Abstract
Mosquitoes are vectors for multiple infectious human diseases and use a variety of sensory cues (olfactory, temperature, humidity and visual) to locate a human host. A comprehensive understanding of the circuitry underlying sensory signalling in the mosquito brain is lacking. Here we used the Q-system of binary gene expression to develop transgenic lines of Anopheles gambiae in which olfactory receptor neurons expressing the odorant receptor co-receptor (Orco) gene are labelled with GFP. These neurons project from the antennae and maxillary palps to the antennal lobe (AL) and from the labella on the proboscis to the suboesophageal zone (SEZ), suggesting integration of olfactory and gustatory signals occurs in this brain region. We present detailed anatomical maps of olfactory innervations in the AL and the SEZ, identifying glomeruli that may respond to human body odours or carbon dioxide. Our results pave the way for anatomical and functional neurogenetic studies of sensory processing in mosquitoes.
Highlights
Mosquitoes are vectors for multiple infectious human diseases and use a variety of sensory cues to locate a human host
The 9,312 bp putative promoter/enhancer region was the largest PCR product 50 to the odorant receptor co-receptor (Orco) ATG start codon we could obtain and it is possible that the actual genomic region needed for Orco expression is located within a smaller portion of this sequence
Using our neurogenetic approach we find that olfactory receptor neurons labelled by the Orco-QF2 driver line send their axons to two distinct areas of the brain: the antennal lobe (AL) and the suboesophageal zone (SEZ) (Fig. 3a)
Summary
Mosquitoes are vectors for multiple infectious human diseases and use a variety of sensory cues (olfactory, temperature, humidity and visual) to locate a human host. We used the Q-system of binary gene expression to develop transgenic lines of Anopheles gambiae in which olfactory receptor neurons expressing the odorant receptor co-receptor (Orco) gene are labelled with GFP These neurons project from the antennae and maxillary palps to the antennal lobe (AL) and from the labella on the proboscis to the suboesophageal zone (SEZ), suggesting integration of olfactory and gustatory signals occurs in this brain region. In situ hybridization and single sensillum electrophysiological recordings in Drosophila, mosquitoes and other insects show that neurons expressing ORs and IRs respond to a variety of volatile odorants including many found in human body odours[11,18,24,25,26], whereas GRs respond to a number of stimuli including tastants, pheromones, warmth and the volatile gas carbon dioxide[22,27]. Orco-expressing neurons comprise B70% of all olfactory neurons in Drosophila, suggesting
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