Although steroid ligand receptor interactions are known to be important in vertebrate embryogenesis and pattern formation, their role in determining the segmentation pattern of the Drosophila embryo is not as clear. Several proteins required for embryonic development in Drosophila have homology to vertebrate steroid receptors, but the ligands for these putative receptors have not yet been identified. Thus, the biological significance of the homology between the ligand binding domains in Drosophila and vertebrate proteins remains in question. This proposal aims to identify the ligand for the putative steroid receptor in Drosophila encoded by the tailless gene. Using a genetic assay for the functional activation of the tailless protein, ten different steroids will be tested for their effects on the segmentation pattern of Drosophila embryos. Upon the identification of a putative ligand for the tailless receptor, the activation of genes regulated by tailless will be measured in the presence of the tailless ligand. Using this approach, it will be possible to elucidate more easily the role of steroid receptor ligand interactions in embryonic pattern formation through the application of Drosophila molecular genetics.
