A base molecular das adaptações visuais nos genes das opsinas de Anableps anableps e Phreatobius cisternarum através da análise de transcriptoma

Abstract

Although vertebrate eyes share the same general organization, many species have developed specializations that improve their visual perception of the environment. These specializations are often reflected in a variety of visual adaptations that involve changes in visual sensitivity, which in turn can be modulated by the variation on the photoreceptors number, by altering the visual pigments or by combining both mechanisms. In the case of adaptive changes in the pigments, these may occur due to structural differences in the pattern of expression and the repertoire amount of the opsin genes family. However, there is no much information regarding adaptive changes on visual pigments over different luminosity on aquatic environments. This research aims to evaluate the molecular basis of the visual adaptations in the opsin genes from Anableps anableps and Phreatobius cisternarum, species present in environments with different light conditions, the first one from a surface environment and the second one from an underground habitat, through transcriptome analysis. This investigation comprises two chapters. The first chapter comprises the studies of the Anableps anableps specie. We combined the analysis of RNA-Seq and in situ hybridization of the eye tissue of this specie aiming to understand them visual adaptations to the aerial-aquatic environment. RNA-Seq data from the eye exhibited a repertoire of 20 non-visual opsin genes, which reflects the environmental heterogeneity these species lives. Likewise, comparative analyzes in protein coding sequences of the opsins allowed the identification of six opsins presenting the typical amino acid motifs of C-type and nine of Group 4, conserved among themselves. In situ hybridization studies on the retina showed asymmetric expression of these non-visual opsins at different stages, as well as during the ocular development. The second chapter presents the studies of the Phreatobius cisternarum specie. We combine histological, molecular and RNA-Seq analyzes to understand the visual and sensorial adaptations of P. cisternarum to the phreatic environment. RNA-Seq data from P. cisternarum head revealed a repertoire of eleven opsin genes, three visual opsins and eight non-visual opsins. Two visual opsins, rh1 and lws, presented amino acid substitutions that potentially contributed to the red and blue shift, respectively. Our histological analysis showed the presence of a rudimentary retina, while the RNA-Seq analysis identified the expression of 38 genes related to the lens fiber cells and 51 genes related to the retinal pigmented epithelium (RPE), indicating that the reduced eyes of P. cisternarum retained some lens structures. The extra-retinal expression of opn4m3 is possibly associated with the peripheral clock regulation. Furthermore, the presence of potential opsin pseudogenes would be regulated by a small retina exposed to a low-light environment. The chapters introduce and provide an overview of the investigation on opsins amino acid substitutions, changes on expression patterns and opsin repertoire size (duplication and pseudogenization), and how these could contribute to the shift in spectral sensitivity and finally visual adaptation of A. anableps and P. cisternarum to their peculiar environment. The present study provides fundamental evidence for the understanding of the adaptive molecular basis in the opsin genes to subterranean and aerial-aquatic environments, in the species P. cisternarum and A. anableps.