Two odor receptors contribute distinct and complex signals in response to structurally similar odor molecules. Scott A. Kreher, Christine Nguyen, Abhiram Nagaraj, Jorge Gacharna, Lorien Menhennett, Raquel Robles, Michael Wesolowski. Department of Biological Sciences, Dominican University, River Forest, IL.

   The first step in sensing an odor is the interaction of an odor molecule with a specific odor receptor (Or) protein. In previous research, we electrophysiologically characterized the entire repertoire of odor receptors in the fruit fly (Drosophila melanogaster) larva and characterized the behavior of larvae in response to these odors. In examination of the behavioral responses of mutants for either Or42a or Or42b to ethyl acetate, we found that each receptor contributed to the behavioral response in a predictable manner: mutants of the high-affinity receptor O42b were not attracted to low concentrations of ethyl acetate and mutants of the low-affinity receptor Or42a were not attracted to high concentrations of ethyl acetate. We extended this analysis to examine how Or42a and Or42b mutants behaviorally responded to three odor molecules that are structurally similar to ethyl acetate. We found that the odor receptor mutations differentially affected behavioral responses to these three odors, and that the responses were not fully predictable from the electrophysiological data set. In two cases, although the odors elicited electrophysiological responses from both Or42a and Or42b, only one odor receptor mutant displayed altered behavioral responses, which were typically loss of attraction phenotypes. Using Or receptor GAL4 lines, we found that we could rescue the behavioral phenotypes of the Or42a and Or42b mutants using the appropriate UAS Or lines. We have found that ectopically expressing Or42a in the native Or42b sensory neuron can elevate behavioral responses to high concentrations of ethyl acetate. These data taken together suggest the importance of sensory neuron context in odor receptor function. A second non-mutually exclusive explanation is that other aspects of odor receptor response are the salient features for odor coding, such as response kinetics.