Temperature is an essential factor of animal metabolism and behavior, yet molecular mechanism underlying thermosensation remains to be revealed. We focus on thermotaxis in C. elegans as a model to analyze thermosensation. Loss-of-function (lf) mutation in
eat-16 encoding RGS, a negative regulator of G protein, causes hyper activation of AWC sensory neuron that functions as thermosensory neurons besides olfactory neurons, thereby leading to cryophilic defect (1). Cryophilic defect of
eat-16 mutant is suppressed by the mutations in G protein-coupled olfactory signaling, suggesting that G protein signaling is essential for thermosensation and that thermosensory and olfactory signaling are transmitted through the similar molecular pathway (1). To identify new molecules involved in G protein-coupled thermosemsation, we isolated 39 suppressors for cryophilic abnormality of
eat-16 through 17600 genomes screening. Of those,
nj65 mutation was a dominant mutation that strongly suppresses
eat-16 mutation, and thermotactic phenotype of
eat-16;
nj65 mutant was almost normal. We found that
nj65d mutant has a missense mutation in the kinase domain of diacylglycerol kinase DGK-1.
dgk-1(lf) mutant shows cryophilic abnormality, which is same abnormality as
eat-16 mutant (2). Interestingly, cryophilic defect of
eat-16(lf) caused by hyper activation of AWC neuron was strongly suppressed by expressing
dgk-1 gene containing
nj65d mutation, but weakly suppressed by wild-type
dgk-1 gene. These results imply that
dgk-1(
nj65d) mutation is a gain-of-function mutation and that DGK-1 normally acts as a negative regulator for AWC activity. Activating DGK generally reduces concentration of diacylglycerol (DG), which is a key activator for protein kinase C (PKC). Previously reported, DG-activated PKC encoded by
ttx-4 gene acts as a positive regulator for AWC olfactory signaling. We found that overexpression of
ttx-4 gene in AWC led to cryophilic abnormality, indicating that PKC TTX-4 also acts as positive regulator for AWC temperature signaling. Based on these results, we speculated that constitutive active form of DGK-1 strongly reduces the intracellular DG in
eat-16;
dgk-1(
nj65d) mutant, thereby leading to inactivation of AWC thermosensory neuron through TTX-4 PKC.
nj55,
nj65,
nj69 mutations isolated in this study also suppressed cryophilic defect of
eat-16 mutant. We found that
nj55 and
nj65 were mapped onto chromosome I, and that
nj69 was mapped between -10.69 and -10.57 on chromosome X, which are covered by cosmid F40F4 containing 14 genes. We are injecting these genes into
eat-16;
nj69 mutant to determine responsible gene for
nj69 mutation. (1) Kuhara et al., this meeting, (2) Okochi et al., 2005, EMBO J..