C. elegans can memorize the food condition in relation to the cultivation temperature and migrate to the cultivation temperature when seeking the food. This response to temperature is called thermotaxis. Several neurons and genes required for thermotaxis have been identified, but molecular mechanism of thermotaxis is still poorly understood. The
ttx-8(
nj21) and
ttx-8(
nj34) mutants show obviously defective thermotaxis and partially defective chemotaxis. We found that
ttx-8(
nj34) maps to the region between +0.92 to +1.18 on the chromosome I (see abstract by Miyara et al., IWM 2003). To molecularly identify the
ttx-8 gene, we injected the relevant cosmids and PCR fragments in
ttx-8 mutants. Abnormal thermotaxis of
ttx-8 mutants was rescued by D2092.5 gene but was not rescued by the adjacent D2092.4 gene, indicating that the D2092.5 is
ttx-8 gene. The predicted protein structure of
ttx-8/D2092.5 gene consists of five transmembrane domains in the amino terminus and four coiled-coil domains in the carboxyl terminus. RIC-3, identified in C. elegans at first and conserved among several species, has transmembrane domains in the amino terminus and coiled-coil domains in the carboxyl terminus as well (Halevi et al., 2002; Halevi et al., 2003). RIC-3 is thought to be required for the maturation of acetylcoline receptor (Halevi et al., 2002), so TTX-8 may play a similar role such as folding, assembly, transmission or anchoring of some kind of membrane protein. To determine the cells where
ttx-8 gene is expressed, we constructed
ttx-8 promoter-gfp fusion gene and injected in N2 strain. GFP expression driven by
ttx-8 promoter was observed in neurons. To investigate whether TTX-8 functions in neurons,
ttx-8 cDNA was expressed in neurons of
ttx-8(
nj34) mutants using
unc-14 promoter which drives the pan-neuronal expression. About 60% of transgenic animals showed normal thermotaxis phenotype, suggesting that TTX-8 functions in neurons. We are in the process of identifying individual neurons where TTX-8 functions, the protein which interacts with TTX-8 by means of Yeast two-hybrid system and analyzing the subcellular localization of TTX-8. Although the protein structure of
ttx-8 gene is conserved among various organisms, the functions of its homologues have not been analyzed yet in any other species. We believe that the further analysis of
ttx-8 in C. elegans would give us new important information about the function of this protein, conserved from nematode to mammals including human.