ttx-6(
nj8) mutants showed cryophilic (cold-seeking) phenotype. Chemotaxis to AWA- and AWC-sensed odorants and to NaCl are normal, but osmotic avoidance are partially defective in this mutant. We found that
ttx-6 encodes EAT-16, a homologue of mammalian RGS 7, 9 or 11, which acts as a negative regulator of G. Previous studies revealed that
eat-16 mutants show hyperactive locomotion and premature egg-laying, and genetically interact with
egl-30 (Gq),
egl-8 (PLC),
goa-1 (Go) and
gpb-2 (G5) [1]. EAT-16 RGS is expressed in many sensory neurons and interneurons [1] including AFD, ASE, ADF, ASH, AWA, AWC, ASJ, AIY and AVA. To gain insight onto the site of action for EAT-16 to direct thermotaxis, we expressed
eat-16 cDNA in different sets of neurons. Expressions of
eat-16 cDNA in either one or all of neurons in thermotaxis circuit such as AFD, AIY, AIZ and RIA of
eat-16 mutants did not rescue the cryophilic phenotype. Surprisingly, expressions of
eat-16 cDNA in neurons including AWC with
odr-3,
odr-1 or
gpa-13 promoter restored cryophilic phenotype. Further, ablation of AWC in
eat-16 mutants suppressed cryophilic phenotype. Thus, EAT-16 acts cell-autonomously in AWC to direct thermotaxis. These results also suggest that AWC has a thermosensory function besides its important role on olfaction and that a thermosensory pathway of AWC is aberrantly activated in
eat-16 mutants. To identify G, a target of EAT-16 in AWC, we constructed and assayed thermotaxis of strains doubly mutant for
eat-16 and G mutations,
odr-3,
gpa-2,
gpa-7, or
gpa-13.
odr-3 completely suppressed cryophilic phenotype caused by
eat-16 mutation, suggesting that ODR-3 activity is regulated by EAT-16 in AWC. We then constructed
eat-16;
odr-1 and
eat-16;
tax-4 double mutants to see whether in AWC the signaling pathway utilized for thermosensation is related to olfactory signaling. Consistent with our model, both
odr-1 and
tax-4 suppressed cryophilic phenotype of
eat-16.We also investigated the contribution of AWC to thermotaxis circuit. In this model, AFD is a major thermosensory neuron, but another unidentified neuron (X) with a minor thermosensory role was also proposed [2]. If neuron X is AWC, we assumed that killing both AFD and AWC would result in athermotactic phenotype as was seen in AFD- and AIZ-killed animals [2]. Consistent with our prediction, AFD- and AWC-killed animals showed completely athermotactic phenotype. [1] Hajdu-Cronin et al., 1999. Genes Dev 13, 1780. [2] Mori and Ohshima, 1995. Nature 376, 344.