| The mammalian olfactory system discriminates thousands of environmental chemicals in a highly sensitive and specific manner. This ability stems in part from tightly regulated expression of odorant receptors (ORs), a family of over 1000 genes distributed in clusters on almost every chromosome. In each sensory neuron, patterning cues organize OR gene availability, and an unknown mechanism selects only one allele of one receptor gene for expression. In this thesis, multiple OR transgenes were created and characterized in mice to provide insight into mechanisms of OR gene choice and to define a DNA sequence important for OR patterning. Transgenes were engineered to contain DNA insulators, sequences that block interaction with outside enhancers in other systems, to test the importance of short and long-range elements in OR expression. Insulator-OR transgenes successfully expressed in a singular and zone-restricted manner, in conformity with most rules observed for ORs in their native context. Results demonstrate that ORs do not require long-range cis enhancers for choice, although some receptors may use such sequences to achieve high-level expression in a large number of cells. In a second approach, chimeric OR transgenes were generated to dissect sequences that restrict OR expression to different regions of the olfactory epithelium. Chimeric transgenes expressed in a domain-restricted manner in regions distinct from endogenous OR counterparts. Analysis revealed that a short promoter sequence upstream of a conserved proximal promoter O/E binding site governs dorsal patterning for the M71 OR. |
