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Fig. 3 Sclerotome-derived fibroblasts give rise to new tenocytes after laser ablation. (A) Experimental timeline for fibroblast photoconversion and lineage tracing in col1a2Kaede; kdrl:EGFP embryos shown in (B) to (D). Ab, antibody; FISH, fluorescence in situ hybridization. (B) Representative images of one injured embryo from 52 hpf to 4 dpi. New Kaedered-positive fibroblasts (arrows) can be seen along the regenerating MTJ (dotted lines) from 1 to 4 dpi. n = 31 embryos. (C) Close-up view of a single Kaedered-positive fibroblast (arrows) at a regenerated MTJ (dotted lines) at 4 dpi. Depth projection (right) reveals several tenocyte-like processes (notched arrowheads) extending laterally from the cell. (D) Coimmunostaining and fluorescent mRNA in situ hybridization showing tenocyte marker tnmd expression (magenta) in the traced fibroblast (arrows) from (C). n = 51 of 64 cells from 21 embryos. Notched arrowheads indicate cell processes. (E) Protocol for Cre-mediated lineage tracing of sclerotome-derived fibroblasts after tenocyte ablation. (F) Representative images of a single injured embryo from 52 hpf to 4 dpi showing new mCherry+ tenocytes (arrows) at the regenerated MTJ. n = 12 embryos. Injury site is indicated by asterisks for all images. Scale bars, 25 μm [(B) and (F)] and 10 μm [(C) and (D)].