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Morrow, JM, Lazic, S, Dixon Fox, M, Kuo, C, Schott, RK, de A Gutierrez, E, Santini, F, Tropepe, V and Chang, BS (2017) A second visual rhodopsin gene, rh1-2, is expressed in zebrafish photoreceptors and found in other ray-finned fishes. J. Exp. Biol. 220:294-303


Rhodopsin (rh1) is the visual pigment expressed in rod photoreceptors of vertebrates that is responsible for initiating the critical first step of dim-light vision. Rhodopsin is usually a single copy gene; however, we previously discovered a novel rhodopsin-like gene expressed in the zebrafish retina, rh1-2, which we identified as a functional photosensitive pigment that binds 11-cis retinal and activates in response to light. Here, we localized expression of rh1-2 in the zebrafish retina to a subset of peripheral photoreceptor cells, which indicates a partially overlapping expression pattern with rh1 We also expressed, purified and characterized Rh1-2, including investigation of the stability of the biologically active intermediate. Using fluorescence spectroscopy, we found the half-life of the rate of retinal release of Rh1-2 following photoactivation to be more similar to that of the visual pigment rhodopsin than to the non-visual pigment exo-rhodopsin (exorh), which releases retinal around 5 times faster. Phylogenetic and molecular evolutionary analyses show that rh1-2 has ancient origins within teleost fishes, is under similar selective pressure to rh1, and likely experienced a burst of positive selection following its duplication and divergence from rh1 These findings indicate that rh1-2 is another functional visual rhodopsin gene, which contradicts the prevailing notion that visual rhodopsin is primarily found as a single copy gene within ray-finned fishes. The reasons for retention of this duplicate gene, as well as possible functional consequences for the visual system, are discussed.


PubMed Online version:10.1242/jeb.145953


Animals; Evolution, Molecular; Phylogeny; Retinal Pigments; Retinal Rod Photoreceptor Cells/metabolism; Rhodopsin/genetics; Rhodopsin/metabolism; Sequence Analysis, DNA; Zebrafish/genetics; Zebrafish/metabolism; Zebrafish Proteins/genetics; Zebrafish Proteins/metabolism