Figure 5. Requirements of Six binding sites for the activities of some but not all tested mesodermal enhancers.

(A) Loss of GFP (green) reporter expression in the Lb-expressing SBM (magneta) driven by a version of the lbl enhancer in which the Six4 binding sites are inactivated (lbl^noSix-GFP) in stage 14 embryos. Compare to the WT version of the lbl enhancer (lbl^WT-lacZ) in Figure 2A. (B) The GFP (green) reporter driven by the WT ap enhancer (ap^WT-GFP) is active in a small subset of lateral Mef2-positive FCs (magenta) in stage 12 embryos. (C) De-repression of the GFP reporter (green) into additional Mef2-positive (magenta) mesodermal cells in a version of the ap enhancer in which the Six4 binding sites are mutated (ap^noSix-GFP) in stage 12 embryos. (D) The GFP (green) reporter driven by a version of the mib2 enhancer in which Six4 binding sites are inactivated (mib2^noSix-GFP) co-expresses with ßgal (magneta) driven by a WT version of the mib2 enhancer (mib2^WT-lacZ) in stage 12 embryos. Compare to WT versions of both GFP and lacZ reporters in Figure 2E. (E) The GFP (green) reporter driven by a version of the Ndg enhancer in which Six4 binding sites are mutated (Ndg^noSix-GFP) also co-expressed with ßgal (magneta) driven by a WT version of the Ndg enhancer (Ndg^WT-lacZ) in stage 12 embryos. The ventral Ndg reporter-expressing cells are not present in the indicated focal plane but do not express the GFP reporter (data not shown). Compare to WT versions of both GFP and lacZ reporters in Figure 2G.