L'Etoile and Bargmann have identified a transmembrane guanylyl cyclase, ODR-1, essential for the ability of Caenorhabditis elegans to sense odorants. Odorant detection is dependent on the catalytic domain of ODR-1 and not the extracellular domain, suggesting that ODR-1 is not ligand-operated itself, but lies downstream of the odorant-detecting receptors. Despite the fact that ODR-1 is a shared signaling component of all odorants tested that were detected by the AWC ciliated olfactory neuron, overexpression of ODR-1 disrupts the adaptation to a specific odorant, butanone. Additionally, ODR-1 overexpression inhibited odorant discrimination (defined by the absence of cross-saturation between two odorants). Thus, in the presence of high concentrations of butanone, the worms did not exhibit chemotaxis to benzaldehyde or isoamyl alcohol; however, in the presence of high concentrations of benzaldehyde or isoamyl alcohol, the worms showed normal chemotaxis to butanone. The adaptation defect did not require catalytic activity, but the discrimination defect did require a functional guanylyl cyclase domain, suggesting that two distinct mechanisms are involved in these processes. The authors suggest that there are mechanisms for insulating odorant signaling pathways to permit odor discrimination despite the use of convergent signaling components.
L'Etoile, N.D. and Bargmann, C.I. (2000) Olfaction and odor discrimination are mediated by the C. elegans guanylyl cyclase ODR-1. Neuron 25: 575-586. [Online Journal]