Worm Breeder's Gazette 14(3): 48 (June 1, 1996)
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.
|1||Dept. of Genetics, University of Washington, Seattle, WA 98195, USA|
|2||Fundamental Research Laboratories, NEC Corporation, Tsukuba 305, Japan. Dept. of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo 154, Japan|
|3||Fundamental Research Laboratories, NEC Corporation, Tsukuba 305, Japan|
|4||Dept. of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo 154, Japan|
|5||Dept. of Biochemistry, Brandeis University, Waltham, MA 02254, USA|
Many genes have been described that can be dominantly mutated to cause muscle activation defects (Mac-d) or hyper-activated muscle (Mac-h). These genes were proposed to encode ion channels or other regulators of cell excitability. Mutations in a third class of genes confer Mac-d phenotypes in some tissues and Mac-h phenotypes in other tissues (Mac-m; muscle activation mixed). Perhaps the Mac-m genes encode regulatory components whose functions are mediated by various gene products in different tissues to produce physiologically opposite phenotypes (1). If this were true, loss-of-function mutations in downstream genes should suppress the dominant Mac-m phenotypes. This notion was tested for the Mac-m gene unc-43 by building double mutants between the unc-43 gain-of-function mutation and loss-of-function mutations in other Mac genes. We found that loss-of-function mutations in the Mac-d gene unc-103 completely suppressed the unc-43(gf) enteric muscle contraction (EMC) defect in defecation, but did not suppress any other unc-43(gf) phenotypes. Other double mutants indicate that the degree of this suppression is specific to unc-103 and unc-43. We propose that unc-103 encodes a tissue-specific effector of unc-43 in the enteric muscles, but that other proteins function downstream of unc-43 in other tissues. Loss-of-function mutations in both unc-103 and unc-43 confer weak suppression of the egl-36(gf) and egl-19(lf) EMC defects. To explain these results, we hypothesize that both unc-103(lf) and unc-43(lf) cause the enteric muscles to be slightly hyper-activated. Based on sequence reported by the genome sequencing consortium (2), we identified a putative K+ channel homolog (C30D11.1) that was a likely candidate for the unc-103 gene. Using C30D11 as a probe of a genomic southern of unc-103 mutant DNAs, we found 1.6 kb insertions in fragments corresponding to C30D11.1 from strains containing the mutator alleles e1597k103, e1597k104, e1597k105, and e1597sa468. These mutations were generated by reverting the unc-103(e1597) dominant phenotypes in a mut-6 background (3). Furthermore, the 1.6 kb insertion was absent in a revertant of e1597k104. Finally, the putative unc-103 gene was completely deleted in the EMS allele e1597n1213. We conclude that unc-103 corresponds to C30D11.1. RT-PCR was used to clone unc-103 cDNAs, and the coding region was sequenced in several such clones. Overall, this predicted protein is 54% identical and 70% similar to the human ether-a-gogo related gene (HERG), an inward rectifying potassium channel shown to be mutant in a form of the hereditary cardiac disorder Long QT Syndrome (4-7). Furthermore, the unc-103 and HERG sequence comparison is more striking in the putative transmembrane and pore domains, with 82% identity and 94% similarity. Given this extremely high similarity, we speculate that unc-103 is a functional homolog of HERG, and that analysis of unc-103, and perhaps unc-43, is relevant to the understanding Long QT Syndrome. (1) Reiner, Weinshenker and Thomas (1995) Genetics 141: 961-976. (2) Wilson et al. (1994) Nature 368:32-38. (3) Uekusa, Nishiwaki, Uchida and Miwa (1994) WBG 13(3): 58. (4) Curran, Splawski, Timothy, Vincent, Green and Keating (1995) Cell 80: 795-803. (5) Sanguinetti, Jiang, Curran and Keating (1995) Cell 81: 299-307. (6) Trudeau, Warmke, Ganetzky and Robertson (1995) Science 269: 92-95. (7) Smith, Baukrowitz and Yellen (1996) Nature 379: 833-836.