Distinct signaling pathways mediate touch and osmosensory responses in a polymodal sensory neuron

Abstract

The Caenorhabditis elegans ASH sensory neurons mediate responses to nose touch, hyperosmolarity, and volatile repellent chemicals. We show here that distinct signaling pathways mediate the responses to touch and hyperosmolarity. ASH neurons distinguish between these stimuli because habituation to nose touch has no effect on the response to high osmolarity or volatile chemicals (1-octanol). Mutations in osm-10 eliminate the response to hyperosmolarity but have no effect on responses to nose touch or to volatile repellents. OSM-10 is a novel cytosolic protein expressed in ASH and three other classes of sensory neurons. Mutations in two other osmosensory-defective genes, eos-1 and eos-2, interact genetically with osm-10. Our analysis suggests that nose touch sensitivity and osmosensation occur via distinct signaling pathways in ASH and that OSM-10 is required for osmosensory signaling.

Fig. 1.

Positional cloning of osm-10.Top, The osm-10 gene maps betweenmec-14 and lin-39 on chromosome III. The osmotic avoidance defect of osm-10(n1602) was rescued by the cosmid T20H4 and the plasmid pKP#51 that contains theosm-10 gene T20H4.1. See Results for details.Bottom, The sequence of the osm-10 cDNA was determined by RT–PCR, leading to the predicted protein sequence shown. The n1602 mutation corresponds to the missense mutation E199K; E199 is lowercase. Amino acids translated in the predicted osm-10(nr2076) protein are in the box. Potential S/T kinase and Y kinase sites are indicated as follows (number of sites): protein kinase C (17) sites areunderlined; casein kinase II (11) sites are inbold; cAMP- and cGMP-dependent kinase phosphorylation sites (6) are in italics; and cyclin-dependent kinase (5) sites are outlined.

Fig. 2.

a, OSM-10 is expressed inASH, ASI, PHA, andPHB. Expression was monitored by staining fixed animals in whole-mount preparations with a polyclonal rabbit anti-OSM-10 antibody. Cells were identified on the basis of their nuclear positions and axon morphologies (Sulston et al., 1983; White et al., 1986). The OSM-10 protein is diffusely distributed throughout the cell body, sensory processes, cilium, and axons of expressing cells. The cellular and subcellular expression pattern of the OSM-10:: GFP reporter construct nuIs11I is identical. Cells ingray are located on the right side of the animal; cells in black are on the left. Scale bars, 25 μm. b, Polyclonal rabbit anti-OSM-10 antisera recognize a 49 kDa band on Western blots from extracts of wild-type, osm-10(n1602), osm-3(p802), and nuIs11(pKP#58, pJM#24) animals. An additional band at ∼60 kDa corresponding to the OSM-10:: GFP fusion protein is visible in the nuIs11I lane. The same blot probed with anti-tubulin antibodies (N356; Amersham) is shown at thebottom. c, OSM-10 immunoreactivity inASH neurons (visualized as in a) is shown. OSM-10 immunoreactivity is excluded from the nucleus.Left, Deconvoluted images of anASH cell body are shown. Middle,Right, OSM-10 immunoreactivity is severely reduced inosm-10(nr2076) animals but is found at wild-type levels in eos-1(nu288) or eos-2(nu268) (data not shown) animals.