Fig. 2. Hypodermal xanthophore origins and TH-dependence.

(A) Autofluorescing aox3:nEos⁺ EL xanthophores (left panels; post-photoconversion: upper right). Later, yellow pigment was absent and each cell had divided (middle right). In the juvenile, 3 cells redifferentiated (arrowheads) and one remained unpigmented (arrow). Overall, 86 photoconverted EL xanthophores generated 71 adult xanthophores and 78 unpigmented cells (n=44 larvae); including all stages examined, marked cells had a 59% probability of dividing (n=82 larvae, 190 EL xanthophores, 283 cells later). (B) In a juvenile in which all aox3⁺ cells had been photoconverted at 5 dpf, two photoconverted EL-derived xanthophores were visible (arrowheads) but so were cells expressing only unconverted nEos (arrows), one of which had differentiated (inset); 9 of 15 juveniles had unconverted cells that developed after 5 dpf (5.8±1.9, range 1–19 cells), of which 54% had differentiated as xanthophores. (C) In thyroid-ablated fish, the likelihood of photoconverted EL xanthophores (arrowheads) persisting into the juvenile did not differ from controls (Χ²=0.01, d.f.=1, P=0.9; Mtz, n=18 larvae; DMSO, n=13 larvae, 20 EL xanthophores); some cells initiated aox3:nEos expression only after 5 dpf (e.g., arrow). Scale bars: 60 μm.