Sensory neurons are critical in responding to the environment by transducing external stimuli into patterned electrical activity. Themotaxis reflects the response to food and temperature stimuli. To reveal molecular mechanisms involved in thermotaxis, we conducted a screen for thermotaxis-defective mutants (see abstract by Okumura et.al ., IWM 2001). Through screening about 6,000 genomes, over twenty thermotaxis-defective mutants were isolated, including
nj20,
nj21,
nj44,
nj45 and
nj46 mutants.
nj20 and
nj21 mutants show cryophilic phenotype, independently of cultivation temperature.
nj44,
nj45 and
nj46 mutants also show cryophilic phenotype, but in cultivation temperature-dependent manner.
nj20 mutants have only defect in thermotaxis: they showed normal chemotaxis and osmotic avoidance. These results suggest that
nj20 mutation affects thermotactic behavior specifically. The other mutants,
nj21,
nj44,
nj45 and
nj46 , showed partial defects in chemotaxis to water-soluble attractant NaCl or volatile chemicals and in osmotic avoidance. We have mapped
nj20 and
nj21 mutations using snip-SNPs methods.
nj21 mutation maps to the region between -6.15 and +4.78 on the chromosome I. We have isolated recombinant lines between two SNPs that covers the -6.15 - +4.78 interval and are now evaluating the thermotactic phenotype of the recombinant lines. After narrowing down the region for
nj21through these mapping procedures, we will attempt to rescue the
nj21 phenotype with the respective cosmid.
nj20 maps to the region around +18.6 on the chromosome X. The complementation test revealed that
nj20 did not complement
dgk-1(
nu62) and thermotactic defect of
nj20 mutants was rescued by the genomic
dgk-1 gene. DGK-1 has been studied for its function at neuromuscular junction, where it acts as the inhibitor of acetylcholine release. Like
dgk-1 (
nu62) mutants,
nj20 animals showed hyperactive locomotion and Egl-c phenotype. Conversely,
dgk-1 (
nu62) mutants exhibited cryophilic phenotype. We also found that some of the mutants affecting locomotion and egg-laying showed thermotactic defects (see abstract by Okumura et.al ., this meeting). We are now investigating the role of
dgk-1 in sensory signaling pathways of thermotaxis.