Constructing a Synthetic Gene Network to Model and Understand Signaling Interactions in Drosophila melanogaster. Ashley Jermusyk, Gregory Reeves. Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC.

   A complex system of gene regulatory circuits controls the signaling processes involved in systems patterning. These circuits act to buffer the developing pattern against noise, thereby minimizing mistakes in gene expression and preventing patterning defects. Despite their importance to patterning and development, hypotheses regarding these gene regulatory circuits have been difficult to test experimentally due to their complexity and high interconnectivity. Therefore, to better understand the fundamental processes involved, we created a synthetic gene network in Drosophila that utilizes genes from yeast and E. coli, namely, gal4, gal80, and lacZ. We expressed gal4 in a graded fashion along the anterior-posterior axis of the embryo, mimicking the endogenous Bicoid gradient. Gal4 activates expression of UAS-linked gal80 and lacZ, while Gal80 inhibits activation by Gal4, creating a negative feedback loop in our system. By using exogenous genes, all interactions within the network can be more fully understood, and their effects can be definitively determined. Our goal was to measure the location and variability in the position of the lacZ domain both with and without the negative feedback loop. This information was combined with model equations of the network to suggest changes that were used to optimize our experimental network. This system provides a direct experimental test of whether negative feedback loops in muticellular systems such as Drosophila, can provide robustness to noisy, diffusive systems.