Abstract
An animal's ability to detect and avoid toxic compounds in the environment is crucial for survival. We show that the nematode Caenorhabditis elegans avoids many water-soluble substances that are toxic and that taste bitter to humans. We have used laser ablation and a genetic cell rescue strategy to identify sensory neurons involved in the avoidance of the bitter substance quinine, and found that ASH, a polymodal nociceptive neuron that senses many aversive stimuli, is the principal player in this response. Two G protein alpha subunits GPA-3 and ODR-3, expressed in ASH and in different, nonoverlapping sets of sensory neurons, are necessary for the response to quinine, although the effect of odr-3 can only be appreciated in the absence of gpa-3. We identified and cloned a new gene, qui-1, necessary for quinine and SDS avoidance. qui-1 codes for a novel protein with WD-40 domains and which is expressed in the avoidance sensory neurons ASH and ADL.