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RSU-1 Maintains Integrity of Caenorhabditis elegans Vulval Muscles by Regulating α-Actinin. G3-GENES GENOMES GENETICS 2020; 10:2507-2517. [PMID: 32461202 PMCID: PMC7341117 DOI: 10.1534/g3.120.401185] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Egg-laying behavior in Caenorhabditis elegans is a well-known model for investigating fundamental cellular processes. In egg-laying, muscle contraction is the relaxation of the vulval muscle to extrude eggs from the vulva. Unlike skeletal muscle, vulval muscle lacks visible striations of the sarcomere. Therefore, vulval muscle must counteract the mechanical stress, caused by egg extrusion and body movement, from inducing cell-shape distortion by maintaining its cytoskeletal integrity. However, the underlying mechanisms that regulate the cellular integrity in vulval muscles remain unclear. Here, we demonstrate that C. elegans egg-laying requires proper vulval muscle 1 (vm1), in which the actin bundle organization of vm1 muscles is regulated by Ras suppressor protein 1 (RSU-1). In the loss of RSU-1, as well as RasLET-60 overactivation, blister-like membrane protrusions and disorganized actin bundles were observed in the vm1 muscles. Moreover, RasLET-60 depletion diminished the defected actin-bundles in rsu-1 mutant. These results reveal the genetic interaction of RSU-1 and RasLET-60 in vivo In addition, our results further demonstrated that the fifth to seventh leucine-rich region of RSU-1 is required to promote actin-bundling protein, α-actinin, for actin bundle stabilization in the vm1 muscles. This expands our understanding of the molecular mechanisms of actin bundle organization in a specialized smooth muscle.
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Janco M, Böcking T, He S, Coster ACF. Interactions of tropomyosin Tpm1.1 on a single actin filament: A method for extraction and processing of high resolution TIRF microscopy data. PLoS One 2018; 13:e0208586. [PMID: 30532204 PMCID: PMC6287813 DOI: 10.1371/journal.pone.0208586] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 11/20/2018] [Indexed: 12/14/2022] Open
Abstract
Skeletal muscle tropomyosin (Tpm1.1) is an elongated, rod-shaped, alpha-helical coiled-coil protein that forms continuous head-to-tail polymers along both sides of the actin filament. In this study we use single molecule fluorescence TIRF microscopy combined with a microfluidic device and fluorescently labelled proteins to measure Tpm1.1 association to and dissociation from single actin filaments. Our experimental setup allows us to clearly resolve Tpm1.1 interactions on both sides of the filaments. Here we provide a semi-automated method for the extraction and quantification of kymograph data for individual actin filaments bound at different Tpm1.1 concentrations. We determine boundaries on the kymograph on each side of the actin filament, based on intensity thresholding, performing fine manual editing of the boundaries (if needed) and extracting user defined kinetic properties of the system. Using our analytical tools we can determine (i) nucleation point(s) and rates, (ii) elongation rates of Tpm1.1, (iii) identify meeting points after the saturation of filament, and when dissociation occurs, (iv) initiation point(s), (v) the final dissociation point(s), as well as (vi) dissociation rates. All of these measurements can be extracted from both sides of the filament, allowing for the determination of possible differences in behaviour on the two sides of the filament, and across concentrations. The robust and repeatable nature of the method allows quantitative, semi-automated analyses to be made of large studies of acto-tropomyosin interactions, as well as for other actin binding proteins or filamentous structures, opening the way for dissection of the dynamics underlying these interactions.
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Affiliation(s)
- Miro Janco
- Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, New South Wales, Australia
| | - Till Böcking
- Single Molecule Science and ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, New South Wales, Australia
| | - Stanley He
- School of Mathematics & Statistics, University of New South Wales, Sydney, New South Wales, Australia
| | - Adelle C. F. Coster
- School of Mathematics & Statistics, University of New South Wales, Sydney, New South Wales, Australia
- * E-mail:
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Ghosh S, Park J, Thomas M, Cruz E, Cardona O, Kang H, Jewett T. Biophysical characterization of actin bundles generated by the Chlamydia trachomatis Tarp effector. Biochem Biophys Res Commun 2018; 500:423-428. [PMID: 29660331 DOI: 10.1016/j.bbrc.2018.04.093] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 04/12/2018] [Indexed: 11/24/2022]
Abstract
Chlamydia trachomatis entry into host cells is mediated by pathogen-directed remodeling of the actin cytoskeleton. The chlamydial type III secreted effector, translocated actin recruiting phosphoprotein (Tarp), has been implicated in the recruitment of actin to the site of internalization. Tarp harbors G-actin binding and proline rich domains required for Tarp-mediated actin nucleation as well as unique F-actin binding domains implicated in the formation of actin bundles. Little is known about the mechanical properties of actin bundles generated by Tarp or the mechanism by which Tarp mediates actin bundle formation. In order to characterize the actin bundles and elucidate the role of different Tarp domains in the bundling process, purified Tarp effectors and Tarp truncation mutants were analyzed using Total Internal Reflection Fluorescence (TIRF) microscopy. Our data indicate that Tarp mediated actin bundling is independent of actin nucleation and the F-actin binding domains are sufficient to bundle actin filaments. Additionally, Tarp-mediated actin bundles demonstrate distinct bending stiffness compared to those crosslinked by the well characterized actin bundling proteins fascin and alpha-actinin, suggesting Tarp may employ a novel actin bundling strategy. The capacity of the Tarp effector to generate novel actin bundles likely contributes to chlamydia's efficient mechanism of entry into human cells.
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Affiliation(s)
- Susmita Ghosh
- Division of Immunity and Pathogenesis, College of Medicine, University of Central Florida, United States
| | - Jinho Park
- NanoScience Technology Center, University of Central Florida, United States; Depatrment of Materials Science and Engineering, University of Central Florida, United States
| | - Mitchell Thomas
- Division of Immunity and Pathogenesis, College of Medicine, University of Central Florida, United States
| | - Edgar Cruz
- NanoScience Technology Center, University of Central Florida, United States
| | - Omar Cardona
- Division of Immunity and Pathogenesis, College of Medicine, University of Central Florida, United States
| | - Hyeran Kang
- NanoScience Technology Center, University of Central Florida, United States; Department of Physics, University of Central Florida, United States
| | - Travis Jewett
- Division of Immunity and Pathogenesis, College of Medicine, University of Central Florida, United States.
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Asgharzadeh P, Özdemir B, Reski R, Röhrle O, Birkhold AI. Computational 3D imaging to quantify structural components and assembly of protein networks. Acta Biomater 2018; 69:206-217. [PMID: 29378323 DOI: 10.1016/j.actbio.2018.01.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Revised: 12/21/2017] [Accepted: 01/16/2018] [Indexed: 12/11/2022]
Abstract
Traditionally, protein structures have been described by the secondary structure architecture and fold arrangement. However, the relatively novel method of 3D confocal microscopy of fluorescent-protein-tagged networks in living cells allows resolving the detailed spatial organization of these networks. This provides new possibilities to predict network functionality, as structure and function seem to be linked at various scales. Here, we propose a quantitative approach using 3D confocal microscopy image data to describe protein networks based on their nano-structural characteristics. This analysis is constructed in four steps: (i) Segmentation of the microscopic raw data into a volume model and extraction of a spatial graph representing the protein network. (ii) Quantifying protein network gross morphology using the volume model. (iii) Quantifying protein network components using the spatial graph. (iv) Linking these two scales to obtain insights into network assembly. Here, we quantitatively describe the filamentous temperature sensitive Z protein network of the moss Physcomitrella patens and elucidate relations between network size and assembly details. Future applications will link network structure and functionality by tracking dynamic structural changes over time and comparing different states or types of networks, possibly allowing more precise identification of (mal) functions or the design of protein-engineered biomaterials for applications in regenerative medicine. STATEMENT OF SIGNIFICANCE Protein networks are highly complex and dynamic structures that play various roles in biological environments. Analyzing the detailed spatial structure of these networks may lead to new insight into biological functions and malfunctions. Here, we propose a tool set that extracts structural information at two scales of the protein network and allows therefore to address questions such as "how is the network built?" or "how networks grow?".
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Hoffmann C, Mao X, Dieterle M, Moreau F, Al Absi A, Steinmetz A, Oudin A, Berchem G, Janji B, Thomas C. CRP2, a new invadopodia actin bundling factor critically promotes breast cancer cell invasion and metastasis. Oncotarget 2017; 7:13688-705. [PMID: 26883198 PMCID: PMC4924671 DOI: 10.18632/oncotarget.7327] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 01/27/2016] [Indexed: 01/11/2023] Open
Abstract
A critical process underlying cancer metastasis is the acquisition by tumor cells of an invasive phenotype. At the subcellular level, invasion is facilitated by actin-rich protrusions termed invadopodia, which direct extracellular matrix (ECM) degradation. Here, we report the identification of a new cytoskeletal component of breast cancer cell invadopodia, namely cysteine-rich protein 2 (CRP2). We found that CRP2 was not or only weakly expressed in epithelial breast cancer cells whereas it was up-regulated in mesenchymal/invasive breast cancer cells. In addition, high expression of the CRP2 encoding gene CSRP2 was associated with significantly increased risk of metastasis in basal-like breast cancer patients. CRP2 knockdown significantly reduced the invasive potential of aggressive breast cancer cells, whereas it did not impair 2D cell migration. In keeping with this, CRP2-depleted breast cancer cells exhibited a reduced capacity to promote ECM degradation, and to secrete and express MMP-9, a matrix metalloproteinase repeatedly associated with cancer progression and metastasis. In turn, ectopic expression of CRP2 in weakly invasive cells was sufficient to stimulate cell invasion. Both GFP-fused and endogenous CRP2 localized to the extended actin core of invadopodia, a structure primarily made of actin bundles. Purified recombinant CRP2 autonomously crosslinked actin filaments into thick bundles, suggesting that CRP2 contributes to the formation/maintenance of the actin core. Finally, CRP2 depletion significantly reduced the incidence of lung metastatic lesions in two xenograft mouse models of breast cancer. Collectively, our data identify CRP2 as a new cytoskeletal component of invadopodia that critically promotes breast cancer cell invasion and metastasis.
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Affiliation(s)
- Céline Hoffmann
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Xianqing Mao
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Monika Dieterle
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg.,NorLux Neuro-Oncology Laboratory, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Flora Moreau
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Antoun Al Absi
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - André Steinmetz
- Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Anaïs Oudin
- NorLux Neuro-Oncology Laboratory, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Guy Berchem
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Bassam Janji
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
| | - Clément Thomas
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, Luxembourg, Luxembourg
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6
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Hoffmann C, Brown-Clay J, Thomas C. Subcellular localization and function of 2LIM proteins in plants and humans. PLANTA 2017; 246:1243-1245. [PMID: 28993895 DOI: 10.1007/s00425-017-2789-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Accepted: 09/29/2017] [Indexed: 06/07/2023]
Affiliation(s)
- Céline Hoffmann
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, 84 Val, Fleuri, Luxembourg, Luxembourg
| | - Josh Brown-Clay
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, 84 Val, Fleuri, Luxembourg, Luxembourg
| | - Clément Thomas
- Laboratory of Experimental Cancer Research, Department of Oncology, Luxembourg Institute of Health, 84 Val, Fleuri, Luxembourg, Luxembourg.
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Zhu J, Nan Q, Qin T, Qian D, Mao T, Yuan S, Wu X, Niu Y, Bai Q, An L, Xiang Y. Higher-Ordered Actin Structures Remodeled by Arabidopsis ACTIN-DEPOLYMERIZING FACTOR5 Are Important for Pollen Germination and Pollen Tube Growth. MOLECULAR PLANT 2017; 10:1065-1081. [PMID: 28606871 DOI: 10.1016/j.molp.2017.06.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 06/02/2017] [Accepted: 06/05/2017] [Indexed: 06/07/2023]
Abstract
Dynamics of the actin cytoskeleton are essential for pollen germination and pollen tube growth. ACTIN-DEPOLYMERIZING FACTORs (ADFs) typically contribute to actin turnover by severing/depolymerizing actin filaments. Recently, we demonstrated that Arabidopsis subclass III ADFs (ADF5 and ADF9) evolved F-actin-bundling function from conserved F-actin-depolymerizing function. However, little is known about the physiological function, the evolutional significance, and the actin-bundling mechanism of these neofunctionalized ADFs. Here, we report that loss of ADF5 function caused delayed pollen germination, retarded pollen tube growth, and increased sensitive to latrunculin B (LatB) treatment by affecting the generation and maintenance of actin bundles. Examination of actin filament dynamics in living cells revealed that the bundling frequency was significantly decreased in adf5 pollen tubes, consistent with its biochemical functions. Further biochemical and genetic complementation analyses demonstrated that both the N- and C-terminal actin-binding domains of ADF5 are required for its physiological and biochemical functions. Interestingly, while both are atypical actin-bundling ADFs, ADF5, but not ADF9, plays an important role in mature pollen physiological activities. Taken together, our results suggest that ADF5 has evolved the function of bundling actin filaments and plays an important role in the formation, organization, and maintenance of actin bundles during pollen germination and pollen tube growth.
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Affiliation(s)
- Jingen Zhu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Qiong Nan
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Tao Qin
- State Key Laboratory of Plant Physiology and Biochemistry, Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Dong Qian
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Tonglin Mao
- State Key Laboratory of Plant Physiology and Biochemistry, Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing 100193, China
| | - Shunjie Yuan
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Xiaorong Wu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Yue Niu
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Qifeng Bai
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Lizhe An
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Yun Xiang
- MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou 730000, China.
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8
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Yang Y, Zhang Y, Li WJ, Jiang Y, Zhu Z, Hu H, Li W, Wu JW, Wang ZX, Dong MQ, Huang S, Ou G. Spectraplakin Induces Positive Feedback between Fusogens and the Actin Cytoskeleton to Promote Cell-Cell Fusion. Dev Cell 2017; 41:107-120.e4. [DOI: 10.1016/j.devcel.2017.03.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Revised: 01/18/2017] [Accepted: 03/10/2017] [Indexed: 10/25/2022]
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9
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Chanoca A, Burkel B, Kovinich N, Grotewold E, Eliceiri KW, Otegui MS. Using fluorescence lifetime microscopy to study the subcellular localization of anthocyanins. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2016; 88:895-903. [PMID: 27500780 DOI: 10.1111/tpj.13297] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2016] [Revised: 07/28/2016] [Accepted: 08/04/2016] [Indexed: 06/06/2023]
Abstract
Anthocyanins are flavonoid pigments that accumulate in most seed plants. They are synthesized in the cytoplasm but accumulate inside the vacuoles. Anthocyanins are pigmented at the lower vacuolar pH, but in the cytoplasm they can be visualized based on their fluorescence properties. Thus, anthocyanins provide an ideal system for the development of new methods to investigate cytoplasmic pools and association with other molecular components. We have analyzed the fluorescence decay of anthocyanins by fluorescence lifetime imaging microscopy (FLIM), in both in vitro and in vivo conditions, using wild-type and mutant Arabidopsis thaliana seedlings. Within plant cells, the amplitude-weighted mean fluorescence lifetime (τm ) correlated with distinct subcellular localizations of anthocyanins. The vacuolar pool of anthocyanins exhibited shorter τm than the cytoplasmic pool. Consistently, lowering the pH of anthocyanins in solution shortened their fluorescence decay. We propose that FLIM is a useful tool for understanding the trafficking of anthocyanins and, potentially, for estimating vacuolar pH inside intact plant cells.
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Affiliation(s)
- Alexandra Chanoca
- Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI, 53706, USA
- Laboratory of Molecular and Cellular Biology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI, 53706, USA
| | - Brian Burkel
- Laboratory for Optical and Computational Instrumentation (LOCI), University of Wisconsin-Madison, 1675 Observatory Drive, Madison, WI, 53706, USA
| | - Nik Kovinich
- Center for Applied Plant Sciences (CAPS), Department of Molecular Genetics and Department of Horticulture and Crop Science, The Ohio State University, 012 Rightmire Hall, 1060 Carmack Rd, Columbus, OH, 43210, USA
| | - Erich Grotewold
- Center for Applied Plant Sciences (CAPS), Department of Molecular Genetics and Department of Horticulture and Crop Science, The Ohio State University, 012 Rightmire Hall, 1060 Carmack Rd, Columbus, OH, 43210, USA
| | - Kevin W Eliceiri
- Laboratory of Molecular and Cellular Biology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI, 53706, USA
- Laboratory for Optical and Computational Instrumentation (LOCI), University of Wisconsin-Madison, 1675 Observatory Drive, Madison, WI, 53706, USA
| | - Marisa S Otegui
- Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI, 53706, USA
- Laboratory of Molecular and Cellular Biology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI, 53706, USA
- Department of Genetics, University of Wisconsin-Madison, 425 Henry Mall, Madison, WI, 53706, USA
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Zhang R, Chang M, Zhang M, Wu Y, Qu X, Huang S. The Structurally Plastic CH2 Domain Is Linked to Distinct Functions of Fimbrins/Plastins. J Biol Chem 2016; 291:17881-96. [PMID: 27261463 DOI: 10.1074/jbc.m116.730069] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Indexed: 01/08/2023] Open
Abstract
Fimbrins/plastins have been implicated in the generation of distinct actin structures, which are linked to different cellular processes. Historically, fimbrins/plastins were mainly considered as generating tight actin bundles. Here, we demonstrate that different members of the fimbrin/plastin family have diverged biochemically during evolution to generate either tight actin bundles or loose networks with distinct biochemical and biophysical properties. Using the phylogenetically and functionally distinct Arabidopsis fimbrins FIM4 and FIM5 we found that FIM4 generates both actin bundles and cross-linked actin filaments, whereas FIM5 only generates actin bundles. The distinct functions of FIM4 and FIM5 are clearly observed at single-filament resolution. Domain swapping experiments showed that cooperation between the conformationally plastic calponin-homology domain 2 (CH2) and the N-terminal headpiece determines the function of the full-length protein. Our study suggests that the structural plasticity of fimbrins/plastins has biologically meaningful consequences, and provides novel insights into the structure-function relationship of fimbrins/plastins as well as shedding light on how cells generate distinct actin structures.
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Affiliation(s)
- Ruihui Zhang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ming Chang
- the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084
| | - Meng Zhang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the University of Chinese Academy of Sciences, Beijing 100049, China
| | - Youjun Wu
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093
| | - Xiaolu Qu
- the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, the Tsinghua-Peking Joint Center for Life Sciences, Beijing 100084, and
| | - Shanjin Huang
- From the Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, the Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084,
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11
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Zhu J, Geisler M. Keeping it all together: auxin-actin crosstalk in plant development. JOURNAL OF EXPERIMENTAL BOTANY 2015; 66:4983-98. [PMID: 26085676 DOI: 10.1093/jxb/erv308] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Polar auxin transport and the action of the actin cytoskeleton are tightly interconnected, which is documented by the finding that auxin transporters reach their final destination by active movement of secretory vesicles along F-actin tracks. Moreover, auxin transporter polarity and flexibility is thought to depend on transporter cycling that requires endocytosis and exocytosis of vesicles. In this context, we have reviewed the current literature on an involvement of the actin cytoskeleton in polar auxin transport and identify known similarities and differences in its structure, function and dynamics in comparison to non-plant organisms. By describing how auxin modulates actin expression and actin organization and how actin and its stability affects auxin-transporter endocytosis and recycling, we discuss the current knowledge on regulatory auxin-actin feedback loops. We focus on known effects of auxin and of auxin transport inhibitors on the stability and organization of actin and examine the functionality of auxin and/or auxin transport inhibitor-binding proteins with respect to their suitability to integrate auxin/auxin transport inhibitor action. Finally, we indicate current difficulties in the interpretation of organ, time and concentration-dependent auxin/auxin transport inhibitor treatments and formulate simple future experimental guidelines.
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Affiliation(s)
- Jinsheng Zhu
- University of Fribourg, Department of Biology-Plant Biology, CH-1700 Fribourg, Switzerland
| | - Markus Geisler
- University of Fribourg, Department of Biology-Plant Biology, CH-1700 Fribourg, Switzerland
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12
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Qu X, Jiang Y, Chang M, Liu X, Zhang R, Huang S. Organization and regulation of the actin cytoskeleton in the pollen tube. FRONTIERS IN PLANT SCIENCE 2015; 5:786. [PMID: 25620974 PMCID: PMC4287052 DOI: 10.3389/fpls.2014.00786] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Accepted: 12/17/2014] [Indexed: 05/18/2023]
Abstract
Proper organization of the actin cytoskeleton is crucial for pollen tube growth. However, the precise mechanisms by which the actin cytoskeleton regulates pollen tube growth remain to be further elucidated. The functions of the actin cytoskeleton are dictated by its spatial organization and dynamics. However, early observations of the distribution of actin filaments at the pollen tube apex were quite perplexing, resulting in decades of controversial debate. Fortunately, due to improvements in fixation regimens for staining actin filaments in fixed pollen tubes, as well as the adoption of appropriate markers for visualizing actin filaments in living pollen tubes, this issue has been resolved and has given rise to the consensus view of the spatial distribution of actin filaments throughout the entire pollen tube. Importantly, recent descriptions of the dynamics of individual actin filaments in the apical region have expanded our understanding of the function of actin in regulation of pollen tube growth. Furthermore, careful documentation of the function and mode of action of several actin-binding proteins expressed in pollen have provided novel insights into the regulation of actin spatial distribution and dynamics. In the current review, we summarize our understanding of the organization, dynamics, and regulation of the actin cytoskeleton in the pollen tube.
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Affiliation(s)
- Xiaolu Qu
- Center for Plant Biology, School of Life Sciences, Tsinghua UniversityBeijing, China
| | - Yuxiang Jiang
- Key Laboratory of Plant Molecular Physiology, Institute of Botany – Chinese Academy of SciencesBeijing, China
| | - Ming Chang
- Key Laboratory of Plant Molecular Physiology, Institute of Botany – Chinese Academy of SciencesBeijing, China
| | - Xiaonan Liu
- Key Laboratory of Plant Molecular Physiology, Institute of Botany – Chinese Academy of SciencesBeijing, China
| | - Ruihui Zhang
- Key Laboratory of Plant Molecular Physiology, Institute of Botany – Chinese Academy of SciencesBeijing, China
| | - Shanjin Huang
- Key Laboratory of Plant Molecular Physiology, Institute of Botany – Chinese Academy of SciencesBeijing, China
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13
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Abstract
Advances in microscopy techniques applied to living cells have dramatically transformed our view of the actin cytoskeleton as a framework for cellular processes. Conventional fluorescence imaging and static analyses are useful for quantifying cellular architecture and the network of filaments that support vesicle trafficking, organelle movement, and response to biotic stress. However, new imaging techniques have revealed remarkably dynamic features of individual actin filaments and the mechanisms that underpin their construction and turnover. In this review, we briefly summarize knowledge about actin and actin-binding proteins in plant systems. We focus on the quantitative properties of the turnover of individual actin filaments, highlight actin-binding proteins that participate in actin dynamics, and summarize the current genetic evidence that has been used to dissect specific aspects of the stochastic dynamics model. Finally, we describe some signaling pathways in which recent data implicate changes in actin filament dynamics and the associated cytoplasmic responses.
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Affiliation(s)
- Jiejie Li
- Department of Biological Sciences and
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14
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Vattepu R, Yadav R, Beck MR. Actin-induced dimerization of palladin promotes actin-bundling. Protein Sci 2014; 24:70-80. [PMID: 25307943 DOI: 10.1002/pro.2588] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Accepted: 10/09/2014] [Indexed: 12/12/2022]
Abstract
A subset of actin binding proteins is able to form crosslinks between two or more actin filaments, thus producing structures of parallel or networked bundles. These actin crosslinking proteins interact with actin through either bivalent binding or dimerization. We recently identified two binding sites within the actin binding domain of palladin, an actin crosslinking protein that plays an important role in normal cell adhesion and motility during wound healing and embryonic development. In this study, we show that actin induces dimerization of palladin. Furthermore, the extent of dimerization reflects earlier comparisons of actin binding and bundling between different domains of palladin. On the basis of these results we hypothesized that actin binding may promote a conformational change that results in dimerization of palladin, which in turn may drive the crosslinking of actin filaments. The proximal distance between two actin binding sites on crosslinking proteins determines the ultrastructural properties of the filament network, therefore we also explored interdomain interactions using a combination of chemical crosslinking experiments and actin cosedimentation assays. Limited proteolysis data reveals that palladin is less susceptible to enzyme digestion after actin binding. Our results suggest that domain movements in palladin are necessary for interactions with actin and are induced by interactions with actin filaments. Accordingly, we put forth a model linking the structural changes to functional dynamics.
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Affiliation(s)
- Ravi Vattepu
- Chemistry Department, Wichita State University, Wichita, Kansas, 67260
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Human muscle LIM protein dimerizes along the actin cytoskeleton and cross-links actin filaments. Mol Cell Biol 2014; 34:3053-65. [PMID: 24934443 DOI: 10.1128/mcb.00651-14] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The muscle LIM protein (MLP) is a nucleocytoplasmic shuttling protein playing important roles in the regulation of myocyte remodeling and adaptation to hypertrophic stimuli. Missense mutations in human MLP or its ablation in transgenic mice promotes cardiomyopathy and heart failure. The exact function(s) of MLP in the cytoplasmic compartment and the underlying molecular mechanisms remain largely unknown. Here, we provide evidence that MLP autonomously binds to, stabilizes, and bundles actin filaments (AFs) independently of calcium and pH. Using total internal reflection fluorescence microscopy, we have shown how MLP cross-links actin filaments into both unipolar and mixed-polarity bundles. Quantitative analysis of the actin cytoskeleton configuration confirmed that MLP substantially promotes actin bundling in live myoblasts. In addition, bimolecular fluorescence complementation (BiFC) assays revealed MLP self-association. Remarkably, BiFC complexes mostly localize along actin filament-rich structures, such as stress fibers and sarcomeres, supporting a functional link between MLP self-association and actin cross-linking. Finally, we have demonstrated that MLP self-associates through its N-terminal LIM domain, whereas it binds to AFs through its C-terminal LIM domain. Together our data support that MLP contributes to the maintenance of cardiomyocyte cytoarchitecture by a mechanism involving its self-association and actin filament cross-linking.
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