Fig. 1. The -58/-56 kb Myf5 enhancer controls gene activity in muscle progenitor cells in limbs and myotomal cells in somites. Whole-mount ß-gal staining of embryos from stable mouse lines that harbor the enhancer containing transgene Myf5-IV. The transgene is strongly expressed in limb buds and myotomes between E10.5 and 11.5 (A-C) and persists in fetal muscles of an E13.0 embryo (D). Strictly myotomal expression is illustrated on the transverse section of an E10.5 embryo (inset in A). Two embryos carrying the control transgene Myf5-XX that lacks the enhancer show no expression in limb buds and significantly reduced expression in somites (E,F). Schematic drawings below the images illustrate the transgene constructs.