Fig. 2: Early epithelial and mesenchymal cell response to joint resection.

a, H&E staining of early injury response in ventral sections at 0 dpjr (n = 5), 1 dpjr (n = 4), 3 dpjr (n = 4), 7 dpjr (n = 6), and 14 dpjr (n = 8). Black arrowhead denotes epithelium and black arrow denotes mesenchyme. a’, Inset shows regenerating chondrocytes (arrow) and bone (asterisk) at 14 dpjr. Black dashed lines indicate cut sites. b, Repeated live imaging of Sox10:Cre;actb2:loxP-BFP-STOP-loxP-DsRed showing dynamics of BFP+ epithelia at the anterior cut site at 1, 10, 20, 30, 40, and 50 minutes post-joint-resection (n = 3). White dashed lines indicate cut sites. White arrows indicate areas of epithelial migration. c, Representative images of PCNA immunofluorescence in sagittal sections of uninjured joint tissue and at 1 dpjr, 3 dpjr, and 7 dpjr. Region of interest for quantification is outlined in magenta dashed lines and resected bone stubs are outlined in solid blue lines. d, Quantification of percentage of PCNA-positive nuclei showing significant increase at 3 dpjr (n = 4 for Uninjured, n = 5 for 1 dpjr, 3 dpjr, and 7 dpjr), p = 0.0017 for Uninjured vs. 3 dpjr, p = 0.0024 for 1 dpjr vs. 3 dpjr, one-way ANOVA with Tukey’s multiple comparison test. e, Representative images of RNAscope smFISH for hmga1a (yellow) and tnfaip6 (magenta) in sagittal sections of uninjured joint tissue and at 3 dpjr. Resected bone stubs are outlined in solid green lines. Region of interest for quantification at 3 dpjr is outlined with light grey dashed line. f, Quantification of smFISH hmga1a and tnfaip6 transcript expression from uninjured and 3 dpjr (n = 3 per time point), p = 0.0386 for hmga1a and p = 0.0487 for tnfaip6, two-tailed unpaired t-test. g-j, Representative image of RNAscope smFISH for hmga1a (yellow), tnfaip6 (magenta), and mki67 (cyan) in sagittal sections of the anterior cut site at 1 dpjr (n = 3) (g), with insets illustrating expression in the periosteal region (h), stromal region (i), and bone-adjacent mesenchyme (j). d, f, Error bars represent SEM. Scale bars, 100 µm (a), 25 µm (a’), 250 µm (b), 300 µm (c, e, g), 20 µm (e inset, h-j). AA, anguloarticular bone; IOP, interopercular bone; Q, quadrate bone; RA, retroarticular bone. Source data are provided as a Source Data file.