title: unc-94 encodes a tropomodulin in Caenorhabditis elegans.
abstract: unc-94 is one of about 40 genes in Caenorhabditis 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-green fluorescent protein 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.
authors.affiliation: Department of Pathology, Emory University, Atlanta, GA 30322, USA.
authors.forename: Tesheka O
authors.initials: TO
authors.lastname: Stevenson
authors.forename: Kristina B
authors.initials: KB
authors.lastname: Mercer
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Cox
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Szewczyk
authors.forename: Catharine A
authors.initials: CA
authors.lastname: Conley
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Hardin
authors.forename: Guy M
authors.initials: GM
authors.lastname: Benian
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D007365:Intercellular Junctions / Q000378:metabolism; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009928:Organ Specificity; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051348:Tropomodulin / Q000235:genetics* / Q000378:metabolism
chemical_list: D000199:Actins; D029742:Caenorhabditis elegans Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D020033:Protein Isoforms; D051348:Tropomodulin; C480760:UNC-94 protein, C elegans