Visualizing fluorescent muscle cell regeneration at single-cell resolution in engrafted prkdc^D3612fs mutant zebrafish. (A) Brightfield and fluorescent merged image of a prkdc^D3612fs mutant fish engrafted with myf5-GFP; mylpfa-mCherry double transgenic skeletal muscle cells at 8 dpt. (B) Confocal images of the same engrafted animal at 4 and 8 dpt. myf5-GFP⁺ muscle progenitor cells (white arrows) appear by 4 dpt and are positioned adjacent to a double-transgenic GFP⁺ and mCherry⁺ fiber by 8 dpt. (C) Merged confocal images of a myf5-GFP; mylpfa-mCherry muscle fibers at 12 dpt (left); the fibers eventually expressed only mCherry by 70 dpt (yellow arrow). (D and E) prkdc^D3612fs engrafted zebrafish with muscle cells isolated from mylpfa-zsYellow and mylpfa-mCherry transgenic donors. Whole animal image (left) with site of engraftment noted by a white arrow and high magnification confocal images (right, merged and single fluorescent confocal stacks are shown). Double fluorescently labeled muscle fiber denoted by white arrow. (E) Quantification of single and double fluorescently positive fibers in all animals analyzed (n = 13). Bars: (A and D, inset) 2 mm; (B) 50 µm; (C and D, rightmost panel) 200 µm.