(G - H) Quantification of the expression patterns in developing embryos, projected along the A-P axis for MED4 (G) and for pain (H) for the different promoter variants, respectively. The errors bars are standard deviations from 3-4 biological replicates measurements (different embryos). The fluorescence background measured in a wild-type embryo is shown as yellow dotted lines. The fluorescence patterns for pain recapitulate the typical hb_ant enhancer activity, characterized by a gradient of reporter expression (black arrow in H) with a sharp drop at around A-P=50%, which was expected for a developmental gene. An exemplary AP profile for the hb_ant enhancer is shown as grey empty triangles (the background was adjusted at about 3000 a.u for better comparison). In contrast, the constructs containing the constitutive MED4 gene promoter lead to a stronger and more homogeneous expression with an only slightly enhanced expression level at the anterior tip (black arrow in G). 