Fig. 6. MAD and CRE sites are important for the DPP response, both in the embryo and in COS cells. (A) Luciferase activity of the lab550 enhancer and two mutant derivatives upon stimulation of DPP signaling in transfected COS-1 cells. The DPP response is expressed as -fold activation over the basal activity of each reporter plasmid alone, which is indicated at the bottom of the graph (see the legend of Fig. 4 for details). The introduction of the four MAD mutations and the introduction of the four CRE mutations lead to a reduction in the response to DPP signaling from 70-fold to 14-fold and 11-fold, respectively. In the embryo, lab550-driven expression (B) was reduced by the introduction of mutations in either the MAD sites (C) or the CRE sites (D). 92/546m300-driven expression (E) was also reduced by mutations in the MAD sites (F) and was hardly detectable after mutating the CRE sites (G).