A genetic circuit that extends the useful range of a BMP morphogen arose alongside insect wing evolution

The range over which a morphogen gradient provides reliable positional information is limited by intrinsic noise. We identify a regulatory circuit that counteracts this constraint for Dpp, a BMP that organizes the anterior/posterior axis of Drosophila wings. The transcriptional repressor Brinker (Brk), a Dpp target, enhances positional precision by repressing Dad, an inhibitory Smad, thereby extending Dpp's effective range. Thus, Brk mediates a feedback circuit that selectively amplifies low-level Dpp signals as would a logarithmic amplifier. This circuit also achieves temporal integration, mitigating the inevitable noise penalty associated with amplification. Although a core component of BMP signaling in flies, Brk is found exclusively in insects. Phylogenetic and expression analyses in the apterygote insect Thermobia domestica suggest that Brk originated in insects and was incorporated into the BMP network in pterygotes, possibly to permit long-range signaling in wing primordia. Brk exemplifies how gene regulatory network (GRN) evolution can enhance developmental precision, thus opening the door to increased morphological complexity.