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14-September-2008 18:02:44 - Melanopsin Opsin 4 melanopsin Identifiers Symbols OPN4; MGC142118; MOP External IDs OMIM: 606665 MGI: 1353425 HomoloGene: 69152 Gene ontology Molecular function: receptor activity 11-cis retinal binding G-protein coupled photoreceptor activity Cellular component: membrane integral to membrane Biological process: signal transduction G-protein coupled receptor protein signaling pathway visual perception phototransduction protein-chromophore linkage regulation of circadian rhythm rhythmic process response to stimulus Orthologs Human Mouse Entrez 94233 30044 Ensembl ENSG00000122375 ENSMUSG00000021799 Uniprot Q9UHM6 Q9QXZ9 Refseq NM_001030015 mRNA NP_001025186 protein NM_013887 mRNA NP_038915 protein Location Chr 10: 88.4 - 88.42 Mb Chr 14: 33.42 - 33.43 Mb Pubmed search 1 2 Melanopsin is a photopigment found in specialized photosensitive ganglion cells of the retina that are involved in the regulation of circadian rhythms, pupillary reflex, and other non-visual responses to light. In structure, melanopsin is an opsin, a retinylidene protein variety of G-protein-coupled receptor. Melanopsin, atypical in vertebrates, functionally resembles invertebrate opsins, including an apparent intrinsic photoisomerase activity.1 It is presumed that melanopsin signals through a G-protein of the Gq family, as invertebrate opsins are known to do, but this is not firmly established. Contents 1 Discovery and function 2 Mechanism 3 Effects on light entrainment 4 Distribution in different species 5 References Discovery and function Melanopsin was originally discovered in 1998 in specialized light-sensitive cells of frog skin by Dr. Ignacio Provencio and his colleagues.2 In 1999 Dr. Russell Foster showed that a third class of photoreceptor existed in mammalian eyes. In 2000, Provencio showed that mammals, including humans, also produce melanopsin and that it is found only in a rare subtype of retinal ganglion cells, the output cells of the retina. The first recordings of light responses from melanopsin ganglion cells were obtained by Dr. David Berson and colleagues at Brown University.3 They also showed that these responses persisted when pharmacological agents blocked synaptic communication in the retina, and when single melanopsin ganglion cells were physically isolated from other retinal cells. These findings showed that melanopsin ganglion cells are intrinsically photosensitive, and thus constitute a third class of photoreceptors in the mammalian retina, joining the better known rod and cone photoreceptors.4 Further studies from Berson's lab have concluded that melanopsin ganglion cells exhibit both light and dark adaptation, that is, that they adjust their sensitivity according to the recent history of light exposure.5 In this respect, they are similar to rods and cones. Whereas rods and cones are responsible for the analysis of images, patterns, motion and color, a number of studies have shown that melanopsin ganglion cells contribute to various reflexive responses of the brain and body to the presence of daylight. Melyan et al in England in 2005 reported rendering a mouse paraneuronal cell line Neuro-2a, which normally is not photosensitive, photoreceptive by the addition of human melanopsin. Under such conditions, melanopsin acts as a sensory photopigment, performing physiological light detection. The melanopsin photoresponse is selectively sensitive to short-wavelength light, while it also has an intrinsic photoisomerase regeneration function that is chromatically shifted to longer wavelengths.6 Mechanism When light activates the melanopsin signaling system, the melanopsin-containing ganglion cells discharge nerve impulses, which are conducted through their axons to specific brain targets. These targets include the olivary pretectal nucleus a center responsible for controlling the pupil of the eye and, through the retinohypothalamic tract RHT, the suprachiasmatic nucleus of the hypothalamus the master pacemaker of circadian rhythms. Melanopsin ganglion cells are thought to influence these targets by releasing from their axon terminals the neurotransmitters glutamate and pituitary adenylate cyclase activating polypeptide PACAP. Melanopsin ganglion cells also receive input from rods and cones that modifies or adds to the input to these pathways. Effects on light entrainment Experiments have shown that entrainment to light, by which periods of behavioral activity or inactivity sleep are synchronized with the light-dark cycle, is not as effective in melanopsin knockout mice, but mice lacking rods and cones still exhibit circadian entrainment. The pupillary reflex is also retained in mice lacking rods and cones but has severely reduced sensitivity, identifying a crucial input from the rods and cones. Blind people who entrain to the 24-hour light/dark cycle have eyes with functioning retinas including the operative non-visual light-sensitive cells7 which convey their signals to the circadian clock via the retinohypothalamic tract.89 Distribution in different species Melanopsin has a very similar pattern of tissue distribution among all mammals studied so far, including rodents, monkeys, and humans. Specifically, melanopsin is expressed only in the retina, and only in 1-2% of the ganglion cells. In non-mammalian vertebrates, however, such as birds, fish and amphibians, melanopsin is found in certain other retinal cells, and also outside the retina in structures known or presumed to be directly photosensitive, such as the iris muscle of the eye, deep brain regions, the pineal gland, and the skin. References ^ Panda, Satchidananda; Surendra K. Nayak, Brice Campo, John R. Walker, John B. Hogenesch, Tim Jegla 28 January 2005. Illumination of the Melanopsin Signaling Pathway HTML: full text. Science 307 5709: 600-4. doi:10.1126/science.1105121. PMID 15681390. Retrieved on 2008-05-04. ^ Provencio I, Jiang G, De Grip W, Hayes W, Rollag M 1998. Melanopsin: An opsin in melanophores, brain, and eye HTML: full text. Proc Natl Acad Sci U S A 95 1: 340-5. doi:10.1073/pnas.95.1.340. PMID 9419377. ^ Berson D, Dunn F, Takao M 2002. Phototransduction by retinal ganglion cells that set the circadian clock HTML: full text. Science 295 5557: 1070-3. doi:10.1126/science.1067262. PMID 11834835. ^ Qiu X, Kumbalasiri T, Carlson S, Wong K, Krishna V, Provencio I, Berson D 2005. Induction of photosensitivity by heterologous expression of melanopsin HTML: full text. Nature 433 7027: 745-9. doi:10.1038/nature03345. PMID 15674243. ^ Wong K, Dunn F, Berson D 2005. Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells. Neuron 48 6: 1001-10. doi:10.1016/j.neuron.2005.11.016. PMID 16364903. ^ Melyan, Z.; E. E. Tarttelin, J. Bellingham, R. J. Lucas, M. W. Hankins Feb 2005. Addition of human melanopsin renders mammalian cells photoresponsive Abstract. Nature 433 7027: 741-5. doi:10.1038/nature03344. PMID 15674244. Retrieved on 2008-05-04. ^ Tu, D. C.; Zhang D, Demas J, Slutsky EB, Provencio I, Holy TE, Van Gelder RN 2005-12-22. Physiologic diversity and development of intrinsically photosensitive retinal ganglion cells. Neuron 48 6: 987-99. doi:10.1016/j.neuron.2005.09.031. PMID 16364902. Retrieved on 2008-02-07. Intrinsically photosensitive retinal ganglion cells ipRGCs mediate numerous nonvisual phenomena, including entrainment of the circadian clock to light-dark cycles, pupillary light responsiveness, and light-regulated hormone release. ^ Czeisler, Charles A.; Theresa L. Shanahan, Elizabeth B. Klerman, Heinz Martens, Daniel J. Brotman, Jonathan S. Emens, Torsten Klein, Joseph F. Rizzo 1995-01-05. Suppression of melatonin secretion in some blind patients by exposure to bright light HTML: full text. N Engl J Med 332 1: 6-11. PMID 7990870. Retrieved on 2008-02-07. The photic pathway used by the circadian system is functionally intact in some blind patients. ^ Arendt, Josephine updated 1 February 2006. Chapter 15. The Pineal Gland and Pineal Tumours. Neuroendocrinology, Hypothalamus, and Pituitary, an E-book ed by Ashley Grossman chapter section: Melatonin Synthesis and Metabolism. Endotext.com. Retrieved on 2008-02-07. Image forming vision rods and cones is not required ... for synchronising /phase shifting the circadian clock. v d e Eye proteins Opsin retinylidene protein Rhodopsin - Melanopsin - Photopsin Crystallin Alpha crystallin Other Arrestin - Guanylate cyclase activator - Recoverin - Rhodopsin kinase v d e Transmembrane receptor: G protein-coupled receptors Class A: Rhodopsin like Adrenergic α1 A, B, D, α2 A, B, C, β1, β2, β3 Eicosanoid CysLT 1, 2, LTB4 1, 2, FPRL1, OXE, Prostaglandin DP, EP 1, 2, 3, 4, PGF, Prostacyclin, Thromboxane Neuropeptide B/W 1, 2, FF 1, 2, S, Y 1, 2, 4, 5 Orphan GPR 1, 3, 4, 6, 12, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 31, 32, 33, 34, 35, 37, 39, 42, 44, 45, 50, 52, 55, 61, 62, 63, 65, 68, 75, 77, 78, 79, 82, 83, 84, 85, 87, 88, 92, 101, 103, 119, 120, 132, 135, 139, 141, 142, 146, 148, 149, 150, 151, 152, 153, 160, 161, 162, 171, 172, 173, 174, 176, 177, 182 Purinergics Adenosine A1, A2a, A2b, A3, P2Y, 1, 2, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14 Serotonin all but 5-HT3 5-HT1 A, B, D, E, F, 5-HT2 A, B, C, 5-HT 4, 5A, 6, 7 Other Acetylcholine M1, M2, M3, M4, M5 - Adrenomedullin - Anaphylatoxin C3a, C5a - Angiotensin 1, 2 - Apelin - Bile acid - Bombesin BRS3, GRPR, NMBR - Bradykinin B1, B2 - Cannabinoid CB1, CB2 - Chemokine - Cholecystokinin A, B - Dopamine D1, D2, D3, D4, D5 - EBI2 - Endothelin A, B - Estrogen - Formyl peptide 1, L1, L2 - Free fatty acid 1, 2, 3, 4 - FSH - Galanin 1, 2, 3 - Gonadotropin-releasing hormone 1, 2 - Ghrelin - Histamine H1, H2, H3, H4 - Kisspeptin - Luteinizing hormone/choriogonadotropin - Lysophospholipid 1, 2, 3, 4, 5, 6, 7, 8 - MAS 1, 1L, D, E, F, G, X1, X2, X3, X4 - Melanocortin 1, 2, 3, 4, 5 - MCHR 1, 2 - Melatonin 1A, 1B- Motilin - neuromedin B, U 1, 2 - Neurotensin 1, 2 - Opioid Delta, Kappa, Mu, Nociceptin, but not Sigma - Olfactory - Opsin 3, 4, 5, 1LW, 1MW, 1SW, RGR, RRH - Orexin 1, 2 - Oxytocin - Oxoglutarate - PAF - Prokineticin 1, 2 - Prolactin-releasing peptide - Protease-activated 1, 2, 3, 4 - Relaxin 1, 2, 3, 4 - Somatostatin 1, 2, 3, 4, 5 - SREB - Succinate - TAAR 1, 2, 3, 5, 6, 8, 9 - Tachykinin 1, 2, 3 - Thyrotropin - Thyrotropin-releasing hormone - Urotensin-II - Vasopressin 1A, 1B, 2 Class B: Secretin like Brain-specific angiogenesis inhibitor 1, 2, 3 - Cadherin 1, 2, 3 - Calcitonin - CD97 - Corticotropin-releasing hormone 1, 2 - EMR 1, 2, 3 - Glucagon GR, GIPR, GLP1R, GLP2R - Growth hormone releasing hormone - PACAPR1- GPR 56, 64, 97, 98, 110, 111, 112, 113, 114, 115, 116, 123, 124, 125, 126, 128, 133, 143, 144, 157 - Latrophilin 1, 2, 3, ELTD1 - Parathyroid hormone 1, 2 - Secretin - Vasoactive intestinal peptide 1, 2 Class C: Metabotropic glutamate / pheromone Calcium-sensing receptor - GABA B 1, 2 - Glutamate receptor Metabotropic glutamate 1, 2, 3, 4, 5, 6, 7, 8 - GPRC6A - GPR 156, 158, 179 - RAIG 1, 2, 3, 4 - Taste receptors TAS1R 1, 2, 3 TAS2R 1, 3, 4, 5, 8, 9, 10, 12, 13, 14, 16, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50 Frizzled / Smoothened Frizzled 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 - Smoothened Retrieved from http://en..org/wiki/Melanopsin Categories: Genes on chromosome 10 | Human proteins | G protein coupled receptors | Circadian rhythmsHidden category: Protein pages needing a picture Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Deutsch Español Português This page was last modified on 7 September 2008, at 01:56
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