Putative Drosophila odor receptor OR43b localizes to dendrites of olfactory neurons

To gain insight into the role of the recently identified Drosophila seven transmembrane receptor family, we analyzed the cellular and subcellular localization of a member of this family, OR43b. The OR43b receptor is expressed exclusively in a subset of olfactory neurons in the third antennal segment. Consistent with a direct role in odorant transduction, receptor protein is concentrated within the dendrites, but is also present in the axons of the olfactory neurons in which it is expressed. OR43b protein is only detectable relatively late in development suggesting it may not be required for synaptic target choice of the olfactory neurons in which it is expressed. Flies carrying deletions removing one copy of OR43b have the same number of OR43b positive cells in the antenna as flies with two copies, suggesting that simple allelic exclusion of odor receptors may not occur in Drosophila. We show the OR43b gene on the balancer chromosome SM5 is expressed at reduced levels and contains nucleotide polymorphisms predicted to alter two amino acids in the receptor, including an arginine(128) to proline substitution in the first extracellular loop. The subcellular localization of OR43b in olfactory neurons supports the idea that some of the recently identified family of seven transmembrane receptors are odor receptors, and that Drosophila and vertebrates may differ in the developmental processes used to establish the neuronal architecture of the olfactory system.