Resolving the Molecular Mechanisms by Which DNA Mutations Alter the Function of a Genetic Switch

Animal genomes likely possesses anywhere from tens of thousands to more than a million mutations that are genetic baggage from DNA replication mistakes or “mutations” that occurred in the past. Each mutation can either improve, reduce, or have no effect on fitness. Moreover, the effects of such mutations can depend on the presence or absence of other mutations, so called epistatic interactions. A goal of evolutionary-developmental biology research is to identify the mutations responsible for the evolution of form and function, and to understand the molecular mechanisms of their effects. This goal remains out of reach, as the effects of mutations and epistatic interactions are difficult to predict without knowing the function of the DNA sequence they reside in. This difficulty is heightened for mutations occurring in cis-regulatory element sequences that act as switches to control gene transcription. We are using a fruit fly model to test hypotheses about the molecular mechanisms by which mutations alter a genetic switch’s activity, and whether these function-altering mutations are subjected to the tyranny of epistatic interactions. Specifically, we are investigating the Drosophila melanogaster dimorphic element that is a transcription-regulating switch for the bric-à-brac genes. Three mutations in the dimorphic element were identified that individually alter the level of bric-à-brac transcription. The presence or absence of epistatic interactions will be determined by measuring the activity of dimorphic elements from related species that have been engineered to possess the Drosophila melanogaster mutations. I will also test the hypothesis that these mutations impart their effects by creating or destroying binding sites for proteins known as transcription factors. The results will provide a sorely needed example where an understanding of molecular mechanisms bridges the gap between a cis-regulatory element’s DNA sequence and it’s in vivo function