FIGURE 3. SMP frequency is reduced in dystrophic mice.

Dystrophic disease in mdx animals is characterized by acute degeneration and regeneration of skeletal muscle during the first month of life, followed by a mild chronic dystrophy that begins at ~6-8 wks. of age and lasts throughout life. (A) Immunostaining for dystrophin protein in wild-type (wt) C57BL/Ka mice reveals protein expression at the cell membrane of every myofiber. In contrast, the majority of myofibers in mdx mice lack dystrophin expression, with the exception of a small number (~1-6% of total myofibers in mice aged 10-20 wks (Wernig et al., 2005)) of revertant fibers generated by skipping of the mutated exon (Lu et al., 2000). Two revertant fibers in the mdx muscle section shown are marked by asterisks (*). (B and C) Flow cytometric analysis of SMP frequency in dystrophic mdx mice shows an ~3-fold decrease in the frequency of SMPs among myofiber-associated cells (B) and an ~2-fold decrease among Sca-1^- myofiber-associated cells (C) harvested from mdx muscle. *P<0.05, **P<0.01 (D and E) Double-sorted SMPs from mdx mice exhibited equivalent in vitro clonal plating efficiency (D, frequency of colony formation from single cells, as in Figure S3) and differentiation capacity (E, % of MyHC-expressing cells after culture in differentiation medium, as in Figure S3) as compared to SMPs sorted from wild type (wt) mice.