Worm Breeder's Gazette 14(4): 69 (October 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Graduate University for Advanced Studies & National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411, Japan
We are interested in the information processing in neural circuits, especially the roles of interneurons. To investigate this problem, we analyzed three of the GABA-A/glycine receptor-like genes found by the C.elegans genome project, which we named ggr-1, ggr-2, ggr-3 (GABA-A or glycine receptor-like genes). In vertebrates, both GABA-A and glycine receptors are ligand-gated chloride channels that generate inhibitory potentials. We studied the spatial expression patterns, using stable transgenic strains carrying ggr-GFP fusion genes. ggr-1 (in cosmid C09G5) is expressed in neurons including AIB, PVR, PVQ, AVH, SMDV, and some motor neurons in the ventral cords. ggr-2 (C45B2) is expressed in neurons including SMDV, SMDD, SIAV, CAN, HSN, DD, and slightly in egg-laying muscles. ggr-3 (F09C12) is expressed in AVA, AVB, SMDD, DVA, SIAD and some other neurons in the nerve ring. To know their roles in behavior, we isolated deletion mutants in those genes by insertion and imprecise excision of Tc1. Although we performed assays of many behaviors such as movement, chemotaxis, osmotic avoidance, mechanosensation, thermotaxis, defecation and male mating activity, we found no defect in the ggr-3 mutant. However, the mutants in ggr-1 and ggr-2 showed abnormalities in thermotaxis. The ggr-1 mutant usually moves isothermally at a temperature lower than the growth temperature, i.e., cryophilic(+) as defined by Mori and Ohshima (Nature 376: 27, 1995). However, although the mutant spends most of the time in a cold area, it occasionally makes isothermal tracks near the growth temperature. It looks as if this mutant has two states, and in a wild-type worm the cryophilic state is repressed by the GGR-1 receptor. Interestingly, ggr-1 is expressed in AIB neuron, which is predicted by Mori and Ohshima to play a minor role in moving towards a colder temperature. We think the cryophilic(+) phenotype is caused by abnormal excitation of AIB due to the lack of the GGR-1 inhibitory receptor. Consistent with the hypothesis, some of the ggr-1 animals recovered the correct thermotactic behavior after laser ablation of AIB. However, since some of the operated animals remained cryophilic, we are now testing if other cells expressing ggr-1 also affect thermotaxis or if ablation is incomplete in these animals. The ggr-2 mutant shows a slightly cryophilic phenotype without isothermal tracking: cryophilic(-). We are now investigating which neuron is responsible for the phenotype. We also found that strychnine, an antagonist of the glycine receptors of vertebrates, makes wild-type worms cryophilic, if it is contained in the assay plates. Since strychnine in the growth plates has no effect, the result may mean that strychnine disrupts the thermoreception or assessment but not the memory-formation process of thermotaxis. Although the ligands of GGR-1 and GGR-2 are unknown for the moment, we plan to examine by cell-ablation whether the target-cells of strychnine for this effect are those expressing ggr-1 or ggr-2.