Lentiviral-infected muscle (control transduction (Tdxn), Smad3 shRNAs, non-target shRNA) was analysed 5 days after injury. a, Haematoxylin and eosin 10-μm cryosections of Smad3 shRNA-1; quantified in b; n = 15, *, **P ≤ 0.05; individual Smad3 shRNA-2, −3 data in Supplementary Fig. 10a; immunodetection of eMyHC myofibres with BrdU+ nuclei. Scale bar, 100μm; O, old; Y, young. c, Isolated satellite cells analysed by western blot for p15, p16, p21 and p27; quantified in d; *P ≤ 0.05, compared with non-target shRNA, control tdxn; data are means ± s.d., n = 3.