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Figure 4
(A) Unpigmented cells of the xanthophore lineage, marked by aox5:nucEosFP transgene expression (see Main text), present at 7.0 mm SL had acquired a pale orange color 1 day later. (Representative of all N = 7 fish examined by repeated imaging during larval development.) Insets show higher magnification images of a corresponding region. (B) Example of a photoconverted, initially unpigmented cell (d0, 7.0 mm SL) that yielded a clone containing both erythrophores and xanthophores (d35, 15.0 mm SL; representative of four of seven clones, with remaining clones containing erythrophores only). Fish were treated with epinephrine to contract pigment before imaging. Arrows indicate erythrophore autofluorescence from red carotenoid pigment, which accumulates adjacent to nuclei following epinephrine treatment; approximate positions of nucEosFP+ nuclei in brightfield images are shown with dashed outlines. Insets, proximal and distal cells in the clone. (C) Percentages of clones containing only erythrophores, only xanthophores, or both cell types. Numbers above bars indicate clone sample sizes examined. In these analyses pigment cells and progenitors stably expressed aox5:nucEosFP (7.5, 8.5 mm SL) or mosaically expressed a different transgene, mitfa:nucEosFP (7.0 mm SL), that had been injected into embryos at the one-cell stage. In zebrafish, mitfa (melanophore-inducing transcription factor a) is expressed by pigment cell progenitors, as well as melanophores and xanthophores (Lister et al., 1999; Saunders et al., 2019), and we found in D. albolineatus that mitfa:nucEosFP was expressed in these cells as well as orange cells of larvae and erythrophores of adults. mitfa:nucEosFP was used for fate mapping at early stages owing to its more robust expression in unpigmented cells. Scale bar: 50 μm.
Bipotential precursor to erythrophores and xanthophores revealed in the fin by fate mapping.