a) genomic environment of six conserved enhancers used in this study. A 50kb genomic interval bracketing each enhancer is shown, including intron/exon structure of overlapping genes (black) and conservation in 17 vertebrates (color shaded boxes; [26]). All enhancers included an ultraconserved core region (Suppl. Table 1; [27]). b) Single and compound enhancer constructs for in vivo testing. c) Enhancer activity of single elements at mouse embryonic day 11.5. d)-i) In vivo activity of heterologous compound enhancers. d) E1+E2, e) E2+E5, f) E3+E4, g) E1+E5, h) E5+E6, i) E1+E2+E5+E6. Only one representative embryo is shown for each single and compound pattern, see Suppl. Table 2 for reproducibility across independent transgenic animals.