title: Evolution of Vertebrate Phototransduction: Cascade Activation.
abstract: We applied high-throughput sequencing to eye tissue from several species of basal vertebrates (a hagfish, two species of lamprey, and five species of gnathostome fish), and we analyzed the mRNA sequences for the proteins underlying activation of the phototransduction cascade. The molecular phylogenies that we constructed from these sequences are consistent with the 2R WGD model of two rounds of whole genome duplication. Our analysis suggests that agnathans retain an additional representative (that has been lost in gnathostomes) in each of the gene families we studied; the evidence is strong for the G-protein α subunit (GNAT) and the cGMP phosphodiesterase (PDE6), and indicative for the cyclic nucleotide-gated channels (CNGA and CNGB). Two of the species (the hagfish Eptatretus cirrhatus and the lamprey Mordacia mordax) possess only a single class of photoreceptor, simplifying deductions about the composition of cascade protein isoforms utilized in their photoreceptors. For the other lamprey, Geotria australis, analysis of the ratios of transcript levels in downstream and upstream migrant animals permits tentative conclusions to be drawn about the isoforms used in four of the five spectral classes of photoreceptor. Overall, our results suggest that agnathan rod-like photoreceptors utilize the same GNAT1 as gnathostomes, together with a homodimeric PDE6 that may be agnathan-specific, whereas agnathan cone-like photoreceptors utilize a GNAT that may be agnathan-specific, together with the same PDE6C as gnathostomes. These findings help elucidate the evolution of the vertebrate phototransduction cascade from an ancestral chordate phototransduction cascade that existed prior to the vertebrate radiation.
authors.affiliation: Eccles Institute of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia trevor.lamb@anu.edu.au.
authors.forename: Trevor D
authors.initials: TD
authors.lastname: Lamb
authors.affiliation: Genome Discovery Unit, John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia Department of Genome Biology, John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia.
authors.forename: Hardip
authors.initials: H
authors.lastname: Patel
authors.affiliation: Genome Discovery Unit, John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia.
authors.forename: Aaron
authors.initials: A
authors.lastname: Chuah
authors.affiliation: Eccles Institute of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia ANU Medical School, Australian National University, Canberra, ACT, Australia.
authors.forename: Riccardo C
authors.initials: RC
authors.lastname: Natoli
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, WA, Australia Oceans Institute, University of Western Australia, Perth, WA, Australia Lions Eye Institute, University of Western Australia, Perth, WA, Australia.
authors.forename: Wayne I L
authors.initials: WI
authors.lastname: Davies
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, WA, Australia Oceans Institute, University of Western Australia, Perth, WA, Australia Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Hart
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, WA, Australia Oceans Institute, University of Western Australia, Perth, WA, Australia Lions Eye Institute, University of Western Australia, Perth, WA, Australia.
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Collin
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, WA, Australia Lions Eye Institute, University of Western Australia, Perth, WA, Australia.
authors.forename: David M
authors.initials: DM
authors.lastname: Hunt
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019143:Evolution, Molecular; D005123:Eye / Q000378:metabolism; D005399:Fishes / Q000235:genetics*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism; D016678:Genome; D005960:Glucosides / Q000235:genetics / Q000378:metabolism; D059014:High-Throughput Nucleotide Sequencing; D007798:Lampreys / Q000235:genetics; D055537:Light Signal Transduction / Q000235:genetics*; D010636:Phenols / Q000378:metabolism; D010802:Phylogeny; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism / Q000502:physiology
chemical_list: D044385:GTP-Binding Protein alpha Subunits; D005960:Glucosides; D010636:Phenols; C009172:rhodioloside
keywords: cyclic nucleotide-gated channel.; phosphodiesterase; phototransduction; rhodopsin; transducin