Encephalopsin: a novel mammalian extraretinal opsin discretely localized in the brain.

We have identified a mammalian opsin, encephalopsin, that shows strong and specific expression in the brain. Encephalopsin defines a new family of opsins and shows highest homology to vertebrate retinal and pineal opsins. Encephalopsin is highly expressed in the preoptic area and paraventricular nucleus of the hypothalamus, both regions implicated in encephalic photoreception in nonmammalian vertebrates. In addition, encephalopsin shows highly patterned expression in other regions of the brain, being enriched in selected regions of the cerebral cortex, cerebellar Purkinje cells, a subset of striatal neurons, selected thalamic nuclei, and a subset of interneurons in the ventral horn of the spinal cord. Rostrocaudal gradients of encephalopsin expression are present in the cortex, cerebellum, and striatum. Radial stripes of encephalopsin expression are seen in the cerebellum. In the cortex and cerebellum, encephalopsin expression is considerably higher and more highly patterned in the adult than in the neonate. Encephalopsin is the first putative extraocular opsin identified in mammals and may play a role in encephalic photoreception.