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The Caenorhabditis elegans unc-78 gene encodes a homologue of actin-interacting protein 1 required for organized assembly of muscle actin filaments.

Ono S - J. Cell Biol. (2001)

Bottom Line: In unc-78 mutants, the striated organization of actin filaments is disrupted, and large actin aggregates are formed in the body wall muscle cells, resulting in defects in their motility.Similar Unc-78 phenotypes are observed in both embryonic and adult muscles.Thus, AIP1 is an important regulator of actin filament organization and localization of ADF/cofilin during development of myofibrils.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Emory University, Atlanta, Georgia 30322, USA. sono@emory.edu

ABSTRACT
Assembly and maintenance of myofibrils require dynamic regulation of the actin cytoskeleton. In Caenorhabditis elegans, UNC-60B, a muscle-specific actin depolymerizing factor (ADF)/cofilin isoform, is required for proper actin filament assembly in body wall muscle (Ono, S., D.L. Baillie, and G.M. Benian. 1999. J. Cell Biol. 145:491--502). Here, I show that UNC-78 is a homologue of actin-interacting protein 1 (AIP1) and functions as a novel regulator of actin organization in myofibrils. In unc-78 mutants, the striated organization of actin filaments is disrupted, and large actin aggregates are formed in the body wall muscle cells, resulting in defects in their motility. Point mutations in unc-78 alleles change conserved residues within different WD repeats of the UNC-78 protein and cause less severe phenotypes than a deletion allele, suggesting that these mutations partially impair the function of UNC-78. UNC-60B is normally localized in the diffuse cytoplasm and to the myofibrils in wild type but mislocalized to the actin aggregates in unc-78 mutants. Similar Unc-78 phenotypes are observed in both embryonic and adult muscles. Thus, AIP1 is an important regulator of actin filament organization and localization of ADF/cofilin during development of myofibrils.

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Genetic map and the structure of the unc-78 gene. (a) A part of the left arm of the X chromosome. (b) Arrangement of genes in the cosmid C04F6 (total 25 kb) predicted by the C. elegans Sequencing Consortium. (c) Exon–intron structure of the unc-78 gene (C06F6.4). Exons are indicated by boxes. The coding regions are represented by black filled regions. SL1 indicates a trans-splicing acceptor site. Locations of deletions and point mutations in unc-78 alleles are shown. (d) Putative WD repeats in UNC-78. Residues that match the consensus sequence (Smith et al. 1999) are indicated by black boxes. Arrows indicate residues that are altered by unc-78 mutations. (e) Phylogenetic analysis of AIP1 proteins. The scale shows the distance between sequences; units indicate the number of residue substitutions.
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Figure 1: Genetic map and the structure of the unc-78 gene. (a) A part of the left arm of the X chromosome. (b) Arrangement of genes in the cosmid C04F6 (total 25 kb) predicted by the C. elegans Sequencing Consortium. (c) Exon–intron structure of the unc-78 gene (C06F6.4). Exons are indicated by boxes. The coding regions are represented by black filled regions. SL1 indicates a trans-splicing acceptor site. Locations of deletions and point mutations in unc-78 alleles are shown. (d) Putative WD repeats in UNC-78. Residues that match the consensus sequence (Smith et al. 1999) are indicated by black boxes. Arrows indicate residues that are altered by unc-78 mutations. (e) Phylogenetic analysis of AIP1 proteins. The scale shows the distance between sequences; units indicate the number of residue substitutions.

Mentions: The unc-78 gene has been mapped to a position between fax-1 and sax-3 on the left arm of the X chromosome (Zallen et al. 1998; Much et al. 2000) (Fig. 1 a). Within this interval, a gene encoding a homologue of AIP1 (C04F6.4) has been predicted by the C. elegans Sequencing Consortium (Fig. 1 b). By sequencing the genomic DNA from five unc-78 alleles, I identified sequence alterations in C04F6.4 (Fig. 1 c). Furthermore, unc-78(gk27), a deletion allele of the C04F6.4 gene (Fig. 1 c), caused a similar but stronger Unc-78 phenotype than other unc-78 alleles (Fig. 2) and failed to complement unc-78(e1217). These results demonstrate that C04F6.4 is the unc-78 gene.


The Caenorhabditis elegans unc-78 gene encodes a homologue of actin-interacting protein 1 required for organized assembly of muscle actin filaments.

Ono S - J. Cell Biol. (2001)

Genetic map and the structure of the unc-78 gene. (a) A part of the left arm of the X chromosome. (b) Arrangement of genes in the cosmid C04F6 (total 25 kb) predicted by the C. elegans Sequencing Consortium. (c) Exon–intron structure of the unc-78 gene (C06F6.4). Exons are indicated by boxes. The coding regions are represented by black filled regions. SL1 indicates a trans-splicing acceptor site. Locations of deletions and point mutations in unc-78 alleles are shown. (d) Putative WD repeats in UNC-78. Residues that match the consensus sequence (Smith et al. 1999) are indicated by black boxes. Arrows indicate residues that are altered by unc-78 mutations. (e) Phylogenetic analysis of AIP1 proteins. The scale shows the distance between sequences; units indicate the number of residue substitutions.
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Related In: Results  -  Collection

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Figure 1: Genetic map and the structure of the unc-78 gene. (a) A part of the left arm of the X chromosome. (b) Arrangement of genes in the cosmid C04F6 (total 25 kb) predicted by the C. elegans Sequencing Consortium. (c) Exon–intron structure of the unc-78 gene (C06F6.4). Exons are indicated by boxes. The coding regions are represented by black filled regions. SL1 indicates a trans-splicing acceptor site. Locations of deletions and point mutations in unc-78 alleles are shown. (d) Putative WD repeats in UNC-78. Residues that match the consensus sequence (Smith et al. 1999) are indicated by black boxes. Arrows indicate residues that are altered by unc-78 mutations. (e) Phylogenetic analysis of AIP1 proteins. The scale shows the distance between sequences; units indicate the number of residue substitutions.
Mentions: The unc-78 gene has been mapped to a position between fax-1 and sax-3 on the left arm of the X chromosome (Zallen et al. 1998; Much et al. 2000) (Fig. 1 a). Within this interval, a gene encoding a homologue of AIP1 (C04F6.4) has been predicted by the C. elegans Sequencing Consortium (Fig. 1 b). By sequencing the genomic DNA from five unc-78 alleles, I identified sequence alterations in C04F6.4 (Fig. 1 c). Furthermore, unc-78(gk27), a deletion allele of the C04F6.4 gene (Fig. 1 c), caused a similar but stronger Unc-78 phenotype than other unc-78 alleles (Fig. 2) and failed to complement unc-78(e1217). These results demonstrate that C04F6.4 is the unc-78 gene.

Bottom Line: In unc-78 mutants, the striated organization of actin filaments is disrupted, and large actin aggregates are formed in the body wall muscle cells, resulting in defects in their motility.Similar Unc-78 phenotypes are observed in both embryonic and adult muscles.Thus, AIP1 is an important regulator of actin filament organization and localization of ADF/cofilin during development of myofibrils.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Emory University, Atlanta, Georgia 30322, USA. sono@emory.edu

ABSTRACT
Assembly and maintenance of myofibrils require dynamic regulation of the actin cytoskeleton. In Caenorhabditis elegans, UNC-60B, a muscle-specific actin depolymerizing factor (ADF)/cofilin isoform, is required for proper actin filament assembly in body wall muscle (Ono, S., D.L. Baillie, and G.M. Benian. 1999. J. Cell Biol. 145:491--502). Here, I show that UNC-78 is a homologue of actin-interacting protein 1 (AIP1) and functions as a novel regulator of actin organization in myofibrils. In unc-78 mutants, the striated organization of actin filaments is disrupted, and large actin aggregates are formed in the body wall muscle cells, resulting in defects in their motility. Point mutations in unc-78 alleles change conserved residues within different WD repeats of the UNC-78 protein and cause less severe phenotypes than a deletion allele, suggesting that these mutations partially impair the function of UNC-78. UNC-60B is normally localized in the diffuse cytoplasm and to the myofibrils in wild type but mislocalized to the actin aggregates in unc-78 mutants. Similar Unc-78 phenotypes are observed in both embryonic and adult muscles. Thus, AIP1 is an important regulator of actin filament organization and localization of ADF/cofilin during development of myofibrils.

Show MeSH