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Geng X, Xia X, Liang Z, Li S, Yue Z, Zhang H, Guo L, Ma S, Jiang S, Lian X, Zhou J, Sung LA, Wang X, Yao W. Tropomodulin1 exacerbates inflammatory response in macrophages by negatively regulating LPS-induced TLR4 endocytosis. Cell Mol Life Sci 2024; 81:402. [PMID: 39276234 DOI: 10.1007/s00018-024-05424-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2024] [Revised: 07/24/2024] [Accepted: 08/17/2024] [Indexed: 09/16/2024]
Abstract
The excessive inflammation caused by the prolonged activation of Toll-like receptor 4 (TLR4) and its downstream signaling pathways leads to sepsis. CD14-mediated endocytosis of TLR4 is the key step to control the amount of TLR4 on cell membrane and the activity of downstream pathways. The actin cytoskeleton is necessary for receptor-mediated endocytosis, but its role in TLR4 endocytosis remains elusive. Here we show that Tropomodulin 1 (Tmod1), an actin capping protein, inhibited lipopolysaccharide (LPS)-induced TLR4 endocytosis and intracellular trafficking in macrophages. Thus it resulted in increased surface TLR4 and the upregulation of myeloid differentiation factor 88 (MyD88)-dependent pathway and the downregulation of TIR domain-containing adaptor-inducing interferon-β (TRIF)-dependent pathway, leading to the enhanced secretion of inflammatory cytokines, such as TNF-α and IL-6, and the reduced secretion of cytokines, such as IFN-β. Macrophages deficient with Tmod1 relieved the inflammatory response in LPS-induced acute lung injury mouse model. Mechanistically, Tmod1 negatively regulated LPS-induced TLR4 endocytosis and inflammatory response through modulating the activity of CD14/Syk/PLCγ2/IP3/Ca2+ signaling pathway, the reorganization of actin cytoskeleton, and the membrane tension. Therefore, Tmod1 is a key regulator of inflammatory response and immune functions in macrophages and may be a potential target for the treatment of excessive inflammation and sepsis.
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Affiliation(s)
- Xueyu Geng
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
- Department of Integration of Chinese and Western Medicine, School of Basic Medical Science, Peking University Health Center, Beijing, 100191, China
| | - Xue Xia
- Nanjing Institute of Measurement and Testing Technology, Nanjing, 210049, Jiangsu Province, China
| | - Zhenhui Liang
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
- Department of Integration of Chinese and Western Medicine, School of Basic Medical Science, Peking University Health Center, Beijing, 100191, China
| | - Shuo Li
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Zejun Yue
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
- Department of Integration of Chinese and Western Medicine, School of Basic Medical Science, Peking University Health Center, Beijing, 100191, China
| | - Huan Zhang
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Lina Guo
- Department of Rehabilitation Medicine, Caoxian People's Hospital, Heze, 274400, Shandong Province, China
| | - Shan Ma
- Chengde Medical College, Chengde, 067000, Hebei Province, China
| | - Siyu Jiang
- Chengde Medical College, Chengde, 067000, Hebei Province, China
| | - Xiang Lian
- Department of Emergency, Beijing Anzhen Hospital, Capital Medical University, Beijing, 100029, China
| | - Jing Zhou
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Lanping Amy Sung
- Department of Bioengineering, University of California, La Jolla, San Diego, CA, 92093, USA
| | - Xifu Wang
- Department of Emergency, Beijing Anzhen Hospital, Capital Medical University, Beijing, 100029, China.
| | - Weijuan Yao
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China.
- Department of Integration of Chinese and Western Medicine, School of Basic Medical Science, Peking University Health Center, Beijing, 100191, China.
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2
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Vasilescu C, Colpan M, Ojala TH, Manninen T, Mutka A, Ylänen K, Rahkonen O, Poutanen T, Martelius L, Kumari R, Hinterding H, Brilhante V, Ojanen S, Lappalainen P, Koskenvuo J, Carroll CJ, Fowler VM, Gregorio CC, Suomalainen A. Recessive TMOD1 mutation causes childhood cardiomyopathy. Commun Biol 2024; 7:7. [PMID: 38168645 PMCID: PMC10761686 DOI: 10.1038/s42003-023-05670-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 12/04/2023] [Indexed: 01/05/2024] Open
Abstract
Familial cardiomyopathy in pediatric stages is a poorly understood presentation of heart disease in children that is attributed to pathogenic mutations. Through exome sequencing, we report a homozygous variant in tropomodulin 1 (TMOD1; c.565C>T, p.R189W) in three individuals from two unrelated families with childhood-onset dilated and restrictive cardiomyopathy. To decipher the mechanism of pathogenicity of the R189W mutation in TMOD1, we utilized a wide array of methods, including protein analyses, biochemistry and cultured cardiomyocytes. Structural modeling revealed potential defects in the local folding of TMOD1R189W and its affinity for actin. Cardiomyocytes expressing GFP-TMOD1R189W demonstrated longer thin filaments than GFP-TMOD1wt-expressing cells, resulting in compromised filament length regulation. Furthermore, TMOD1R189W showed weakened activity in capping actin filament pointed ends, providing direct evidence for the variant's effect on actin filament length regulation. Our data indicate that the p.R189W variant in TMOD1 has altered biochemical properties and reveals a unique mechanism for childhood-onset cardiomyopathy.
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Affiliation(s)
- Catalina Vasilescu
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
| | - Mert Colpan
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, AZ, 85724, USA
| | - Tiina H Ojala
- Department of Pediatric Cardiology, Helsinki University Hospital and University of Helsinki, 00290, Helsinki, Finland
| | - Tuula Manninen
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
| | - Aino Mutka
- Department of Pathology, Helsinki University Hospital and University of Helsinki, 00290, Helsinki, Finland
| | - Kaisa Ylänen
- Tampere Center for Child, Adolescent and Maternal Health Research, Faculty of Medicine and Health Technology, Tampere University and University Hospital, 33521, Tampere, Finland
| | - Otto Rahkonen
- Department of Pediatric Cardiology, Helsinki University Hospital and University of Helsinki, 00290, Helsinki, Finland
| | - Tuija Poutanen
- Tampere Center for Child, Adolescent and Maternal Health Research, Faculty of Medicine and Health Technology, Tampere University and University Hospital, 33521, Tampere, Finland
| | - Laura Martelius
- Department of Pediatric Radiology, Helsinki University Hospital and University of Helsinki, 00290, Helsinki, Finland
| | - Reena Kumari
- HiLIFE Institute of Biotechnology, University of Helsinki, 00014, Helsinki, Finland
| | - Helena Hinterding
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
| | - Virginia Brilhante
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
| | - Simo Ojanen
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
| | - Pekka Lappalainen
- HiLIFE Institute of Biotechnology, University of Helsinki, 00014, Helsinki, Finland
| | | | - Christopher J Carroll
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland
- Molecular and Clinical Sciences, St. George's, University of London, London, United Kingdom
| | - Velia M Fowler
- Department of Biological Sciences, University of Delaware, Newark, DE, 19711, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, AZ, 85724, USA.
- Cardiovascular Research Institute, Department of Medicine, Icahn School of Medicine, New York, NY, 10029, USA.
| | - Anu Suomalainen
- Research Programs Unit, Stem Cells and Metabolism, Biomedicum-Helsinki, University of Helsinki, 00290, Helsinki, Finland.
- HUSlab, Helsinki University Hospital, University of Helsinki, 00290, Helsinki, Finland.
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3
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Liu X, Xia X, Wang X, Zhou J, Sung LA, Long J, Geng X, Zeng Z, Yao W. Tropomodulin1 Expression Increases Upon Maturation in Dendritic Cells and Promotes Their Maturation and Immune Functions. Front Immunol 2021; 11:587441. [PMID: 33552047 PMCID: PMC7856346 DOI: 10.3389/fimmu.2020.587441] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Accepted: 12/03/2020] [Indexed: 12/12/2022] Open
Abstract
Dendritic cells (DCs) are the most potent antigen-presenting cells. Upon maturation, DCs express costimulatory molecules and migrate to the lymph nodes to present antigens to T cells. The actin cytoskeleton plays key roles in multiple aspects of DC functions. However, little is known about the mechanisms and identities of actin-binding proteins that control DC maturation and maturation-associated functional changes. Tropomodulin1 (Tmod1), an actin-capping protein, controls actin depolymerization and nucleation. We found that Tmod1 was expressed in bone marrow-derived immature DCs and was significantly upregulated upon lipopolysaccharide (LPS)-induced DC maturation. By characterizing LPS-induced mature DCs (mDCs) from Tmod1 knockout mice, we found that compared with Tmod1+/+ mDCs, Tmod1-deficient mDCs exhibited lower surface expression of costimulatory molecules and chemokine receptors and reduced secretion of inflammatory cytokines, suggesting that Tmod1 deficiency retarded DC maturation. Tmod1-deficient mDCs also showed impaired random and chemotactic migration, deteriorated T-cell stimulatory ability, and reduced F-actin content and cell stiffness. Furthermore, Tmod1-deficient mDCs secreted high levels of IFN-β and IL-10 and induced immune tolerance in an experimental autoimmune encephalomyelitis (EAE) mouse model. Mechanistically, Tmod1 deficiency affected TLR4 signaling transduction, resulting in the decreased activity of MyD88-dependent NFκB and MAPK pathways but the increased activity of the TRIF/IRF3 pathway. Rescue with exogenous Tmod1 reversed the effect of Tmod1 deficiency on TLR4 signaling. Therefore, Tmod1 is critical in regulating DC maturation and immune functions by regulating TLR4 signaling and the actin cytoskeleton. Tmod1 may be a potential target for modulating DC functions, a strategy that would be beneficial for immunotherapy for several diseases.
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Affiliation(s)
- Xianmei Liu
- School of Basic Medical Sciences, School of Biology and Engineering, Guizhou Medical University, Guiyang, China
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Xue Xia
- School of Basic Medical Sciences, School of Biology and Engineering, Guizhou Medical University, Guiyang, China
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Xifu Wang
- Department of Emergency, Beijing Anzhen Hospital, Capital Medical University, Beijing, China
| | - Jing Zhou
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Lanping Amy Sung
- Department of Bioengineering, University of California, San Diego, La Jolla, CA, United States
| | - Jinhua Long
- School of Basic Medical Sciences, School of Biology and Engineering, Guizhou Medical University, Guiyang, China
| | - Xueyu Geng
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Zhu Zeng
- School of Basic Medical Sciences, School of Biology and Engineering, Guizhou Medical University, Guiyang, China
| | - Weijuan Yao
- Hemorheology Center, Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
- Department of Integration of Chinese and Western Medicine, School of Basic Medical Science, Peking University Health Center, Beijing, China
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Quantitative proteomics reveals TMOD1-related proteins associated with water balance regulation. PLoS One 2019; 14:e0219932. [PMID: 31339916 PMCID: PMC6656345 DOI: 10.1371/journal.pone.0219932] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2019] [Accepted: 07/03/2019] [Indexed: 01/22/2023] Open
Abstract
The distal tubule and collecting duct in kidney regulate water homeostasis. TMOD1 is an actin capping protein that plays an important role in controlling the organization of actin filaments. In this study, we found TMOD1 was specifically expressed in distal tubules and collecting ducts. To investigate the role of TMOD1, we created Tmod1flox/flox mice and bred them with Ksp-Cre mice to generate tubule-specific Tmod1 knockout mice, Tmod1flox/flox/Ksp-Cre+ (designated as TFK). As compared with control mice, TFK mice showed oliguria, hyperosmolality urine, and high blood pressure. To determine the mechanisms underlying this phenotype, we performed label-free quantitative proteomics on kidneys of TFK and control mice. Total of 83 proteins were found differentially expressed. Bioinformatic analysis indicated that biological processes, including protein phosphorylation and metabolic process, were involved in TMOD1 regulatory network. Gene set enrichment analysis showed that multiple pathways, such as phosphatidylinositol signaling system and GnRH signaling pathway, were strongly associated with Tmod1 knockout. Western blot validated the down-regulation of three proteins, TGFBR2, SLC25A11, and MTFP1, in kidneys of TFK mice. Our study provides valuable information on the molecular functions and the regulatory network of Tmod1 gene in kidney, as well as the new mechanisms for the regulation of water balance.
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Sugie J, Intaglietta M, Sung LA. Water transport and homeostasis as a major function of erythrocytes. Am J Physiol Heart Circ Physiol 2018; 314:H1098-H1107. [PMID: 29393658 DOI: 10.1152/ajpheart.00263.2017] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Erythrocytes have long been known to change volumes and shapes in response to different salt concentrations. Aquaporin-1 (AQP1) was discovered in their membranes more than 20 yr ago. The physiological roles of volume changes and AQP1 expression, however, have remained unclear. We propose that rapid water exchange through AQP1 coupled with large capacity for volume change may allow erythrocytes to play an important role in water regulation. In this study, we showed that erythrocytes in situ gradually reduced their volumes by 39% in response to the hyperosmotic corticomedullary gradient within mouse kidneys. AQP1 knockout (KO) erythrocytes, however, displayed only minimal reduction. Constructing a microfluidic device resembling capillary flow with an extracellular fluorescent reporter demonstrated that water exchanges between erythrocytes and their hypotonic or hypertonic surroundings in vitro reached steady state in ~60 ms. AQP1 KO erythrocytes, however, did not show significant change. To simulate the water transport in circulation, we built basic units consisting of three compartments (i.e., erythrocyte, plasma, and interstitial fluid) using Kedem-Katchalsky equations for membrane transport, and connected multiple units to account for the blood flow. These simulations agreed with experimental results. Importantly, volume-changing erythrocytes in capillaries always "increase" the osmotic gradient between plasma and interstitial fluid, making them function as "micropumps" to speed up the regulation of local osmolarity. Trillions of these micropumps, mobile throughout the body, may further contribute to water homeostasis. These insights suggest that the enhanced exchange of water, in addition to O2 and CO2, may well be the third major function of erythrocytes. NEW & NOTEWORTHY Physiological roles of erythrocyte volume change and aquaporin-1 were proposed and investigated here. We conclude that fast water transport by aquaporin-1 coupled with large volume-change capacity allows erythrocytes to enhance water exchange with local tissues. Furthermore, their huge number and mobility allow them to contribute to body water homeostasis.
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Affiliation(s)
- Joseph Sugie
- Department of Bioengineering, University of California-San Diego , La Jolla, California
| | - Marcos Intaglietta
- Department of Bioengineering, University of California-San Diego , La Jolla, California
| | - Lanping Amy Sung
- Department of Bioengineering, University of California-San Diego , La Jolla, California
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6
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Arslan B, Colpan M, Gray KT, Abu-Lail NI, Kostyukova AS. Characterizing interaction forces between actin and proteins of the tropomodulin family reveals the presence of the N-terminal actin-binding site in leiomodin. Arch Biochem Biophys 2017; 638:18-26. [PMID: 29223925 DOI: 10.1016/j.abb.2017.12.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 11/18/2017] [Accepted: 12/05/2017] [Indexed: 11/18/2022]
Abstract
Tropomodulin family of proteins includes several isoforms of tropomodulins (Tmod) and leiomodins (Lmod). These proteins can sequester actin monomers or nucleate actin polymerization. Although it is known that their actin-binding properties are isoform-dependent, knowledge on how they vary in strengths of interactions with G-actin is missing. While it is confirmed in many studies that Tmods have two actin-binding sites, information on number and location of actin-binding sites in Lmod2 is controversial. We used atomic force microscopy to study interactions between G-actin and proteins of the tropomodulin family. Unbinding forces between G-actin and Tmod1, Tmod2, Tmod3, or Lmod2 were quantified. Our results indicated that Tmod1 and Tmod3 had unimodal force distributions, Tmod2 had a bimodal distribution and Lmod2 had a trimodal distribution. The number of force distributions correlates with the proteins' abilities to sequester actin or to nucleate actin polymerization. We assigned specific unbinding forces to the individual actin-binding sites of Tmod2 and Lmod2 using mutations that destroy actin-binding sites of Tmod2 and truncated Lmod2. Our results confirm the existence of the N-terminal actin-binding site in Lmod2. Altogether, our data demonstrate how the differences between the number and the strength of actin-binding sites of Tmod or Lmod translate to their functional abilities.
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Affiliation(s)
- Baran Arslan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Mert Colpan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States; Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85721, United States
| | - Kevin T Gray
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Nehal I Abu-Lail
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
| | - Alla S Kostyukova
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
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Fowler VM, Dominguez R. Tropomodulins and Leiomodins: Actin Pointed End Caps and Nucleators in Muscles. Biophys J 2017; 112:1742-1760. [PMID: 28494946 DOI: 10.1016/j.bpj.2017.03.034] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 03/27/2017] [Accepted: 03/30/2017] [Indexed: 12/29/2022] Open
Abstract
Cytoskeletal structures characterized by actin filaments with uniform lengths, including the thin filaments of striated muscles and the spectrin-based membrane skeleton, use barbed and pointed-end capping proteins to control subunit addition/dissociation at filament ends. While several proteins cap the barbed end, tropomodulins (Tmods), a family of four closely related isoforms in vertebrates, are the only proteins known to specifically cap the pointed end. Tmods are ∼350 amino acids in length, and comprise alternating tropomyosin- and actin-binding sites (TMBS1, ABS1, TMBS2, and ABS2). Leiomodins (Lmods) are related in sequence to Tmods, but display important differences, including most notably the lack of TMBS2 and the presence of a C-terminal extension featuring a proline-rich domain and an actin-binding WASP-Homology 2 domain. The Lmod subfamily comprises three somewhat divergent isoforms expressed predominantly in muscle cells. Biochemically, Lmods differ from Tmods, acting as powerful nucleators of actin polymerization, not capping proteins. Structurally, Lmods and Tmods display crucial differences that correlate well with their different biochemical activities. Physiologically, loss of Lmods in striated muscle results in cardiomyopathy or nemaline myopathy, whereas complete loss of Tmods leads to failure of myofibril assembly and developmental defects. Yet, interpretation of some of the in vivo data has led to the idea that Tmods and Lmods are interchangeable or, at best, different variants of two subfamilies of pointed-end capping proteins. Here, we review and contrast the existing literature on Tmods and Lmods, and propose a model of Lmod function that attempts to reconcile the in vitro and in vivo data, whereby Lmods nucleate actin filaments that are subsequently capped by Tmods during sarcomere assembly, turnover, and repair.
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Affiliation(s)
- Velia M Fowler
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California.
| | - Roberto Dominguez
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
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8
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Colpan M, Ly T, Grover S, Tolkatchev D, Kostyukova AS. The cardiomyopathy-associated K15N mutation in tropomyosin alters actin filament pointed end dynamics. Arch Biochem Biophys 2017; 630:18-26. [PMID: 28732641 DOI: 10.1016/j.abb.2017.07.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 06/28/2017] [Accepted: 07/13/2017] [Indexed: 10/19/2022]
Abstract
Correct assembly of thin filaments composed of actin and actin-binding proteins is of crucial importance for properly functioning muscle cells. Tropomyosin (Tpm) mediates the binding of tropomodulin (Tmod) and leiomodin (Lmod) at the slow-growing, or pointed, ends of the thin filaments. Together these proteins regulate thin filament lengths and actin dynamics in cardiac muscle. The K15N mutation in the TPM1 gene is associated with familial dilated cardiomyopathy (DCM) but the effect of this mutation on Tpm's function is unknown. In this study, we introduced the K15N mutation in striated muscle α-Tpm (Tpm1.1) and investigated its interaction with actin, Tmod and Lmod. The mutation caused a ∼3-fold decrease in the affinity of Tpm1.1 for actin. The binding of Lmod and Tmod to Tpm1.1-covered actin filaments also decreased in the presence of the K15N mutation. Furthermore, the K15N mutation in Tpm1.1 disrupted the inhibition of actin polymerization and affected the competition between Tmod1 and Lmod2 for binding at the pointed ends. Our data demonstrate that the K15N mutation alters pointed end dynamics by affecting molecular interactions between Tpm1.1, Lmod2 and Tmod1.
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Affiliation(s)
- Mert Colpan
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States; Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85721, United States.
| | - Thu Ly
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Samantha Grover
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Dmitri Tolkatchev
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States
| | - Alla S Kostyukova
- Voiland School of Chemical Engineering & Bioengineering, Washington State University, Pullman, WA 99164-6515, United States.
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Abstract
Cardiac and skeletal striated muscles are intricately designed machines responsible for muscle contraction. Coordination of the basic contractile unit, the sarcomere, and the complex cytoskeletal networks are critical for contractile activity. The sarcomere is comprised of precisely organized individual filament systems that include thin (actin), thick (myosin), titin, and nebulin. Connecting the sarcomere to other organelles (e.g., mitochondria and nucleus) and serving as the scaffold to maintain cellular integrity are the intermediate filaments. The costamere, on the other hand, tethers the sarcomere to the cell membrane. Unique structures like the intercalated disc in cardiac muscle and the myotendinous junction in skeletal muscle help synchronize and transmit force. Intense investigation has been done on many of the proteins that make up these cytoskeletal assemblies. Yet the details of their function and how they interconnect have just started to be elucidated. A vast number of human myopathies are contributed to mutations in muscle proteins; thus understanding their basic function provides a mechanistic understanding of muscle disorders. In this review, we highlight the components of striated muscle with respect to their interactions, signaling pathways, functions, and connections to disease. © 2017 American Physiological Society. Compr Physiol 7:891-944, 2017.
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Affiliation(s)
- Christine A Henderson
- Department of Cellular and Molecular Medicine, The University of Arizona, Tucson, Arizona, USA.,Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, USA
| | - Christopher G Gomez
- Department of Cellular and Molecular Medicine, The University of Arizona, Tucson, Arizona, USA.,Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, USA
| | - Stefanie M Novak
- Department of Cellular and Molecular Medicine, The University of Arizona, Tucson, Arizona, USA.,Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, USA
| | - Lei Mi-Mi
- Department of Cellular and Molecular Medicine, The University of Arizona, Tucson, Arizona, USA.,Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine, The University of Arizona, Tucson, Arizona, USA.,Sarver Molecular Cardiovascular Research Program, The University of Arizona, Tucson, Arizona, USA
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10
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Li S, Mo K, Tian H, Chu C, Sun S, Tian L, Ding S, Li TR, Wu X, Liu F, Zhang Z, Xu T, Sun LV. Lmod2 piggyBac mutant mice exhibit dilated cardiomyopathy. Cell Biosci 2016; 6:38. [PMID: 27274810 PMCID: PMC4893230 DOI: 10.1186/s13578-016-0101-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 05/03/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Leiomodin proteins, Lmod1, Lmod2 and Lmod3, are key regulators of the thin filament length in muscles. While Lmod1 is specifically expressed in smooth muscles, both Lmod2 and Lmod3 are expressed in striated muscles including both cardiac and skeletal muscles. We and others have previously shown that Lmod3 mainly function in skeletal muscles and the mutant mice display disorganized sarcomere. Lmod2 protein has been found to act as an actin filament nucleator in both cell-free assays and in cultured rat and chicken cardiomyocytes. RESULTS To better understand the function of Lmod2 in vivo, we have identified and characterized a piggyBac (PB) insertional mouse mutant. Our analysis revealed that the PB transposon inserts in the first exon of the Lmod2 gene and severely disrupts its expression. We found that Lmod2 (PB/PB) mice exhibit typical dilated cardiomyopathy (DCM) with ventricular arrhythmias and postnatal lethality. Electron microscope reveals that the Lmod2 (PB/PB) hearts carry disordered sarcomere, disarrayed thin filaments, and distorted intercalated discs (ICDs). Those ICDs display not only decreased convolutions, but also reduced electron-dense staining, indicating less ICDs component proteins in Lmod2 (PB/PB) hearts. Consistent with the phenotype, the expression of the ICD component genes, β-catenin and Connexin43, are down-regulated. CONCLUSIONS Taken together, our data reveal that Lmod2 is required in heart thin filaments for integrity of sarcomere and ICD and deficient mice exhibit DCM with ventricular arrhythmias and postnatal lethality. The Lmod2 (PB/PB) mutant offers a valuable resource for interrogation of pathogenesis and development of therapeutics for DCM.
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Affiliation(s)
- Shuang Li
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China
| | - Kaiqi Mo
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China
| | - Hong Tian
- Cardiac Center, Children's Hospital of Fudan University, Shanghai, China
| | - Chen Chu
- Cardiac Center, Children's Hospital of Fudan University, Shanghai, China
| | - Shuna Sun
- Cardiac Center, Children's Hospital of Fudan University, Shanghai, China
| | - Lei Tian
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China ; Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, New Haven, CT USA
| | - Sheng Ding
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China ; Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, New Haven, CT USA
| | - Tong-Ruei Li
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China
| | - Xiaohui Wu
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China
| | - Fang Liu
- Cardiac Center, Children's Hospital of Fudan University, Shanghai, China
| | - Zhen Zhang
- Shanghai Pediatric Congenital Heart Institute, Institute of Pediatric Translational Medicine, Shanghai Children's Medical Center, Shanghai Jiaotong University, School of Medicine, Shanghai, China
| | - Tian Xu
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China ; Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, New Haven, CT USA
| | - Ling V Sun
- State Key Laboratory of Genetic Engineering and National Center for International Research of Development and Disease, Fudan-Yale Center for Biomedical Research, Innovation Center for International Cooperation of Genetics and Development, Institute of Developmental Biology and Molecular Medicine, School of Life Sciences, Children's Hospital of Fudan University, Fudan University, Shanghai, China
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11
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Mazelet L, Parker MO, Li M, Arner A, Ashworth R. Role of Active Contraction and Tropomodulins in Regulating Actin Filament Length and Sarcomere Structure in Developing Zebrafish Skeletal Muscle. Front Physiol 2016; 7:91. [PMID: 27065876 PMCID: PMC4814503 DOI: 10.3389/fphys.2016.00091] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 02/26/2016] [Indexed: 01/13/2023] Open
Abstract
Whilst it is recognized that contraction plays an important part in maintaining the structure and function of mature skeletal muscle, its role during development remains undefined. In this study the role of movement in skeletal muscle maturation was investigated in intact zebrafish embryos using a combination of genetic and pharmacological approaches. An immotile mutant line (cacnb1 (ts25) ) which lacks functional voltage-gated calcium channels (dihydropyridine receptors) in the muscle and pharmacological immobilization of embryos with a reversible anesthetic (Tricaine), allowed the study of paralysis (in mutants and anesthetized fish) and recovery of movement (reversal of anesthetic treatment). The effect of paralysis in early embryos (aged between 17 and 24 hours post-fertilization, hpf) on skeletal muscle structure at both myofibrillar and myofilament level was determined using both immunostaining with confocal microscopy and small angle X-ray diffraction. The consequences of paralysis and subsequent recovery on the localization of the actin capping proteins Tropomodulin 1 & 4 (Tmod) in fish aged from 17 hpf until 42 hpf was also assessed. The functional consequences of early paralysis were investigated by examining the mechanical properties of the larval muscle. The length-force relationship, active and passive tension, was measured in immotile, recovered and control skeletal muscle at 5 and 7 day post-fertilization (dpf). Recovery of muscle function was also assessed by examining swimming patterns in recovered and control fish. Inhibition of the initial embryonic movements (up to 24 hpf) resulted in an increase in myofibril length and a decrease in width followed by almost complete recovery in both moving and paralyzed fish by 42 hpf. In conclusion, myofibril organization is regulated by a dual mechanism involving movement-dependent and movement-independent processes. The initial contractile event itself drives the localization of Tmod1 to its sarcomeric position, capping the actin pointed ends and ultimately regulating actin length. This study demonstrates that both contraction and contractile-independent mechanisms are important for the regulation of myofibril organization, which in turn is necessary for establishing proper skeletal muscle structure and function during development in vivo in zebrafish.
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Affiliation(s)
- Lise Mazelet
- School of Biological and Chemical Sciences, Queen Mary, University of London London, UK
| | - Matthew O Parker
- School of Health Sciences and Social Work, University of Portsmouth Portsmouth, UK
| | - Mei Li
- Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden
| | - Anders Arner
- Department of Physiology and Pharmacology, Karolinska Institutet Stockholm, Sweden
| | - Rachel Ashworth
- The Blizard Institute/Institute of Health Sciences Education, Barts and The London School of Medicine and Dentistry London, UK
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12
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Knockout of Lmod2 results in shorter thin filaments followed by dilated cardiomyopathy and juvenile lethality. Proc Natl Acad Sci U S A 2015; 112:13573-8. [PMID: 26487682 DOI: 10.1073/pnas.1508273112] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Leiomodin 2 (Lmod2) is an actin-binding protein that has been implicated in the regulation of striated muscle thin filament assembly; its physiological function has yet to be studied. We found that knockout of Lmod2 in mice results in abnormally short thin filaments in the heart. We also discovered that Lmod2 functions to elongate thin filaments by promoting actin assembly and dynamics at thin filament pointed ends. Lmod2-KO mice die as juveniles with hearts displaying contractile dysfunction and ventricular chamber enlargement consistent with dilated cardiomyopathy. Lmod2-null cardiomyocytes produce less contractile force than wild type when plated on micropillar arrays. Introduction of GFP-Lmod2 via adeno-associated viral transduction elongates thin filaments and rescues structural and functional defects observed in Lmod2-KO mice, extending their lifespan to adulthood. Thus, to our knowledge, Lmod2 is the first identified mammalian protein that functions to elongate actin filaments in the heart; it is essential for cardiac thin filaments to reach a mature length and is required for efficient contractile force and proper heart function during development.
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13
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Cell type-restricted expression of erythrocyte tropomodulin Isoform41 in exon 1 knockout/LacZ knock-in heterozygous mice. Gene Expr Patterns 2015; 17:45-55. [PMID: 25721257 DOI: 10.1016/j.gep.2015.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Revised: 02/03/2015] [Accepted: 02/13/2015] [Indexed: 01/26/2023]
Abstract
Full-length erythrocyte tropomodulin (E-Tmod or Tmod1) isoform of 41 kDa is an actin nucleation protein and caps the pointed end of tropomyosin-coated actin filaments. It participates in the length control of short actin protofilaments in the erythrocyte membrane skeletal network as well as the organization of microfilaments in non-erythroid cells. Recently we discovered and characterized a truncated isoform of 29 kDa, which lacks the N-terminal sequence encoded by exons 1 and 2 required for nucleation and capping. Thus, it is important to study the expression pattern of solely the E-Tmod41 isoform in tissues. We utilized our exon 1 knockout (KO) mouse model with a knock-in lacZ reporter gene which reports the expression of E-Tmod41, but not E-Tmod29. Because this homozygous isoform-specific KO is an embryonic lethal mutation, we used heterozygous mice. X-gal staining localized specific signals at the single cell level and revealed a timed expression during embryonic development and restricted expression in adult mice. Our results showed that E-Tmod41 expressing cells include developing and young erythroid cells, developing somites, young fiber cells in the lens, certain subtype(s) of tubular cells in the kidney, smooth muscle cells in various tissues, and horizontal cells in the retina. A comparison with previous studies revealed that most if not all tissues known to express E-Tmod contained lacZ-expressing cells. Interestingly, some tubular cells were lacZ-positive while others in the same renal tubule were not, indicating heterogeneity within the tubular cells. Combined with double immunocytochemistry, we further localized E-Tmod41 to dendritic spines of horizontal cells. These timed and cell-type restricted expressions of E-Tmod41 suggest a role of actin nucleation and/or short actin protofilaments in these cell types and sub-cellular structures.
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14
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Nworu CU, Kraft R, Schnurr DC, Gregorio CC, Krieg PA. Leiomodin 3 and tropomodulin 4 have overlapping functions during skeletal myofibrillogenesis. J Cell Sci 2014; 128:239-50. [PMID: 25431137 DOI: 10.1242/jcs.152702] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Precise regulation of thin filament length is essential for optimal force generation during muscle contraction. The thin filament capping protein tropomodulin (Tmod) contributes to thin filament length uniformity by regulating elongation and depolymerization at thin filament ends. The leiomodins (Lmod1-3) are structurally related to Tmod1-4 and also localize to actin filament pointed ends, but in vitro biochemical studies indicate that Lmods act instead as robust nucleators. Here, we examined the roles of Tmod4 and Lmod3 during Xenopus skeletal myofibrillogenesis. Loss of Tmod4 or Lmod3 resulted in severe disruption of sarcomere assembly and impaired embryonic movement. Remarkably, when Tmod4-deficient embryos were supplemented with additional Lmod3, and Lmod3-deficient embryos were supplemented with additional Tmod4, sarcomere assembly was rescued and embryonic locomotion improved. These results demonstrate for the first time that appropriate levels of both Tmod4 and Lmod3 are required for embryonic myofibrillogenesis and, unexpectedly, both proteins can function redundantly during in vivo skeletal muscle thin filament assembly. Furthermore, these studies demonstrate the value of Xenopus for the analysis of contractile protein function during de novo myofibril assembly.
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Affiliation(s)
- Chinedu U Nworu
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Robert Kraft
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Daniel C Schnurr
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
| | - Paul A Krieg
- Department of Cellular and Molecular Medicine, Sarver Molecular Cardiovascular Research Program, University of Arizona, 1656 E. Mabel St, Tucson, AZ 85724, USA
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15
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Bliss KT, Tsukada T, Novak SM, Dorovkov MV, Shah SP, Nworu C, Kostyukova AS, Gregorio CC. Phosphorylation of tropomodulin1 contributes to the regulation of actin filament architecture in cardiac muscle. FASEB J 2014; 28:3987-95. [PMID: 24891520 DOI: 10.1096/fj.13-246009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 05/19/2014] [Indexed: 01/09/2023]
Abstract
Tropomodulin1 (Tmod1) is an actin-capping protein that plays an important role in actin filament pointed-end dynamics and length in striated muscle. No mechanisms have been identified to explain how Tmod1's functional properties are regulated. The purpose of this investigation was to explore the functional significance of the phosphorylation of Tmod1 at previously identified Thr54. Rat cardiomyocytes were assessed for phosphorylation of Tmod1 using Pro-Q Diamond staining and (32)P labeling. Green fluorescent protein-tagged phosphorylation-mimic (T54E) and phosphorylation-deficient (T54A) versions of Tmod1 were expressed in cultured cardiomyocytes, and the ability of these mutants to assemble and restrict actin lengths was observed. We report for the first time that Tmod1 is phosphorylated endogenously in cardiomyocytes, and phosphorylation at Thr54 causes a significant reduction in the ability of Tmod1 to assemble to the pointed end compared with that of the wild type (WT; 48 vs. 78%, respectively). In addition, overexpression of Tmod1-T54E restricts actin filament lengths by only ∼3%, whereas Tmod1-WT restricts the lengths significantly by ∼8%. Finally, Tmod1-T54E altered the actin filament-capping activity in polymerization assays. Taken together, our data suggest that pointed-end assembly and Tmod1's thin filament length regulatory function are regulated by its phosphorylation state.
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Affiliation(s)
- Katherine T Bliss
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Takehiro Tsukada
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Stefanie Mares Novak
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | | | - Samar P Shah
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, New Jersey, USA; and
| | - Chinedu Nworu
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA
| | - Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, Piscataway, New Jersey, USA; and School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, USA
| | - Carol C Gregorio
- Department of Cellular and Molecular Medicine and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona, USA;
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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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17
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McKeown CR, Nowak RB, Gokhin DS, Fowler VM. Tropomyosin is required for cardiac morphogenesis, myofibril assembly, and formation of adherens junctions in the developing mouse embryo. Dev Dyn 2014; 243:800-17. [PMID: 24500875 DOI: 10.1002/dvdy.24115] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 01/31/2014] [Accepted: 02/03/2014] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND We explored a function for tropomyosin (TM) in mammalian myofibril assembly and cardiac development by analyzing a deletion in the mouse TPM1 gene targeting αTM1, the major striated muscle TM isoform. RESULTS Mice lacking αTM1 are embryonic lethal at E9.5 with enlarged, misshapen, and non-beating hearts characterized by an abnormally thin myocardium and reduced trabeculae. αTM1-deficient cardiomyocytes do not assemble striated myofibrils, instead displaying aberrant non-striated F-actin fibrils with α-actinin puncta dispersed irregularly along their lengths. αTM1's binding partner, tropomodulin1 (Tmod1), is also disorganized, and both myomesin-containing thick filaments as well as titin Z1Z2 fail to assemble in a striated pattern. Adherens junctions are reduced in size in αTM1-deficient cardiomyocytes, α-actinin/F-actin adherens belts fail to assemble at apical cell-cell contacts, and cell contours are highly irregular, resulting in abnormal cell shapes and a highly folded cardiac surface. In addition, Tmod1-deficient cardiomyocytes exhibit failure of α-actinin/F-actin adherens belt assembly. CONCLUSIONS Absence of αTM1 resulting in unstable F-actin may preclude sarcomere formation and/or lead to degeneration of partially assembled sarcomeres due to unregulated actomyosin interactions. Our data also identify a novel αTM1/Tmod1-based pathway stabilizing F-actin at cell-cell junctions, which may be required for maintenance of cell shapes during embryonic cardiac morphogenesis.
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Affiliation(s)
- Caroline R McKeown
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California
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18
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Fraser ST. The modern primitives: applying new technological approaches to explore the biology of the earliest red blood cells. ISRN HEMATOLOGY 2013; 2013:568928. [PMID: 24222861 PMCID: PMC3814094 DOI: 10.1155/2013/568928] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 08/25/2013] [Indexed: 01/01/2023]
Abstract
One of the most critical stages in mammalian embryogenesis is the independent production of the embryo's own circulating, functional red blood cells. Correspondingly, erythrocytes are the first cell type to become functionally mature during embryogenesis. Failure to achieve this invariably leads to in utero lethality. The recent application of technologies such as transcriptome analysis, flow cytometry, mutant embryo analysis, and transgenic fluorescent gene expression reporter systems has shed new light on the distinct erythroid lineages that arise early in development. Here, I will describe the similarities and differences between the distinct erythroid populations that must form for the embryo to survive. While much of the focus of this review will be the poorly understood primitive erythroid lineage, a discussion of other erythroid and hematopoietic lineages, as well as the cell types making up the different niches that give rise to these lineages, is essential for presenting an appropriate developmental context of these cells.
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Affiliation(s)
- Stuart T. Fraser
- Disciplines of Physiology, Anatomy and Histology, Bosch Institute, School of Medical Sciences, University of Sydney, Medical Foundation Building K25, 92-94 Parramatta Road, Camperdown, NSW 2050, Australia
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19
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The switch role of the Tmod4 in the regulation of balanced development between myogenesis and adipogenesis. Gene 2013; 532:263-71. [PMID: 24036428 DOI: 10.1016/j.gene.2013.08.088] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Revised: 08/16/2013] [Accepted: 08/28/2013] [Indexed: 11/21/2022]
Abstract
Tmod4 (Tropomodulin 4) is a member of Tmod family that plays important role in thin filament length regulation and myofibril assembly. We found that the expression levels of Tmod4 were higher in skeletal muscle and adipose tissues. However, the function and regulation of the Tmod4 gene in the myogenesis and adipogenesis remains unclear. In this study, we found that the expression of Tmod4 was decreased in myogenesis while increased in adipogenesis. Then, the transcriptional regulation analysis of Tmod4 promoter showed that Tmod4 could be regulated directly by myogenic factors and adipogenic factors. Furthermore, the roles of Tmod4 in the myogenesis and adipogenesis were confirmed by its over-expression in C2C12 cells and 3T3 cells, which suggested that Tmod4 could promote adipogenesis by up-regulating the adipogenic factors but moderately delay the myogenesis. These results indicated that the Tmod4 gene may play as a switch between myogenesis and adipogenesis, which resulted in the balanced development between skeletal muscle and adipose tissue. Therefore, the model for switch role of the Tmod4 in the balanced regulation between myogenesis and adipogenesis was proposed. It is showed that the expression of Tmod4 was activated in adipogenesis by adipogenic factors while inhibited in myogenesis by myogenic factors. Moreover, Tmod4 could promote adipogenesis by up-regulating the expression of adipogenic factors while moderately delaying the myogenesis. Our study provides an important basis for further understanding the regulation and function of porcine Tmod4 in muscle and fat development.
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20
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Baron MH, Vacaru A, Nieves J. Erythroid development in the mammalian embryo. Blood Cells Mol Dis 2013; 51:213-9. [PMID: 23932234 DOI: 10.1016/j.bcmd.2013.07.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Accepted: 06/25/2013] [Indexed: 12/22/2022]
Abstract
Erythropoiesis is the process by which progenitors for red blood cells are produced and terminally differentiate. In all vertebrates, two morphologically distinct erythroid lineages (primitive, embryonic, and definitive, fetal/adult) form successively within the yolk sac, fetal liver, and marrow and are essential for normal development. Red blood cells have evolved highly specialized functions in oxygen transport, defense against oxidation, and vascular remodeling. Here we review key features of the ontogeny of red blood cell development in mammals, highlight similarities and differences revealed by genetic and gene expression profiling studies, and discuss methods for identifying erythroid cells at different stages of development and differentiation.
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Affiliation(s)
- Margaret H Baron
- Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of Developmental and Regenerative Biology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; The Black Family Stem Cell Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
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21
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Colpan M, Moroz NA, Kostyukova AS. Tropomodulins and tropomyosins: working as a team. J Muscle Res Cell Motil 2013; 34:247-60. [PMID: 23828180 DOI: 10.1007/s10974-013-9349-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 05/24/2013] [Indexed: 11/25/2022]
Abstract
Actin filaments are major components of the cytoskeleton in eukaryotic cells and are involved in vital cellular functions such as cell motility and muscle contraction. Tmod and TM are crucial constituents of the actin filament network, making their presence indispensable in living cells. Tropomyosin (TM) is an alpha-helical, coiled coil protein that covers the grooves of actin filaments and stabilizes them. Actin filament length is optimized by tropomodulin (Tmod), which caps the slow growing (pointed end) of thin filaments to inhibit polymerization or depolymerization. Tmod consists of two structurally distinct regions: the N-terminal and the C-terminal domains. The N-terminal domain contains two TM-binding sites and one TM-dependent actin-binding site, whereas the C-terminal domain contains a TM-independent actin-binding site. Tmod binds to two TM molecules and at least one actin molecule during capping. The interaction of Tmod with TM is a key regulatory factor for actin filament organization. The binding efficacy of Tmod to TM is isoform-dependent. The affinities of Tmod/TM binding influence the proper localization and capping efficiency of Tmod at the pointed end of actin filaments in cells. Here we describe how a small difference in the sequence of the TM-binding sites of Tmod may result in dramatic change in localization of Tmod in muscle cells or morphology of non-muscle cells. We also suggest most promising directions to study and elucidate the role of Tmod-TM interaction in formation and maintenance of sarcomeric and cytoskeletal structure.
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Affiliation(s)
- Mert Colpan
- The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, 118 Dana Hall, Spokane St., Pullman, WA, 99164, USA
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22
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Fowler VM. The human erythrocyte plasma membrane: a Rosetta Stone for decoding membrane-cytoskeleton structure. CURRENT TOPICS IN MEMBRANES 2013; 72:39-88. [PMID: 24210427 DOI: 10.1016/b978-0-12-417027-8.00002-7] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The mammalian erythrocyte, or red blood cell (RBC), is a unique experiment of nature: a cell with no intracellular organelles, nucleus or transcellular cytoskeleton, and a plasma membrane with uniform structure across its entire surface. By virtue of these specialized properties, the RBC membrane has provided a template for discovery of the fundamental actin filament network machine of the membrane skeleton, now known to confer mechanical resilience, anchor membrane proteins, and organize membrane domains in all cells. This chapter provides a historical perspective and critical analysis of the biochemistry, structure, and physiological functions of this actin filament network in RBCs. The core units of this network are nodes of ~35-37 nm-long actin filaments, interconnected by long strands of (α1β1)₂-spectrin tetramers, forming a 2D isotropic lattice with quasi-hexagonal symmetry. Actin filament length and stability is critical for network formation, relying upon filament capping at both ends: tropomodulin-1 at pointed ends and αβ-adducin at barbed ends. Tropomodulin-1 capping is essential for precise filament lengths, and is enhanced by tropomyosin, which binds along the short actin filaments. αβ-adducin capping recruits spectrins to sites near barbed ends, promoting network formation. Accessory proteins, 4.1R and dematin, also promote spectrin binding to actin and, with αβ-adducin, link to membrane proteins, targeting actin nodes to the membrane. Dissection of the molecular organization within the RBC membrane skeleton is one of the paramount achievements of cell biological research in the past century. Future studies will reveal the structure and dynamics of actin filament capping, mechanisms of precise length regulation, and spectrin-actin lattice symmetry.
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Affiliation(s)
- Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California, USA.
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23
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Gokhin DS, Nowak RB, Kim NE, Arnett EE, Chen AC, Sah RL, Clark JI, Fowler VM. Tmod1 and CP49 synergize to control the fiber cell geometry, transparency, and mechanical stiffness of the mouse lens. PLoS One 2012; 7:e48734. [PMID: 23144950 PMCID: PMC3492431 DOI: 10.1371/journal.pone.0048734] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 09/28/2012] [Indexed: 11/25/2022] Open
Abstract
The basis for mammalian lens fiber cell organization, transparency, and biomechanical properties has contributions from two specialized cytoskeletal systems: the spectrin-actin membrane skeleton and beaded filament cytoskeleton. The spectrin-actin membrane skeleton predominantly consists of α2β2-spectrin strands interconnecting short, tropomyosin-coated actin filaments, which are stabilized by pointed-end capping by tropomodulin 1 (Tmod1) and structurally disrupted in the absence of Tmod1. The beaded filament cytoskeleton consists of the intermediate filament proteins CP49 and filensin, which require CP49 for assembly and contribute to lens transparency and biomechanics. To assess the simultaneous physiological contributions of these cytoskeletal networks and uncover potential functional synergy between them, we subjected lenses from mice lacking Tmod1, CP49, or both to a battery of structural and physiological assays to analyze fiber cell disorder, light scattering, and compressive biomechanical properties. Findings show that deletion of Tmod1 and/or CP49 increases lens fiber cell disorder and light scattering while impairing compressive load-bearing, with the double mutant exhibiting a distinct phenotype compared to either single mutant. Moreover, Tmod1 is in a protein complex with CP49 and filensin, indicating that the spectrin-actin network and beaded filament cytoskeleton are biochemically linked. These experiments reveal that the spectrin-actin membrane skeleton and beaded filament cytoskeleton establish a novel functional synergy critical for regulating lens fiber cell geometry, transparency, and mechanical stiffness.
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Affiliation(s)
- David S. Gokhin
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Roberta B. Nowak
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Nancy E. Kim
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
| | - Ernest E. Arnett
- Department of Biological Structure, University of Washington, Seattle, Washington, United States of America
| | - Albert C. Chen
- Department of Bioengineering, University of California San Diego, La Jolla, California, United States of America
| | - Robert L. Sah
- Department of Bioengineering, University of California San Diego, La Jolla, California, United States of America
| | - John I. Clark
- Department of Biological Structure, University of Washington, Seattle, Washington, United States of America
| | - Velia M. Fowler
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America
- * E-mail:
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Bao Y, Kake T, Hanashima A, Nomiya Y, Kubokawa K, Kimura S. Actin capping proteins, CapZ (β-actinin) and tropomodulin in amphioxus striated muscle. Gene 2012; 510:78-86. [DOI: 10.1016/j.gene.2012.07.081] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Revised: 07/24/2012] [Accepted: 07/31/2012] [Indexed: 01/08/2023]
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Cox-Paulson EA, Walck-Shannon E, Lynch AM, Yamashiro S, Zaidel-Bar R, Eno CC, Ono S, Hardin J. Tropomodulin protects α-catenin-dependent junctional-actin networks under stress during epithelial morphogenesis. Curr Biol 2012; 22:1500-5. [PMID: 22771044 DOI: 10.1016/j.cub.2012.06.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Revised: 04/09/2012] [Accepted: 06/06/2012] [Indexed: 10/28/2022]
Abstract
α-catenin is central to recruitment of actin networks to the cadherin-catenin complex, but how such networks are subsequently stabilized against stress applied during morphogenesis is poorly understood. To identify proteins that functionally interact with α-catenin in this process, we performed enhancer screening using a weak allele of the C. elegans α-catenin, hmp-1, thereby identifying UNC-94/tropomodulin. Tropomodulins (Tmods) cap the minus ends of F-actin in sarcomeres. They also regulate lamellipodia, can promote actin nucleation, and are required for normal cardiovascular development and neuronal growth-cone morphology. Tmods regulate the morphology of cultured epithelial cells, but their role in epithelia in vivo remains unexplored. We find that UNC-94 is enriched within a HMP-1-dependent junctional-actin network at epidermal adherens junctions subject to stress during morphogenesis. Loss of UNC-94 leads to discontinuity of this network, and high-speed filming of hmp-1(fe4);unc-94(RNAi) embryos reveals large junctional displacements that depend on the Rho pathway. In vitro, UNC-94 acts in combination with HMP-1, leading to longer actin bundles than with HMP-1 alone. Our data suggest that Tmods protect actin filaments recruited by α-catenin from minus-end subunit loss, enabling them to withstand the stresses of morphogenesis.
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Affiliation(s)
- Elisabeth A Cox-Paulson
- Department of Biology, State University of New York at Geneseo, 353 Integrated Science Center, 1 College Circle, Geneseo, NY 14454, USA
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Formation, contraction, and mechanotransduction of myofribrils in cardiac development: clues from genetics. Biochem Res Int 2012; 2012:504906. [PMID: 22720160 PMCID: PMC3376475 DOI: 10.1155/2012/504906] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 04/11/2012] [Accepted: 04/15/2012] [Indexed: 01/24/2023] Open
Abstract
Congenital heart disease (CHD) is the most common birth defect in humans. It is a leading infant mortality factor worldwide, caused by defective cardiac development. Mutations in transcription factors, signalling and structural molecules have been shown to contribute to the genetic component of CHD. Recently, mutations in genes encoding myofibrillar proteins expressed in the embryonic heart have also emerged as an important genetic causative factor of the disease, which implies that the contraction of the early heart primordium contributes to its morphogenesis. This notion is supported by increasing evidence suggesting that not only contraction but also formation, mechanosensing, and mechanotransduction of the cardiac myofibrillar proteins influence heart development. In this paper, we summarize the genetic clues supporting this idea.
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Yamashiro S, Gokhin DS, Kimura S, Nowak RB, Fowler VM. Tropomodulins: pointed-end capping proteins that regulate actin filament architecture in diverse cell types. Cytoskeleton (Hoboken) 2012; 69:337-70. [PMID: 22488942 DOI: 10.1002/cm.21031] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2011] [Revised: 03/23/2012] [Accepted: 03/26/2012] [Indexed: 01/31/2023]
Abstract
Tropomodulins are a family of four proteins (Tmods 1-4) that cap the pointed ends of actin filaments in actin cytoskeletal structures in a developmentally regulated and tissue-specific manner. Unique among capping proteins, Tmods also bind tropomyosins (TMs), which greatly enhance the actin filament pointed-end capping activity of Tmods. Tmods are defined by a TM-regulated/Pointed-End Actin Capping (TM-Cap) domain in their unstructured N-terminal portion, followed by a compact, folded Leucine-Rich Repeat/Pointed-End Actin Capping (LRR-Cap) domain. By inhibiting actin monomer association and dissociation from pointed ends, Tmods regulate actin dynamics and turnover, stabilizing actin filament lengths and cytoskeletal architecture. In this review, we summarize the genes, structural features, molecular and biochemical properties, actin regulatory mechanisms, expression patterns, and cell and tissue functions of Tmods. By understanding Tmods' functions in the context of their molecular structure, actin regulation, binding partners, and related variants (leiomodins 1-3), we can draw broad conclusions that can explain the diverse morphological and functional phenotypes that arise from Tmod perturbation experiments in vitro and in vivo. Tmod-based stabilization and organization of intracellular actin filament networks provide key insights into how the emergent properties of the actin cytoskeleton drive tissue morphogenesis and physiology.
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Affiliation(s)
- Sawako Yamashiro
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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28
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Cantù C, Bosè F, Bianchi P, Reali E, Colzani MT, Cantù I, Barbarani G, Ottolenghi S, Witke W, Spinardi L, Ronchi AE. Defective erythroid maturation in gelsolin mutant mice. Haematologica 2012; 97:980-8. [PMID: 22271892 DOI: 10.3324/haematol.2011.052522] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND During late differentiation, erythroid cells undergo profound changes involving actin filament remodeling. One of the proteins controlling actin dynamics is gelsolin, a calcium-activated actin filament severing and capping protein. Gelsolin-null (Gsn(-/-)) mice generated in a C57BL/6 background are viable and fertile.1 DESIGN AND METHODS We analyzed the functional roles of gelsolin in erythropoiesis by: (i) evaluating gelsolin expression in murine fetal liver cells at different stages of erythroid differentiation (using reverse transcription polymerase chain reaction analysis and immunohistochemistry), and (ii) characterizing embryonic and adult erythropoiesis in Gsn(-/-) BALB/c mice (morphology and erythroid cultures). RESULTS In the context of a BALB/c background, the Gsn(-/-) mutation causes embryonic death. Gsn(-/-) embryos show defective erythroid maturation with persistence of circulating nucleated cells. The few Gsn(-/-) mice reaching adulthood fail to recover from phenylhydrazine-induced acute anemia, revealing an impaired response to stress erythropoiesis. In in vitro differentiation assays, E13.5 fetal liver Gsn(-/-) cells failed to undergo terminal maturation, a defect partially rescued by Cytochalasin D, and mimicked by administration of Jasplakinolide to the wild-type control samples. CONCLUSIONS In BALB/c mice, gelsolin deficiency alters the equilibrium between erythrocyte actin polymerization and depolymerization, causing impaired terminal maturation. We suggest a non-redundant role for gelsolin in terminal erythroid differentiation, possibly contributing to the Gsn(-/-) mice lethality observed in mid-gestation.
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Affiliation(s)
- Claudio Cantù
- Dipartimento di Biotecnologie e Bioscienze, Università Milano-Bicocca, Milan, Italy
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Dwyer J, Iskratsch T, Ehler E. Actin in striated muscle: recent insights into assembly and maintenance. Biophys Rev 2011; 4:17-25. [PMID: 28510000 DOI: 10.1007/s12551-011-0062-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Accepted: 11/17/2011] [Indexed: 01/28/2023] Open
Abstract
Striated muscle cells are characterised by a para-crystalline arrangement of their contractile proteins actin and myosin in sarcomeres, the basic unit of the myofibrils. A multitude of proteins is required to build and maintain the structure of this regular arrangement as well as to ensure regulation of contraction and to respond to alterations in demand. This review focuses on the actin filaments (also called thin filaments) of the sarcomere and will discuss how they are assembled during myofibrillogenesis and in hypertrophy and how their integrity is maintained in the working myocardium.
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Affiliation(s)
- Joseph Dwyer
- The Randall Division of Cell and Molecular Biophysics and The Cardiovascular Division, King's College London, British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, London, SE1 1UL, UK
| | - Thomas Iskratsch
- The Randall Division of Cell and Molecular Biophysics and The Cardiovascular Division, King's College London, British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, London, SE1 1UL, UK.,Biological Sciences, Columbia University, 713 Fairchild Center, New York, NY, 10027, USA
| | - Elisabeth Ehler
- The Randall Division of Cell and Molecular Biophysics and The Cardiovascular Division, King's College London, British Heart Foundation Centre of Research Excellence, New Hunt's House, Guy's Campus, London, SE1 1UL, UK.
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Nanda V, Miano JM. Leiomodin 1, a new serum response factor-dependent target gene expressed preferentially in differentiated smooth muscle cells. J Biol Chem 2011; 287:2459-67. [PMID: 22157009 DOI: 10.1074/jbc.m111.302224] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Smooth muscle cell (SMC) differentiation is defined largely by a number of cell-restricted genes governed directly by the serum response factor (SRF)/myocardin (MYOCD) transcriptional switch. Here, we describe a new SRF/MYOCD-dependent, SMC-restricted gene known as Leiomodin 1 (Lmod1). Conventional and quantitative RT-PCRs indicate that Lmod1 mRNA expression is enriched in SMC-containing tissues of the mouse, whereas its two paralogs, Lmod2 and Lmod3, exhibit abundant expression in skeletal and cardiac muscle with very low levels in SMC-containing tissues. Western blotting and immunostaining of various adult and embryonic mouse tissues further confirm SMC-specific expression of the LMOD1 protein. Comparative genomic analysis of the human LMOD1 and LMOD2 genes with their respective mouse and rat orthologs shows high conservation between the three exons and several noncoding sequences, including the immediate 5' promoter region. Two conserved CArG boxes are present in both the LMOD1 and LMOD2 promoter regions, although LMOD1 displays much higher promoter activity and is more responsive to SRF/MYOCD stimulation. Gel shift assays demonstrate clear binding between SRF and the two CArG boxes in human LMOD1. Although the CArG boxes in LMOD1 and LMOD2 are similar, only LMOD1 displays SRF or MYOCD-dependent activation. Transgenic mouse studies reveal wild type LMOD1 promoter activity in cardiac and vascular SMC. Such activity is abolished upon mutation of both CArG boxes. Collectively, these data demonstrate that Lmod1 is a new SMC-restricted SRF/MYOCD target gene.
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Affiliation(s)
- Vivek Nanda
- Aab Cardiovascular Research Institute, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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31
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Tropomodulin capping of actin filaments in striated muscle development and physiology. J Biomed Biotechnol 2011; 2011:103069. [PMID: 22013379 PMCID: PMC3196151 DOI: 10.1155/2011/103069] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 08/18/2011] [Indexed: 11/17/2022] Open
Abstract
Efficient striated muscle contraction requires precise assembly and regulation of diverse actin filament systems, most notably the sarcomeric thin filaments of the contractile apparatus. By capping the pointed ends of actin filaments, tropomodulins (Tmods) regulate actin filament assembly, lengths, and stability. Here, we explore the current understanding of the expression patterns, localizations, and functions of Tmods in both cardiac and skeletal muscle. We first describe the mechanisms by which Tmods regulate myofibril assembly and thin filament lengths, as well as the roles of closely related Tmod family variants, the leiomodins (Lmods), in these processes. We also discuss emerging functions for Tmods in the sarcoplasmic reticulum. This paper provides abundant evidence that Tmods are key structural regulators of striated muscle cytoarchitecture and physiology.
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Mechanobiology of Erythrocytes from Adult Mice Homozygous for a Targeted Disruption of the E-Tmod Gene at Exon 1. Cell Mol Bioeng 2011. [DOI: 10.1007/s12195-011-0203-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022] Open
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Gokhin DS, Fowler VM. Cytoplasmic gamma-actin and tropomodulin isoforms link to the sarcoplasmic reticulum in skeletal muscle fibers. ACTA ACUST UNITED AC 2011; 194:105-20. [PMID: 21727195 PMCID: PMC3135406 DOI: 10.1083/jcb.201011128] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Tropomodulins, cytoplasmic γ-actin, and small ankyrin 1.5 mechanically stabilize the sarcoplasmic reticulum and maintain myofibril alignment in skeletal muscle fibers. The sarcoplasmic reticulum (SR) serves as the Ca2+ reservoir for muscle contraction. Tropomodulins (Tmods) cap filamentous actin (F-actin) pointed ends, bind tropomyosins (Tms), and regulate F-actin organization. In this paper, we use a genetic targeting approach to examine the effect of Tmod1 deletion on the organization of cytoplasmic γ-actin (γcyto-actin) in the SR of skeletal muscle. In wild-type muscle fibers, γcyto-actin and Tmod3 defined an SR microdomain that was distinct from another Z line–flanking SR microdomain containing Tmod1 and Tmod4. The γcyto-actin/Tmod3 microdomain contained an M line complex composed of small ankyrin 1.5 (sAnk1.5), γcyto-actin, Tmod3, Tm4, and Tm5NM1. Tmod1 deletion caused Tmod3 to leave its SR compartment, leading to mislocalization and destabilization of the Tmod3–γcyto-actin–sAnk1.5 complex. This was accompanied by SR morphological defects, impaired Ca2+ release, and an age-dependent increase in sarcomere misalignment. Thus, Tmod3 regulates SR-associated γcyto-actin architecture, mechanically stabilizes the SR via a novel cytoskeletal linkage to sAnk1.5, and maintains the alignment of adjacent myofibrils.
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Affiliation(s)
- David S Gokhin
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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34
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Tsukada T, Kotlyanskaya L, Huynh R, Desai B, Novak SM, Kajava AV, Gregorio CC, Kostyukova AS. Identification of residues within tropomodulin-1 responsible for its localization at the pointed ends of the actin filaments in cardiac myocytes. J Biol Chem 2010; 286:2194-204. [PMID: 21078668 DOI: 10.1074/jbc.m110.186924] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tropomodulin is a tropomyosin-dependent actin filament capping protein involved in the structural formation of thin filaments and in the regulation of their lengths through its localization at the pointed ends of actin filaments. The disordered N-terminal domain of tropomodulin contains three functional sites: two tropomyosin-binding and one tropomyosin-dependent actin-capping sites. The C-terminal half of tropomodulin consists of one compact domain containing a tropomyosin-independent actin-capping site. Here we determined the structural properties of tropomodulin-1 that affect its roles in cardiomyocytes. To explore the significance of individual tropomyosin-binding sites, GFP-tropomodulin-1 with single mutations that destroy each tropomyosin-binding site was expressed in cardiomyocytes. We demonstrated that both sites are necessary for the optimal localization of tropomodulin-1 at thin filament pointed ends, with site 2 acting as the major determinant. To investigate the functional properties of the tropomodulin C-terminal domain, truncated versions of GFP-tropomodulin-1 were expressed in cardiomyocytes. We discovered that the leucine-rich repeat (LRR) fold and the C-terminal helix are required for its proper targeting to the pointed ends. To investigate the structural significance of the LRR fold, we generated three mutations within the C-terminal domain (V232D, F263D, and L313D). Our results show that these mutations affect both tropomyosin-independent actin-capping activity and pointed end localization, most likely by changing local conformations of either loops or side chains of the surfaces involved in the interactions of the LRR domain. Studying the influence of these mutations individually, we concluded that, in addition to the tropomyosin-independent actin-capping site, there appears to be another regulatory site within the tropomodulin C-terminal domain.
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Affiliation(s)
- Takehiro Tsukada
- Department of Cell Biology and Anatomy and the Molecular Cardiovascular Research Program, University of Arizona, Tucson, Arizona 85724, USA
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35
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Ono S. Dynamic regulation of sarcomeric actin filaments in striated muscle. Cytoskeleton (Hoboken) 2010; 67:677-92. [PMID: 20737540 PMCID: PMC2963174 DOI: 10.1002/cm.20476] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Revised: 07/21/2010] [Accepted: 07/29/2010] [Indexed: 01/08/2023]
Abstract
In striated muscle, the actin cytoskeleton is differentiated into myofibrils. Actin and myosin filaments are organized in sarcomeres and specialized for producing contractile forces. Regular arrangement of actin filaments with uniform length and polarity is critical for the contractile function. However, the mechanisms of assembly and maintenance of sarcomeric actin filaments in striated muscle are not completely understood. Live imaging of actin in striated muscle has revealed that actin subunits within sarcomeric actin filaments are dynamically exchanged without altering overall sarcomeric structures. A number of regulators for actin dynamics have been identified, and malfunction of these regulators often result in disorganization of myofibril structures or muscle diseases. Therefore, proper regulation of actin dynamics in striated muscle is critical for assembly and maintenance of functional myofibrils. Recent studies have suggested that both enhancers of actin dynamics and stabilizers of actin filaments are important for sarcomeric actin organization. Further investigation of the regulatory mechanism of actin dynamics in striated muscle should be a key to understanding how myofibrils develop and operate.
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Affiliation(s)
- Shoichiro Ono
- Department of Pathology and Department of Cell Biology, Emory University, Atlanta, Georgia 30322, USA.
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36
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Tsukada T, Pappas CT, Moroz N, Antin PB, Kostyukova AS, Gregorio CC. Leiomodin-2 is an antagonist of tropomodulin-1 at the pointed end of the thin filaments in cardiac muscle. J Cell Sci 2010; 123:3136-45. [PMID: 20736303 DOI: 10.1242/jcs.071837] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Regulation of actin filament assembly is essential for efficient contractile activity in striated muscle. Leiomodin is an actin-binding protein and homolog of the pointed-end capping protein, tropomodulin. These proteins are structurally similar, sharing a common domain organization that includes two actin-binding sites. Leiomodin also contains a unique C-terminal extension that has a third actin-binding WH2 domain. Recently, the striated-muscle-specific isoform of leiomodin (Lmod2) was reported to be an actin nucleator in cardiomyocytes. Here, we have identified a function of Lmod2 in the regulation of thin filament lengths. We show that Lmod2 localizes to the pointed ends of thin filaments, where it competes for binding with tropomodulin-1 (Tmod1). Overexpression of Lmod2 results in loss of Tmod1 assembly and elongation of the thin filaments from their pointed ends. The Lmod2 WH2 domain is required for lengthening because its removal results in a molecule that caps the pointed ends similarly to Tmod1. Furthermore, Lmod2 transcripts are first detected in the heart after it has begun to beat, suggesting that the primary function of Lmod2 is to maintain thin filament lengths in the mature heart. Thus, Lmod2 antagonizes the function of Tmod1, and together, these molecules might fine-tune thin filament lengths.
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Affiliation(s)
- Takehiro Tsukada
- Department of Cell Biology and Anatomy, and Sarver Molecular Cardiovascular Research Program, University of Arizona, Tucson, AZ 85724, USA
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37
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Yao W, Sung LA. Erythrocyte tropomodulin isoforms with and without the N-terminal actin-binding domain. J Biol Chem 2010; 285:31408-17. [PMID: 20675374 DOI: 10.1074/jbc.m110.130278] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Erythrocyte tropomodulin (E-Tmod or Tmod1) of 41 kDa is a tropomyosin (TM)-binding protein that caps the slow-growing end of the actin filaments. Its N-terminal half is flexible, whereas the C-terminal half has a single domain structure. E-Tmod/TM5 complex may function as a "molecular ruler" generating actin protofilaments of ∼37 nm. Here we report the discovery of a short isoform of 29 kDa that lacks the N-terminal actin-binding domain (N-ABD) but retains the C-terminal actin-binding domain (C-ABD). E-Tmod29 can be generated by alternative splicing from an upstream promoter or by multiple transcriptional start sites from a downstream promoter. Promoter switching leads to a surge of E-Tmod41 in reticulocytes, which degrades quickly in the cytosol. We expressed recombinant isoforms in Escherichia coli and tested their binding toward TM5, G-actin, and F-actin. Solid-phase binding assays show that, without the N-terminal 102 residues, E-Tmod29 binds to TM5 or G-actin more strongly than E-Tmod41 does, but barely binds to F-actin after TM5 binding. Differential bindings explain the distinct localizations of E-Tmod29 in the cytosol and E-Tmod41 on the membrane. Sequential bindings and immunofluorescent staining further suggest that 1) TM5 binding to E-Tmod41 may open up the flexible N-terminal half, exposing N-ABD and unblocking C-ABD; 2) N-ABD binds to F-actin and C-ABD binds to G-actin; and 3) F-actin binding to N-ABD may prevent G-actin from binding to C-ABD. E-Tmod29 may thus modulate the availability of TM5 and G-actin for E-Tmod41 to construct the protofilament-based membrane skeletal network for circulating erythrocytes.
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Affiliation(s)
- Weijuan Yao
- Department of Bioengineering, University of California, San Diego, California 92093-0412, USA
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38
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Tropomodulin 1-null mice have a mild spherocytic elliptocytosis with appearance of tropomodulin 3 in red blood cells and disruption of the membrane skeleton. Blood 2010; 116:2590-9. [PMID: 20585041 DOI: 10.1182/blood-2010-02-268458] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The short actin filaments in the red blood cell (RBC) membrane skeleton are capped at their pointed ends by tropomodulin 1 (Tmod1) and coated with tropomyosin (TM) along their length. Tmod1-TM control of actin filament length is hypothesized to regulate spectrin-actin lattice organization and membrane stability. We used a Tmod1 knockout mouse to investigate the in vivo role of Tmod1 in the RBC membrane skeleton. Western blots of Tmod1-null RBCs confirm the absence of Tmod1 and show the presence of Tmod3, which is normally not present in RBCs. Tmod3 is present at only one-fifth levels of Tmod1 present on wild-type membranes, but levels of actin, TMs, adducins, and other membrane skeleton proteins remain unchanged. Electron microscopy shows that actin filament lengths are more variable with spectrin-actin lattices displaying abnormally large and more variable pore sizes. Tmod1-null mice display a mild anemia with features resembling hereditary spherocytic elliptocytosis, including decreased RBC mean corpuscular volume, cellular dehydration, increased osmotic fragility, reduced deformability, and heterogeneity in osmotic ektacytometry. Insufficient capping of actin filaments by Tmod3 may allow greater actin dynamics at pointed ends, resulting in filament length redistribution, leading to irregular and attenuated spectrin-actin lattice connectivity, and concomitant RBC membrane instability.
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Gokhin DS, Lewis RA, McKeown CR, Nowak RB, Kim NE, Littlefield RS, Lieber RL, Fowler VM. Tropomodulin isoforms regulate thin filament pointed-end capping and skeletal muscle physiology. ACTA ACUST UNITED AC 2010; 189:95-109. [PMID: 20368620 PMCID: PMC2854367 DOI: 10.1083/jcb.201001125] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
In skeletal muscle fibers, tropomodulin 1 (Tmod1) can be compensated for, structurally but not functionally, by Tmod3 and -4. During myofibril assembly, thin filament lengths are precisely specified to optimize skeletal muscle function. Tropomodulins (Tmods) are capping proteins that specify thin filament lengths by controlling actin dynamics at pointed ends. In this study, we use a genetic targeting approach to explore the effects of deleting Tmod1 from skeletal muscle. Myofibril assembly, skeletal muscle structure, and thin filament lengths are normal in the absence of Tmod1. Tmod4 localizes to thin filament pointed ends in Tmod1-null embryonic muscle, whereas both Tmod3 and -4 localize to pointed ends in Tmod1-null adult muscle. Substitution by Tmod3 and -4 occurs despite their weaker interactions with striated muscle tropomyosins. However, the absence of Tmod1 results in depressed isometric stress production during muscle contraction, systemic locomotor deficits, and a shift to a faster fiber type distribution. Thus, Tmod3 and -4 compensate for the absence of Tmod1 structurally but not functionally. We conclude that Tmod1 is a novel regulator of skeletal muscle physiology.
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Affiliation(s)
- David S Gokhin
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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40
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Nowak RB, Fischer RS, Zoltoski RK, Kuszak JR, Fowler VM. Tropomodulin1 is required for membrane skeleton organization and hexagonal geometry of fiber cells in the mouse lens. ACTA ACUST UNITED AC 2009; 186:915-28. [PMID: 19752024 PMCID: PMC2753162 DOI: 10.1083/jcb.200905065] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Hexagonal packing geometry is a hallmark of close-packed epithelial cells in metazoans. Here, we used fiber cells of the vertebrate eye lens as a model system to determine how the membrane skeleton controls hexagonal packing of post-mitotic cells. The membrane skeleton consists of spectrin tetramers linked to actin filaments (F-actin), which are capped by tropomodulin1 (Tmod1) and stabilized by tropomyosin (TM). In mouse lenses lacking Tmod1, initial fiber cell morphogenesis is normal, but fiber cell hexagonal shapes and packing geometry are not maintained as fiber cells mature. Absence of Tmod1 leads to decreased gammaTM levels, loss of F-actin from membranes, and disrupted distribution of beta2-spectrin along fiber cell membranes. Regular interlocking membrane protrusions on fiber cells are replaced by irregularly spaced and misshapen protrusions. We conclude that Tmod1 and gammaTM regulation of F-actin stability on fiber cell membranes is critical for the long-range connectivity of the spectrin-actin network, which functions to maintain regular fiber cell hexagonal morphology and packing geometry.
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Affiliation(s)
- Roberta B Nowak
- Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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Kostyukova AS. Capping complex formation at the slow-growing end of the actin filament. BIOCHEMISTRY (MOSCOW) 2009; 73:1467-72. [PMID: 19216712 DOI: 10.1134/s0006297908130075] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Actin filaments are polar; their barbed (fast-growing) and pointed (slow-growing) ends differ in structure and dynamic properties. The slow-growing end is regulated by tropomodulins, a family of capping proteins that require tropomyosins for optimal function. There are four tropomodulin isoforms; their distributions vary depending on tissue type and change during development. The C-terminal half of tropomodulin contains one compact domain represented by alternating alpha-helices and beta-structures. The tropomyosin-independent actin-capping site is located at the C-terminus. The N-terminal half has no regular structure; however, it contains a tropomyosin-dependent actin-capping site and two tropomyosin-binding sites. One tropomodulin molecule can bind two tropomyosin molecules. Effectiveness of tropomodulin binding to tropomyosin depends on the tropomyosin isoform. Regulation of tropomodulin binding at the pointed end as well as capping effectiveness in the presence of specific tropomyosins may affect formation of local cytoskeleton and dynamics of actin filaments in cells.
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Affiliation(s)
- A S Kostyukova
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
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42
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Davis J, Westfall MV, Townsend D, Blankinship M, Herron TJ, Guerrero-Serna G, Wang W, Devaney E, Metzger JM. Designing heart performance by gene transfer. Physiol Rev 2008; 88:1567-651. [PMID: 18923190 DOI: 10.1152/physrev.00039.2007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The birth of molecular cardiology can be traced to the development and implementation of high-fidelity genetic approaches for manipulating the heart. Recombinant viral vector-based technology offers a highly effective approach to genetically engineer cardiac muscle in vitro and in vivo. This review highlights discoveries made in cardiac muscle physiology through the use of targeted viral-mediated genetic modification. Here the history of cardiac gene transfer technology and the strengths and limitations of viral and nonviral vectors for gene delivery are reviewed. A comprehensive account is given of the application of gene transfer technology for studying key cardiac muscle targets including Ca(2+) handling, the sarcomere, the cytoskeleton, and signaling molecules and their posttranslational modifications. The primary objective of this review is to provide a thorough analysis of gene transfer studies for understanding cardiac physiology in health and disease. By comparing results obtained from gene transfer with those obtained from transgenesis and biophysical and biochemical methodologies, this review provides a global view of cardiac structure-function with an eye towards future areas of research. The data presented here serve as a basis for discovery of new therapeutic targets for remediation of acquired and inherited cardiac diseases.
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Affiliation(s)
- Jennifer Davis
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA
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43
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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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44
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McKeown CR, Nowak RB, Moyer J, Sussman MA, Fowler VM. Tropomodulin1 is required in the heart but not the yolk sac for mouse embryonic development. Circ Res 2008; 103:1241-8. [PMID: 18927466 DOI: 10.1161/circresaha.108.178749] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tropomodulin (Tmod)1 caps the pointed ends of actin filaments in sarcomeres of striated muscle myofibrils and in the erythrocyte membrane skeleton. Targeted deletion of mouse Tmod1 leads to defects in cardiac development, fragility of primitive erythroid cells, and an absence of yolk sac vasculogenesis, followed by embryonic lethality at embryonic day 9.5. The Tmod1-null embryonic hearts do not undergo looping morphogenesis and the cardiomyocytes fail to assemble striated myofibrils with regulated F-actin lengths. To test whether embryonic lethality of Tmod1 nulls results from defects in cardiac myofibrillogenesis and development or from erythroid cell fragility and subsequent defects in yolk sac vasculogenesis, we expressed Tmod1 specifically in the myocardium of the Tmod1-null mice under the control of the alpha-myosin heavy chain promoter Tg(alphaMHC-Tmod1). In contrast to Tmod1-null embryos, which fail to undergo cardiac looping and have defective yolk sac vasculogenesis, both cardiac and yolk sac morphology of Tmod1(-/-Tg(alphaMHC-Tmod1)) embryos are normal at embryonic day 9.5. Tmod1(-/-Tg(alphaMHC-Tmod1)) embryos develop into viable and fertile mice, indicating that expression of Tmod1 in the heart is sufficient to rescue the Tmod1-null embryonic defects. Thus, although loss of Tmod1 results in myriad defects and embryonic lethality, the Tmod1(-/-) primary defect is in the myocardium. Moreover, Tmod1 is not required in erythrocytes for viability, nor do the Tmod1(-/-) fragile primitive erythroid cells affect cardiac development, yolk sac vasculogenesis, or viability in the mouse.
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Affiliation(s)
- Caroline R McKeown
- The Scripps Research Institute, Department of Cell Biology, La Jolla, CA 92037, USA
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45
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Ajima R, Akazawa H, Kodama M, Takeshita F, Otsuka A, Kohno T, Komuro I, Ochiya T, Yokota J. Deficiency of Myo18B in mice results in embryonic lethality with cardiac myofibrillar aberrations. Genes Cells 2008; 13:987-99. [PMID: 18761673 DOI: 10.1111/j.1365-2443.2008.01226.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Myo18B is an unconventional myosin family protein expressed predominantly in muscle cells. Although conventional myosins are known to be localized on the A-bands and function as a molecular motor for muscle contraction, Myo18B protein was localized on the Z-lines of myofibrils in striated muscles. Like Myo18A, another 18th class of myosin, the N-terminal unique domain of the protein and not the motor domain and the coiled-coil tail is critical for its localization to F-actin in myocytes. Myo18B expression was induced by myogenic differentiation through the binding of myocyte-specific enhancer factor-2 to its promoter. Deficiency of Myo18B caused an embryonic lethality in mice accompanied by disruption of myofibrillar structures in cardiac myocytes at embryonic day 10.5. Thus, Myo18B is a unique unconventional myosin that is predominantly expressed in myocytes and whose expression is essential for the development and/or maintenance of myofibrillar structure.
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Affiliation(s)
- Rieko Ajima
- Biology Division, National Cancer Center Research Institute, Tokyo 104-0045, Japan
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46
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Lighthouse DV, Buszczak M, Spradling AC. New components of the Drosophila fusome suggest it plays novel roles in signaling and transport. Dev Biol 2008; 317:59-71. [PMID: 18355804 PMCID: PMC2410214 DOI: 10.1016/j.ydbio.2008.02.009] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2007] [Accepted: 02/02/2008] [Indexed: 12/18/2022]
Abstract
The fusome plays an essential role in prefollicular germ cell development within insects such as Drosophila melanogaster. Alpha-spectrin and the adducin-like protein Hu-li tai shao (Hts) are required to maintain fusome integrity, synchronize asymmetric cystocyte mitoses, form interconnected 16-cell germline cysts, and specify the initial cell as the oocyte. By screening a library of protein trap lines, we identified 14 new fusome-enriched proteins, including many associated with its characteristic vesicles. Our studies reveal that fusomes change during development and contain recycling endosomal and lysosomal compartments in females but not males. A significant number of fusome components are dispensable, because genetic disruption of tropomodulin, ferritin-1 heavy chain, or scribble, does not alter fusome structure or female fertility. In contrast, rab11 is required to maintain the germline stem cells, and to maintain the vesicle content of the spectrosome, suggesting that the fusome mediates intercellular signals that depend on the recycling endosome.
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Affiliation(s)
- Daniel V Lighthouse
- Howard Hughes Medical Institute Research Laboratories, Department of Embryology, Carnegie Institution, Baltimore, MD 21218, USA
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47
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Yao W, Nathanson J, Lian I, Gage FH, Sung LA. Mouse erythrocyte tropomodulin in the brain reported by lacZ knocked-in downstream from the E1 promoter. Gene Expr Patterns 2007; 8:36-46. [PMID: 17920339 DOI: 10.1016/j.modgep.2007.08.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Revised: 07/19/2007] [Accepted: 08/22/2007] [Indexed: 01/14/2023]
Abstract
Erythrocyte tropomodulin (E-Tmod, Tmod1) is a tropomyosin-binding protein that caps the slow-growing end of actin filaments. In erythrocytes, it may favor the formation of short actin protofilaments needed for elastic cell deformation. Previously we created a knockout mouse model in which lacZ was knocked-in downstream of the E1 promoter to report the expression of full length E-Tmod. Here we utilize E-Tmod(+/lacZ) mice to study E-Tmod expression patterns in the CNS. X-gal staining and in situ hybridization of adults revealed its restricted expression in the olfactory bulb, hippocampus, cerebral cortex, basal ganglia, nuclei of brain stem and cerebellum. In neonates, signals in the cortex and caudate putamen increased from days 15 to 40. Immunohistochemistry also revealed that signals for beta-galactosidase coincided with that of NeuN, a post-mitotic nuclear marker for neurons, but not that for GFAP+ astrocytes or APC+ oligodendrocytes, suggesting E-Tmod/lacZ-positive cells in the CNS were neurons. Large neurons, e.g., mitral cells in olfactory bulb and mossy cells in hilus of the dentate gyrus are among those that expressed very high levels of E-Tmod in the CNS.
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Affiliation(s)
- Weijuan Yao
- Department of Bioengineering and Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093-0412, USA
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48
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Kostyukova AS, Hitchcock-Degregori SE, Greenfield NJ. Molecular basis of tropomyosin binding to tropomodulin, an actin-capping protein. J Mol Biol 2007; 372:608-18. [PMID: 17706248 PMCID: PMC2134803 DOI: 10.1016/j.jmb.2007.05.084] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Revised: 05/19/2007] [Accepted: 05/26/2007] [Indexed: 11/28/2022]
Abstract
The tropomodulin (Tmod) family of proteins that cap the pointed, slow-growing end of actin filaments require tropomyosin (TM) for optimal function. Earlier studies identified two regions in Tmod1 that bind the N terminus of TM, though the ability of different isoforms to bind the two sites is controversial. We used model peptides to determine the affinity and define the specificity of the highly conserved N termini of three short, non-muscle TMs (alpha, gamma, delta-TM) for the two Tmod1 binding sites using circular dichroism spectroscopy, native gel electrophoresis, and chemical crosslinking. All TM peptides have high affinity for the second Tmod1 binding site (within residues 109-144; alpha-TM, 2.5 nM; gamma-TM, delta-TM, 40-90 nM), but differ >100-fold for the first site (residues 1-38; alpha-TM, 90 nM; undetectable at 10 microM, gamma-TM, delta-TM). Residue 14 (R in alpha; Q in gamma and delta) and, to a lesser extent, residue 4 (S in alpha; T in gamma and delta) are primarily responsible for the differences. The functional consequence of the sequence differences is reflected in more effective inhibition of actin filament elongation by full-length alpha-TMs than gamma-TM in the presence of Tmod1. The binding sites of the two Tmod1 peptides on a model TM peptide differ, as defined by comparing (15)N,(1)H HSQC spectra of a (15)N-labeled model TM peptide in both the absence and presence of Tmod1 peptide. The NMR and CD studies show that there is an increase in alpha-helix upon Tmod1-TM complex formation, indicating that intrinsically disordered regions of the two proteins become ordered upon binding. A model proposed for the binding of Tmod to actin and TM at the pointed end of the filament shows how the Tmod-TM accentuates the asymmetry of the pointed end and suggests how subtle differences among TM isoforms may modulate actin filament dynamics.
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Affiliation(s)
- Alla S Kostyukova
- Department of Neuroscience and Cell Biology, Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA
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49
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Blatnik JS, Schmid-Schönbein GW, Sung LA. The influence of fluid shear stress on the remodeling of the embryonic primary capillary plexus. Biomech Model Mechanobiol 2005; 4:211-20. [PMID: 16315050 DOI: 10.1007/s10237-005-0001-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Accepted: 06/14/2005] [Indexed: 11/26/2022]
Abstract
The primary capillary plexus in early yolk sacs is remodeled into matured vitelline vessels aligned in the direction of blood flow at the onset of cardiac contraction. We hypothesized that the influence of fluid shear stress on cellular behaviors may be an underlying mechanism by which some existing capillary channels remain open while others are closed during remodeling. Using a recently developed E-Tmod knock-out/lacZ knock-in mouse model, we showed that erythroblasts exhibited rheological properties similar to those of a viscous cell suspension. In contrast, the non-erythroblast (NE) cells, which attach among themselves within the yolk sac, are capable of lamellipodia extension and cell migration. Isolated NE cells in a parallel-plate flow chamber exposed to fluid shear stress, however, ceased lamellipodia extension. Such response may minimize NE cell migration into domains exposed to fluid shear stress. A two-dimensional mathematical model incorporating these cellular behaviors demonstrated that shear stress created by the blood flow initiated by the embryonic heart contraction might be needed for the remodeling of primary capillary plexus.
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Affiliation(s)
- Jeffrey S Blatnik
- Department of Bioengineering, University of California, San Diego, 9500 Gilman Dr, 0412, La Jolla, CA 92093, USA
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50
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Vera C, Skelton R, Bossens F, Sung LA. 3-D nanomechanics of an erythrocyte junctional complex in equibiaxial and anisotropic deformations. Ann Biomed Eng 2005; 33:1387-404. [PMID: 16240087 DOI: 10.1007/s10439-005-4698-y] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2003] [Accepted: 03/24/2005] [Indexed: 10/25/2022]
Abstract
The erythrocyte membrane skeleton deforms constantly in circulation, but the mechanics of a junctional complex (JC) in the network is poorly understood. We previously proposed a 3-D mechanical model for a JC (Sung, L. A., and C. Vera. Protofilament and hexagon: A three-dimensional mechanical model for the junctional complex in the erythrocyte membrane skeleton. Ann Biomed Eng 31:1314-1326, 2003) and now developed a mathematical model to compute its equilibrium by dynamic relaxation. We simulated deformations of a single unit in the network to predict the tension of 6 alphabeta spectrin (Sp) (top, middle, and bottom pairs), and the attitude of the actin protofilament [pitch (theta), yaw (phi) and roll (psi) angles]. In equibiaxial deformation, 6 Sp would not begin their first round of "single domain unfolding in cluster" until the extension ratio (lambda) reach approximately 3.6, beyond the maximal sustainable lambda of approximately 2.67. Before Sp unfolds, the protofilament would gradually raise its pointed end away from the membrane, while phi and psi remain almost unchanged. In anisotropic deformation, protofilaments would remain tangent but swing and roll drastically at least once between lambda(i) = 1.0 and approximately 2.8, in a deformation angle- and lambda(i)-dependent fashion. This newly predicted nanomechanics in response to deformations may reveal functional roles previous unseen for a JC, and molecules associated with it, during erythrocyte circulation.
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Affiliation(s)
- Carlos Vera
- Department of Bioengineering, Jacobs School of Engineering, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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