Fig. 2. Deletion of floxed Myog sequences using CMV-cre and analysis of embryonic skeletal muscle at E18.5. (A) Southern genome hybridization of yolk-sac DNA digested with EcoRI from embryos resulting from a Myog^flox/+;CMV-cre/+ intercross and probed with Myog cDNA. Deletion of the floxed myogenin sequences produced a 3 kb EcoRI fragment representing the Myog^flox allele. The 4 kb EcoRI fragment represents the wild-type allele (Myog⁺). Lanes 1 and 2 show DNA from Myog^flox/flox embryos; lanes 3 and 4 show Myog^flox/+ embryos; and lanes 5 and 6 show wild-type embryos. (B) Diaphragms of E18.5 Myog^+/-, Myog^-/- and Myog^flox/flox embryos. The genotype is shown above each image. Scale bar: 100 µm. (C) Hindlimb sections from E18.5 Myog^flox/+ and Myog^flox/flox embryos immunostained with polyclonal M225 anti-myogenin antibody. Arrows indicate positively stained cells. Scale bar: 100 µm.