Seeing the light to change colour: An evolutionary perspective on the role of melanopsin in neuroendocrine circuits regulating light‐mediated skin pigmentation |
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Authors: | Gabriel E Bertolesi Sarah McFarlane |
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Institution: | Hotchkiss Brain Institute, Alberta Children's Hospital Research Institute, Department of Cell Biology and Anatomy, University of Calgary, Calgary, AB, Canada |
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Abstract: | Melanopsin photopigments, Opn4x and Opn4m, were evolutionary selected to “see the light” in systems that regulate skin colour change. In this review, we analyse the roles of melanopsins, and how critical evolutionary developments, including the requirement for thermoregulation and ultraviolet protection, the emergence of a background adaptation mechanism in land‐dwelling amphibian ancestors and the loss of a photosensitive pineal gland in mammals, may have helped sculpt the mechanisms that regulate light‐controlled skin pigmentation. These mechanisms include melanopsin in skin pigment cells directly inducing skin darkening for thermoregulation/ultraviolet protection; melanopsin‐expressing eye cells controlling neuroendocrine circuits to mediate background adaptation in amphibians in response to surface‐reflected light; and pineal gland secretion of melatonin phased to environmental illuminance to regulate circadian and seasonal variation in skin colour, a process initiated by melanopsin‐expressing eye cells in mammals, and by as yet unknown non‐visual opsins in the pineal gland of non‐mammals. |
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Keywords: | α ‐melanocyte stimulating hormone intrinsically photosensitive horizontal cell intrinsically photosensitive retinal ganglion cell melanosome melatonin |
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