Sensory Perception

Avoiding CO2

Science Signaling  11 Jan 2011:
Vol. 4, Issue 155, pp. ec12
DOI: 10.1126/scisignal.4155ec12

Animals have evolved to detect and respond to changes in environmental CO2, either as an attractant or as an avoidance cue, depending on the species. CO2-sensing systems in some insects and mammals have been identified and rely on different signaling systems. Hallem et al. found that the CO2-sensing system in the nonparasitic nematode Caenorhabditis elegans relied on a system similar to that identified in mammals. With calcium imaging of a genetically encoded reporter, the authors identified a particular pair of neurons, BAG neurons, as responding with an increase in calcium concentration to increases in CO2 and found that this response desensitized in response to prolonged exposure. By testing calcium signaling in BAG neurons of animals with genetic mutations in genes encoding various signaling molecules, the authors identified genes encoding subunits (TAX-2 and TAX-4) of the cGMP-gated cation channel, as well as a regulator of G protein signaling (RGS-3), as important for CO2 responsiveness. Both of these components functioned in the BAG neurons. To identify additional participants in the pathway, the authors performed transcriptional profiling of BAG neurons and identified gcy-9, encoding a receptor-type guanylate cyclase, as a transcript that was significantly enriched in the BAG neurons compared with its expression in other embryonic cells. Worms with gcy-9 mutations failed to properly respond to CO2, and the BAG neurons did not show CO2-evoked calcium transients. This analysis revealed that nematodes have a CO2-sensing system similar to that in mammals, relying on receptor-type guanylate cyclase instead of the G protein–coupled receptor signaling system used in insects.

E. A. Hallem, W. C. Spencer, R. D. McWhirter, G. Zeller, S. R. Henz, G. Rätsch, D. M. Miller III, H. R. Horvitz, P. W. Sternberg, N. Ringstad, Receptor-type guanylate cyclase is required for carbon dioxide sensation by Caenorhabditis elegans. Proc. Natl. Acad. Sci. U.S.A. 108, 254–259 (2011). [Abstract] [Full Text]