Engineering "Drosophila" development at the gene and protein levels

During development, cells must differentiate, divide, move and even die in a coordinated manner. These processes must be tightly organized in space and time in order to form functional structures. Cell behavior is coordinated by cell-cell communication via physical and chemical signals. These signals trigger distinct cellular responses depending on the genetic constrains of target cells. This cross- talk between the genome and the cellular environment is responsible of the stunning robustness of development. In this thesis, we have developed technologies to manipulate the genetic sequences and/or their readout (using CRISPR/Cas), the proteins (via protein binders) and the interaction between the two (by combining CRISPR/Cas and protein binders). Using these technologies, we have dissected two biological processes, the mechanisms of gradient formation via morphogens and the control of tissue development via enhancers.
Morphogens are locally-produced signals that form gradients in a target tissue and activate gene expression in a concentration-dependent manner. Gene regulation via morphogens is one of the best studied developmental patterning processes. Yet, the mechanisms by which morphogen gradients are established are still poorly understood. We have dissected the mechanisms of gradient formation of both Bone Morphogenetic Proteins (BMPs) and Hedgehog (Hh). We found that, in the imaginal wing disc of Drosophila, BMPs require the formation of heterodimers for its secretion. Our model explains how two ligands with different but overlapping expression patterns are responsible of the patterning of the wing. In contrast, our experiments on Hh support a model in which Hh travels in association with filopodial structures, in a lipid-dependent fashion. These filopodia bridge distant cells, mediating direct cell-cell exchange of the morphogen.
Enhancers are regions of the genome that integrate the changes in the nuclear proteome to trigger appropriate gene expression. We have focused on the study of the regulation of apterous (ap) during early wing disc development. ap coordinates the division of the wing into ventral and dorsal compartment. We have uncovered the role of the apterous early enhancer, identified some of its regulators and carefully described the consequences of its miss-regulation. Our study uncovered new molecular players of wing formation and sheds light on how the tissue axes are stablished.