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Imaging of Actin Cytoskeleton in the Nematode Caenorhabditis elegans. Methods Mol Biol 2021. [PMID: 34542852 DOI: 10.1007/978-1-0716-1661-1_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
The nematode Caenorhabditis elegans is one of the major model organisms in cell and developmental biology. This organism is easy to culture in laboratories and suitable for microscopic investigation of the cytoskeleton. Because the worms are small and transparent, the actin cytoskeleton in many tissues and cells can be observed with appropriate visualization techniques without sectioning or dissection. This chapter describes the introduction to representative methods for imaging the actin cytoskeleton in C. elegans and a protocol for staining worms with fluorescent phalloidin.
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Ono S. Regulation of structure and function of sarcomeric actin filaments in striated muscle of the nematode Caenorhabditis elegans. Anat Rec (Hoboken) 2015; 297:1548-59. [PMID: 25125169 DOI: 10.1002/ar.22965] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 02/26/2014] [Accepted: 02/26/2014] [Indexed: 02/01/2023]
Abstract
The nematode Caenorhabditis elegans has been used as a valuable system to study structure and function of striated muscle. The body wall muscle of C. elegans is obliquely striated muscle with highly organized sarcomeric assembly of actin, myosin, and other accessory proteins. Genetic and molecular biological studies in C. elegans have identified a number of genes encoding structural and regulatory components for the muscle contractile apparatuses, and many of them have counterparts in mammalian cardiac and skeletal muscles or striated muscles in other invertebrates. Applicability of genetics, cell biology, and biochemistry has made C. elegans an excellent system to study mechanisms of muscle contractility and assembly and maintenance of myofibrils. This review focuses on the regulatory mechanisms of structure and function of actin filaments in the C. elegans body wall muscle. Sarcomeric actin filaments in C. elegans muscle are associated with the troponin-tropomyosin system that regulates the actin-myosin interaction. Proteins that bind to the side and ends of actin filaments support ordered assembly of thin filaments. Furthermore, regulators of actin dynamics play important roles in initial assembly, growth, and maintenance of sarcomeres. The knowledge acquired in C. elegans can serve as bases to understand the basic mechanisms of muscle structure and function.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, Georgia; Department of Cell Biology, Emory University, Atlanta, Georgia
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3
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Cox-Paulson E, Cannataro V, Gallagher T, Hoffman C, Mantione G, Mcintosh M, Silva M, Vissichelli N, Walker R, Simske J, Ono S, Hoops H. The minus-end actin capping protein, UNC-94/tropomodulin, regulates development of the Caenorhabditis elegans intestine. Dev Dyn 2014; 243:753-64. [PMID: 24677443 DOI: 10.1002/dvdy.24118] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 09/25/2013] [Accepted: 01/31/2014] [Indexed: 01/27/2023] Open
Abstract
BACKGROUND Tropomodulins are actin-capping proteins that regulate the stability of the slow-growing, minus-ends of actin filaments. The C. elegans tropomodulin homolog, UNC-94, has sequence and functional similarity to vertebrate tropomodulins. We investigated the role of UNC-94 in C. elegans intestinal morphogenesis. RESULTS In the embryonic C. elegans intestine, UNC-94 localizes to the terminal web, an actin- and intermediate filament-rich structure that underlies the apical membrane. Loss of UNC-94 function results in areas of flattened intestinal lumen. In worms homozygous for the strong loss-of-function allele, unc-94(tm724), the terminal web is thinner and the amount of F-actin is reduced, pointing to a role for UNC-94 in regulating the structure of the terminal web. The non-muscle myosin, NMY-1, also localizes to the terminal web, and we present evidence that increasing actomyosin contractility by depleting the myosin phosphatase regulatory subunit, mel-11, can rescue the flattened lumen phenotype of unc-94 mutants. CONCLUSIONS The data support a model in which minus-end actin capping by UNC-94 promotes proper F-actin structure and contraction in the terminal web, yielding proper shape of the intestinal lumen. This establishes a new role for a tropomodulin in regulating lumen shape during tubulogenesis.
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4
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Biochemical and cell biological analysis of actin in the nematode Caenorhabditis elegans. Methods 2011; 56:11-7. [PMID: 21945576 DOI: 10.1016/j.ymeth.2011.09.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 09/06/2011] [Accepted: 09/10/2011] [Indexed: 11/21/2022] Open
Abstract
The nematode Caenorhabditis elegans has long been a useful model organism for muscle research. Its body wall muscle is obliquely striated muscle and exhibits structural similarities with vertebrate striated muscle. Actin is the core component of the muscle thin filaments, which are highly ordered in sarcomeric structures in striated muscle. Genetic studies have identified genes that regulate proper organization and function of actin filaments in C. elegans muscle, and sequence of the worm genome has revealed a number of conserved candidate genes that may regulate actin. To precisely understand the functions of actin-binding proteins, such genetic and genomic studies need to be complemented by biochemical characterization of these actin-binding proteins in vitro. This article describes methods for purification and biochemical characterization of actin from C. elegans. Although rabbit muscle actin is commonly used to characterize actin-binding proteins from many eukaryotic organisms, we detect several quantitative differences between C. elegans actin and rabbit muscle actin, highlighting that use of actin from an appropriate source is important in some cases. Additionally, we describe probes for cell biological analysis of actin in C. elegans.
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Yamashiro S, Cox EA, Baillie DL, Hardin JD, Ono S. Sarcomeric actin organization is synergistically promoted by tropomodulin, ADF/cofilin, AIP1 and profilin in C. elegans. J Cell Sci 2008; 121:3867-77. [PMID: 18984629 DOI: 10.1242/jcs.040477] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Sarcomeric organization of thin and thick filaments in striated muscle is important for the efficient generation of contractile forces. Sarcomeric actin filaments are uniform in their lengths and regularly arranged in a striated pattern. Tropomodulin caps the pointed end of actin filaments and is a crucial regulator of sarcomere assembly. Here, we report unexpected synergistic functions of tropomodulin with enhancers of actin filament dynamics in Caenorhabditis elegans striated muscle. Pointed-end capping by tropomodulin inhibited actin filament depolymerization by ADF/cofilin in vitro. However, in vivo, the depletion of tropomodulin strongly enhanced the disorganization of sarcomeric actin filaments in ADF/cofilin mutants, rather than antagonistically suppressing the phenotype. Similar phenotypic enhancements by tropomodulin depletion were also observed in mutant backgrounds for AIP1 and profilin. These in vivo effects cannot be simply explained by antagonistic effects of tropomodulin and ADF/cofilin in vitro. Thus, we propose a model in which tropomodulin and enhancers of actin dynamics synergistically regulate elongation and shortening of actin filaments at the pointed end.
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Affiliation(s)
- Sawako Yamashiro
- Department of Pathology and Department of Cell Biology, Emory University, Atlanta, GA 30322, USA
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6
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Neidt EM, Scott BJ, Kovar DR. Formin differentially utilizes profilin isoforms to rapidly assemble actin filaments. J Biol Chem 2008; 284:673-684. [PMID: 18978356 DOI: 10.1074/jbc.m804201200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Cells contain multiple formin isoforms that drive the assembly of profilin-actin for diverse processes. Given that many organisms also contain several profilin isoforms, specific formin/profilin pairs might be matched to optimally stimulate actin polymerization. We utilized a combination of bulk actin polymerization and single filament total internal reflection fluorescence microscopy assays to measure the effect of different profilin isoforms on the actin assembly properties of the cytokinesis formins from fission yeast (Cdc12p) and the nematode worm (CYK-1). We discovered that Cdc12p only effectively utilizes the single fission yeast profilin isoform SpPRF. Conversely, CYK-1 prefers the essential worm cytokinesis profilin CePFN-1 to the two non-essential worm profilin isoforms (SpPRF = CePFN-1 > CePFN-2 > CePFN-3). Chimeras containing the profilin-binding formin homology 1 (FH1) domain from one formin and the barbed-end associated FH2 domain from the other formin, revealed that both the FH1 and FH2 domains help confer profilin isoform specialization. Although the Cdc12p and CYK-1 FH1 domains cannot differentiate between profilin isoforms in the absence of actin, formin FH1 domains appear to preferentially select specific isoforms of profilin-actin. Surprisingly, analysis of profilin point mutants revealed that differences in highly conserved residues in both the poly-L-proline and actin binding regions of profilin do not explain their differential utilization by formin. Therefore, rapid formin-mediated elongation of profilin-actin depends upon favorable interactions of profilin-actin with the FH1 domain as well as the barbed-end associated FH2 domain. Specific formin FH1FH2 domains are tailored to optimally utilize actin bound to particular profilin isoforms.
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Affiliation(s)
- Erin M Neidt
- Departments of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637
| | - Bonnie J Scott
- Departments of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637
| | - David R Kovar
- Departments of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637; Departments of Molecular Genetics and Cell Biology and Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637.
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Hooper SL, Hobbs KH, Thuma JB. Invertebrate muscles: thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle. Prog Neurobiol 2008; 86:72-127. [PMID: 18616971 PMCID: PMC2650078 DOI: 10.1016/j.pneurobio.2008.06.004] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Revised: 05/08/2008] [Accepted: 06/12/2008] [Indexed: 11/26/2022]
Abstract
This is the second in a series of canonical reviews on invertebrate muscle. We cover here thin and thick filament structure, the molecular basis of force generation and its regulation, and two special properties of some invertebrate muscle, catch and asynchronous muscle. Invertebrate thin filaments resemble vertebrate thin filaments, although helix structure and tropomyosin arrangement show small differences. Invertebrate thick filaments, alternatively, are very different from vertebrate striated thick filaments and show great variation within invertebrates. Part of this diversity stems from variation in paramyosin content, which is greatly increased in very large diameter invertebrate thick filaments. Other of it arises from relatively small changes in filament backbone structure, which results in filaments with grossly similar myosin head placements (rotating crowns of heads every 14.5 nm) but large changes in detail (distances between heads in azimuthal registration varying from three to thousands of crowns). The lever arm basis of force generation is common to both vertebrates and invertebrates, and in some invertebrates this process is understood on the near atomic level. Invertebrate actomyosin is both thin (tropomyosin:troponin) and thick (primarily via direct Ca(++) binding to myosin) filament regulated, and most invertebrate muscles are dually regulated. These mechanisms are well understood on the molecular level, but the behavioral utility of dual regulation is less so. The phosphorylation state of the thick filament associated giant protein, twitchin, has been recently shown to be the molecular basis of catch. The molecular basis of the stretch activation underlying asynchronous muscle activity, however, remains unresolved.
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Affiliation(s)
- Scott L. Hooper
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
| | - Kevin H. Hobbs
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
| | - Jeffrey B. Thuma
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
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Yamashiro S, Gimona M, Ono S. UNC-87, a calponin-related protein in C. elegans, antagonizes ADF/cofilin-mediated actin filament dynamics. J Cell Sci 2007; 120:3022-33. [PMID: 17684058 PMCID: PMC2365702 DOI: 10.1242/jcs.013516] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Stabilization of actin filaments is critical for supporting actomyosin-based contractility and for maintaining stable cellular structures. Tropomyosin is a well-characterized ubiquitous actin stabilizer that inhibits ADF/cofilin-dependent actin depolymerization. Here, we show that UNC-87, a calponin-related Caenorhabditis elegans protein with seven calponin-like repeats, competes with ADF/cofilin for binding to actin filaments and inhibits ADF/cofilin-dependent filament severing and depolymerization in vitro. Mutations in the unc-87 gene suppress the disorganized actin phenotype in an ADF/cofilin mutant in the C. elegans body wall muscle, supporting their antagonistic roles in regulating actin stability in vivo. UNC-87 and tropomyosin exhibit synergistic effects in stabilizing actin filaments against ADF/cofilin, and direct comparison reveals that UNC-87 effectively stabilizes actin filaments at much lower concentrations than tropomyosin. However, the in vivo functions of UNC-87 and tropomyosin appear different, suggesting their distinct roles in the regulation of actomyosin assembly and cellular contractility. Our results demonstrate that actin binding via calponin-like repeats competes with ADF/cofilin-driven cytoskeletal turnover, and is critical for providing the spatiotemporal regulation of actin filament stability.
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Affiliation(s)
- Sawako Yamashiro
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
| | - Mario Gimona
- Unit of Actin Cytoskeleton Regulation, Consorzio Mario Negri Sud, Department of Cell Biology and Oncology, Via Nazionale 8a, 66030 Santa Maria, Imbaro, Italy
| | - Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
- *Author for correspondence (e-mail: )
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Ono S. Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 258:1-82. [PMID: 17338919 DOI: 10.1016/s0074-7696(07)58001-0] [Citation(s) in RCA: 212] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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10
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Corsi AK. A biochemist's guide to Caenorhabditis elegans. Anal Biochem 2006; 359:1-17. [PMID: 16942745 PMCID: PMC1855192 DOI: 10.1016/j.ab.2006.07.033] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2006] [Revised: 07/11/2006] [Accepted: 07/17/2006] [Indexed: 10/24/2022]
Affiliation(s)
- Ann K Corsi
- Department of Biology, The Catholic University of America, Washington, DC 20064, USA.
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Ono K, Yu R, Mohri K, Ono S. Caenorhabditis elegans kettin, a large immunoglobulin-like repeat protein, binds to filamentous actin and provides mechanical stability to the contractile apparatuses in body wall muscle. Mol Biol Cell 2006; 17:2722-34. [PMID: 16597697 PMCID: PMC1474806 DOI: 10.1091/mbc.e06-02-0114] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Kettin is a large actin-binding protein with immunoglobulin-like (Ig) repeats, which is associated with the thin filaments in arthropod muscles. Here, we report identification and functional characterization of kettin in the nematode Caenorhabditis elegans. We found that one of the monoclonal antibodies that were raised against C. elegans muscle proteins specifically reacts with kettin (Ce-kettin). We determined the entire cDNA sequence of Ce-kettin that encodes a protein of 472 kDa with 31 Ig repeats. Arthropod kettins are splice variants of much larger connectin/titin-related proteins. However, the gene for Ce-kettin is independent of other connectin/titin-related genes. Ce-kettin localizes to the thin filaments near the dense bodies in both striated and nonstriated muscles. The C-terminal four Ig repeats and the adjacent non-Ig region synergistically bind to actin filaments in vitro. RNA interference of Ce-kettin caused weak disorganization of the actin filaments in body wall muscle. This phenotype was suppressed by inhibiting muscle contraction by a myosin mutation, but it was enhanced by tetramisole-induced hypercontraction. Furthermore, Ce-kettin was involved in organizing the cytoplasmic portion of the dense bodies in cooperation with alpha-actinin. These results suggest that kettin is an important regulator of myofibrillar organization and provides mechanical stability to the myofibrils during contraction.
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Affiliation(s)
- Kanako Ono
- Department of Pathology, Emory University, Atlanta, GA 30322
| | - Robinson Yu
- Department of Pathology, Emory University, Atlanta, GA 30322
| | - Kurato Mohri
- Department of Pathology, Emory University, Atlanta, GA 30322
| | - Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, GA 30322
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12
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Mohri K, Ono K, Yu R, Yamashiro S, Ono S. Enhancement of actin-depolymerizing factor/cofilin-dependent actin disassembly by actin-interacting protein 1 is required for organized actin filament assembly in the Caenorhabditis elegans body wall muscle. Mol Biol Cell 2006; 17:2190-9. [PMID: 16525019 PMCID: PMC1446098 DOI: 10.1091/mbc.e05-11-1016] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Regulated disassembly of actin filaments is involved in several cellular processes that require dynamic rearrangement of the actin cytoskeleton. Actin-interacting protein (AIP) 1 specifically enhances disassembly of actin-depolymerizing factor (ADF)/cofilin-bound actin filaments. In vitro, AIP1 actively disassembles filaments, caps barbed ends, and binds to the side of filaments. However, how AIP1 functions in the cellular actin cytoskeletal dynamics is not understood. We compared biochemical and in vivo activities of mutant UNC-78 proteins and found that impaired activity of mutant UNC-78 proteins to enhance disassembly of ADF/cofilin-bound actin filaments is associated with inability to regulate striated organization of actin filaments in muscle cells. Six functionally important residues are present in the N-terminal beta-propeller, whereas one residue is located in the C-terminal beta-propeller, suggesting the presence of two separate sites for interaction with ADF/cofilin and actin. In vitro, these mutant UNC-78 proteins exhibited variable alterations in actin disassembly and/or barbed end-capping activities, suggesting that both activities are important for its in vivo function. These results indicate that the actin-regulating activity of AIP1 in cooperation with ADF/cofilin is essential for its in vivo function to regulate actin filament organization in muscle cells.
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Affiliation(s)
- Kurato Mohri
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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13
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Yamashiro S, Mohri K, Ono S. The two Caenorhabditis elegans actin-depolymerizing factor/cofilin proteins differently enhance actin filament severing and depolymerization. Biochemistry 2006; 44:14238-47. [PMID: 16245940 PMCID: PMC1910702 DOI: 10.1021/bi050933d] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Actin-depolymerizing factor (ADF)/cofilin enhances the turnover of actin filaments by two separable activities: filament severing and pointed-end depolymerization. Multicellular organisms express multiple ADF/cofilin isoforms in a tissue-specific manner, and the vertebrate proteins are grouped into ADFs and cofilins on the basis of their biochemical activity. A recent comparative study has shown that ADF has greater severing and depolymerizing activities than cofilin [Chen, H., Bernstein, B. W., Sneider, J. M., Boyle, J. A., Minamide, L. S., and Bamburg, J. R. (2004) Biochemistry 43, 7127-7142]. Here, we show that the two Caenorhabditis elegans ADF/cofilin isoforms exhibit different activities for severing and depolymerizing actin filaments. The ADF-like non-muscle isoform UNC-60A had greater activities to cause net depolymerization and inhibit polymerization than the cofilin-like muscle isoform UNC-60B. Surprisingly, UNC-60B exhibited much stronger severing activity than UNC-60A, which was the opposite of what was observed for vertebrate counterparts. Moreover, UNC-60B induced much faster pointed-end depolymerization of rabbit muscle actin than UNC-60A, while UNC-60A caused slightly faster depolymerization of C. elegans actin than UNC-60B. These results suggest that cofilin-like UNC-60B is kinetically more efficient in enhancing actin turnover than ADF-like UNC-60A, while ADF-like UNC-60A is suitable for maintaining higher concentrations of monomeric actin. These functional differences might be specifically adapted for different actin dynamics in muscle and non-muscle cells.
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Affiliation(s)
- Sawako Yamashiro
- Department of Pathology, Emory University, Atlanta, Georgia 30322, USA
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Willis JH, Munro E, Lyczak R, Bowerman B. Conditional dominant mutations in the Caenorhabditis elegans gene act-2 identify cytoplasmic and muscle roles for a redundant actin isoform. Mol Biol Cell 2006; 17:1051-64. [PMID: 16407404 PMCID: PMC1382297 DOI: 10.1091/mbc.e05-09-0886] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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.
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Affiliation(s)
- John H Willis
- Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA
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15
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Abstract
This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.
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Affiliation(s)
- Scott L Hooper
- Neuroscience Program, Department of Biological Sciences, Irvine Hall, Ohio University, Athens, Ohio 45701, USA.
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16
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Anyanful A, Ono K, Johnsen RC, Ly H, Jensen V, Baillie DL, Ono S. The RNA-binding protein SUP-12 controls muscle-specific splicing of the ADF/cofilin pre-mRNA in C. elegans. ACTA ACUST UNITED AC 2004; 167:639-47. [PMID: 15545320 PMCID: PMC1781344 DOI: 10.1083/jcb.200407085] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tissue-specific alternative pre-mRNA splicing is essential for increasing diversity of functionally different gene products. In Caenorhabditis elegans, UNC-60A and UNC-60B, nonmuscle and muscle isoforms of actin depolymerizing factor (ADF)/cofilin, are expressed by alternative splicing of unc-60 and regulate distinct actin-dependent developmental processes. We report that SUP-12, a member of a new family of RNA recognition motif (RRM) proteins, including SEB-4, regulates muscle-specific splicing of unc-60. In sup-12 mutants, expression of UNC-60B is decreased, whereas UNC-60A is up-regulated in muscle. sup-12 mutations strongly suppress muscle defects in unc-60B mutants by allowing expression of UNC-60A in muscle that can substitute for UNC-60B, thus unmasking their functional redundancy. SUP-12 is expressed in muscle and localized to the nuclei in a speckled pattern. The RRM domain of SUP-12 binds to several sites of the unc-60 pre-mRNA including the UG repeats near the 3′-splice site in the first intron. Our results suggest that SUP-12 is a novel tissue-specific splicing factor and regulates functional redundancy among ADF/cofilin isoforms.
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Affiliation(s)
- Akwasi Anyanful
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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17
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Mohri K, Ono S. Actin filament disassembling activity of Caenorhabditis elegans actin-interacting protein 1 (UNC-78) is dependent on filament binding by a specific ADF/cofilin isoform. J Cell Sci 2003; 116:4107-18. [PMID: 12953066 DOI: 10.1242/jcs.00717] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Actin-interacting protein 1 (AIP1) is a conserved WD-repeat protein that enhances actin filament disassembly only in the presence of actin depolymerizing factor (ADF)/cofilin. In the nematode Caenorhabditis elegans, an AIP1 ortholog is encoded by the unc-78 gene that is required for organized assembly of muscle actin filaments. We produced bacterially expressed UNC-78 protein and found that it enhances actin filament disassembly preferentially in the presence of a specific ADF/cofilin isoform. Extensive and rapid filament disassembly by UNC-78 was observed in the presence of UNC-60B, a muscle-specific C. elegans ADF/cofilin isoform. UNC-78 also reduced the rate of spontaneous polymerization and enhanced subunit dissociation from filaments in the presence of UNC-60B. However, in the presence of UNC-60A, a non-muscle C. elegans ADF/cofilin isoform, UNC-78 only slightly enhanced filament disassembly. Interestingly, UNC-78 failed to enhance disassembly by mouse muscle-type cofilin. Using mutant forms of UNC-60B, we demonstrated that the F-actin-specific binding site of UNC-60B at the C terminus is required for filament disassembly by UNC-78. UNC-78 was expressed in body wall muscle and co-localized with actin where UNC-60B was also present. Surprisingly, UNC-78 was co-localized with actin in unc-60B null mutants, suggesting that the AIP1-actin interaction is not dependent on ADF/cofilin in muscle. These results suggest that UNC-78 closely collaborates with UNC-60B to regulate actin dynamics in muscle cells.
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Affiliation(s)
- Kurato Mohri
- Department of Pathology, Emory University, Atlanta, GA 30322, USA
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Vorobiev S, Strokopytov B, Drubin DG, Frieden C, Ono S, Condeelis J, Rubenstein PA, Almo SC. The structure of nonvertebrate actin: implications for the ATP hydrolytic mechanism. Proc Natl Acad Sci U S A 2003; 100:5760-5. [PMID: 12732734 PMCID: PMC156274 DOI: 10.1073/pnas.0832273100] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The structures of Saccharomyces cerevisiae, Dictyostelium, and Caenorhabditis elegans actin bound to gelsolin segment-1 have been solved and refined at resolutions between 1.9 and 1.75 A. These structures reveal several features relevant to the ATP hydrolytic mechanism, including identification of the nucleophilic water and the roles of Gln-137 and His-161 in positioning and activating the catalytic water, respectively. The involvement of these residues in the catalytic mechanism is consistent with yeast genetics studies. This work highlights both structural and mechanistic similarities with the small and trimeric G proteins and restricts the types of mechanisms responsible for the considerable enhancement of ATP hydrolysis associated with actin polymerization. The conservation of functionalities involved in nucleotide binding and catalysis also provide insights into the mechanistic features of members of the family of actin-related proteins.
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Affiliation(s)
- S Vorobiev
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
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19
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Abstract
Tropomyosin binds to actin filaments and is implicated in stabilization of actin cytoskeleton. We examined biochemical and cell biological properties of Caenorhabditis elegans tropomyosin (CeTM) and obtained evidence that CeTM is antagonistic to ADF/cofilin-dependent actin filament dynamics. We purified CeTM, actin, and UNC-60B (a muscle-specific ADF/cofilin isoform), all of which are derived from C. elegans, and showed that CeTM and UNC-60B bound to F-actin in a mutually exclusive manner. CeTM inhibited UNC-60B-induced actin depolymerization and enhancement of actin polymerization. Within isolated native thin filaments, actin and CeTM were detected as major components, whereas UNC-60B was present at a trace amount. Purified UNC-60B was unable to interact with the native thin filaments unless CeTM and other associated proteins were removed by high-salt extraction. Purified CeTM was sufficient to restore the resistance of the salt-extracted filaments from UNC-60B. In muscle cells, CeTM and UNC-60B were localized in different patterns. Suppression of CeTM by RNA interference resulted in disorganized actin filaments and paralyzed worms in wild-type background. However, in an ADF/cofilin mutant background, suppression of CeTM did not worsen actin organization and worm motility. These results suggest that tropomyosin is a physiological inhibitor of ADF/cofilin-dependent actin dynamics.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
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20
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Abstract
The ADF/cofilins are a family of actin-binding proteins expressed in all eukaryotic cells so far examined. Members of this family remodel the actin cytoskeleton, for example during cytokinesis, when the actin-rich contractile ring shrinks as it contracts through the interaction of ADF/cofilins with both monomeric and filamentous actin. The depolymerizing activity is twofold: ADF/cofilins sever actin filaments and also increase the rate at which monomers leave the filament's pointed end. The three-dimensional structure of ADF/cofilins is similar to a fold in members of the gelsolin family of actin-binding proteins in which this fold is typically repeated three or six times; although both families bind polyphosphoinositide lipids and actin in a pH-dependent manner, they share no obvious sequence similarity. Plants and animals have multiple ADF/cofilin genes, belonging in vertebrates to two types, ADF and cofilins. Other eukaryotes (such as yeast, Acanthamoeba and slime moulds) have a single ADF/cofilin gene. Phylogenetic analysis of the ADF/cofilins reveals that, with few exceptions, their relationships reflect conventional views of the relationships between the major groups of organisms.
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Affiliation(s)
- Sutherland K Maciver
- Genes and Development Interdisciplinary Group, Department of Biomedical Sciences, University of Edinburgh, George Square, Edinburgh EH8 9XD, Scotland, UK.
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Ono S, McGough A, Pope BJ, Tolbert VT, Bui A, Pohl J, Benian GM, Gernert KM, Weeds AG. The C-terminal tail of UNC-60B (actin depolymerizing factor/cofilin) is critical for maintaining its stable association with F-actin and is implicated in the second actin-binding site. J Biol Chem 2001; 276:5952-8. [PMID: 11050090 DOI: 10.1074/jbc.m007563200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin depolymerizing factor (ADF)/cofilin changes the twist of actin filaments by binding two longitudinally associated actin subunits. In the absence of an atomic model of the ADF/cofilin-F-actin complex, we have identified residues in ADF/cofilin that are essential for filament binding. Here, we have characterized the C-terminal tail of UNC-60B (a nematode ADF/cofilin isoform) as a novel determinant for its association with F-actin. Removal of the C-terminal isoleucine (Ile152) by carboxypeptidase A or truncation by mutagenesis eliminated F-actin binding activity but strongly enhanced actin depolymerizing activity. Replacement of Ile152 by Ala had a similar but less marked effect; F-actin binding was weakened and depolymerizing activity slightly enhanced. Truncation of both Arg151 and Ile152 or replacement of Arg151 with Ala also abolished F-actin binding and enhanced depolymerizing activity. Loss of F-actin binding in these mutants was accompanied by loss or greatly decreased severing activity. All of the variants of UNC-60B interacted with G-actin in an indistinguishable manner from wild type. Cryoelectron microscopy showed that UNC-60B changed the twist of F-actin to a similar extent to vertebrate ADF/cofilins. Helical reconstruction and structural modeling of UNC-60B-F-actin complex reveal how the C terminus of UNC-60B might be involved in one of the two actin-binding sites.
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Affiliation(s)
- S Ono
- Department of Pathology, Emory University, Atlanta, Georgia 30322, USA.
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Ono S, Baillie DL, Benian GM. UNC-60B, an ADF/cofilin family protein, is required for proper assembly of actin into myofibrils in Caenorhabditis elegans body wall muscle. J Cell Biol 1999; 145:491-502. [PMID: 10225951 PMCID: PMC2185080 DOI: 10.1083/jcb.145.3.491] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Caenorhabditis elegans unc-60 gene encodes two functionally distinct isoforms of ADF/cofilin that are implicated in myofibril assembly. Here, we show that one of the gene products, UNC-60B, is specifically required for proper assembly of actin into myofibrils. We found that all homozygous viable unc-60 mutations resided in the unc-60B coding region, indicating that UNC-60B is responsible for the Unc-60 phenotype. Wild-type UNC-60B had F-actin binding, partial actin depolymerizing, and weak F-actin severing activities in vitro. However, mutations in UNC-60B caused various alterations in these activities. Three missense mutations resulted in weaker F-actin binding and actin depolymerizing activities and complete loss of severing activity. The r398 mutation truncated three residues from the COOH terminus and resulted in the loss of severing activity and greater actin depolymerizing activity. The s1307 mutation in a putative actin-binding helix caused greater activity in actin-depolymerizing and severing. Using a specific antibody for UNC-60B, we found varying protein levels of UNC-60B in mutant animals, and that UNC-60B was expressed in embryonic muscles. Regardless of these various molecular phenotypes, actin was not properly assembled into embryonic myofibrils in all unc-60 mutants to similar extents. We conclude that precise control of actin filament dynamics by UNC-60B is required for proper integration of actin into myofibrils.
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Affiliation(s)
- S Ono
- Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia 30322, USA.
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