Fig. 2: Cartilage ablation disrupts myofiber development in zebrafish.

a Myofibrils with cross-sectional images of am muscle at 81 hpf are shown. b The length of individual muscle cells at 81hpf are shown in the box plot (median bounded by IQR, whiskers=1.5x IQR). ^*P < 0.0001, unpaired two-tailed Student’s t test (n = 27, 31, and 24 for ctrl, sox9, and runx2b, respectively). c Number of myofibers per muscle were quantified from cross-sectional images of am muscle at 81hpf and shown in the box plot (median bounded by IQR, whiskers =1.5x IQR). ^*P < 0.0002, unpaired two-tailed Student’s t test (n = 7, 10, and 7 for ctrl, sox9, and runx2b, respectively). d Individual muscle cells at 81hpf are shown with internal nuclei. e Muscle cells at 81hpf were classified according to the number of nuclei and the percentage of muscle cells is shown. On average, 5 different myofibers were counted for nuclei per embryo. Values are means of n = 5 embryos ±SD. ^*P < .0001, two-sided Fisher’s exact test. f The sarcomere structures of control and perturbed embryos are visualized with anti-MyHC staining at 81hpf. g The actin organization is visualized in am muscle at different times in a control embryo. The same staining is shown as a heatmap on the right, in which 16-bit intensity value was normalized to that of cortical action in pq cartilage and log-transformed (base: 2). The boundary between am muscle and pq cartilage is shown with a dashed line. The pink arrowhead indicates the tip of the am muscle. h The actin organization is visualized in am muscle at 52hpf in different perturbation conditions. The box area is magnified and shown below. The boundary between am muscle and pq cartilage is shown with dashed line. Red arrowhead shows actin at the cartilage-muscle interface. Blue arrowheads show the actin structure of myofibrils. Images are 10 μm oblique slices. i The expression patterns of the indicated genes in control and perturbed embryos are visualized with in situ hybridization at 72hpf. Scale bar; (a), (d), (h), and (i, left inset) 20 μm. f 5 μm. (i, right panels) 50 μm. pq palatoquadrate, am adductor mandibulae, IQR interquartile range.