Fig. 6

Larval myofibers are distinct from their adult counterparts. (A) Illustrations of zebrafish at larval, juvenile and adult stages reflect relative size differences; dissociated myofibers were subjected to imaging analysis. (B) Representative confocal images of dissociated myofibers collected from palmuscle-Dual at 14 dpf, 70 dpf, and 1.7 years of age. (C?E) Quantification of myofiber length (C), volume (D), and total nuclear number within each myofiber (E). (F) Real-time monitoring of oxygen consumption rate (OCR; percentage) from freshly dissociated larval and adult myofibers. Mitochondrial stress modulators: oligomycin (oligo), FCCP, and antimycin A/rotenone (AA/Rot). Solid lines indicate mean and colored shadows highlight standard error. (G, H) Quantitative changes in spare respiratory capacity (SRC; percentage) and extracellular acidification rate (ECAR; percentage). (I) Timeline of the treatment and tracking schemes. (J) Histological examinations of the tagged myofibers in the middle-trunk region of animals at 10 and 16 mpf. White dashed line encircles the area containing fast muscle fibers. Of note, Tg(myofiber:iCre#2) labeled both fast and slow myofiber populations at adult stages. White asterisks highlight the slow myofiber domains. F310 Ab stains fast myofibers. (K, L) Quantification of tagged myofiber number (K) and percent area occupied by the tagged myofibers (L). The tagged myofiber numbers from three consecutive cross-sections were counted and averaged for each individual. Of note, comparisons were made between animals with at least 10% of the labeled area per cross-section. Data from biological replicates are shown as violin plots (solid lines, median; dashed lines, quartiles; C?E), mean ± standard error (G, H) and mean ± standard deviation (K, L). Significance was examined by Kruskal?Wallis test with Dunnett?s correction (C?E); two-tailed Student?s t-test (G, H) or two-tailed Mann?Whitney test (K). Percent differences and P values are shown above the horizontal lines for intergroup comparisons. n = number of myofibers (C?E) or animals (K, L). Stitched image (B, J). Scale bars, 100 µm (B); 1 mm (J). dpf, days post-fertilization. mpf, months post-fertilization. Source data are available online for this figure.