Fig. 4. Deletional analysis of the Gata4 lateral mesoderm enhancer identifies a highly conserved element that is necessary and sufficient for enhancer function in vivo. (A) Schematic diagram of the deletion constructs of the Gata4 lateral mesoderm enhancer. The genomic organization of the G2 region of Gata4 is depicted at the top. Red boxes represent three regions of high sequence homology between the opossum and mouse Gata4 genes, denoted as CR1, CR2 and CR3. The nucleotide positions of each deletion construct, relative to G2, are denoted on the left, and mesoderm expression directed by each construct is summarized by a plus (mesodermal expression) or a minus (no detectable mesodermal expression) to the right of the line representing each construct. The column on the far right indicates the number of independent transgenic lines or F0 embryos that expressed lacZ in the septum transversum and lateral mesoderm as a fraction of the total number of transgene-positive F0 embryos or lines examined. (B-H) Representative transgenic embryos for each of the deletion constructs depicted in A were collected at 9.5 dpc and X-gal stained. G2, G22 and G24 directed strong expression in the septum transversum (ST) and visceral mesoderm (B,D,F). G24 encompasses only the region surrounding the highly conserved CR2. G25 contains only 308 bp of CR2 and was sufficient to direct only very weak expression in septum transversum and gut mesoderm (G). Deletion of CR2 (2495-3738) from G2 to generate G26 completely ablated transgene activity (H). Arrowheads indicate visceral mesoderm.