Denominator Problems in a Muscle Stem Cell Study?

In a recent article, Cerletti et al. (2008) report the preparation of a new, highly myogenic subset of skeletal muscle satellite cells that bestows functional benefits when grafted into the dystrophic muscles of mdx mice. Cerletti et al. (2008) used FACS to sort these skeletal muscle precursors (SMPs), defined by a number of antigenic markers, from the population of cells adhering to freshly isolated muscle fibers of mice that express green fluorescent protein (GFP) as a genetic label. These SMPs were then grafted into the muscles of normal mice damaged by injection of a toxin or into the muscles of dystrophic mdx mice, which exhibit spontaneous muscle degeneration.