The Caenorhabditis elegans odr-2 gene encodes a novel Ly-6-related proteinrequired for olfaction

Caenorhabditis elegans odr-2 mutants are defective in the ability to chemot ax to odorants that are recognized by the two AWC olfactory neurons. Like m all) other olfactory mutants, they retain responses to high concentrations of AWC-sensed odors; we show here that these residual responses are caused by the ability of other olfactory neurons (the AWA neurons) to be recruited at high odor concentrations. odr-2 encodes a membrane-associated protein r elated. to the LV-G superfamily of GPI-linked signaling proteins and is the founding member of a C. elegans gene family with at least seven other memb ers. Alternative splicing of odr-2 yields three predicted proteins that dif fer only at the extreme amino terminus. The three isoforms have different p romoters, and one isoform mar; have a unique role in olfaction. An epitope- tagged ODR-2 protein is expressed at high levels in sensor) neurons, motor neurons, and interneurons and is enriched in axons. The AWC neurons are sup erficially normal ill their development and structure in odr-2 mutants, but their function is impaired. Our results suggest that ODR-2 may regulate AW C signaling within the neuronal network required for chemotaxis.