Fig. S1

col1a2:mCherry-NTR transgenic line allows the labeling of collagen-producing cells, and wt1a-derived cells express col1a2 after cryoinjury. (A) Immunofluorescence of heart sections with anti-col1a1 (green) and mCherry (red). Nuclei are counterstained with DAPI. (B–E) Merged and individual channels of the boxed area in A. Arrowheads mark mCherry⁺ cells that are surrounded by col1a1. (F–N) Lineage tracing of wt1a⁺ cells. (F) 4-Hydroxytamoxifen (4-OHT) was added to adult wt1a:CreER^T2;ubb:Switch uninjured fish 10 and 9 d before dissection. (G–N) Immunofluorescence staining with anti-col1a1 (green) and mCherry (red) of heart sections of uninjured hearts (G–J) or 7 d postinjury (dpi) hearts (K–N). Nuclei are DAPI-counterstained (blue). Arrowheads mark wt1a-derived cells. (O) Experimental scheme for tracing the fate of wt1a-derived cells expressing col1a2. The wt1a:CreER^T2 line was crossed with the col1a2:loxP-tagBFP-STOP-loxPmCherry- NTR line, in which mCherry-NTR is not expressed. Upon 4-OHT administration, recombination of loxP sites leads to activation of mCherry expression under the control of a col1a2 promoter. Hearts from animals at 7 dpi were dissected and sectioned. (P–S) Immunofluorescence of heart sections with antimyosin heavy chain (MHC; green), and mCherry (red). Nuclei are counterstained with DAPI. (Q–S) Merged and individual channels of the boxed area in P. Arrowheads mark mCherry⁺ cells, which express col1a2. ba, bulbus arteriosus; v, ventricle. [Scale bars, 25 μm (B, G, H, K, L, and Q) and 100 μm (A and P).]