Opsins are members of the G protein-coupled receptor superfamily. In addition to the visual opsins, mammals possess several photoreceptive non-visual opsins that are expressed in tissues outside the eye. The opsin-3 gene is strongly expressed in brain and testis and weakly expressed in liver, placenta, heart, lung, skeletal muscle, kidney, and pancreas. The gene is expressed in the skin[8] and may also be expressed in the retina. The protein has the canonical features of a photoreceptive opsin protein,[7] however in human skin, OPN3 is not photoreceptive and acts as a negative regulator of melanogenesis.[9]
When OPN3 analogues are expressed in neurons, activation by light inhibits neurotransmitter release.[10][11] This makes these analogues useful tools for optogenetic silencing, a method to study the impact of specific neurons on brain function.
^Halford S, Freedman MS, Bellingham J, Inglis SL, Poopalasundaram S, Soni BG, et al. (March 2001). "Characterization of a novel human opsin gene with wide tissue expression and identification of embedded and flanking genes on chromosome 1q43". Genomics. 72 (2): 203–208. doi:10.1006/geno.2001.6469. PMID11401433.
Halford S, Bellingham J, Ocaka L, Fox M, Johnson S, Foster RG, Hunt DM (2002). "Assignment of panopsin (OPN3) to human chromosome band 1q43 by in situ hybridization and somatic cell hybrids". Cytogenetics and Cell Genetics. 95 (3–4): 234–235. doi:10.1159/000059351. PMID12063405. S2CID24099335.
Kasper G, Taudien S, Staub E, Mennerich D, Rieder M, Hinzmann B, et al. (July 2002). "Different structural organization of the encephalopsin gene in man and mouse". Gene. 295 (1): 27–32. doi:10.1016/S0378-1119(02)00799-0. PMID12242008.
Alam NA, Gorman P, Jaeger EE, Kelsell D, Leigh IM, Ratnavel R, et al. (December 2003). "Germline deletions of EXO1 do not cause colorectal tumors and lesions which are null for EXO1 do not have microsatellite instability". Cancer Genetics and Cytogenetics. 147 (2): 121–127. doi:10.1016/S0165-4608(03)00196-1. PMID14623461.
