DEVELOPMENTAL-CHANGES IN THE SUBCELLULAR-LOCALIZATION OF R-CADHERIN IN CHICK RETINAL-PIGMENT EPITHELIUM

It has been reported that in the chick embryonic retina, N-cadherin fi rst appears at the very early stages and is subsequently substituted b y R-cadherin at the middle to late stages of development. To examine t he role of R-cadherin in the morphogenesis of chick retinal pigment ep ithelium (RPE), the distribution of this adhesion molecule was studied by immunofluorescence cytochemistry and immunoelectron microscopy fro m embryonic day (E) 6 to hatching. R-cadherin immunoreactivity was det ected at E6, and was strongest at E12-13. During these stages, R-cadhe rin was expressed uniformly on the lateral plasma membranes of RPE cel ls in contact with each other. Thereafter, R-cadherin immunoreactivity was markedly decreased, with intense immunoreactivity restricted to z onulae adherentes in latero-apical regions at E16. R-cadherin immunore activity was no longer detectable in the newly hatched chick RPE, even though morphologically well developed zonulae adherentes were present in latero-apical regions. No immunoreactivity was detected on the api cal side facing the neural retina or on the basal side facing the basa l lamina at any stage of development. These findings indicate that R-c adherin plays an important role as a major cadherin subtype in the mor phogenesis of chick embryo RPE, and is involved initially in non-speci fic cell-cell adhesions, and subsequently in the formation and mainten ance of developing zonulae adherentes.