Retinal pigment epithelium-derived rhodopsin homolog (RRH) is a member of the Opsin subfamily of GPCRs. It is thought to affect retinal pigment epithelium physiology by detecting light directly or by monitoring the concentration of retinoids or other photoreceptor-derived compounds. In immunohistochemistry, RRH has membranous positivity primarily in the pigmented retinal epithelium of the eye. It is also found in subsets of neurons in the subiculum and in subsets of anterior pituitary cells, as well as area CA1 of the hippocampus, the supraoptic nucleus of the hypothalamus, and the hypoglossal nucleus of the medulla. Outside of the nervous system, pancreatic acini and plasma cells show variable or faint positivity. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804