The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States
Chun-Chieh Lin
The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States; Mortimer B. Zuckermann Mind Brain Behavior Institute, Columbia University, New York, United States
Alina Vulpe
Physiology & Neurobiology Department, University of Connecticut, Mansfield, United States
Ali Afify
The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, United States
Sydney Ballou
Physiology & Neurobiology Department, University of Connecticut, Mansfield, United States
Maria Brbic
Department of Computer Science, Stanford University, Stanford, United States
Drosophila Connectomics Group, Department of Zoology, University of Cambridge, Cambridge, United Kingdom; Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
Hongjie Li
Department of Biology, Howard Hughes Medical Institute, Stanford University, Stanford, United States
Karen Menuz
Physiology & Neurobiology Department, University of Connecticut, Mansfield, United States
Drosophila melanogaster olfactory neurons have long been thought to express only one chemosensory receptor gene family. There are two main olfactory receptor gene families in Drosophila, the odorant receptors (ORs) and the ionotropic receptors (IRs). The dozens of odorant-binding receptors in each family require at least one co-receptor gene in order to function: Orco for ORs, and Ir25a, Ir8a, and Ir76b for IRs. Using a new genetic knock-in strategy, we targeted the four co-receptors representing the main chemosensory families in D. melanogaster (Orco, Ir8a, Ir76b, Ir25a). 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 all olfactory sensory neuron classes and is co-expressed in 82% of Orco+ neuron classes, including all neuron classes in the maxillary palp. Orco, Ir8a, and Ir76b expression patterns are also more expansive than previously assumed. Single sensillum recordings from Orco-expressing Ir25a mutant antennal and palpal neurons identify changes in olfactory responses. We also find co-expression of Orco and Ir25a in Drosophila sechellia and Anopheles coluzzii olfactory neurons. These results suggest that co-expression of chemosensory receptors is common in insect olfactory neurons. Together, our data present the first comprehensive map of chemosensory co-receptor expression and reveal their unexpected widespread co-expression in the fly olfactory system.
