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E.R. Loew, W.L. Davies, D.M. Hunt, J.K. Bowmaker; Different LWS Opsins Expressed in Individual Members of Twin Cones in Teleosts . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2837.
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© ARVO (1962-2015); The Authors (2016-present)
Fishes of the genus Esox (e.g. pike, pickerel, muskellunge) are highly visual. However, no spectral/opsin data on their photoreceptors have yet been reported. This study seeks to address this omission.
The peak sensitivities of the rod and cone photoreceptors in retinal tissue from three species, Esox niger, E. lucius & E. masquinongy, were obtained by microspectrophotometry. Opsin genes were PCR amplified from retinal cDNA and from genomic DNA.
Microspectrophotometry of intact outer segments identifies a rod pigment with max at 530 nm, a single cone with max at 516 nm and, most interestingly, morphological twin cones containing pigments with max values of approximately 616 nm in one member and 630 nm in the other. All pigments were best fitted by vitamin A2–based templates. The most likely explanation for the twin member difference is the expression of two different LWS cone opsins. Molecular data indicate that multiple LWS genes are present and expressed in the retina.
The presence of twin cones with spectrally–shifted LWS pigments in all species of the genus points to an important visual function that may be linked to hue discrimination in the 600nm and 750 nm region of the spectrum. The two pigments most likely arise from the expression of a different LWS gene in each member and molecular changes in the LWS opsin proteins of vitamin A1–based pigments have been well documented. The basis of these shifts in vitamin A2–based pigments is discussed.
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