Development and Fate of Interphotoreceptor Matrix Components During Dysplastic Photoreceptor Differentiation: A Lectin Cytochemical Study of Rod-Cone Dysplasia 1

Abstract

The autosomal recessive retinal degeneration rod-cone dysplasia 1 ( rcd1) affects Irish setter dogs during early postnatal development. The disease is the result of a cyclic guanosine monophosphate metabolic abnormality and morphological evidence of disease onset correlates with initiation of photoreceptor outer segment formation. Rod photoreceptors are affected earlier and more severely than cones. Postnatal development of specific interphotoreceptor matrix (IPM) constituents was examined in tissue sections and extracted matrix preparations from control and affected dogs using peanut agglutinin (PNA) and wheat germ agglutinin (WGA) lectin cytochemistry. These lectins bind two photoreceptor-specific domains through their affinity for specific terminal carbohydrate sequences present on proteoglycans and glycoproteins in the IPM. Development of rod and cone matrix domains in the normal dog occurs in parallel to the development and differentiation of outer segments (between postnatal days 10 and 60 in the dog); during this period the lectin specificity or distribution in the rcd1 retina did not differ from the normal control. Structural changes of the matrix domains were present and reflected the morphological alterations of the diseased and degenerating photoreceptor cells. Cone domains were present around severely degenerated cone cells as long as these cells were found within the interphotoreceptor space. The matrix domain investing surviving cones did not differ significantly from the normal to indicate an altered binding specificity or structure. The rod domain was still present around rod inner segments in late degeneration. The matrix domains are present in the IPM as long as the photoreceptor cell body remains in the interphotoreceptor space; photoreceptor loss results in disappearance of the matrix. We detected no change in matrix composition or distribution with the lectins used, either during development or degeneration, despite the serious biochemical and structural abnormalities of the photoreceptor cell that are characteristic of the disease.