title: Evolution of the vertebrate phototransduction cascade activation steps.
abstract: We examine the molecular phylogeny of the proteins underlying the activation steps of vertebrate phototransduction, for both agnathan and jawed vertebrate taxa. We expand the number of taxa analysed and we update the alignment and tree building methodology from a previous analysis. For each of the four primary components (the G-protein transducin alpha subunit, GαT, the cyclic GMP phosphodiesterase, PDE6, and the alpha and beta subunits of the cGMP-gated ion channel, CNGC), the phylogenies appear consistent with expansion from an ancestral proto-vertebrate cascade during two rounds of whole-genome duplication followed by divergence of the agnathan and jawed vertebrate lineages. In each case, we consider possible scenarios for the underlying gene duplications and losses, and we apply relevant constraints to the tree construction. From tests of the topology of the resulting trees, we obtain a scenario for the expansion of each component during 2R that accurately fits the observations. Similar analysis of the visual opsins indicates that the only expansion to have occurred during 2R was the formation of Rh1 and Rh2. Finally, we propose a hypothetical scenario for the conversion of an ancestral chordate cascade into the proto-vertebrate phototransduction cascade, prior to whole-genome duplication. Together, our models provide a plausible account for the origin and expansion of the vertebrate phototransduction cascade.
authors.affiliation: Eccles Institute of Neuroscience, John Curtin School of Medical Research, The Australian National University, ACT 2600, Australia. Electronic address: Trevor.Lamb@anu.edu.au.
authors.forename: Trevor D
authors.initials: TD
authors.lastname: Lamb
authors.affiliation: The Lions Eye Institute, The University of Western Australia, WA 6009, Australia; School of Biological Sciences, The University of Western Australia, WA 6009, Australia.
authors.forename: David M
authors.initials: DM
authors.lastname: Hunt
mesh_terms: D000818:Animals; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6 / Q000235:genetics / Q000502:physiology; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics / Q000502:physiology; D019143:Evolution, Molecular; D020440:Gene Duplication; D006801:Humans; D008957:Models, Genetic; D055355:Opsins / Q000235:genetics / Q000502:physiology; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology; D010802:Phylogeny; D015293:Transducin / Q000235:genetics / Q000502:physiology; D014714:Vertebrates / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D014785:Vision, Ocular / Q000235:genetics* / Q000502:physiology*
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; D055355:Opsins; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; D015293:Transducin
keywords: Cyclic nucleotide-gated channel; Evolution; Opsin; Phosphodiesterase; Phototransduction; Transducin