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      Seeing the light to change colour: An evolutionary perspective on the role of melanopsin in neuroendocrine circuits regulating light-mediated skin pigmentation

      1 , 1

      Pigment Cell & Melanoma Research

      Wiley

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          Genetics, development and evolution of adaptive pigmentation in vertebrates.

          The study of pigmentation has played an important role in the intersection of evolution, genetics, and developmental biology. Pigmentation's utility as a visible phenotypic marker has resulted in over 100 years of intense study of coat color mutations in laboratory mice, thereby creating an impressive list of candidate genes and an understanding of the developmental mechanisms responsible for the phenotypic effects. Variation in color and pigment patterning has also served as the focus of many classic studies of naturally occurring phenotypic variation in a wide variety of vertebrates, providing some of the most compelling cases for parallel and convergent evolution. Thus, the pigmentation model system holds much promise for understanding the nature of adaptation by linking genetic changes to variation in fitness-related traits. Here, I first discuss the historical role of pigmentation in genetics, development and evolutionary biology. I then discuss recent empirically based studies in vertebrates, which rely on these historical foundations to make connections between genotype and phenotype for ecologically important pigmentation traits. These studies provide insight into the evolutionary process by uncovering the genetic basis of adaptive traits and addressing such long-standing questions in evolutionary biology as (1) are adaptive changes predominantly caused by mutations in regulatory regions or coding regions? (2) is adaptation driven by the fixation of dominant mutations? and (3) to what extent are parallel phenotypic changes caused by similar genetic changes? It is clear that coloration has much to teach us about the molecular basis of organismal diversity, adaptation and the evolutionary process.
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            A novel human opsin in the inner retina.

            Here we report the identification of a novel human opsin, melanopsin, that is expressed in cells of the mammalian inner retina. The human melanopsin gene consists of 10 exons and is mapped to chromosome 10q22. This chromosomal localization and gene structure differs significantly from that of other human opsins that typically have four to seven exons. A survey of 26 anatomical sites indicates that, in humans, melanopsin is expressed only in the eye. In situ hybridization histochemistry shows that melanopsin expression is restricted to cells within the ganglion and amacrine cell layers of the primate and murine retinas. Notably, expression is not observed in retinal photoreceptor cells, the opsin-containing cells of the outer retina that initiate vision. The unique inner retinal localization of melanopsin suggests that it is not involved in image formation but rather may mediate nonvisual photoreceptive tasks, such as the regulation of circadian rhythms and the acute suppression of pineal melatonin. The anatomical distribution of melanopsin-positive retinal cells is similar to the pattern of cells known to project from the retina to the suprachiasmatic nuclei of the hypothalamus, a primary circadian pacemaker.
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              Role of melanopsin in circadian responses to light.

              Melanopsin has been proposed as an important photoreceptive molecule for the mammalian circadian system. Its importance in this role was tested in melanopsin knockout mice. These mice entrained to a light/dark cycle, phase-shifted after a light pulse, and increased circadian period when light intensity increased. Induction of the immediate-early gene c-fos was observed after a nighttime light pulse in both wild-type and knockout mice. However, the magnitude of these behavioral responses in knockout mice was 40% lower than in wild-type mice. Although melanopsin is not essential for the circadian clock to receive photic input, it contributes significantly to the magnitude of photic responses.
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                Author and article information

                Journal
                Pigment Cell & Melanoma Research
                Pigment Cell Melanoma Res.
                Wiley
                17551471
                May 2018
                May 2018
                January 05 2018
                : 31
                : 3
                : 354-373
                Affiliations
                [1 ]Hotchkiss Brain Institute; Alberta Children's Hospital Research Institute; Department of Cell Biology and Anatomy; University of Calgary; Calgary AB Canada
                Article
                10.1111/pcmr.12678
                © 2018

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