Purpose: The retinal pigment epithelium (RPE) lines the interface between the neural retina and the choroid. Early in chicken development, the 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, which is more typical of simple transporting epithelia. The authors examined whether the distribution of integrins is regulated by the neural retina.
Methods: Individual integrins were examined by studying the individual 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 development, 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 was determined by reconstituting the RPE:neural retinal interface in explant culture. Absent the neural retina, alpha 6 and beta 1 were removed 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 or intercellular interactions determine the distribution of individual integrins. Further, the changes in integrin distribution during development reflect the maturation of the primordial interphotoreceptor matrix or photoreceptor cell layer.