Metazoan thermosensation is imperfectly understood. We are using both classical and reverse genetics to clarify thermosensation in C. elegans . Thermal uncoupling of a daf-c mutation : The
daf-7 (
e1372 ) mutation renders dauer formation highly temperature-sensitive (100% dauers at 25 deg. C.; ~1% dauers at 15 deg. C.; refs. 1-2). This phenotype is not due to DAF-7 thermolability, since null mutations have similar sensitivity (3). Hobert et al. (2) demonstrated that
ttx-3 uncouples this thermosensitivity, inducing
daf-7 (
e1372 ) to produce ~30% dauers at 15 deg. C. and ~50% non-dauers at 25 deg. C. Thermosensory mutations should thus be obtainable by first screening mutagenized
daf-7 (
e1372 ) at 25 deg. C. for dauer suppressors, and then examining each suppressed strain for 1% dauer production at 15 deg. C. We have screened ~24,000 mutant genomes in F2 and ~190,000 in F1, obtaining 21 independent lines which showed dauer suppression at 25 deg. C. but dauer or pseudodauer production at 15 deg. C. Work to assign them to complementation groups is underway.
gcy-8 : This gene, encoding a guanylate cyclase receptor, was found by Yu et al. (4) to be expressed solely in the thermoreceptor AFD. However, it is unclear whether this gene actually mediates thermal signals in AFD. We are using reverse genetics to assay loss and gain of
gcy-8 function in
daf-7 (
e1372 ) animals. Ablation of function is being tried by RNAi. Increase of function is being tried through a
gcy-8 transgene with a mutation homologous to E974A in atrial natriuretic peptide, which induces constitutive activity in cell culture (5). If GCY-8 actually directly carries thermal signals, we predict that loss- and gain-of-function
gcy-8 mutations should have opposite effects on dauer formation of
daf-7 (
e1372 ) animals at 15 deg. versus 25 deg. C. 1. Swanson and Riddle (1981), Dev. Biol. 84 , 27-40. 2. Hobert et al. (1997), Neuron 19 , 345-357. 3. Ren et al. (1996), Science 274 , 1389-1391. 4. Yu et al. (1997), Proc. Natl. Acad. Sci. USA 94 , 3384-3387. 5. Wedel et al. (1997), Proc. Natl. Acad. Sci. USA 94 , 459-462.