ZFIN ID: ZDB-PUB-161105-12
A second visual rhodopsin gene, rh1-2, is expressed in zebrafish photoreceptors and found in other ray-finned fishes
Morrow, J.M., Lazic, S., Fox, M.D., Kuo, C., Schott, R.K., Gutierrez, E.A., Santini, F., Tropepe, V., Chang, B.S.
Date: 2017
Source: The Journal of experimental biology   220(Pt 2): 294-303 (Journal)
Registered Authors: Lazic, Savo, Tropepe, Vincent
Keywords: Visual pigment, Vision, Gene duplication, GPCR, Teleost
MeSH Terms:
  • 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
PubMed: 27811293 Full text @ J. Exp. Biol.
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ABSTRACT
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 localize 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 express, purify, and characterize Rh1-2, including investigations of the stability of the biologically active intermediate. Using fluorescence spectroscopy, we find the half-life of the rate of retinal release of Rh1-2 following photoactivation to be more similar to 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 pressures 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.
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