Purchase this article with an account.
S. S. Deeb, F. Greutzner, J. A. Marshall Graves, M. J. Wakefield; The Visual Pigments of the Platypus: Gene Duplication Resulted in Evolution of LWS and SWS2 Pigment Genes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3181.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To determine the sequence of the visual pigments of the platypus (Ornithorhynchus anatinus), an extraordinary mammal, and infer their spectral properties and evolutionary pathways.
IInitially, we prepared platypus retinal RNA and used primers of the middle-wave-sensitive (MWS), long-wave-sensitive (LWS) and short-wave sensitive (SWS1) pigments corresponding to sequences that are highly conserved among mammals to PCR amplify the corresponding pigments of the platypus. Subsequently, when the platypus genome sequence became available, we obtained all sequence data and genomic positions of all visual pigments in the draft assembly.
Amplification from the retinal RNA revealed the expression of LWS pigment mRNA that is homologous in sequence and spectral properties to the primate LWS visual pigments. However, we were unable to amplify the mammalian SWS1 pigment. Examination of the sequences in the platypus genome database revealed the existence on the X-chromosome of an LWS pigment gene, as expected. Unexpectedly, we found an SWS2 pigment gene in close proximity to the LWS gene within a region of conserved synteny. The encoded SWS2 pigment is predicted to have a wavelength of maximal absorption of about 440 nm, and is paralogous to SWS pigments typically found in birds, fish and reptiles but not in mammals. In addition, the platypus has a typical rhodopsin 1 protein-encoding gene.
A duplication event of an ancestral cone visual pigment gene on the X-chromosome of the platypus, followed by sequence divergence and adaptation, resulted in the expression of LWS and SWS2 visual pigments. This suggests that the platypus has dichromatic color vision.
This PDF is available to Subscribers Only