Morphogens are secreted proteins that regulate key processes during development, such as cell proliferation, growth and patterning. They are produced from a localized source and somehow establish a concentration gradient. Decapentaplegic (Dpp), the Drosophila BMP, is expressed at the anterior-posterior (AP) boundary of the wing imaginal disc, generating an AP morphogenetic gradient that regulates the expression of key genes involved in the wing development. Despite the broad knowledge regarding its function, the mechanism by which the Dpp gradient is established and how it synchronizes proliferation and patterning has been under debate for years.
In order to analyze the behavior of Dpp and its effects in development, we have modified the endogenous dpp locus by CRISPR/Cas9, replacing the first coding exon by a transgenic dpp tandem. This gene tandem can be manipulated via FLP/FRT recombination. With the help of this system, we studied the behavior of the Dpp gradient, tracking the intracellular and extracellular Dpp populations.
We have imaged and measured Dpp gradient formation, protein degradation and other parameters involved in the movement of Dpp, in an effort to model the gradient dynamics. Our results show a fast protein turnover in the producing cells, as well as a high retention of the extracellular Dpp population. Our current data suggest that the gradient is generated by restricted Dpp diffusion and oppose to a free diffusion model, where fast protein degradation is required.