Fig. 2. A transcriptional enhancer from Mef2c is sufficient to direct expression to the anterior heart field in vivo. A 6142 bp fragment of the mouse Mef2c gene was cloned into the lacZ reporter plasmid HSP68-lacZ and used to generate transgenic mice. Representative X-gal stained, transgenic embryos are shown at 7.5 days post coitum (dpc) (A), 8.0 dpc (B), 9.5 dpc (C,D), and 11.5 dpc (F,G). X-gal stained hearts are shown from a transgenic fetus collected at 16.5 dpc (I) and a transgenic adult dissected at 12 weeks of age (J). (E,H) Transverse sections of transgenic embryos collected and X-gal stained at 9.5 dpc and 11.5 dpc, respectively. No expression was observed outside the anterior heart field at any stage. (A) Parafrontal view; (B,C,F) lateral views from the right; (D,G,I,J) ventral views. BA, branchial arches; LA, left atrium; LV, left ventricle; NT, neural tube; OFT, outflow tract; PA, pulmonary artery; RA, right atrium; RV, right ventricle. Arrowheads denote expression in the pharyngeal mesoderm/anterior heart field. Five independent transgenic lines all displayed nearly identical patterns of expression.