Robustness of the Dpp morphogen activity gradient depends on negative feedback regulation by the inhibitory Smad, Dad

Abstract

Developmental patterning relies on morphogen concentration gradients, which generally provide invariable positional information despite genetic fluctuations. Theoretical studies have predicted robust patterning; however, little experimental evidence exists to support this idea. In this report, we examine the robustness of the Decapentaplegic (Dpp) (a Drosophila homologue of bone morphogenetic protein [BMP]) activity gradient in the presence of fluctuations in Dpp receptor levels. Dpp activity can be measured by the degree of phosphorylation of Mothers against dpp (Mad), a major signal transducer. We determined that phosphorylated Mad (pMad) levels remain constant when an extra copy of thickveins (tkv), which encodes the receptor, is introduced into the wild-type background. Higher Tkv levels, expressed under the control of an artificial promoter, result in constant pMad levels. This prompted us to study the mechanisms that underlie pMad level maintenance even when Tkv levels are increased. We focused on the inhibitory Smad, daughters against dpp (dad), which is induced by Dpp signaling and negatively regulates Dpp activity. In the absence of dad, pMad levels significantly increase when Tkv levels increase. These results suggest that Dpp activity gradient robustness when Tkv levels increase depends, at least in part, on negative feedback regulation by dad.

SMOC can act as both an antagonist and an expander of BMP signaling

“…In the absence of pent , medial-lateral diffusion of Dpp will be restricted by Dally because there is no Pent to compete for Dally binding sites (Figure 8B). The resulting high level of medially localized Dpp signaling, indicated by Mad phosphorylation (pMad) (Vuilleumier et al, 2010), has been shown to induce expression of the inhibitory Smad, daughters against dpp ( dad ), promoting a negative feedback loop to limit the range of Dpp signaling (Tsuneizumi et al, 1997; Ogiso et al, 2011). In the absence of dally , Dpp diffusion will also be restricted as Dally-binding is required to establish both Dpp and Pent gradients (Vuilleumier et al, 2010).…”

Regulatory Mechanisms of Metamorphic Neuronal Remodeling Revealed Through a Genome-Wide Modifier Screen in Drosophila melanogaster

“…First, we tested whether the suppression caused by RNAi for Dad , Oli , and Myc could be phenocopied with independent loss-of-function alleles for each gene (no independent alleles were available for CG10565 ). We crossed the test stock to Dad 212 (Ogiso et al 2011), Myc 2 (Maines et al 2004), Myc 4 (Pierce et al 2004), Oli Δ 9 (Oyallon et al 2012), and their respective genetic background strains at 30°. Dad 212 , Myc 4 , and Oli Δ 9 contain small deletions and are likely molecular null alleles, and Myc 2 is the result of a point mutation and is a strong, homozygous lethal allele.…”

Robust and precise morphogen-mediated patterning: trade-offs, constraints and mechanisms

“…This approach has been generally applied for studying the formation and robustness of morphogen gradients [17][18][19][20]26]. We use the experimental observations of the wing disc in Drosophila [28,32,35,36] to constrain and calibrate our model, which may be applied to other morphogen-mediated patterning systems.…”

“…Experimental evidence in the Drosophila wing disc reveals complex roles of the receptor in morphogenmediated patterning, in which Dfz2 (Wg receptor) broadens the range of Wg action by stabilizing it from degradation [8] and overexpressing Tkv (Dpp receptor) shrinks the Dpp gradient [27]. Both experimental [28] and theoretical [29] studies suggest that downregulation and overexpression of Tkv have crucial effects on the shape and robustness of morphogen activity.…”