unc-94 encodes a tropomodulin in C. elegans

• Type of Material: Article
• Authors: Tesheka O. Stevenson, Emory University; Kristina B. Mercer, Emory University; Elisabeth A. Cox, University of Wisconsin; Nathaniel J. Szewczyk, NASA Ames Research Center; Catharine A. Conley, NASA Ames Research Center; Jeffrey D. Hardin, University of Wisconsin; Guy Benian, Emory University
• Language: English
• Date: 2007-12-07
• Publisher: Elsevier
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2007 Elsevier Ltd.
• License: Creative Commons Attribution-NonCommerical-NoDerivs 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1016/j.jmb.2007.10.005
• Title of Journal or Parent Work: Journal of Molecular Biology
• ISSN: 0022-2836
• Volume: 374
• Issue: 4
• Start Page: 936
• End Page: 950
• Grant/Funding Information: These studies were supported by grant AR052133 from the National Institutes of Health to G.M.B., by grant GM58038 from the National Institutes of Health and grant 4218 from the Muscular Dystrophy Association to J.H.; Caenorhabditis Genetics Center is supported by the National Center for Research Resources of the National Institutes of Health.
• Keywords: striated muscle; tropomodulin; C. elegans; myofibrils; thin filaments
• Research Categories: Biology, General; Health Sciences, Pathology; Biology, Molecular

Abstract

unc-94 is one of about 40 genes in C. elegans, that when mutant, displays an abnormal muscle phenotype. Two mutant alleles of unc-94, su177 and sf20, show reduced motility and brood size, and disorganization of muscle structure. In unc-94 mutants, immunofluorescence microscopy shows that a number of known sarcomeric proteins are abnormal, but the most dramatic effect is in the localization of F-actin, with some, abnormally accumulated near muscle cell-to-cell boundaries. Electron microscopy shows that unc-94(sf20) mutants have large accumulations of thin filaments near the boundaries of adjacent muscle cells. Multiple lines of evidence prove that unc-94 encodes a tropomodulin, a conserved protein known from other systems to bind to both actin and tropomyosin at the pointed ends of actin thin filaments. su177 is a splice site mutation in intron 1, which is specific to one of the two unc-94 isoforms, isoform-a; sf20, has a stop codon in exon 5, which is shared by both isoform-a and isoform-b. The use of promoter-GFP constructs in transgenic animals revealed that unc-94a is expressed in body wall, vulval and uterine muscles, whereas unc-94b is expressed in pharyngeal, anal depressor, vulval and uterine muscles, and in spermatheca and intestinal epithelial cells. By western blot, anti-UNC-94 antibodies detect polypeptides of expected size from wild type, wild type-sized proteins of reduced abundance from unc-94(su177), and no detectable unc-94 products from unc-94(sf20). Using these same antibodies, UNC-94 localizes as two closely spaced parallel lines flanking the M-lines, consistent with localization to the pointed ends of thin filaments. In addition, UNC-94 is localized near muscle cell to cell boundaries.