Hybridization Chain Reaction RNA Whole-Mount Fluorescence In situ Hybridization of Chemosensory Genes in Mosquito Olfactory Appendages

Mosquitoes are effective vectors of deadly diseases and can navigate their chemical environment using chemosensory receptors expressed in their olfactory appendages. Understanding how chemosensory receptors are spatially organized in the peripheral olfactory appendages can offer insights into how odor is encoded in the mosquito olfactory system and inform new ways to combat the spread of mosquito-borne diseases. The emergence of third-generation hybridization chain reaction RNA whole-mount fluorescence in situ hybridization (HCR RNA WM-FISH) allows for spatial mapping and simultaneous expression profiling of multiple chemosensory genes. Here, we describe a stepwise approach for performing HCR RNA WM-FISH on the Anopheles mosquito antenna and maxillary palp. We investigated the sensitivity of this technique by examining the expression profile of ionotropic olfactory receptors. We asked if the HCR WM-FISH technique described was suitable for multiplexed studies by tethering RNA probes to three spectrally distinct fluorophores. Results provided evidence that HCR RNA WM-FISH is robustly sensitive to simultaneously detect multiple chemosensory genes in the antenna and maxillary palp olfactory appendages. Further investigations attest to the suitability of HCR WM-FISH for co-expression profiling of double and triple RNA targets. This technique, when applied with modifications, could be adaptable to localize genes of interest in the olfactory tissues of other insect species or in other appendages.