Fig. 4. Muscle degeneration and regeneration is required for RF expansion. (A) The percentage of central nucleated fibers in each strain of mice. The number of regenerating fibers decreases from mdx, to M3, to AX11 to CS1 mice aged 5 weeks and 10 weeks. (B) Correlation between the number of RFs and the percentage of centrally nucleated fibers in each strain at 10 weeks of age. (C) Correlation between the number of clusters and the percentage of central nucleated fibers in each strain at 10 weeks of age. The direct correlation between the number of RFs or clusters and centrally nucleated fibers suggests that the muscle degeneration and regeneration is an essential step in the expansion of RFs. Values are mean ± s.e.m. for 4-10 muscles per group. *Significant difference (P<0.05) from mdx muscles of the same age.