Gain-of-function mutations in three genes in the nematode Caenorhabditis elegans (deg-1, mec-4, and mec-10) lead to the vacuolated degeneration of specific nerve cells. Most of the affected cells have mechanosensory function. all three genes encode novel proteins (degenerins) that appear to be membrane proteins. Similar mammalian proteins form the amiloride- sensitive channels that control sodium uptake in kidney, colon, and lung. The similarity with the mammalian proteins and the affects of mutations on touch sensitivity suggest that the degenerins may be components of mechanosensory receptors. By studying these proteins, we wish to gain information not only about this new class of channel proteins, but also about the molecular basis of mechanosensory transduction.
The specific aims of this research are: 1. To identify functional elements within the degenerins. We will use both in vitro and in vivo mutagenesis to characterize various domains within the degenerin proteins. These domains include a putative extracellular gating domain, regions that may interact with extracellular components, glycosylation sites, and phosphorylation sites. We will also test the inter-changeability of degenerin proteins. 2. To characterize genes that enhance or suppress degenerin activity. Several genes modulate degenerin function. We will clone the modulatory genes, sequence wild-type and mutant alleles, and examine their patterns of expression. 3. To test predictions of our model for touch receptor function. we will examine the relationship of the unique touch cell microtubules with the plasma membrane and degenerins within it, test predicted protein interactions and screen for new ones using the yeast two hybrid system, and test predicted interactions between the deg-3 acetylcholine receptor and the touch cell mechanoreceptor. 4. To investigate the embryonic lethality associated with an unusual deg- 1 mutation. The u506 mutation produces a cold-sensitive lethal phenotype either because of extra cell death or from neuronal hyperactivity. We will identify the affected cell(s) and test its importance in embryonic development by laser ablation.
