Scaling a Dpp morphogen gradient through feedback control of receptors and co-receptors. Zhu et al.
Gradients of decapentaplegic (Dpp) pattern Drosophila wing imaginal discs, establishing gene expression boundaries at specific locations. As discs grow, Dpp gradients expand, keeping relative boundary positions approximately stationary. Such scaling fails in mutants for Pentagone (pent), a gene repressed by Dpp that encodes a diffusible protein that expands Dpp gradients. Although these properties fit a recent mathematical model of automatic gradient scaling, that model requires an expander that spreads with minimal loss throughout a morphogen field. Here we show that Pent’s actions are confined to within just a few cell diameters of its site of synthesis, and can be phenocopied by manipulating non-diffusible Pent targets strictly within the Pent expression domain. Using genetics and mathematical modeling we develop an alternative model of scaling, driven by feedback down-regulation of Dpp receptors and co-receptors. Among the model’s predictions is a size beyond which scaling fails—something we observe directly in wing discs. These data support a publication in Developmental Cell, June 22, 2020.