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Fig. 1

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ZDB-IMAGE-170615-26
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Figures for Enright et al., 2015
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Figure Caption

Fig. 1 Modeling the Rhodopsin-Porphyropsin Switch

(A) The conversion of retinol (vitamin A1) to 3,4-didehydroretinol (vitamin A2) underlies the rhodopsin-to-porphyropsin switch and is driven by a previously unidentified dehydrogenase that catalyzes the addition of a double bond to the β-ionone ring.

(B) This vitamin A1 to A2 switch is widely used by a variety of vertebrates and can be deployed at key stages of the life cycle: e.g., during upstream migration in sea lamprey (Petromyzon marinus) and Coho salmon (Oncorhynchus kisutch) and upon metamorphosis in amphibians such as the northern leopard frog (Lithobates pipiens) [ 9; 10 ; 11].

(C and D) To model this switch, zebrafish were treated with thyroid hormone (300 μg/l L-thyroxine [T4]) for 3 weeks. Retinoids were then isolated from pooled RPE and retina of three individuals, reduced using sodium borohydride, and analyzed by HPLC. Retinoids from TH-treated fish have a shorter retention time than those from vehicle-treated fish.

(E) The absorbance spectrum of the predominant retinoid from control fish closely matches the absorbance spectrum of a vitamin A1 standard, with a λmax of 326 nm.

(F) The predominant retinoid from TH-treated fish has an absorbance spectrum that matches that of the vitamin A2 standard, with a λmax of 355 nm.

(G) The American bullfrog (Lithobates catesbeianus) often sits at the water’s surface and possesses exclusively A1-based visual pigments in the ventral retina and a mixture of A1- and A2-based visual pigments in the dorsal retina, possibly facilitating downward vision into the murky, red-shifted water [ 12 ; 13].

(H and I) The dorsal third of the RPE from two American bullfrogs was dissected, pooled, and analyzed by HPLC and found to contain a mixture of vitamin A1 and vitamin A2. Only vitamin A1 was identified in the ventral third of the RPE. All absorbance values are normalized and represented as arbitrary units (a.u.).

Acknowledgments
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