Chronobiology
Author: Flavio S J de Souza | Email: fsouza.ingebi@gmail.com
Flávio S J de Souza1°2°, Ricardo Romero1°2°
1° Instituto de Fisiología, Biología Molecular y Neurociencias, CONICET
2° Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, UBA
Non-mammalian vertebrates have a pineal complex with light-sensing capability as well as a neuroendocrine, melatonin-secreting function. Along with the deep pineal gland, many lizards (Squamata), as well as the tuatara (Rhynchocephalia) have a parietal eye, a structure derived from the parapineal containing photoreceptor cells that express an array of non-visual opsins that differ from the visual opsin repertoire of the retina, like pinopsin (opnp), parapinopsin (opnpp) and parietopsin (opnpt). A fourth member of the group, vertebrate-ancient opsin (VA-opsin), is expressed in the brain. Here, we have searched 50 lepidosaurian genomes (tuatara + lizards) for pineal non-visual opsins to check for the gain and loss of these genes during reptile evolution. Remarkably, we have identified a new opsin gene, which we termed “lepidosaur opsin” (lepidopsin) which is phylogenetically close to opnpp and is present in the genome of the tuatara and most lizards. Our survey of pineal non-visual opsins has revealed i) losses of non-visual opsins in specific lizard clades, ii) an apparent correlation between the presence of a parietal eye and diversity of non-visual opsin repertoire and iii) the gain of a new opsin during early lepidosaur evolution. Future studies on the photochemical nature of lepidopsin and the expression patterns of non-visual opsins in the parietal eye and pineal should help illuminate the functions of this class of opsins in reptiles.