West Coast Worm Meeting Abstracts - Caenorhabditis elegans ...

ROLES OF OSM-9/CAPSAICIN RECEPTOR FAMILY
MEMBERS IN SENSORY BEHAVIORS
D. Tobin 1 , D. Madsen 2 , G. Moulder 3 , R. Barstead 3 , A.V. Maricq 2 , M.
deBono 4 , C. Bargmann 1
1University of California San Francisco, HHMI
2University of Utah
3Oklahoma Medical Research Foundation
4MRC, Cambridge
West Coast Worm Meeting 2000
The osm-9 gene is required for a wide range of sensory modalities in C. elegans including
chemosensation, mechanosensation, osmosensation, and certain forms of olfactory adaptation. osm-9
encodes a putative ion channel with striking homology to the vertebrate capsaicin receptor, a cation
channel expressed in pain-sensing neurons and gated by the active component of chili peppers. In the
amphid neuron AWA, OSM-9 localizes to sensory cilia, suggesting a direct role in sensory transduction.
The vertebrate capsaicin receptor VR1 responds to heat, capsaicin, and low pH. Expression of
mamamlian VR1 under an AWA-specific promoter partially rescued osm-9’s AWA defects. Thus, the
homology between the two proteins may have functional relevance. However, OSM-9 is not sensitive to
capsaicin. We found that expression of mammalian VR1 in C. elegans nociceptive neurons created a
robust capsaicin-avoidance behavior. Heterologous expression of VR1 should be a useful tool for specific,
drug-inducible neuronal activation.
Four relatives of osm-9 are each expressed in subsets of osm-9-expressing cells. We call these genes
ocr (osm-9/capsaicin receptor-related)genes and have generated mutations in two of them. ocr-1 is
expressed primarily in AWA while ocr-2 is expressed in AWA, ASH, ADL, and ADF. Based on their
expression patterns and similarity to osm-9 we hypothesized that the OCR channels might coassemble
with OSM-9 to form heteromultimeric complexes. Mutations in ocr-2 recapitulate some of osm-9’s defects:
there are dramatic defects in AWA-mediated chemotaxis and ASH-mediated avoidance behaviors. We
propose that different combinations of subunits may account for the distinct functions of osm-9 in different
sensory neurons.
Interestingly, ocr-2 has a role in C. elegans social behavior. npr-1 encodes a putative neuropeptide
receptor that regulates the choice between solitary and social foraging behavior. osm-9 and ocr-2 mutants
suppress the clumping behavior of npr-1 mutants. We have performed single-cell rescue experiments to
identify the neurons in which ocr-2 expression is required for social behavior. Identification of these
neurons should help define the sensory signals and neuronal circuitry that mediate clumping.
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