(a–c) Whole mounts showing cardiac-specific β-gal activity in transgenic mouse embryos with 4.2 kb enhancer-lacZ construct (Supplementary Fig. 2a) at indicated time points. (d) Transverse section of (c) showing β-gal expression in pharyngeal mesoderm (pm), pharyngeal endoderm (pe), dorsal aorta (da), myocardium (mc), endocardium (ec). (e,f) β-gal expression in embryonic day (E) 15.5 (e) or post-natal (P21) (f) heart. Ao, aorta; pa, pulmonary artery. (g,h) Transverse sections of (f); co, coronary artery. (i,j) Section in-situ hybridization of miR-145 in P21 heart section. (h) and (j) represent higher magnification of boxed areas. (pcm, precardiac mesoderm; ht, heart; h, head; ot, outflow tract; rv, right ventricle; lv, left ventricle; cv, cardinal vein; ra, right atrium; la, left atrium).