C. elegans senses temperature mainly by a pair of sensory neurons (AFD) and shows a characteristic behavior towards the temperature called thermotaxis. Several mutants that are defective in thermotaxis have been isolated, and these mutants can be divided into three classes: cryophilic (cold-seeking), thermophilic (heat-seeking), and athermotactic (non-temperature responsive) phenotype. Analyses of these mutants identified several genes involved in thermotaxis.
tax-4 encoding a cyclic nucleotide-gated cation channel (CNG channel) is essential for thermosensation in AFD.
tax-4 is also required for olfaction by sensory neuron AWC, implicating similar components in thermosensory and olfactory signal transduction. In AFD, three guanylyl cyclase genes,
gcy-8,
gcy-18 and
gcy-23 , play an essential role for thermosensation (see abstract by Inada et al .). Analysis of
eat-16 mutant, which is defective in a regulator of G protein signaling (RGS), revealed that AWC olfactory neuron functions as a thermosensory neuron and that
odr-1 guanylyl cyclase is involved in thermosensory signal transduction in AWC (Okumura et al ., submitted). To investigate genetic interaction of these four guanylyl cyclases and TAX-4 CNG channel, we constructed
tax-4;
gcy-23 gcy-8 gcy-18 and
gcy-23 gcy-8 gcy-18;
odr-1 quadruple mutants, and examined their thermotaxis phenotype. While
gcy-23 gcy-8 gcy-18 mutants showed cryophilic and athermotactic phenotype,
tax-4;
gcy-23 gcy-8 gcy-18 mutants showed athermotactic phenotype like
tax-4 mutants, suggesting that
tax-4 is epistatic to
gcy-8,
gcy-18 and
gcy-23 .
gcy-23 gcy-8 gcy-18;
odr-1 mutants showed athermotactic phenotype, although
odr-1 single mutants showed almost normal thermotactic phenotype. This result suggests that ODR-1, which is an essential component in olfactory signal transduction, functions in thermosensory signal transduction in AWC. Our results are consistent with a molecular model in which three guanylyl cyclases (GCY-8, GCY-18 and GCY-23) and ODR-1 function upstream of TAX-4 CNG channel for thermosensation in AFD and AWC, respectively.