Fig. 6. E-boxes are required for Bop expression in developing skeletal muscle. Mutation of the three E-boxes in the Bop upstream region (construct 7 in Fig. 2B) caused a loss of skeletal muscle expression without affecting expression in the heart, as seen in a whole-mount lateral view (A,B) and transverse sections (C) of five independent F0 transgenic embryos at E11.5. a, atrium; rv, right ventricle; lv, left ventricle; oft, outflow tract.