Fig. 1.
Functional screen and identification of epicardial enhancers. (A) Epicardial lacZ expression in E11.5 mouse hearts 1 to 3 days after transfection of a CMV-lacZ plasmid. Whole-mount and transverse-section views are presented. (B and C) Enhancer activity of each conserved region (CR) in the epicardium [(B), n = 2 to 4 hearts] and in HEK293 cells [(C), n = 3] (mean ± SEM). (D) Relative activity. The data for Raldh2 CR2 and Wt1 CR14 are highlighted in red. (E and F) Raldh2 CR2 and Wt1 CR14 are sufficient and necessary to direct epicardial gene expression. Displayed are transgenic hearts that express a nuclear lacZ (nlacZ) driven by an enhancer (left), an EGFP reporter in a control BAC (middle), or an EGFP reporter in an enhancer-deleted BAC (right). The number of embryos that show epicardial reporter activity out of the total number of transgenic embryos is shown. Scale bars, 200 μm. *P < 0.05; **P < 0.01.