Fig. EV5

Larval myofibers are functionally distinct from adult myofibers. (A) Illustration of zebrafish at larval and adult stages, reflecting their relative size differences. (B, C) RT-qPCR analyses of expression of the intermediate filament desma (B), and sarcomere myosin myhc4 (C) in whole animals (14 dpf) or dissected muscle tissues (1.7 years of age). (D) Cross-sectional image of the middle-trunk region of the animal at 16 mpf with tagged myofibers. F310 Ab stains fast myofibers. (E) Magnified view of the trunk region indicated in (D) by red dashed box. (F) Individual tagged myofibers from cross-sectional images shown in pseudocolor (left) and with respective ROI numbers (right). (G) Timeline of the treatment and tracking scheme. (H) Schematic drawing of the progressive shift in hyperplastic growth zone across different developmental stages. (I–K) Histological examinations of the tagged myofibers in the middle-trunk region from larvae to adult stage, showing growth zone shift from the periphery at 29 dpf (I), to the interstitial space at 43 dpf (J), and ultimately to the deep region of the myotome at 16 mpf (K). White dashed boxes outline the magnified regions shown to the right of each panel. F310 Ab stains fast myofibers. Data from biological replicates are shown as mean ± standard error (B, C). Significance was examined by two-tailed Student’s t-test. Percent differences and P values are shown above the horizontal lines for intergroup comparisons. n = the number of biological replicates. Scale bars, 1 mm (D); 200 µm (E, I); 300 µm (J); 500 µm (K). dpf, days post-fertilization; mpf, months post-fertilization.