An extended family of novel vertebrate photopigments is widely expressed and displays a diversity of function.

Light affects animal physiology and behavior more than simply through classical visual, image-forming pathways. Nonvisual photoreception regulates numerous biological systems, including circadian entrainment, DNA repair, metabolism, and behavior. However, for the majority of these processes, the photoreceptive molecules involved are unknown. Given the diversity of photophysiological responses, the question arises whether a single photopigment or a greater diversity of proteins within the opsin superfamily detect photic stimuli. Here, a functional genomics approach identified the full complement of photopigments in a highly light-sensitive model vertebrate, the zebrafish (Danio rerio), and characterized their tissue distribution, expression levels, and biochemical properties. The results presented here reveal the presence of 42 distinct genes encoding 10 classical visual photopigments and 32 nonvisual opsins, including 10 novel opsin genes comprising four new pigment classes. Consistent with the presence of light-entrainable circadian oscillators in zebrafish, all adult tissues examined expressed two or more opsins, including several novel opsins. Spectral and electrophysiological analyses of the new opsins demonstrate that they form functional photopigments, each with unique chromophore-binding and wavelength specificities. This study has revealed a remarkable number and diversity of photopigments in zebrafish, the largest number so far discovered for any vertebrate. Found in amphibians, reptiles, birds, and all three mammalian clades, most of these genes are not restricted to teleosts. Therefore, nonvisual light detection is far more complex than initially appreciated, which has significant biological implications in understanding photoreception in vertebrates.

Next-generation sequencing in health-care delivery: lessons from the functional analysis of rhodopsin.

PURPOSE: The interpretation of genetic information has always been challenging, but next-generation sequencing produces data on such a vast scale that many more variants of uncertain pathogenicity will be found. We exemplify this issue with reference to human rhodopsin, in which pathogenic mutations can lead to autosomal dominant retinitis pigmentosa. METHODS: Rhodopsin variants, with unknown pathogenicity, were found in patients by next-generation and Sanger sequencing and a multidisciplinary approach was used to determine their functional significance. RESULTS: Four variants in rhodopsin were identified: F45L, P53R, R69H, and M39R, with the latter two substitutions being novel. We investigated the cellular transport and photopigment function of all four human substitutions and found that the F45L and R69H variants behave like wild-type and are highly unlikely to be pathogenic. By contrast, P53R (a de novo change) and M39R were retained in the endoplasmic reticulum with significantly reduced functionality and are clearly pathogenic. CONCLUSION: Potential pathogenicity of variants requires careful assessment using clinical, genetic, and functional data. We suggest that a multidisciplinary pathway of assessment, using several functional assays, will be required if next-generation sequencing is to be used effectively, reliably, and safely in the clinical environment.