Patterning of body parts in multicellular organisms relies on the interpretation of transcription factor (TF) concentrations by genetic networks. To determine the extent by which absolute TF concentration dictates gene expression and morphogenesis programs that ultimately lead to patterns in Drosophila embryos, we manipulate maternally supplied patterning determinants and measure readout concentration at the position of various developmental markers. When we increase the overall amount of the maternal TF Bicoid 5-fold, Bicoid concentrations in cells at positions of the cephalic furrow, an early morphological marker, differ by a factor of two. This finding apparently contradicts the traditional threshold-dependent readout model, which predicts that the Bicoid concentrations at these positions should be identical. In contrast, Bicoid concentration at target gene expression boundaries is nearly unchanged during early developmental times, but adjusts dynamically toward the same 2-fold change as development progresses. Thus the Drosophila segmentation gene network responds faithfully to Bicoid concentration during early development, in agreement with the threshold model, but subsequently partially adapts in response to altered Bicoid dosage, driving segmentation patterns towards their wild-type positions. This dynamic response requires other maternal regulators such as Torso and Nanos, suggesting that integration of maternal input information is not achieved through molecular interactions at the time of readout, but through the subsequent collective interplay of the network.

Liu et al. - LiveImaging_data_structureLiveImaging_data_structure.mat contains a data structure named "FlyLines" with Bicoid-GFP intensity gradient and cephalic furrow (CF) position measurements of fly embryos from live two-photon imaging for 29 fly lines.Liu et al. - Immunofluorescence_data_structureImmunoFluorescence_data_structure.mat contains a data structure named "Sessions" that contains raw gap ( Hb, Kr, Gt and Kni) and pair rule (Eve) gene expression (protein) intensity profiles measured using immunofluorescence imaging for fly embryos during n.c. 14 for 6 fly lines from our Bicoid-GFP fly line library.Liu et al. - BcdGFP_embryos_raw_dataHigh-resolution images of 28 embryos acquired by live two-photon microscopy; dorsal view, coronal plane (linear pixel dimension 0.46 micrometer). Embryos express Bcd-GFP fusion protein in a bcdE1 null mutant background (flyline 2XA). For 23 embryos two time points are provided: 16+/-2 min after mitosis 13 (for Bicoid gradient measurement) and 67+/-2 min after mitosis 13 (for cephalic furrow position measurement). Two additional embryos are provided for early time point (09 and 12); three additional embryos are provided for late time point (15, 24 and 28). Embryo 05 is missing from dataset. This dataset reproduces gradients in Figure 1C of main text.