title: Endothelin modulates the circadian expression of non-visual opsins.
abstract: The non-visual opsin, melanopsin, expressed in the mammalian retina, is considered a circadian photopigment because it is responsible to entrain the endogenous biological clock. This photopigment is also present in the melanophores of Xenopus laevis, where it was first described, but its role in these cells is not fully understood. X. laevis melanophores respond to light with melanin granule dispersion, the maximal response being achieved at the wavelength of melanopsin maximal excitation. Pigment dispersion can also be triggered by endothelin-3 (ET-3). Here we show that melanin translocation is greater when a blue light pulse was applied in the presence of ET-3. In addition, we demonstrated that mRNA levels of the melanopsins Opn4x and Opn4m exhibit temporal variation in melanophores under light/dark (LD) cycles or constant darkness, suggesting that this variation is clock-driven. Moreover, under LD cycles the oscillations of both melanopsins show a circadian profile suggesting a role for these opsins in the photoentrainment mechanism. Blue-light pulse decreased Opn4x expression, but had no effect on Opn4m. ET-3 abolishes the circadian rhythm of expression of both opsins; in addition the hormone increases Opn4x expression in a dose-, circadian time- and light-dependent way. ET-3 also increases the expression of its own receptor, in a dose-dependent manner. The variation of melanopsin levels may represent an adaptive mechanism to ensure greater melanophore sensitivity in response to environmental light conditions with ideal magnitude in terms of melanin granule dispersion, and consequently color change.
authors.affiliation: Department of Physiology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil.
authors.forename: Maria Nathália de Carvalho Magalhães
authors.initials: MN
authors.lastname: Moraes
authors.affiliation: Department of Physiology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil.
authors.forename: Leonardo Henrique Ribeiro Graciani de
authors.initials: LH
authors.lastname: Lima
authors.affiliation: Department of Physiology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil.
authors.forename: Bruno Cesar Ribeiro
authors.initials: BC
authors.lastname: Ramos
authors.affiliation: Department of Physiology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil; Department of Physiology, Institute of Biological Sciences, Federal University of Minas Gerais, Belo Horizonte, Brazil.
authors.forename: Maristela de Oliveira
authors.initials: Mde O
authors.lastname: Poletini
authors.affiliation: Department of Physiology, Institute of Biosciences, University of São Paulo, São Paulo, Brazil. Electronic address: amdlcast@ib.usp.br.
authors.forename: Ana Maria de Lauro
authors.initials: AM
authors.lastname: Castrucci
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology* / Q000528:radiation effects; D016232:Endothelins / Q000494:pharmacology*; D008027:Light; D008543:Melanins / Q000378:metabolism; D008547:Melanophores / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D017440:Photoperiod; D017466:Receptors, Endothelin / Q000235:genetics / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism*; D014982:Xenopus laevis; D000099210:Melanopsin
chemical_list: D016232:Endothelins; D008543:Melanins; D017466:Receptors, Endothelin; D017299:Rod Opsins; D000099210:Melanopsin
keywords: Circadian rhythms; Endothelin; Melanophores; Melanopsins; Xenopus laevis