Mechanosensation and osmosensation are essential, yet poorly understood processes. The ASH neurons in C. elegans detect mechanical, osmotic and chemical stimuli; laser ablation studies indicate that they are primarily responsible for detecting light touch to the nose, high osmolarity and volatile repellents (1-octanol) (CGC82; WBG 10(1):89; CGC2309 and CGC1374). We are studying the molecular pathways involved in detecting and distinguishing these stimuli using modality specific mutations - those defective in responding to only 1 or 2 of the ASH stimuli. OSM-10, a novel cytoplasmic protein with 38 putative phosphorylation sites, is required specifically for osmosensation (ECWM97 #226), as an
osm-10 null allele,
nr2076 , disrupts osmosensation but not mchanosensation nor chemosensation. (Thanks NemaPharm). An E to K mutation in a putative tyrosine phosphorylation site of OSM-10 also disrupts osmosensation. Thus,
osm-10 may play a role in intracellular signal transduction. To elucidate the function of
osm-10 and to identify other components of the ASH-mediated osmosensory pathway, we are isolating putative OSM-10 interacting proteins using the yeast two-hybrid system. (Thanks to M. Walhout, H. Endoh and M. Vidal). The expression patterns and the gene disruption phenotypes of putative interactors will be determined to test the biological relevance of the interactions. We are also characterizing 2 new modality specific mutations
osm-16(
rt6ts) and not
(rt32) .
rt6 animals are defective in their response to high osmolarity and 1-octanol, but are normal in nose touch avoidance. Thus,
rt6 may encode a component of the signal transduction machinery shared by osmosensation and chemosensation, but not by mechanosensation.
rt6 maps to the right end of the X chromosome near
unc-7 . Further mapping and cloning of
rt6 is now underway.
rt32 animals are defective in nose touch response, but are wild-type for other ASH-mediated responses. We are currently mapping
rt32 . Characterization of
rt6 and
rt32 mutants should lead us to the better understanding of mechanosensation and osmosensation, as well as the molecular mechanisms involved in distinguishing different stimuli.