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.

Genetic Analysis of a Polymodal Circuit

Vinh Chung1, Kenneth Lecointe1, Chris Korey2, Anne Hart3

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.