Opsins as main regulators of skin biology

Opsins are light-sensitive proteins that are found across the animal kingdom. In mammals, opsins are classically associated with image-forming processes, a function exerted by cone and rod opsins. In early 2000, melanopsin was identified in the human retina as an important regulator of non-image forming events such as melatonin suppression, pupillary constriction, and circadian rhythm adjustment. The presence of different opsins and the biological processes that these proteins regulate in the skin are increasingly being described. Currently, opsins are considered light as well as thermosensors in the skin. However, additional regulatory functions, in a light and thermo-independent fashion, mostly likely via protein-protein interaction have set a new field of study. The goal of this review is to critically revise the literature on the role of opsins in skin physiology as well as in melanoma cancer.