Part I: Studies on the Drosophila selector gene apterous and compartment boundary formation

This PhD Thesis is divided into two different, separate parts.
In the first part, I focus on the transcriptional regulation of the Drosophila selector gene apterous (ap).
During animal development, selector gene activity is known to be important for the subdivision of cell populations into distinct functional units, called compartments. ap is essential for the subdivision into a dorsal and ventral compartment of the wing imaginal disc. This compartmentalization is a prerequisite for proper wing development. While the function of ap as a dorsal selector gene has been studied extensively, the regulation of its expression during wing development is poorly understood. In the presented studies, the transcriptional regulation of ap was analyzed by classical means and extended by novel approaches, which allowed direct manipulation of the endogenous locus. By combining all those approaches, we identified three separable cis-regulatory elements that work in synergy to regulate the expression of ap during wing imaginal disc development and gained insight into the general patterning of the wing disc and the de novo formation of a compartment boundary.
In the second part, I focus on the development and application of a novel class of protein binders, called nanobodies.
Protein-protein interactions are key to almost all biological processes. So far, protein functions in vivo have been mostly studied by genetic manipulations. However, to describe and understand protein functions in their respective native environment, it is very important and necessary to manipulate proteins directly in vivo. Towards this end, the discovery and development of a new class of protein binders (nanobodies) was essential. Nanobodies are protein binders based on single-domain antibody scaffolds. Conveniently, randomized nanobody libraries have been engineered that hypothetically allow the isolation of nanobodies against any protein of interest. As the field of protein binders is still very young, we wanted to explore the possibility to generate novel specific nanobodies. Using phage display, I did isolate new specific nanobodies. Importantly, we demonstrated that these new nanobodies work intracellularly in cell culture and in vivo.