Fig. 6. (A) The activation of P1 promoter by the 781 bp sequence of the P2 regulatory region. Two short conserved elements (mouse/human) are located in this sequence with a cluster of binding sites for known transcription factors. (B) A schematic shows deletional analysis of the conserved putative endocardial enhancers (ECEs). (C-F) Whole-mount staining of E11.5 embryos (C,D) or isolated hearts (E,F) demonstrates that the ECE-HSP-lacZ, but not the ECE-HSP-lacZ reporter (data not shown), is sufficient to direct gene expression specifically in the pro-valve endocardial cells of forming valves and septa. ao, aorta; pt, pulmonary trunk; la, left atrium; ra, right atrium; lv, left ventricle; rv, right ventricle; avc, atrioventricular canal; arrow, AVC; arrowhead, OFT.