title: O2-sensing neurons control CO2 response in C. elegans.
abstract: Sensory behaviors are often flexible, allowing animals to generate context-appropriate responses to changing environmental conditions. To investigate the neural basis of behavioral flexibility, we examined the regulation of carbon dioxide (CO2) response in the nematode Caenorhabditis elegans. CO2 is a critical sensory cue for many animals, mediating responses to food, conspecifics, predators, and hosts (Scott, 2011; Buehlmann et al., 2012; Chaisson and Hallem, 2012). In C. elegans, CO2 response is regulated by the polymorphic neuropeptide receptor NPR-1: animals with the N2 allele of npr-1 avoid CO2, whereas animals with the Hawaiian (HW) allele or an npr-1 loss-of-function (lf) mutation appear virtually insensitive to CO2 (Hallem and Sternberg, 2008; McGrath et al., 2009). Here we show that ablating the oxygen (O2)-sensing URX neurons in npr-1(lf) mutants restores CO2 avoidance, suggesting that NPR-1 enables CO2 avoidance by inhibiting URX neurons. URX was previously shown to be activated by increases in ambient O2 (Persson et al., 2009; Zimmer et al., 2009; Busch et al., 2012). We find that, in npr-1(lf) mutants, O2-induced activation of URX inhibits CO2 avoidance. Moreover, both HW and npr-1(lf) animals avoid CO2 under low O2 conditions, when URX is inactive. Our results demonstrate that CO2 response is determined by the activity of O2-sensing neurons and suggest that O2-dependent regulation of CO2 avoidance is likely to be an ecologically relevant mechanism by which nematodes navigate gas gradients.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, Los Angeles, California 90095, USA.
authors.forename: Mayra A
authors.initials: MA
authors.lastname: Carrillo
authors.forename: Manon L
authors.initials: ML
authors.lastname: Guillermin
authors.forename: Sophie
authors.initials: S
authors.lastname: Rengarajan
authors.forename: Ryo P
authors.initials: RP
authors.lastname: Okubo
authors.forename: Elissa A
authors.initials: EA
authors.lastname: Hallem
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D017173:Caenorhabditis elegans / Q000187:drug effects / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism* / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D029742:Caenorhabditis elegans Proteins; D002245:Carbon Dioxide; D010100:Oxygen