To identify new molecular components involved in thermosensation, we have isolated thermotaxis-defective mutants using the interaction between dauer formation and thermosensation (see abstract in IWM 2001).
ttx-6(
nj8) mutants always displayed cryophilic phenotype, independently of cultivation temperature, but displayed normal chemotactic behavior toward NaCl and volatile odorants. We cloned
ttx-6 and found that it encodes EAT-16. EAT-16 is the GGL (G-Gamma subunit Like)-containing RGS (Regulators of G protein Signaling) protein which acts as a negative regulator of heterotrimeric G-alpha protein. The expression of
eat-16 cDNA in either one of or all of thermotaxis neurons of
eat-16 mutants did not rescue cryophilic phenotype. Amazingly, the specific expression of
eat-16 cDNA in AWC olfactory neurons rescued the thermotactic defect. This result indicates that
eat-16 functions cell-autonomously in AWC, and also suggests that AWC has a thermosensory function. To identify the target G-alpha protein of EAT-16, we focused on G-alpha genes expressed in AWC,
gpa-2 ,
gpa-13 ,
odr-3 ,
goa-1 and
gpa-7 . Behavioral analysis of the loss-of-function mutants for these G-alpha genes revealed that
gpa-13 mutants displayed thermophilic and athermotactic phenotype and
goa-1 mutants displayed cryophilic phenotype. The phenotypic spectrum of
gpa-13 mutants is consistent with being a target of EAT-16 in AWC.
eat-16 mutants are also abnormal in frequency of reversal movement regulated by command interneurons.
eat-16 showed about 50% reduction in the duration of forward movement compared to wild type. The specific expression of EAT-16 in command interneurons using
glr-1p::
eat-16 cDNA in
eat-16 mutants rescued this abnormality in movement. This means that EAT-16 functions as a regulator in command interneurons. Genetic studies revealed that
eat-16 is involved in G protein signaling pathways in locomotion rate and egg-laying. The reduction-of-function mutants for
goa-1 (Go-alpha) and
dgk-1 (DAG-kinase) and the overexpression mutants for
egl-10 (RGS for GOA-1) and
egl-30 (Gq-alpha) all displayed cryophilic phenotype such as
eat-16 mutants, suggesting the involvement of the G protein signaling in thermotaxis.