Gap junctions are widely found in neural circuits, although their functional significance is poorly understood. Invertebrate gap junctions are formed by innexins and vertebrate gap junctions are formed by connexins. Although there is no significant amino acid sequence similarity between innexins and connexins, structurally compelling evidence indicates that innexins are functional analogues of the connexins. The mutant for innexin gene
inx-4 is abnormal in the ability of migration to the cultivation temperature on a thermal gradient. When wild type individuals are cultivated at a certain temperature with food and then placed on a thermal gradient, most animals migrate to the cultivation temperature. Intriguingly,
inx-4 mutants instead migrate to a slightly higher temperature than the cultivation temperature. To identify cells expressing
inx-4, we constructed the fusion gene containing the
inx-4 genomic fragment and the 3.4kb upstream fragment fused to GFP. We observed the expression pattern of full-length
inx-4::gfp in AFD, AWC, AIY, RIA, AIB, AVA, AVE, AVK, RIM, RMDV neuron etc. AFD, AWC, AIY, RIA are identified to regulate thermotaxis, especially AFD being a major thermosensory neuron. We introduced
inx-4 cDNA under the control of AFD specific promoter into the
inx-4(
ok2373) mutant at several doses. When
inx-4 cDNA was introduced at 20ng/ml, the thermophilic phenotype of
inx-4(
ok2373) mutants changed to cryophilic phenotype rather than normal phenotype. At 0.2ng/ml, phenotypes of transgenic lines were divided into three classes. Out of nine lines, two lines restored normal migration to cultivation temperature, three lines were thermophilic like the
inx-4(
ok2373) mutant itself and four lines exhibited cryophilic phenotype. These results indicate
inx-4 is involved in thermotaxis in a dose-dependent manner.