Abstract
The gradient of Decapentaplegic (Dpp) in the Drosophila wing has served as a paradigm to characterize the role of morphogens in regulating patterning. However, the role of this gradient in regulating tissue size is a topic of intense debate as proliferative growth is homogenous. Here, we combined the Gal4/UAS system and a temperature-sensitive Gal80 molecule to induce RNAi-mediated depletion of dpp and characterise the spatial and temporal requirement of Dpp in promoting growth. We show that Dpp emanating from the AP compartment boundary is required throughout development to promote growth by regulating cell proliferation and tissue size. Dpp regulates growth and proliferation rates equally in central and lateral regions of the developing wing appendage and reduced levels of Dpp affects similarly the width and length of the resulting wing. We also present evidence supporting the proposal that graded activity of Dpp is not an absolute requirement for wing growth.
Highlights
Decapentaplegic (Dpp), the Drosophila BMP homolog, has served as a paradigm to characterize the role of morphogens in regulating patterning of developing tissues (Affolter and Basler, 2007; Restrepo et al, 2014)
In the developing Drosophila wing disc, Dpp is expressed in a central stripe that corresponds to the anterior-posterior (AP) compartment boundary, and its gradient provides a series of concentration thresholds throughout the tissue that set the transcriptional state of target genes in discrete domains of gene expression as a function of their distance from the source (Lecuit et al, 1996; Nellen et al, 1996)
We have used a collection of dpp-RNAi hairpins and the GAL4/UAS system combined with the temperature-sensitive Gal80 molecule to control the depletion of dpp expression in time and space and characterize the spatial and temporal requirement of Dpp in promoting the growth of the different regions of the wing primordium: the wing blade, the wing hinge and the body wall
Summary
Decapentaplegic (Dpp), the Drosophila BMP homolog, has served as a paradigm to characterize the role of morphogens in regulating patterning of developing tissues (Affolter and Basler, 2007; Restrepo et al, 2014). Graded activation of the Dpp transducer MAD and the inverse gradient of Brinker, a transcriptional repressor negatively regulated by Dpp, contribute to the transcriptional regulation of Dpp target genes in discrete domains (Affolter and Basler, 2007; Restrepo et al, 2014). The classical ‘steepness model’ proposes that the juxtaposition of cells sensing disparate levels of the morphogen promotes proliferative growth (Lawrence and Struhl, 1996; Rogulja and Irvine, 2005) This model is questioned by the observation that the Dpp-gradient scales with the size of the wing primordium and that the slope of the gradient does not change (Wartlick et al, 2011).
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