25 September 2015
Department of Biosystems Science and Engineering
Developmental mechanisms are highly conserved, yet act in embryos of very different sizes. How scaling is achieved has remained elusive. Quantitative data from the Drosophila wing imaginal disc reveals that the Decapentaplegic (Dpp) morphogen gradient scales with the outgrowing tissue, while the amplitude of the Dpp gradient increases continuously. I will present a generally applicable mechanism for dynamic scaling on growing domains which quantitatively agrees with data from the Drosophila wing imaginal disc. I will further show that pre-steady state diffusion-based dispersal of morphogens not only permits scaling but results in a zone within the growing domain where the concentration remains constant over the patterning period, in spite of the increasing gradient amplitude. The position of the zone, predicted based on quantitative data for the Dpp morphogen, corresponds to where the Dpp-dependent gene expression boundaries of spalt (sal) and daughters against dpp (dad) emerge. The patterning mechanism also explains the extraordinary robustness that is observed for variations in Dpp production, and offers an explanation for the dual role of Dpp in controlling patterning and growth. Pre-steady-state dynamics are pervasive in morphogen-controlled systems, thus making this a probable general mechanism for the scaled read-out of morphogen gradients in growing developmental systems.
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