APICAL POLARIZATION OF N-CAM IN RETINAL-PIGMENT EPITHELIUM IS DEPENDENT ON CONTACT WITH THE NEURAL RETINA

The retinal pigment epithelium (RPE) is unique among epithelia in that its apical surface does not face a lumen, but, instead, is specialize d for interaction with the neural retina. The molecules involved in th e interaction of the RPE with the neural retina are not known. We show here that the neural cell adhesion molecule (N-CAM) is found both on the apical surface of RPE in situ and on the outer segments of photore ceptors, fulfilling an important requisite for an adhesion role betwee n both structures. Strikingly, culture of RPE results in rapid redistr ibution of N-CAM to the basolateral surface. This is not due to an iso form shift, since the N-CAM expressed by cultured cells (140 kD) is th e same as that expressed by RPE in vivo. Rather, the reversed polarity of N-CAM appears to result from the disruption of the contact between the RPE and the photoreceptors of the neural retina. We suggest that N-CAM in RPE and photoreceptors participate in these interactions.