Figure 2.

Cell cycle progression and cell fate decisions are dysregulated in regenerating sdc3^−/− muscles in vivo. (A–G) Proliferation is impaired in sdc3^−/− SCs. Sections from wild-type TA muscles show fewer BrdU⁺ cells (arrows in A indicate BrdU⁺ cells; E shows a quantification of A), more P-H3⁺ cells (arrows in B indicate P-H3⁺ cells; F shows a quantification of B), and fewer TUNEL⁺ cells (C) than those from sdc3^−/− TA muscles (G shows a quantification of C). (D and J) Cell fate decisions are altered in sdc3^−/− SCs. The number of Pax7⁺ sublaminar cells (SCs) per tissue area is reduced (arrows in D indicate Pax7⁺ cells; H shows a quantification of D), the myofiber cross-sectional area is increased (I), and the total number of myofibers per tissue area is reduced (J) in sdc3^−/− TA muscles 3 mo after injury compared with wild-type muscles. Medians of the myofiber cross-sectional area distribution for each genotype at 3 mo after injury are shown in I. Curves in I represent polynomial functions that best fit the plotted myofiber size distributions; broken line, wild type; solid line, sdc3^−/−. A minimum of 1,000 myofibers and four sections per each biological replica were scored. Inset panels in B–D show enlarged views of the boxed regions. Open bars, wild type; shaded bars, sdc3^−/−. Error bars indicate SEM. **, P < 0.01. Bars, 30 µm.