A second visual rhodopsin gene, rh1-2, is expressed in zebrafish photoreceptors and found in other ray-finned fishes.
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.
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada, M5S 3G5.|Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada, M5S 3B2.
James M
JM
Morrow
Department of Molecular Genetics, University of Toronto, Toronto, Canada, M5S 1A8.
Savo
S
Lazic
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada, M5S 3G5.
Monica
M
Dixon Fox
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada, M5S 3G5.
Claire
C
Kuo
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada, M5S 3B2.
Ryan K
RK
Schott
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada, M5S 3B2.
Eduardo
E
de A Gutierrez
Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA.
Francesco
F
Santini
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada, M5S 3G5.|Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Canada, M5T 3A9.|Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, Canada, M5S 3B2.
Vincent
V
Tropepe
Department of Cell and Systems Biology, University of Toronto, Toronto, Canada, M5S 3G5 belinda.chang@utoronto.ca.|Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada, M5S 3B2.|Centre for the Analysis of Genome Evolution and Function, University of Toronto, Toronto, Canada, M5S 3B2.
Belinda S W
0000-0002-6525-4429
BS
Chang
D000818:Animals; D019143:Evolution, Molecular; D010802:Phylogeny; D012168:Retinal Pigments; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism; D012243:Rhodopsin / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D015027:Zebrafish / Q000235:genetics* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics* / Q000378:metabolism
D012168:Retinal Pigments; D029961:Zebrafish Proteins; C000622706:rhol protein, zebrafish; D012243:Rhodopsin
GPCR; Gene duplication; Teleost; Vision; Visual pigment