Worm Breeder's Gazette 15(1): 40 (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.
Massachusetts General Hospital Cancer Center Charlestown, MA and Dept. of Pathology Harvard Medical School, Boston, MA
Osmosensation has been molecularly characterized in unicellular organisms but relatively little is known about osmosensation in multicellular organisms. Electrophysiological recordings in many cell types and analysis of mscL function in E. coli suggests that osmotic receptors may be mechanosensory channels gated by membrane stretch. Alternatively, osmosensation in yeast utilizes a MAP kinase signal transduction cascade. We are using C. elegans as a model system to elucidate the molecular mechanism of osmosensation in the nervous system. When C. elegans encounters high osmolarity, they reverse direction to avoid the stimulus (CGC82). Laser ablation studies demonstrated that ASH is primarily responsible for the detection of an osmotic barrier (Thomas and Horvitz, unpublished; CGC2309). The ASH neurons are also primarily responsible for detecting nose touch and volatile repellents. osm-10 is specifically required for osmosensation (Thomas and Horvitz, WBG 10(3):167). Wild type (N2) animals cross an osmotic barrier only 0-5% of the time whereas osm-10(n1602) animals cross the barrier 90-95% of the time using the Osm assay of de Vries and Plasterk (personal communication). osm-10 encodes a novel protein of 419 amino acids which is expressed by the ASH and ASI sensory neurons in the nose and by PHA and PHB in the tail (Hart and Kaplan, in prep). The OSM-10 protein contains 38 putative serine and threonine phosphorylation sites suggesting that it may be involved in signal transduction. OSM-10 protein localizes to the cytoplasm, supporting this hypothesis. osm-10(n1602) is a recessive allele which is a genetic, though not a molecular null. It changes an E to a K codon in a putative tyrosine phosphorylation site. OSM-10 protein expression in osm-10(n1602) animals is normal by Western blot and immunohistochemical analysis. To identify additional proteins which are involved in osmosensation, we are identifying and cloning genes which interact with osm-10(n1602)III. Two such interactors, namely nu288 IVand nu268 III, have been identified so far (Kass and Kaplan, unpublished results). nu288 and nu268 are weak recessive Osm mutants. However, animals which are n1602 /+; nu288 /+ or n1602 /nu268 cross the osmotic barrier fifty percent of the time. osm-10 (n1602) heterozygotes respond normally in Osm assays. nu268 maps to the same chromosome as osm-10. However, we hope they are non-allelic; no mutations were found in osm-10 exons in nu268 animals. The genetic interaction of these genes suggest that they may be in the same signal transduction pathway. Further mapping of nu288 and nu268 is in progress. We are also screening to identify more alleles of osm-10, more nonallelic, noncomplementers of osm-10, and other genes which are involved in the osmosensation pathway. We hope that characterization of these genes will lead us to a better understanding of how multicellular organisms sense osmotic stimuli and differentiate multiple sensory modalities.