title: Conditional dominant mutations in the Caenorhabditis elegans gene act-2 identify cytoplasmic and muscle roles for a redundant actin isoform.
abstract: Animal genomes each encode multiple highly conserved actin isoforms that polymerize to form the microfilament cytoskeleton. Previous studies of vertebrates and invertebrates have shown that many actin isoforms are restricted to either nonmuscle (cytoplasmic) functions, or to myofibril force generation in muscle cells. We have identified two temperature-sensitive and semidominant embryonic-lethal Caenorhabditis elegans mutants, each with a single mis-sense mutation in act-2, one of five C. elegans genes that encode actin isoforms. These mutations alter conserved and adjacent amino acids predicted to form part of the ATP binding pocket of actin. At the restrictive temperature, both mutations resulted in aberrant distributions of cortical microfilaments associated with abnormal and striking membrane ingressions and protrusions. In contrast to the defects caused by these dominant mis-sense mutations, an act-2 deletion did not result in early embryonic cell division defects, suggesting that additional and redundant actin isoforms are involved. Accordingly, we found that two additional actin isoforms, act-1 and act-3, were required redundantly with act-2 for cytoplasmic function in early embryonic cells. The act-1 and -3 genes also have been implicated previously in muscle function. We found that an ACT-2::GFP reporter was expressed cytoplasmically in embryonic cells and also was incorporated into contractile filaments in adult muscle cells. Furthermore, one of the dominant act-2 mutations resulted in uncoordinated adult movement. We conclude that redundant C. elegans actin isoforms function in both muscle and nonmuscle contractile processes.
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Willis
authors.forename: Edwin
authors.initials: E
authors.lastname: Munro
authors.forename: Rebecca
authors.initials: R
authors.lastname: Lyczak
authors.forename: Bruce
authors.initials: B
authors.lastname: Bowerman
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000378:metabolism*; D002455:Cell Division; D016764:Cell Polarity; D022081:Cell Surface Extensions / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000166:cytology; D047108:Embryonic Development; D005799:Genes, Dominant / Q000235:genetics*; D017238:Genes, Helminth / Q000235:genetics*; D008969:Molecular Sequence Data; D009132:Muscles / Q000378:metabolism*; D009154:Mutation / Q000235:genetics*; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism
chemical_list: C510971:Act-2 protein, C elegans; D000199:Actins; D029742:Caenorhabditis elegans Proteins; D020033:Protein Isoforms