Strikingly, CD45+:Sca1+ cells expressed Myf5 (data not shown) and MyoD (Figure 2F–2I) protein after infection only with Pax7 (HAN-Pax7), and not with puromycin-alone control virus (HAN-puro), indicating that these cells undergo myogenesis in response to Pax7. This evidence concerns the gene MYF5 and infection.