Melanopsin and the Non-visual Photochemistry in the Inner Retina of Vertebrates

DIAZ, N.M.; MORERA L. P.; GUIDO M.E.

PHOTOCHEMISTRY AND PHOTOBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015

0031-8655

Melanopsin (Opn4), a member of the G protein-coupled receptor family, is a vitamin A-based opsin in the vertebrate retina that has been shown to be involved in the synchronization of circadian rhythms, pupillary light reflexes, melatonin suppression and other light-regulated tasks. In non-mammalian vertebrates there are two Opn4 genes, Opn4m and Opn4x, the mammalian and Xenopus orthologs, respectively. Opn4x is only expressed in non-mammalian vertebrates including reptiles, fish and birds, while Opn4m is found in a subset of retinal ganglion cells (RGCs), the intrinsically photosensitive (ip) RGCs of the inner retina of both mammals and non-mammalian vertebrates. All opsins described utilize retinaldehyde as chromophore, photoisomerized from 11-cis- to all-trans-retinal upon light exposure. Visual retinal photoreceptor cones and rods, responsible for day and night vision respectively, recycle retinoids through a process called the visual cycle that involves the retinal pigment epithelium (RPE) or glial Müller cells. Although Opn4 has been characterized as a bistable photopigment, little is known about the mechanism/s involved in its chromophore regeneration. In this review, we will attempt to shed light on the visual cycle taking place in the inner retina and discuss the state of the art in the non-visual photochemistry of vertebrates. This article is protected by copyright. All rights reserved.