XB-FEAT-985294

gpr50

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Notes on adaptive evolution, function, orthogy and phylogeny of Mtnr gene family

Source: Bertolesi et al 2020. The regulation of skin pigmentation in response to environmental light by pineal Type II opsins and skin melanophore melatonin receptors. article online here.

While life in different photic environments may have promoted the diversification of opsins, the characteristics of pigmented skin cells and the genetic diversification of Mtnrs were likely influenced by the advent of thermoregulation. Pigment granules aggregate and disperse in skin melanophores of ectotherms, whereas in homeotherms, melanocytes release pigments that are then captured by neighboring keratinocytes [16]. The advent of skin isolation systems (fur and feathers in mammals and birds, respectively) during the evolution of thermoregulation [17], likely influenced both the phenotypic change (aggregation/dispersion vs. secretion) and the role of the Mtnrs in the skin. While three mtnrs are described in vertebrates (mtnr1a; mtnr1b and mtnr1c) [18], mtnr1c, initially identified in Xenopus skin melanophores [19], disappeared in therian mammalian lineages [20]. The Mtnr1c mammalian orthologue, GPR50, is expressed in hypothalamic thermoregulatory circuits, where it plays an important role in adaptative thermogenesis, despite having lost the ability to bind melatonin [21]. The presence of mtnr1a and mtnr1b in mammalian melanocytes [22], and mtnr1c in melanophores [19], argue that any or all Mtnrs could trigger pigment aggregation in non-mammalian vertebrates. The actual repertoire of Mtnrs involved, however, is unknown.