E. coli , food for C. elegans in a laboratory, is a special attractive source for C. elegans . When well-fed wild type animals are put on an E. coli lawn, they stay in or near the lawn for several hours. We think that food contains multiple chemical cues, and this behavior is the result of reception and integration of these multiple nutrient signals. Mutants defective in the behavior of staying in a bacterial lawn should include mutants defective in signal processing of these multiple cues. To investigate the mechanisms of this food response, we developed an assay system and analyzed 50 known mutants that showed defects in sensory behaviors or neurotransmission. We found that one of the mutants,
dyf-3 , shows a higher frequency of leaving an E. coli lawn than that of the wild type. In
dyf-3 , we visualized sensory cilia of amphid neurons by expressing GFP and found that these neurons have stunted cilia and abnormal posterior projection. Further, electron microscopic analysis confirmed shortened cilia of amphid neurons. Most cilium structure mutants, unlike
dyf-3 mutant, stayed in a food lawn as wild type did, although some, such as
che-2 , showed weak moving out phenotype. These observations suggest that the leaving phenotype does not simply depend on cilium structure abnormalities. The
dyf-3 gene encodes three proteins with different N-terminals. The largest DYF-3 protein has 404 amino acids that are 38% identical with those of a predicted human protein of unknown function. The
dyf-3::gfp fusion gene is expressed in 26 chemosensory neurons.
dyf-3 mutant animals expressing wild type
dyf-3 cDNA only in ASI neurons uptake a fluorescent dye DiI only in ASI neurons, suggesting that
dyf-3 acts cell autonomously. Cell-specific expression of
dyf-3 cDNA in a
dyf-3 mutant and genetic mosaic analysis suggest that expression of
dyf-3 in ASG sensory neurons is required for stable staying on food. Although it was previously reported that ASG chemosensory neurons have a minor role in chemotaxis to water-soluble compounds and dauer formation, the function of these neurons is poorly understood. This work will provide further information about ASG functions.