Abstract
Adult female mosquitoes rely on olfactory cues like carbon dioxide and other small molecules to find vertebrate hosts to acquire blood. The molecular physiology of the mosquito olfactory system is critical for their host preferences. Many laboratory strains of the yellow fever mosquito Aedes aegypti have been established since the late 19th century. These strains have been used for most molecular studies in this species. Some earlier comparative studies have identified significant physiological differences between different laboratory strains. In this study, we used a Y-tube olfactometer to determine the attraction of females of seven different strains of Ae. aegypti to a human host: UGAL, Rockefeller, Liverpool, Costa Rica, Puerto Rico, and two odorant receptor co-receptor (Orco) mutants Orco2 and Orco16. We performed RNA-seq using antennae of Rockefeller, Liverpool, Costa Rica, and Puerto Rico females. Our results showed that female Aedes aegypti from the Puerto Rico strain had significantly reduced attraction rates toward human hosts compared to all other strains. RNA-seq analyses of the antenna transcriptomes of Rockefeller, Liverpool, Costa Rica, and Puerto Rico strains revealed distinct differences in gene expression between the four strains, but conservation in gene expression patterns of known human-sensing genes. However, we identified several olfaction-related genes that significantly vary between strains, including receptors with significantly different expression in mosquitoes from the Puerto Rico strain and the other strains.
Highlights
The chemical sense of olfaction plays an important role in the life of all insects, in locating food sources, and in other sensory-mediated behaviors like mating and egg deposition (Fleischer and Krieger, 2018)
When the human hand was treated with DEET, prior to the experiment, females from all strains showed a significant reduction in attraction (Figures 1B,C)
FPKM of all sensation-associated genes in each sample were generated and included the following chemosensory gene categories: odorant receptors (ORs) and the obligate odorant receptor co-receptor (ORCO), gustatory receptors (GRs), ionotropic receptors (IRs), and odorant binding proteins (OBPs), as well as other genes associated with olfaction including pickpocket (PPK) and transient receptor potential (TRP) channels
Summary
The chemical sense of olfaction plays an important role in the life of all insects, in locating food sources, and in other sensory-mediated behaviors like mating and egg deposition (Fleischer and Krieger, 2018). 2013, 2014; Bohbot et al, 2014) These olfactory regions are covered with sensilla, small hair-like structures containing odor-sensing neurons called olfactory receptor neurons (ORNs) (Carey and Carlson, 2011). ORNs within the sensilla express chemosensory receptor proteins from three protein families that detect specific types of odorants. ORs form heteromers with an odorant receptor co-receptor protein (ORCO) (Fleischer et al, 2018). This ORORCO complex functions as a ligand gated ion channel for odor sensation (Vosshall and Hansson, 2011). Previous research has shown that members of these aforementioned protein families are expressed in the antennae of insects (Brito et al, 2016; Pelosi et al, 2018; Venthur and Zhou, 2018) including Aedes aegypti (Matthews et al, 2016)
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