Heterologous expression of insect IRs in transgenicDrosophila melanogaster

Abstract

Among insect chemosensory receptors, the broadly conserved Ionotropic Receptors (IRs) remain some of the least investigated. Several studies have documented IR activation by recording insect’s neuronal activityin situ, some demonstrated their activation when expressed in oocytes fromXenopus, others made use of theDrosophila“ionotropic receptor decoders” to functionally mis-express IRs from the same species or from the closely relatedD. sechellia. Here we demonstrated that both substituting tuning IRs ofD. melanogasterand expressing heterologous IRs from other insects alongside theDrosophilanative ones result in functional heteromeric complexes. By these methods, we functionally characterized the IR41a1 subunit of the codling mothCydia pomonella, which demonstrated binding to polyamines with different pharmacological characteristics and the IR75d subunit of the spotted wing drosophilaDrosophila suzukii, which binds hexanoic acid. Then we expressed theD. suzukiiacid sensor IR64a into theD. melanogaster“ionotropic receptor decoder” neuron, which resulted in the inhibition to the main activators of other neurons housed in the same sensillum ofD. melanogaster, as an evidence of its possible functional expression, but it did not show response to acids.In situhybridization on the antennae ofD. suzukiiunveiled a wide expression of this subunit in neurons proximal to the sacculus. Structural analysis did not explain absence of IR64a binding to acids, but it identified key amino acid features that may justify possible hexanoic acid binding for IR75d. While our findings add to the derophanization efforts conducted on the chemosensors of the aforementioned pests, they demonstrated potential for the use of neurons of transgenicDrosophilaas a tool to functionally characterize IRs from different insect species.