Opsin 4 (melanopsin)
Identifiers
Symbol(s)	OPN4; MGC142118; MOP
External IDs	OMIM: 606665 MGI: 1353425 HomoloGene: 69152
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. The Human Genome Organisation (HUGO is an organization involved in the Human Genome Project, a project about mapping the human genome The Mouse Genome Informatics (MGI website is run by The Jackson Laboratory. HomoloGene, a tool of the National Center for Biotechnology Information (NCBI is a system for automated detection of homologs (similarity attributable to descent The Entrez Global Query Cross-Database Search System is a powerful Federated search engine or Web portal that allows users to search many discrete Health sciences Ensembl is a joint scientific project between the European Bioinformatics Institute and the Wellcome Trust Sanger Institute, which was launched in 1999 in response to the imminent UniProt is the uni versal prot ein resource a central repository of Protein data created by combining Swiss-Prot, TrEMBL PubMed is a free search engine for accessing the MEDLINE database of citations and abstracts of biomedical research articles Photopigments are unstable pigments that undergo a chemical change Photosensitive ganglion cells, or melanopsin-containing ganglion cells, are a recently discovered type of nerve cell in the Retina of the mammalian The vertebrate retina is a light sensitive part inside the inner layer of the Eye. In structure, melanopsin is an opsin, a retinylidene protein variety of G-protein-coupled receptor. Opsins are a group of light-sensitive 35-55 kDa membrane-bound G protein-coupled receptors of the Retinylidene protein family found in Photoreceptor cells Retinylidene proteins are a family of proteins that use Retinal as Chromophore for Light reception G protein-coupled receptors ( GPCRs) also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and

Melanopsin, atypical in vertebrates, functionally resembles invertebrate opsins, including an apparent intrinsic photoisomerase activity. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate A photoisomerase is a Protein in the Eye that is responsible for isomerizing Photopigments In order for the eye to function propertly a ^[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. GTP chemical structurepng|thumb|180px| Guanosine triphosphate]] G proteins short for guanine nucleotide-binding proteins, are a family of Proteins involved

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. Ignacio Provencio is the discoverer of Melanopsin, a photopigment found in specialized photosensitive ganglion cells of the retina ^[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. David M Berson is Professor of Medical Science at Brown University. Brown University is a highly esteemed private University located in Providence, Rhode Island and is a member of the Ivy League. ^[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. Pharmacology (from Greek grc φάρμακον pharmakon, "drug" and grc -λογία -logia) is the study of how Drugs 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. Photosensitivity is the amount to which an object reacts upon receiving Photons especially Visible light. Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron ^[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. In ocular physiology adaptation is the ability of the Eye to adjust to various levels of darkness and light ^[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 (day)light.

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. In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell

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). Pretectum is a structure located in the Midbrain. It receives binocular input from the Eyes and is involved with the pupillary light reflex. The Retinohypothalamic tract (RHT is a photic input pathway involved in Circadian rhythms. The suprachiasmatic nucleus ( SCN) is a bilateral region of the brain located in the Hypothalamus, that is responsible for controlling endogenous Circadian rhythms The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis

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). See Chemical synapse for an introduction to concepts and terminology used in this article Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its Adenylate cyclase activating polypeptide 1 (pituitary, also known as ADCYAP1, is a human Gene.

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. In Chronobiology, entrainment of a Circadian system is the alignment of its own period and phase to the period and phase of an external rhythm A gene knockout is a genetic technique in which an organism is engineered to carry genes that have been made inoperative (have been "knocked out" of the organism 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 cells^[7] which convey their signals to the "circadian clock" via the retinohypothalamic tract. ^[8][9]

Distribution in different species

Melanopsin has a very similar pattern of tissue distribution among all mammals studied so far, including rodents, monkeys, and humans. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands Rodentia is an order of Mammals also known as rodents, characterised by two continuously-growing incisors in the upper and lower jaws which must A monkey is any member of either the New World monkeys or Old World monkeys two of the three groupings of Simian Primates the third group being Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus 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. Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Prehistoric amphibian Amphibians (class Amphibia such as Frogs Toads Salamanders Newts Gymnophiona, Sirens and The pineal gland (also called the pineal body, epiphysis cerebri, or epiphysis) is a small endocrine gland in the vertebrate Brain

References

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