Abstract
How morphogen gradients control patterning and growth in developing tissues remains largely unknown due to lack of tools manipulating morphogen gradients. Here, we generate two membrane-tethered protein binders that manipulate different aspects of Decapentaplegic (Dpp), a morphogen required for overall patterning and growth of the Drosophila wing. One is “HA trap” based on a single-chain variable fragment (scFv) against the HA tag that traps HA-Dpp to mainly block its dispersal, the other is “Dpp trap” based on a Designed Ankyrin Repeat Protein (DARPin) against Dpp that traps Dpp to block both its dispersal and signaling. Using these tools, we found that, while posterior patterning and growth require Dpp dispersal, anterior patterning and growth largely proceed without Dpp dispersal. We show that dpp transcriptional refinement from an initially uniform to a localized expression and persistent signaling in transient dpp source cells render the anterior compartment robust against the absence of Dpp dispersal. Furthermore, despite a critical requirement of dpp for the overall wing growth, neither Dpp dispersal nor direct signaling is critical for lateral wing growth after wing pouch specification. These results challenge the long-standing dogma that Dpp dispersal is strictly required to control and coordinate overall wing patterning and growth.
Highlights
How morphogen gradients control patterning and growth in developing tissues remains largely unknown due to lack of tools manipulating morphogen gradients
One is HA trap based on anti-HA scFv that traps HA-Dpp through the HA tag to mainly block Dpp dispersal, the other is Dpp trap based on anti-Dpp Designed Ankyrin Repeat Protein (DARPin) that directly binds to Dpp to block Dpp dispersal and signaling in the source cells. These tools allowed us to distinguish the requirements of Dpp dispersal and cell-autonomous signaling in the source cells for wing pouch growth and patterning. We show, using these tools, that while posterior patterning and growth require Dpp dispersal, anterior patterning and growth largely proceed without Dpp dispersal but require cell-autonomous Dpp signaling in the source cells
How can relatively normal patterning and growth be achieved without Dpp dispersal? Since phosphorylated Mad (pMad) was completely lost in dpp mutants (Fig. 4g) but remained active in the source cells upon HA trap expression (Fig. 3 and Supplementary Fig. 2a−j), we asked whether Dpp signaling in the source cells could account for the minor phenotypes caused by HA trap
Summary
How morphogen gradients control patterning and growth in developing tissues remains largely unknown due to lack of tools manipulating morphogen gradients. One is “HA trap” based on a single-chain variable fragment (scFv) against the HA tag that traps HA-Dpp to mainly block its dispersal, the other is “Dpp trap” based on a Designed Ankyrin Repeat Protein (DARPin) against Dpp that traps Dpp to block both its dispersal and signaling Using these tools, we found that, while posterior patterning and growth require Dpp dispersal, anterior patterning and growth largely proceed without Dpp dispersal. Small, high-affinity protein binders, such as nanobodies, single-chain variable fragments (scFvs), Designed Ankyrin Repeat Proteins (DARPins), and others, have emerged as versatile tools to fill this gap By fusing these protein binders to wellcharacterized protein domains and expressing the fusion proteins in vivo, protein function can be directly manipulated in a predicted manner[1,2,3,4,5]. The precise contribution of Wg dispersal requires further investigations[13,14,15,16], the study raises the question of how important morphogen dispersal is for tissue patterning and growth in general
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