Worm Breeder's Gazette 14(1): 44 (October 1, 1995)
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.
Dept. Biochemistry, NYU Medical School, 550 First Ave., New York, NY 10016
Genetic data suggest that unc-8 IV encodes a subunit of a Na+ channel homologous to the passive leak Na+ channels subserving transepithelial salt and water transport in mammals. Physiological, biochemical, and genetic experiments indicate that the ion channel is a multi-subunit structure, of which two mammalian components have been molecularly identified: ENaC's and CFTR (Stutts et. al., Science 269:847). To identify other genes encoding proteins with important roles in ion channel function, extragenic unc-8 suppressor and enhancer mutations were sought. Two unc-8 suppressor loci, sup-40 I and sup-41 IV were described previously (Shreffler et. al. Genetics 139:1261). We describe here gene interactions of two new unc-8 supressor loci, sup-42(lb88) X and sup-43(lb141) II, and an enhancer locus, enu-2(lb140). Sup-43(lb141) is an unusual allele specific suppressor of unc-8(e49). Single mutants of either sup-43(lb141) or unc-8(e49) express a coiler Unc phenotype, while the double mutant sup-43(lb141);unc-8(e49) behaves as wild-type. These three mutations were initially isolated by the sole criterion of amelioration or exacerbation of unc-8 locomotion defects, however, each displays unselected cell swelling phenotypes which further suggest an effect on membrane permeability: sup-42(lb88) causes swelling of embryonic cells, while sup-43(lb141) and enu-2(lb140) cause vacuoles within body wall muscle, similar in appearance to those caused by unc-105(n490). Waterston et. al. have shown that unc-105 is a member of the ENaC gene family. The phenotypic similarities between sup-43(lb141), enu-2(lb140) and unc-105(n490) are underscored by the observation that each exhibits striking synthetic lethality in combination with a fourth mutation, ndg-4(lb108). Ndg-4(lb108) confers strong resistance to nordihydroguairetic acid (NDG), a non-specific lipoxygenase inhibitor; dominant unc-8 mutations are moderately NDG resistant. Strikingly, many unc-105(n490);ndg-4(lb108) mutant embryos are severely vacuolated, while embryonic vacuoles are not observed in either single mutant. While the biochemical basis of ndg-4(lb108) drug resistance is not yet understood, interactions between ndg-4(lb108) and mutations in three different genes causing vacuoles within body wall muscle strongly suggest some commonality of action. Interactions with ndg-4 are particularly intriguing in the light of reports of effects of lipo- and epoxygenase inhibitors on CFTR (e.g., Kersting et. al. PNAS 90:4047). We speculate that unc-8 suppressor mutations may act by up-regulating an endogenous eicosanoid inhibitor of ENaC activity. We are currently analysing a novel unc-8 suppressor strain which expresses a pale egg phenotype identical to that of ndg-4. The gene expression patterns inferred from single and double mutant phenotypes in this and previous work suggest that overlapping sets of gene products are available for construction of Na+ leak channels in motorneurons, and body wall muscle, and early development. Phenotypic effects are exerted in motorneurons by unc-8(dom.), sup-40-43, and mec-6(l-o-f), in body wall muscle by unc-8(dom. or null), sup-43(lb141), enu-2(lb140), unc-105(n490), and ndg-4(lb108), and in developing eggs or embryos by sup-40(lb130), sup-42(lb88), sup-43(lb141), enu-2(lb140), unc-105(n490), and ndg-4(lb108).