTOSOLIC SIALIDASE IN PHOTORECEPTOR CELLS

The binding sites of the antibody to cytosolic sialidase on the rat an d monkey photoreceptor cells were examined immunohistochemically using the avidin-biotinylated peroxidase method. In the rat photoreceptor c ells, the antibody bound diffusely to the inner segment and the outer nuclear layers which are composed chiefly of rod cells. In the monkey photoreceptor cells, the antibody bound to the rod inner segments whic h were clearly distinct, morphologically, from the cone inner segments . The antibody also bound to the rod cell bodies in the outer nuclear layer. These binding patterns show that the antibody bound preferentia lly to rod photoreceptor cells. This observation is consistent with pr evious lectin histochemical findings that sialoglycans are preferentia lly present on the surfaces of rod photoreceptors, and in the rod-asso ciated interphotoreceptor matrix. Sialidase in rod inner segments may function by balancing with sialyltransferase, also preferentially expr essed in rod inner segments, to form sialyl residues on the termini of sugar chains in the rod-associated sialoglycoconjugates.