THE NEURAL RETINA MAINTAINS INTEGRINS IN THE APICAL MEMBRANE OF THE RPE EARLY IN DEVELOPMENT

Purpose. The retinal pigment epithelium (RPE) lines the interface betw een the neural retina and the choroid. Early in chicken development, t he beta 1 family of integrins resides in the apical (facing the neural retina) and basolateral (facing the choroid) membranes of RPE. Later in development, integrins reside only in the basolateral membranes, wh ich is more typical of simple transporting epithelia. The authors exam ined whether the distribution of integrins is regulated by the neural retina. Methods. Individual integrins were examined by studying the in dividual alpha-subunits that form heterodimers with the beta 1 subunit . The expression and distribution of these subunits were determined by immunoblotting and immunocytochemistry. Results. Subunits alpha 3 and alpha 6 exemplified contrasting behaviors. Early and late in developm ent, alpha 3 was found only in the basal membranes. As was beta 1 the distribution of alpha 6 was nonpolarized early in development but was basal later in development. The effect of the immature neural retina w as determined by reconstituting the RPE:neural retinal interface in ex plant culture. Absent the neural retina, alpha 6 and beta 1 were remov ed from the apical membrane. When present, the immature neural retina maintained both subunits in the apical membrane. The neural retina was effective only if the outer (primordial photoreceptor) surface of the retina apposed the RPE. Conclusions. These data suggest that matrix o r intercellular interactions determine the distribution of individual integrins. Further, the changes in integrin distribution during develo pment reflect the maturation of the primordial interphotoreceptor matr ix or photoreceptor cell layer.