Date of Award
insect chemosensation, Or83b, drosophila, olfactory sensory neurons
Among other functions, chemosensory systems play a crucial role in the host-seeking behaviors of insects that allow them to find their preferred food sources. Quite often, however, these host-seeking behaviors have a negative impact on either human health or livelihood. The following details investigations into the evolution and molecular mechanisms of two distinct pathways involved in insect chemosensation. The atypical odorant receptor gene, Or83b, is co-expressed with other ORs in most olfactory sensory neurons (OSNs) of the Drosophila antenna. OR83b acts as a generic heterodimeric partner for other ORs coupling them to the ciliary trafficking machinery, which is responsible for delivering the OR complexes to their site of action, the OSN dendrites. Flies lacking Or83b have marked electrophysiological and behavioral olfactory defects presumably because the OR cargo of OR83b is degraded when it cannot traffic properly. The amino acid sequence of OR83b has been remarkably well conserved over the course of evolution. Homologues have been identified in insects as diverse as beetles, moths, honeybees, and locusts. Several of these are true orthologues that can rescue the Or83b mutant phenotype indicating that the function of OR83b has also been conserved. At least one population of neurons in the fly antenna is Or83bindependent. These neurons, which respond to changes in CO2 concentration, co-express a pair of chemosensory receptors belonging to the gustatory receptor family, Gr21a and Gr63a. Transgenic misexpression of these two receptors can confer CO2 sensitivity on a neuron that is normally CO2-insensitive. Gr63a1 mutant flies lack all electrophysiological and behavioral responses to CO2. Clear homologues of these two genes are co-expressed in the mosquito organ that responds to CO2 implying that they act as the mosquito CO2 receptors as well. It seems that many insects, including the malaria mosquito, use these two pathwaysâ€”one Or83b-dependent and one Or83b-independentâ€”to track host odors, which synergize with CO2 plumes to modulate host-seeking behavior. Thus, not only is the evolutionary history of these insect chemosensory pathways incredibly interesting, both pathways make attractive targets for the rational design of novel insect control measures designed to interrupt host seeking.
Jones, Walton D., "Insect Host Seeking: Investigations into the Molecular Mechanisms of Chemosensation" (2007). Student Theses and Dissertations. 19.