Delayed maturation and fiber type analysis of regenerating fibers in CHC22-transgenic mice.

A) Hematoxylin and eosin staining of transverse muscle sections from WT or CHC22 transgenic mice after cardiotoxin injection at day 0, on the indicated days (D). Control (CTRL) sections were prepared from uninjured muscle. On day 28, some CHC22 myofibers were similar in cross-sectional area and diameter to WT myofibers; however, smaller myofibers (<40 µm diameter, marked by asterisks) were more frequently observed in the CHC22-mice compared to WT mice (scale bar, 20 µm; n = 3). B) The mean cross-sectional area of myofibers with centrally located nuclei from WT (white bars) and CHC22-mice (black bars) was calculated and plotted for each indicated day after cardiotoxin injection. Control mice for each strain were not injected with cardiotoxin. There was a statistically significant difference in the average fiber cross-sectional area between WT mice and CHC22-mice on days 14 and 28 after injection (n = 3, evaluating 1200–2000 myofibers per mouse; **p<0.01), as determined by Student’s t test. C) Transverse sections of muscle from CHC22-mice and WT mice, harvested 28 days after cardiotoxin injection, were stained for NADH-TR in order to determine the myofiber type. Oxidative (red) myofibers appear dark, glycolytic (white) myofibers appear light and intermediate (pink) myofibers appear intermediate in color. D) Fibers in 28-day regenerating muscle from CHC22-mice (black bars) and WT mice (white bars) were classified by type and their cross-sectional area measured in pixels using ImageJ (n = 3, evaluating ∼1500 fibers per mouse, *p<0.05, by Student’s t test). E) The percent of each fiber type in 28-day regenerating muscle from CHC22-mice (black bars) and WT mice (white bars) from the analysis in D is plotted.