This abstract was not presented at the symposium.
Well-controlled gene expression is critical for the proper development and function of many traits. Highly-specific temporal and spatial expression patterns are often due to the overlapping activities of activator and repressor sequences that form cis-regulatory elements called enhancers. While many studies have shown that evolutionary changes in enhancers can result in novel traits, few studies illuminate how enhancers originate, how activator and repressor sequences interact during enhancer evolution, and the order in which they evolve. Here, we traced the evolutionary origin of a recently evolved enhancer that drives the expression of the fatty acyl-CoA elongase, bond, specifically in the semicircular wall epithelium (swe) of the Drosophila male ejaculatory bulb (EB). We show that this enhancer consists of two activator regions that drive bond expression in the entire EB and a repressor region that restricts expression specifically to the EB swe. Interestingly, the repressor region preceded the evolution of the two activator regions. The evolution of the first activator region, consisting of two putative Abdominal-B sites, did not drive expression in the EB due to the action of the repressor region. Expression of bond in the EB swe requires the evolution of the second activator region, which does not drive expression on its own, but synergizes with the first activator region and the repressor region to produce a highly-specific spatial expression pattern. Our results show that the origin and evolution of a novel enhancer require multiple steps and the evolution of repressor sequences can precede the evolution of activator sequences.
A 2 n tree-based Cartesian grid generation method has been developed recently for complex geometries to simulate viscous flows. The "viscous" Cartesian grid is capable of resolving boundary layers with high-aspect ratio projected viscous layer grids. Compared with an Octree data structure, the 2 n tree data structure supports anisotropic grid adaptations in any of the coordinate directions in an arbitrary manner. This capability enables flow features such as shocks, shear layers, and wakes to be resolved very efficiently. In this paper, steady-state Navier-Stokes Computational Fluid Dynamics (CFD) analyses were performed on a cylindrical body Ogive using five different turbulence models in the commercial flow solver Cobalt with the 2 n based Cartesian grid generator. Turbulence models tested were the Spalart-Allmaras (SA), Menter-Shear-Stress Transport (SST), coupled Detached Eddy Simulation-Spalart-Allmaras (DES-SA), coupled Detached Eddy Simulation-Shear Stress Transport (DES-SST), and the κ-ω model. The geometry model consisted of a 3-caliber nose with a cubic profile followed by a 10 caliber cylindrical body. Surface pressures and off body vortex flows were computed and compared to well documented experimental results for a test case at Mach 2.4 and 14° Angle-Of-Attack (AOA). Overall results showed that all turbulence models compared well with experimental with κ-ω giving the best results.
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