Worm Breeder's Gazette 15(1): 41 (October 1, 1997)
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.
|1||Harvard University, Cambridge, MA 02138|
|2||Harvard Medical School, Boston, MA|
|3||Massachusetts General Hospital Cancer Center, Charelstown, MA|
|3||Harvard Medical School, Department of Pathology, Boston, MA|
Our research addresses how neurons can detect and differentiate among several types or modes of sensory stimulation. The ASH polymodal sensory neurons detect touch to the nose (Not), changes in osmotic pressure (Osm), and volatile repellents (Sos). Several genes required for detecting one or more of these three stimuli have been identified. glr-1 is specifically required for nose touch (CGC 2309). N2 worms respond to nose touch 90-100% of the time, while glr-1 mutants respond only 3-5% of the time. However, glr-1 mutants are nonOsm and nonSos. Similarly, osm-10 is Osm nonNot and nonSos (Thomas & Horvitz, unpub. data and Hart & Kaplan, in prep.). We use the Osm assay of de Vries and Plasterk (pers. comm.), in which worms are placed in a ring of 8M glycerol and diacetyl is placed outside the ring to function as an attractant. Only 0-5% of the N2 worms escape the glycerol ring and swim toward the attractant. Up to 90% of osm-10 mutants escape the ring. We are less interested in genes that function in the detection of more than one stimulus or in mutant strains that are defective in ASH sensory process morphology. osm-3 animals are Dyf Osm Not but nonSos (CGC 1757). Genes which are required for detection of all three stimuli have also been identified. For example, eat-4 mutants are nonDyf Osm Not and Sos (WM 96;36). We hope to identify mutations which perturb response to just one stimulus detected by ASH. These mutations are likely to be specifically involved in detection or response to a stimulus. We create mutations by EMS mutagenesis and use behavioral screens to isolate the mutants. The progeny are tested for response to other ASH stimuli and for DiO staining (Dyf). Only morphologically normal ASH neurons stain with DiO. We discard mutant strains which are defective in DiO staining. Mutants which are normal for DiO staining and defective for response to just one stimulus are most valuable in probing sensory mechanisms. For example, glr-1 mutants, which are normal for DiO and defective only for nose touch, revealed that nose touch is encoded in the ASH circuit through the use of glutamate and glutamate receptors. We have screened 6,300 worms for Not and have isolated 12 Not strains. Characterization of these strains is not completed. After screening 4,018 worms for Osm, we have isolated 1 Osm strain, which is modality specific. Screening 2,732 worms for Sos yielded 12 Sos strains, 2 of which are modality specific. Our future plans include identification of more mutations, mapping, and cloning these modality specific genes. Results of this research will provide information on sensory signal encoding and the proteins involved in signal transduction in the C. elegans nervous system. Ultimately, the research will elucidate the mechanisms for encoding different stimuli in C. elegans as well as in organisms of greater complexity.