Chemosensory GPCRSRI-14 are required for concentraion dependent odor preference in C. elegans

Abstract

Animals must recognize and discriminate among thousands of chemicals in order to generate the correct behavioral response. Understanding basic design of a sensory system in simple animals gives the opportunity to elucidate detailed molecular and neural mechanisms underlying sensory responses in higher animals. C. elegans detects a large number of odorants via three neurons pairs including the AWC, and elicit a multitude of olfactory behaviors (Bargmann, 1993, Cell). Previous genetic and behavioral experiments have identified set of signaling genes including olfactory receptors, but the knowledge is still limited. Specifically, the mechanisms of how the same odorants can elicit either attractive or aversive responses depending on the chemical concentration are not known yet. First, we are trying to construct a comprehensive map of odorants and their receptors in C. elegans. We screened more than 29 volatile chemicals that are not tested previously, and found that animals respond to 13volatiles. We further identified that the AWC neurons are required for chemotactic responses to these chemicals. We then performed candidate gene searches and found that the chemosensory GPCR mutants sra-13, str-2, or a un-linked mutant lsk46 exhibit specific defects in chemotactic responses to 2-Furyl methyl ketone, Ethyl pyruvate, or 1- propanol, respectively. Interestingly, we also found that chemosensory GPCR sri-14 are required for both attraction to low concentration DMTS and aversion to high concentration DMTS. The defect of DMTS chemotaxis in sri-14 mutants were restored when we expressed the wild-type sri-14 gene to the AWC neurons. We next found that Ca2+ response of AWC to low concentration DMTS was decreased in sri-14 mutants. We are currently measuring the Ca2+ response of ASH to high concentration DMTS compared to the sri-14, and trying to investigate the neural circuitry mechanism how the SRI-14 regulates both aversive and chemotactic behaviors in C. elegans.