Olfaction It Takes Two to Sense CO₂

Elizabeth M. Adler

Science's STKE, AAAS, Washington, DC 20005, USA

Many insects detect CO₂, thereby obtaining critical information about their environment; bloodsucking insects like mosquitoes, for instance, follow CO₂ trails to locate potential hosts. Drosophila detect CO₂ through a subset of olfactory sensory neurons that do not express odorant family receptors (known to sense other volatile chemicals) but do express Gr21a, which is classified as belonging to the gustatory receptor family (see Wilson). Jones et al. showed that a second gustatory receptor gene, Gr63a, was coexpressed with Gr21a in CO₂-sensing neurons in both adult and larval Drosophila. Moreover, the mosquito homologs of Gr21a and Gr63a were coexpressed in a subset of neurons in the mosquito organ through which CO_{2 ­­}is sensed. When Gr21a and Gr63a were coexpressed in neurons that are normally unresponsive to CO₂, these neurons became responsive, although neither receptor alone was sufficient to confer CO₂ sensitivity. Furthermore, mutant flies lacking Gr63a were insensitive to CO₂, as determined both behaviorally and through electrophysiological recordings. Thus, the authors conclude that coexpression of Gr21a and Gr63a is required for CO₂ detection in Drosophila, a finding that may have implications for the development of repellants against blood-feeding insects.

W. D. Jones, P. Cayirlioglu, I. Grunwald Kadow, L. B. Vosshall, Two chemosensory receptors together mediate carbon dioxide detection in Drosophila. Nature 445, 86-90 (2007).[PubMed]

R. I. Wilson, Scent secrets of insects. Nature 445, 30-31 (2007). [PubMed]

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