Vision evolved 700 million years ago

New study sheds light on how and when vision evolved
Press release issued 29 October 2012

Opsins, the light-sensitive proteins key to vision, may have evolved earlier and undergone fewer genetic changes than previously believed, according to a new study from the National University of Ireland Maynooth and the University of Bristol published today in Proceedings of the National Academy of Sciences (PNAS) .

The study, which used computer modelling to provide a detailed picture of how and when opsins evolved, sheds light on the origin of sight in animals, including humans. The evolutionary origins of vision remain hotly debated, partly due to inconsistent reports of phylogenetic relationships among the earliest opsin-possessing animals.

Dr Davide Pisani of Bristol's Schools of Biological Sciences and Earth Sciences and colleagues at NUI Maynooth performed a computational analysis to test every hypothesis of opsin evolution proposed to date. The analysis incorporated all available genomic information from all relevant animal lineages, including a newly sequenced group of sponges (Oscarella carmela) and the Cnidarians, a group of animals thought to have possessed the world's earliest eyes.

...

http://www.bris.ac.uk/news/2012/8888.html

Metazoan opsin evolution reveals a simple route to animal vision
Roberto Feudaa, Sinead C. Hamiltona, James O. McInerneya, and Davide Pisania
Edited by David M. Hillis, University of Texas at Austin, Austin, TX, and approved September 13, 2012
(received for review March 21, 2012)

Abstract

All known visual pigments in Neuralia (Cnidaria, Ctenophora, and Bilateria) are composed of an opsin (a seven-transmembrane G protein-coupled receptor), and a light-sensitive chromophore, generally retinal. Accordingly, opsins play a key role in vision. There is no agreement on the relationships of the neuralian opsin subfamilies, and clarifying their phylogeny is key to elucidating the origin of this protein family and of vision. We used improved methods and data to resolve the opsin phylogeny and explain the evolution of animal vision. We found that the Placozoa have opsins, and that the opsins share a common ancestor with the melatonin receptors. Further to this, we found that all known neuralian opsins can be classified into the same three subfamilies into which the bilaterian opsins are classified: the ciliary (C), rhabdomeric (R), and go-coupled plus retinochrome, retinal G protein-coupled receptor (Go/RGR) opsins. Our results entail a simple scenario of opsin evolution. The first opsin originated from the duplication of the common ancestor of the melatonin and opsin genes in a eumetazoan (Placozoa plus Neuralia) ancestor, and an inference of its amino acid sequence suggests that this protein might not have been light-sensitive. Two more gene duplications in the ancestral neuralian lineage resulted in the origin of the R, C, and Go/RGR opsins. Accordingly, the first animal with at least a C, an R, and a Go/RGR opsin was a neuralian progenitor.

http://www.pnas.org/content/early/2012/10/25/1204609109.abstract

Metazoan opsin evolution reveals a simple route to animal vision
Roberto Feuda, Sinead C. Hamilton, James O. McInerney and Davide Pisani

Supplementary Online Materials

Data mining and data set assembly. To identify homologues of sequences from
GPCRdb in non-bilaterian metazoans we performed a series of blastP searches against the
genomes of Hydra magnipapillata, Nematostella vectensis and Trichoplax adherens.
These searches were seeded using the sequences we obtained from GPCRdb. To further
enrich our data set of putative opsin homologues from non-bilaterian metazoans, we used
our set of opsins to seed a series of blastP searches against the genome of the placozoan
Trichoplax adherens, and against a large set of predicted GPCRs from the two available
sponge genomes (that of the demosponge Amphimedon queenslandica, and that of the
homoscleromorph Oscarella carmela).

...

http://www.pnas.org/content/suppl/2012/10/26/1204609109.DCSupplemental/sapp.pdf