ena-STUDY-UNIVERSITY OF KANSAS-06-12-2020-19:26:05:544-286
We know very little about the genetic basis for color and color-pattern in squamate reptiles - a group with over 10,000 species of snakes and lizards. Using transcriptomic comparisons between orange, yellow and white tissues from an anole lizard, we identified 6 color and 7 color-pattern candidate genes in squamates that are conserved across other vertebrates like mammals, birds or fish. Among color genes, we identified the first candidate gene for converting yellow xanthophylls to red ketocarotenoids in squamates, and a sex-linked protein that transports carotenoids from the bloodstream into the pigment cells. A new model for the genetics of coloration in squamates informed by our data suggests that the genes and associated pathways underlying both color and color-pattern are broadly conserved across vertebrates.
Despite the importance of color for vertebrate evolution, few studies have identified candidate color and color-pattern genes across squamate reptiles - a group with over 10,000 lizards, snakes and amphisbaenas. To bridge this gap, we performed comparative transcriptomic analyses of white, orange, and yellow colored skin in a polymorphic species of anole lizard. Squamates (like fish and amphibians) possess three types of pigment cells: iridophores, xanthophores/erythrophores, and melanophores. Iridophores use guanine-filled platelets to scatter light and produce white structural colors, while erythorphores/xanthophores and melanophores use pteridines/carotenoids and melanins, respectively, to produce pigment-based colors. Our analyses identified 13 candidate genes for squamate color and color-pattern: six previously involved in pigment synthesis across vertebrates and seven previously linked to chromatophore development in zebrafish (Danio). In comparisons between white and pigment-rich orange and yellow tissues, we found that white tissues up-regulated the guanine pathway and iridophore development genes, while pigment-rich tissues up-regulated the pteridine pathway and xantophore/erythophore development genes. In comparisons between orange and yellow tissues, orange tissues up-regulated the pteridine and carotenoid pathways as well as melanophore maintenance genes; among the carotenoid pathway genes up-regulated by orange tissues we identified both genes responsible for carotenoid uptake and metabolism. We propose that anoles use carotenoids and pteridines to produce orange coloration, and that this process likely involves ketolation of xanthophylls to synthesize ketocarotenoids. In addition, we identify two candidate ketolase genes for squamates, and propose that a differentially expressed sex-linked gene should be a focus for studies on anole local adaptation and speciation.
Despite the importance of color for vertebrate evolution, few studies have identified candidate color and color-pattern genes across squamate reptiles - a group with over 10,000 lizards, snakes and amphisbaenas. To bridge this gap, we performed comparative transcriptomic analyses of white, orange, and yellow colored skin in a polymorphic species of anole lizard. Squamates (like fish and amphibians) possess three types of pigment cells: iridophores, xanthophores/erythrophores, and melanophores. Iridophores use guanine-filled platelets to scatter light and produce white structural colors, while erythorphores/xanthophores and melanophores use pteridines/carotenoids and melanins, respectively, to produce pigment-based colors. Our analyses identified 13 candidate genes for squamate color and color-pattern: six previously involved in pigment synthesis across vertebrates and seven previously linked to chromatophore development in zebrafish (Danio). In comparisons between white and pigment-rich orange and yellow tissues, we found that white tissues up-regulated the guanine pathway and iridophore development genes, while pigment-rich tissues up-regulated the pteridine pathway and xantophore/erythophore development genes. In comparisons between orange and yellow tissues, orange tissues up-regulated the pteridine and carotenoid pathways as well as melanophore maintenance genes; among the carotenoid pathway genes up-regulated by orange tissues we identified both genes responsible for carotenoid uptake and metabolism. We propose that anoles use carotenoids and pteridines to produce orange coloration, and that this process likely involves ketolation of xanthophylls to synthesize ketocarotenoids. In addition, we identify two candidate ketolase genes for squamates, and propose that a differentially expressed sex-linked gene should be a focus for studies on anole local adaptation and speciation.