Abstract
Animal pigment patterns play important roles in behavior and, in many species, red coloration serves as an honest signal of individual quality in mate choice. Among Danio fishes, some species develop erythrophores, pigment cells that contain red ketocarotenoids, whereas other species, like zebrafish (D. rerio) only have yellow xanthophores. Here, we use pearl danio (D. albolineatus) to assess the developmental origin of erythrophores and their mechanisms of differentiation. We show that erythrophores in the fin of D. albolineatus share a common progenitor with xanthophores and maintain plasticity in cell fate even after differentiation. We further identify the predominant ketocarotenoids that confer red coloration to erythrophores and use reverse genetics to pinpoint genes required for the differentiation and maintenance of these cells. Our analyses are a first step toward defining the mechanisms underlying the development of erythrophore-mediated red coloration in Danio and reveal striking parallels with the mechanism of red coloration in birds.
Highlights
Red and orange pigments deposited in the skin provide key signals that are subject to sexual or natural selection
We focused on D. albolineatus since erythrophores are abundant in this species and are separated spatially from other pigment cells, an arrangement likely to facilitate analysis (Goodrich and Greene, 1959)
Erythrophores occur at lower densities and were more likely to be binucleated (Figure 2B, middle and right panels; Figure 2—figure supplement 1C and D), a characteristic associated with a mature state of differentiation in stripe melanophores of zebrafish (Saunders et al, 2019)
Summary
Red and orange pigments deposited in the skin provide key signals that are subject to sexual or natural selection. Red chromatophores are known as erythrophores, whereas yellow or orange chromatophores are referred to as xanthophores Besides accumulating carotenoids, both cell types can produce and retain pteridine pigments that sometimes contribute to visible coloration (Schartl et al, 2016; Parichy, 2021). By screening candidate genes identified through transcriptomic comparisons of erythrophore- and xanthophore-containing fin tissues, we demonstrate requirements for several genes in red or yellow coloration These include loci encoding a cytochrome P450 monooxygenase, belonging to the same protein family as an enzyme previously implicated in avian red coloration (Lopes et al, 2016), as well as two genes not previously implicated in red coloration. These results lay the groundwork for future biochemical analyses of carotenoid processing, dissection of mechanisms of erythrophore fate specification, and comparative analyses of species-s pecific losses or gains of erythrophore-dependent coloration
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