CYTOPLASMIC RETINAL LOCALIZATION OF AN EVOLUTIONARY HOMOLOG OF THE VISUAL PIGMENTS

A rhodopsin-related protein is preferentially exressed at high levels in retinal pigment epithelium (RPE) and in Muller cells. The putative RPE-retinal G protein-coupled receptor (RGR) was localized in light-adapted bovine retina by means of electron microscopic immunocytochemistry. In the RPE, the protein was localized to a widespread intracellular compartment. Except for the region adjacent to the basal surface, the RPE cytoplasm was labeled throughout the cell including the apical surface. In Muller cells also RGR was found in the intracellular compartment, especially in the cytoplasm in the region of the Muller cell endfeet and proximal cell processes. Subcellular fractionation studies of bovine RPE and neural retina indicated that RGR is a membrane-bound protein. The intracellular localization of RGR is a unique variation in the subcellular distribution of seven-transmembrane-domain receptors and suggests an unconventional role for RGR m the signal transduction process. © 1994 Academic Press Limited.