Fig. 2. (A) Schematic diagram of the Nfatc1 promoter/enhancer reporter constructs. (B) Transient transgenic embryos following X-gal staining documents that the 6.2-kb NheI-XhoI P1 promoter-reporter (NX-lacZ) does not produce endocardial gene expression at E11.5. However, the BB-HSP-lacZ enhancer-reporter, containing 4.1 kb BssHII-BssHII fragment of the P2 (intron 1) regulatory region, linked to the HSP68 minimal promoter, is able to drive expression specifically in the endocardial lumen of the atrioventricular canal (AVC) and in the conal (c) and truncal (t) regions of the developing outflow tract. No expression is detected in the atrium (a) or ventricle (v) or in the extracardiac vasculature. (C) Table summaries this group of transgenic experiments. TG, transgenic embryos; ECS, endocardial-specific expression; ET, ectopic expression.