Fig. 3

NHOs are derived from Prrx1 expressing FAPs. a Prrx1^ZsG mice received an intramuscular injection of CDTX with or without SCI, and muscle samples were harvested at the indicated time points and processed for IHF. Representative images illustrating the distribution of ZsGreen⁺ FAP-derived cells in (b) uninjured muscle and c regenerated injured muscle 14 days post-CDTX injection in the Prrx1^ZsG mice without SCI (n = 3 mice/group). d Representative images from the Prrx1^ZsG mice with SCI and CDTX-mediated muscle injury 28 days post-surgery: IHF illustrating the colocalization of ZsGreen⁺ FAP-derived cells with (i–v) collagen I⁺ matrix (red) or (vi-x) osteocalcin⁺ osteoblasts (red). (iii-v) are enlarged images of the yellow box in (ii), whereas (viii-x) are enlarged images of the yellow box in (vii). The white dashed line indicates the boundary between regenerating muscle and the fibrotic area containing NHOs. Nuclei stained in DAPI (blue). White circles indicate osteocalcin⁺ osteoblasts that also express ZsGreen. Scale bars: (b, c) 100 μm; (d) (i) 300 μm (ii, vii) 100 μm (iii-v, viii-x) 50 μm