Widespread Polymodal Chemosensory Receptor Expression in Drosophila Olfactory Neurons

ABSTRACT Drosophila olfactory neurons have long been thought to express only one chemosensory receptor modality. Using a new genetic knock-in strategy, we targeted the four co-receptors representing the chemosensory modes in Drosophila (Orco, Ir25a, Ir8a, Ir76b). Co-receptor knock-in expression patterns were verified as accurate representations of endogenous expression. We find extensive overlap in expression among the different co-receptors. As defined by innervation into antennal lobe glomeruli, Ir25a is broadly expressed in 88% of olfactory neuron classes and is co-expressed in 64% of Orco+ neuron classes, including all neuron classes in the maxillary palp. Orco, Ir8a, and Ir76b expression patterns are also expanded. Single sensillum recordings from Orco-expressing Ir25a mutant antennal and palpal neurons identify significant changes in olfactory responses. These results suggest polymodal expression and function of chemosensory receptors is common in olfactory neurons. We present a new map of the olfactory system reflecting this polymodal expression.