The molecular basis of CO ₂ reception in Drosophila

Abstract

CO2 elicits a response from many insects, including mosquito vectors of diseases such as malaria and yellow fever, but the molecular basis of CO2 detection is unknown in insects or other higher eukaryotes. Here we show that Gr21a and Gr63a, members of a large family of Drosophila seven-transmembrane-domain chemoreceptor genes, are coexpressed in chemosensory neurons of both the larva and the adult. The two genes confer CO2 response when coexpressed in an in vivo expression system, the ''empty neuron system.'' The response is highly specific for CO2 and dependent on CO2 concentration. The response shows an equivalent dependence on the dose of Gr21a and Gr63a. None of 39 other chemosensory receptors confers a comparable response to CO2. The identification of these receptors may now allow the identification of agents that block or activate them. Such agents could affect the responses of insect pests to the humans they seek.chemoreceptors ͉ insect ͉ Gr genes

A Systematic Analysis of Drosophila Gustatory Receptor Gene Expression in Abdominal Neurons which Project to the Central Nervous System

“…Genetic approaches disrupting the activity of Gr68a-expressing neurons, Gr32a, Gr33a, or Gr39a, cause alterations in courtship behavior, consistent with a role in pheromone detection (Bray and Amrein, 2003;Miyamoto and Amrein, 2008;Watanabe et al, 2011). Gr21a and Gr63a together mediate the CO 2 response in the antenna (Jones et al, 2007;Kwon et al, 2007). Gr28b was recently found to be critical for light-induced responses in the Drosophila larvae (Xiang et al, 2010), consistent with the light-sensing role of its C. elegans homolog lite-1 (Liu et al, 2010).…”

A Drosophila gustatory receptor required for the responses to sucrose, glucose, and maltose identified by mRNA tagging

“…Two of the Gr RNAs (Gr22e and Gr32a) were predicted to be enriched in Gr66a-positive neurons because the corresponding GAL4 reporters have been shown to be expressed in subsets of Gr66a GRNs (4,5). In addition, we examined Gr63a expression, which was unlikely to be coexpressed with either Gr5a or Gr66a because this Gr encodes a CO 2 receptor (33,34). Gr64b belonged to a distinct branch that included the seven Grs most related to Gr5a (28-45% amino acid identities; referred to here as the Gr-S group).…”

“…An indication that at least some Grs form obligatory heteromultimers is that misexpression of just one of the two CO 2 receptor genes, Gr21a or Gr63a, in CO 2 -insensitive antennal neurons is insufficient to confer CO 2 sensitivity to these cells. However, coexpression of both Gr21a and Gr63a induces CO 2 responsiveness (33,34). Misexpression of just Gr64a in Gr66a GRNs did not elicit an aversive response to sucrose, glucose, or maltose or result in sugar-induced action potentials in Gr66a GRNs (Y.J.…”

SNMP is a signaling component required for pheromone sensitivity in Drosophila

“…Mutants lacking Or83b are insensitive to most odorants due to lack of functional receptors exposed to the environment. Or83b mutants detect CO 2 normally because this gas is detected by gustatory receptors Gr21a and Gr63a (9,10), and gustatory receptors do not require Or83b for function (8). vainsA mutants, like previously reported Or83b mutants, have normal CO 2 responses but lack responses to general odorants ( Fig.…”