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Velia M Fowler - One of the best experts on this subject based on the ideXlab platform.
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Tropomodulin Isoform-Specific Regulation of Dendrite Development and Synapse Formation
The Journal of Neuroscience, 2018Co-Authors: Omotola F. Omotade, Velia M Fowler, Yanfang Rui, Wenliang Lei, H. Criss Hartzell, James Q. ZhengAbstract:Neurons of the central nervous system (CNS) elaborate highly branched dendritic arbors that host numerous dendritic spines, which serve as the postsynaptic platform for most excitatory synapses. The actin cytoskeleton plays an important role in dendrite development and spine formation, but the underlying mechanisms remain incompletely understood. Tropomodulins (Tmods) are a family of actin-binding proteins that cap the slow growing (pointed) end of actin filaments, thereby regulating the stability, length, and architecture of complex actin networks in diverse cell types. Three members of the Tmod family, Tmod1, Tmod2, and Tmod3 are expressed in the vertebrate CNS, but their function in neuronal development is largely unknown. In this study, we present evidence that Tmod1 and Tmod2 exhibit distinct roles in regulating spine development and dendritic arborization, respectively. Using rat hippocampal tissues from both sexes, we find that Tmod1 and Tmod2 are expressed with distinct developmental profiles: Tmod2 is expressed early during hippocampal development, whereas Tmod1 expression coincides with synaptogenesis. We then show that knockdown of Tmod2, but not Tmod1, severely impairs dendritic branching. Both Tmod1 and Tmod2 are localized to a distinct sub-spine region where they regulate local F-actin stability. However, knockdown of Tmod1, but not Tmod2, disrupts spine morphogenesis and impairs synapse formation. Collectively, these findings demonstrate that regulation of the actin cytoskeleton by different members of the Tmod family plays an important role in distinct aspects of dendrite and spine development. SIGNIFICANCE STATEMENT The Tropomodulin family of molecules is best known for controlling the length and stability of actin myofilaments in skeletal muscles. While several Tropomodulin members are expressed in the brain, fundamental knowledge about their role in neuronal function is limited. In this study, we show the unique expression profile and subcellular distribution of Tmod1 and Tmod2 in hippocampal neurons. While both Tmod1 and Tmod2 regulate F-actin stability, we find that they exhibit isoform-specific roles in dendrite development and synapse formation: Tmod2 regulates dendritic arborization whereas Tmod1 is required for spine development and synapse formation. These findings provide novel insight into the actin regulatory mechanisms underlying neuronal development, thereby shedding light on potential pathways disrupted in a number of neurological disorders.
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2016Co-Authors: Zhenhua Sui, Velia M Fowler, Roberta B. Nowak, Chad Sanada, Stephanie Halene, Diane S. Krause, Ph. D, Key PointsAbstract:Regulation of actin polymerization by Tropomodulin3 controls megakaryocyte actin organization and platelet biogenesis Running Title: Tropomodulin3 controls platelet formation and size Scientific category
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Tropomodulin 1 directly controls thin filament length in both wild-type and Tropomodulin 4-deficient skeletal muscle.
Development, 2015Co-Authors: David S. Gokhin, Julien Ochala, Andrea A. Domenighetti, Velia M FowlerAbstract:The sarcomeric Tropomodulin (Tmod) isoforms Tmod1 and Tmod4 cap thin filament pointed ends and functionally interact with the leiomodin (Lmod) isoforms Lmod2 and Lmod3 to control myofibril organization, thin filament lengths, and actomyosin crossbridge formation in skeletal muscle fibers. Here, we show that Tmod4 is more abundant than Tmod1 at both the transcript and protein level in a variety of muscle types, but the relative abundances of sarcomeric Tmods are muscle specific. We then generate Tmod4(-/-) mice, which exhibit normal thin filament lengths, myofibril organization, and skeletal muscle contractile function owing to compensatory upregulation of Tmod1, together with an Lmod isoform switch wherein Lmod3 is downregulated and Lmod2 is upregulated. However, RNAi depletion of Tmod1 from either wild-type or Tmod4(-/-) muscle fibers leads to thin filament elongation by ∼15%. Thus, Tmod1 per se, rather than total sarcomeric Tmod levels, controls thin filament lengths in mouse skeletal muscle, whereas Tmod4 appears to be dispensable for thin filament length regulation. These findings identify Tmod1 as the key direct regulator of thin filament length in skeletal muscle, in both adult muscle homeostasis and in developmentally compensated contexts.
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Control of thin filament lengths by sarcomeric Tropomodulin isoforms: insights from mouse models (1102.2)
The FASEB Journal, 2014Co-Authors: David S. Gokhin, Velia M FowlerAbstract:The uniform lengths of skeletal muscle thin filaments are controlled by actin subunit exchange at pointed ends (P-ends). Each P-end is capped by two sarcomeric Tropomodulin (Tmod) molecules, with T...
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Pointed-end capping by Tropomodulin modulates actomyosin crossbridge formation in skeletal muscle fibers
The FASEB Journal, 2013Co-Authors: Julien Ochala, David S. Gokhin, Hiroyuki Iwamoto, Velia M FowlerAbstract:In skeletal muscle, thick and thin filaments are arranged in a myofibrillar lattice. Tropomodulin 1 (Tmod1) is a pointed-end capping and tropomyosin-binding protein that controls thin-filament assembly, stability, and lengths. It remains unknown whether Tmods have other functional roles, such as regulating muscle contractility. To investigate this, we recorded and analyzed the mechanical properties and X-ray diffraction patterns of single membrane-permeabilized skeletal muscle fibers from mice lacking Tmod1. Results show that absence of Tmod1 and its replacement by Tmod3 and Tmod4 may impair initial tropomyosin movement over actin subunits during thin-filament activation, thus reducing both the fraction of actomyosin crossbridges in the strongly bound state (−29%) and fiber force-generating capacity (−31%). Therefore, Tmods are novel regulators of actomyosin crossbridge formation and muscle contractility, and future investigations and models of skeletal muscle force production must incorporate Tmods.—Ochala, J., Gokhin, D. S., Iwamoto, H., Fowler, V. M. Pointed-end capping by Tropomodulin modulates actomyosin crossbridge formation in skeletal muscle fibers.
Alla S Kostyukova - One of the best experts on this subject based on the ideXlab platform.
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Congenital myopathy-related mutations in tropomyosin disrupt regulatory function through altered actin affinity and Tropomodulin binding.
The FEBS Journal, 2019Co-Authors: Joanna Moraczewska, Alla S Kostyukova, Katarzyna Robaszkiewicz, Małgorzata Śliwinska, Marta Czajkowska, Han Wen, Wenjun ZhengAbstract:Tropomyosin (Tpm) binds along actin filaments and regulates myosin binding to control muscle contraction. Tropomodulin binds to the pointed end of a filament and regulates actin dynamics, which maintains the length of a thin filament. To define the structural determinants of these Tpm functions, we examined the effects of two congenital myopathy mutations, A4V and R91C, in the Tpm gene, TPM3, which encodes the Tpm3.12 isoform, specific for slow-twitch muscle fibers. Mutation A4V is located in the Tropomodulin-binding, N-terminal region of Tpm3.12. R91C is located in the actin-binding period 3 and directly interacts with actin. The A4V and R91C mutations resulted in a 2.5-fold reduced affinity of Tpm3.12 homodimers for F-actin in the absence and presence of troponin, and a two-fold decrease in actomyosin ATPase activation in the presence of Ca2+ . Actomyosin ATPase inhibition in the absence of Ca2+ was not affected. The Ca2+ sensitivity of ATPase activity was decreased by R91C, but not by A4V. In vitro, R91C altered the ability of Tropomodulin 1 (Tmod1) to inhibit actin polymerization at the pointed end of the filaments, which correlated with the reduced affinity of Tpm3.12-R91C for Tmod1. Molecular dynamics simulations of Tpm3.12 in complex with F-actin suggested that both mutations reduce the affinity of Tpm3.12 for F-actin binding by perturbing the van der Waals energy, which may be attributable to two different molecular mechanisms-a reduced flexibility of Tpm3.12-R91C and an increased flexibility of Tpm3.12-A4V.
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Characterizing interaction forces between actin and proteins of the Tropomodulin family reveals the presence of the N-terminal actin-binding site in leiomodin
Archives of Biochemistry and Biophysics, 2018Co-Authors: Baran Arslan, Mert Colpan, Kevin T. Gray, Nehal I. Abu-lail, Alla S KostyukovaAbstract: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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An AFM Investigation of the Nanoscale Forces that Govern the Interactions between Actin and Proteins of Tropomodulin Family
Biophysical Journal, 2017Co-Authors: Baran Arslan, Mert Colpan, Kevin T. Gray, Nehal I. Abu-lail, Alla S KostyukovaAbstract:Tropomodulin family of proteins includes several isoforms of Tropomodulins (Tmod) and leiomodins (Lmod), which are differentially expressed in various tissues. They bind to the pointed end of an actin filament and regulate dynamics at that end. By binding to G-actin they sequester actin or nucleate actin polymerization. Of Tmod isoforms, Tmod2 is the best nucleator and Tmod3 is the best in sequestering. Although these properties are isoform-dependent, knowledge on how they vary in their strength of interactions to actin is missing.
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Tropomyosin-binding properties modulate competition between Tropomodulin isoforms
Archives of Biochemistry and Biophysics, 2016Co-Authors: Mert Colpan, Kevin T. Gray, Natalia Moroz, Dillon A. Cooper, Christian A. Diaz, Alla S KostyukovaAbstract:The formation and fine-tuning of cytoskeleton in cells are governed by proteins that influence actin filament dynamics. Tropomodulin (Tmod) regulates the length of actin filaments by capping the pointed ends in a tropomyosin (TM)-dependent manner. Tmod1, Tmod2 and Tmod3 are associated with the cytoskeleton of non-muscle cells and their expression has distinct consequences on cell morphology. To understand the molecular basis of differences in the function and localization of Tmod isoforms in a cell, we compared the actin filament-binding abilities of Tmod1, Tmod2 and Tmod3 in the presence of Tpm3.1, a non-muscle TM isoform. Tmod3 displayed preferential binding to actin filaments when competing with other isoforms. Mutating the second or both TM-binding sites of Tmod3 destroyed its preferential binding. Our findings clarify how Tmod1, Tmod2 and Tmod3 compete for binding actin filaments. Different binding mechanisms and strengths of Tmod isoforms for Tpm3.1 contribute to their divergent functional capabilities.
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Mutations changing Tropomodulin affinity for tropomyosin alter neurite formation and extension.
PeerJ, 2013Co-Authors: Natalia Moroz, Laurent Guillaud, Brinda Desai, Alla S KostyukovaAbstract:Assembly of the actin cytoskeleton is an important part of formation of neurites in developing neurons. Tropomodulin, a tropomyosin-dependent capping protein for the pointed end of the actin filament, is one of the key players in this process. Tropomodulin binds tropomyosin in two binding sites. Tmod1 and Tmod2, Tropomodulin isoforms found in neurons, were overexpressed in PC12 cells, a model system for neuronal differentiation. Tmod1 did not affect neuronal differentiation; while cells expressing Tmod2 showed a significant reduction in the number and the length of neurites. Both Tropomodulins bind short α-, γ- and δ-tropomyosin isoforms. Mutations in one of the tropomyosin-binding sites of Tmod1, which increased its affinity to short γ- and δ-tropomyosin isoforms, caused a decrease in binding short α-tropomyosin isoforms along with a 2-fold decrease in the length of neurites. Our data demonstrate that Tmod1 is involved in neuronal differentiation for proper neurite formation and outgrowth, and that Tmod2 inhibits these processes. The mutations in the tropomyosin-binding site of Tmod1 impair neurite outgrowth, suggesting that the integrity of this binding site is critical for the proper function of Tmod1 during neuronal differentiation.
Huda Y. Zoghbi - One of the best experts on this subject based on the ideXlab platform.
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JCB Article Aberrant
2013Co-Authors: Kimberly L. Fritz-six, Carol C Gregorio, Patrick R. Cox, Huda Y. Zoghbi, Robert S. Fischer, Velia M FowlerAbstract:myofibril assembly in Tropomodulin1 null mice leads to aborted heart development and embryonic lethalit
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Mice lacking Tropomodulin-2 show enhanced long-term potentiation, hyperactivity, and deficits in learning and memory
Molecular and Cellular Neuroscience, 2003Co-Authors: Patrick R. Cox, Velia M Fowler, J. David Sweatt, Richard Paylor, Huda Y. ZoghbiAbstract:Abstract Actin filaments control cell morphology and are essential to the growth of dendritic spines and the plasticity of hippocampal long-term potentiation (LTP). The length of these filaments is regulated in muscle and nonmuscle cell types by Tropomodulins 1–4 (Tmod1–4), a family of proteins that cap the pointed ends of actin filaments. To investigate whether Tropomodulins could play a role in synaptic plasticity, learning, memory, or behavior, we created mice lacking Tropomodulin-2 ( Tmod2 ), which is highly expressed in neuronal structures. Tmod2 lacZ−/− mice are viable and fertile and exhibit no gross morphological or anatomical abnormalities, but behavioral analysis found hyperactivity, reduced sensorimotor gating, and impaired learning and memory. Electrophysiological analysis revealed enhanced LTP in Tmod2 lacZ−/− mice. These studies suggest that Tmod2 plays a role in behavior, learning, memory, and synaptic plasticity.
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Genomic organization of Tropomodulins 2 and 4 and unusual intergenic and intraexonic splicing of YL-1 and Tropomodulin 4
BMC Genomics, 2001Co-Authors: Patrick R. Cox, Teepu Siddique, Huda Y. ZoghbiAbstract:Background The Tropomodulins (TMODs) are a family of proteins that cap the pointed ends of actin filaments. Four TMODs have been identified in humans, with orthologs in mice. Mutations in actin or actin-binding proteins have been found to cause several human diseases, ranging from hypertrophic cardiomyopathy to immunodefiencies such as Wiskott-Aldrich syndrome. We had previously mapped Tropomodulin 2 (TMOD2) to the genomic region containing the gene for amyotrophic lateral sclerosis 5 (ALS5). We determined the genomic structure of Tmod2 in order to better analyze patient DNA for mutations; we also determined the genomic structure of Tropomodulin 4 (TMOD4).
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Genomic organization of Tropomodulins 2 and 4 and unusual intergenic and intraexonic splicing of YL-1 and Tropomodulin 4
BMC Genomics, 2001Co-Authors: Patrick R. Cox, Teepu Siddique, Huda Y. ZoghbiAbstract:Background The Tropomodulins (TMODs) are a family of proteins that cap the pointed ends of actin filaments. Four TMODs have been identified in humans, with orthologs in mice. Mutations in actin or actin-binding proteins have been found to cause several human diseases, ranging from hypertrophic cardiomyopathy to immunodefiencies such as Wiskott-Aldrich syndrome. We had previously mapped Tropomodulin 2 (TMOD2) to the genomic region containing the gene for amyotrophic lateral sclerosis 5 (ALS5). We determined the genomic structure of Tmod2 in order to better analyze patient DNA for mutations; we also determined the genomic structure of Tropomodulin 4 (TMOD4). Results In this study, we determined the genomic structure of TMOD2 and TMOD4 and found the organization of both genes to be similar. Sequence analysis of TMOD2 revealed no mutations or polymorphisms in ALS5 patients or controls. Interestingly, we discovered that another gene, YL-1, intergenically splices into TMOD4. YL-1 encodes six exons, the last of which is 291 bp from a 5' untranslated exon of TMOD4. We used 5' RACE and RT-PCR from TMOD4 to identify several intergenic RACE products. YL-1 was also found to undergo unconventional splicing using non-canonical splice sites within exons (intraexonic splicing) to produce several alternative transcripts. Conclusions The genomic structure of TMOD2 and TMOD4 have been delineated. This should facilitate future mutational analysis of these genes. In addition, intergenic splicing at TMOD4/YL-1 was discovered, demonstrating yet another level of complexity of gene organization and regulation.
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Sequencing, expression analysis, and mapping of three unique human Tropomodulin genes and their mouse orthologs.
Genomics, 2000Co-Authors: Patrick R. Cox, Huda Y. ZoghbiAbstract:Tropomodulin (TMOD) is the actin-capping protein for the slow-growing end of filamentous actin, and a neuronal-specific isoform, neuronal Tropomodulin (NTMOD), is the major binding protein to brain tropomyosin in rat. The Drosophila TMOD homolog, Sanpodo, alters sibling cell fate determination, so we used a cross-species approach to identify additional TMOD family members that may play a critical role in this process. We characterized the human and mouse orthologs to rat NTMOD (TMOD2 and Tmod2, respectively) as well as two novel Tropomodulin family members (TMOD3, Tmod3 and TMOD4, Tmod4). Their expression patterns vary extensively, from ubiquitous (TMOD3 and Tmod3) to muscle (TMOD4) or neuronal tissues only (TMOD2 and Tmod2). TMOD2 and TMOD3 map next to one another on chromosome 15q21.1-q21.2, and their mouse orthologs map to a homologous region on mouse chromosome 9; TMOD4 maps to the telomeric end of 1q12 and Tmod4 to a homologous region of mouse chromosome 3. Their location and expression patterns make TMOD2 and TMOD3 candidate genes for amyotrophic lateral sclerosis 5 (ALS5) and dyslexia-1 (DYX1) and TMOD4 a candidate gene for limb girdle muscular dystrophy 1B (LGMD1B). Our mapping efforts revealed new regions of paralogy among chromosomes 1q, 9q, 15q, and 19p.
Mark A Sussman - One of the best experts on this subject based on the ideXlab platform.
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Hypertrophic defect unmasked by calcineurin expression in asymptomatic Tropomodulin overexpressing transgenic mice.
Cardiovascular Research, 2000Co-Authors: Mark A Sussman, Sara Welch, Raisa Klevitsky, Robert L Price, Sandra A Witt, Thomas R Kimball, Timothy E. Hewett, Angela Walker, Hae W. Lim, Jeffery D. MolkentinAbstract:Objective: Dilation and hypertrophy often occur concurrently in cardiomyopathy, yet the interaction between these two functionally distinct conditions remains unknown. Methods: Combinatorial effects of hypertrophy and dilation were investigated by cross-breeding of two cardiomyopathic transgenic mouse lines which develop either hypertrophy (calcineurin-mediated) or dilation (Tropomodulin-mediated). Results: Altering the intensity of signals driving hypertrophy and dilation in cross-bred litters resulted in novel disease phenotypes different from either parental line. Augmenting the calcineurin-dependent hypertrophic stimulus in Tropomodulin overexpressing transgenics elevated heart:body weight ratios, increased ventricular wall thickness, and significantly accelerated mortality. These effects were evident in calcineurin cross-breeding to Tropomodulin backgrounds of transgene homozygosity (severe dilation) or heterozygosity (mild dilation to asymptomatic). Molecular analyses indicated that Tropomodulin and calcineurin signaling events in the first week after birth were critical for determination of disease outcome, substantiated by demonstration that temporary neonatal inhibition of Tropomodulin expression prevents dilation. Conclusions: This study shows that postnatal timing of altered signaling in cardiomyopathic transgenic mouse models is a pivotal part of determining outcome. In addition, intensifying hypertrophic stimulation exacerbates dilated cardiomyopathy, supporting the concept of shared molecular signaling between hypertrophy and dilation.
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Altered Expression of Tropomodulin in Cardiomyocytes Disrupts the Sarcomeric Structure of Myofibrils
Circulation Research, 1998Co-Authors: Mark A Sussman, Robert L Price, Susanna Baqué, Chang Sub Uhm, Mathew P. Daniels, David G. Simpson, Louis Terracio, Larry KedesAbstract:Abstract —Tropomodulin is a tropomyosin-binding protein that terminates “pointed-end” actin filament polymerization. To test the hypothesis that regulation of Tropomodulin:actin filament stoichiometry is critical for maintenance of actin filament length, Tropomodulin levels were altered in cells by infection with recombinant adenoviral expression vectors, which produce either sense or antisense Tropomodulin mRNA. Neonatal rat cardiomyocytes were infected, and sarcomeric actin filament organization was examined. Confocal microscopy indicated that overexpression of Tropomodulin protein shortened actin filaments and caused myofibril degeneration. In contrast, decreased Tropomodulin content resulted in the formation of abnormally long actin filament bundles. Despite changes in myofibril structure caused by altered Tropomodulin expression, total protein turnover of the cardiomyocytes was unaffected. Biochemical analyses of infected cardiomyocytes indicated that changes in actin distribution, rather than altered actin content, accounted for myofibril reorganization. Ultrastructural analysis showed thin-filament disarray and revealed the presence of leptomeres after Tropomodulin overexpression. Tropomodulin-mediated effects constitute a novel mechanism to control actin filaments, and our findings demonstrate that regulated Tropomodulin expression is necessary to maintain stabilized actin filament structures in cardiac muscle cells.
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myofibril degeneration caused by Tropomodulin overexpression leads to dilated cardiomyopathy in juvenile mice
Journal of Clinical Investigation, 1998Co-Authors: Mark A Sussman, Sara Welch, Natalie Cambon, Raisa Klevitsky, Robert L Price, Sandra A Witt, Timothy E. Hewett, Thomas R KimballAbstract:Loss of myofibril organization is a common feature of chronic dilated and progressive cardiomyopathy. To study how the heart compensates for myofibril degeneration, transgenic mice were created that undergo progressive loss of myofibrils after birth. Myofibril degeneration was induced by overexpression of Tropomodulin, a component of the thin filament complex which determines and maintains sarcomeric actin filament length. The Tropomodulin cDNA was placed under control of the alpha-myosin heavy chain gene promoter to overexpress Tropomodulin specifically in the myocardium. Offspring with the most severe phenotype showed cardiomyopathic changes between 2 and 4 wk after birth. Hearts from these mice present characteristics consistent with dilated cardiomyopathy and a failed hypertrophic response. Histological analysis showed widespread loss of myofibril organization. Confocal microscopy of isolated cardiomyocytes revealed intense Tropomodulin immunoreactivity in transgenic mice together with abnormal coincidence of Tropomodulin and alpha-actinin reactivity at Z discs. Contractile function was compromised severely as determined by echocardiographic analyses and isolated Langendorff heart preparations. This novel experimentally induced cardiomyopathy will be useful for understanding dilated cardiomyopathy and the effect of thin filament-based myofibril degeneration upon cardiac structure and function.
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Chicken skeletal muscle Tropomodulin: novel localization and characterization.
Cell and Tissue Research, 1996Co-Authors: Mark A Sussman, Mathew P. Daniels, Masamichi Ito, Bernhard E. Flucher, Sara Buranen, Larry KedesAbstract:Tropomodulin is a 40.6-kDa isoform-specific tropomyosin-binding protein which inhibits actin filament elongation from the slow-growing (pointed) end and localizes at or near the pointed ends of thin filaments in rat skeletal muscle. Immunofluorescent localization using affinity-purified anti-Tropomodulin antibodies in avian myofibril preparations demonstrates novel immunoreactivity at the Z-disc in addition to the previously reported localization at the periphery of I-Z-I brushes where actin filaments terminate. Identical results were obtained using antibody preparations generated against either bacterially expressed Tropomodulin or human erythrocyte Tropomodulin. Chicken muscle preparations contain Mr 43000 polypeptides which bind antibodies generated against Tropomodulin in Western blot analysis, as well as 125I-labeled tropomyosin in blot overlays. Tropomodulin mRNA expression in adult muscle was confirmed by RNase protection assays, and the sequence of our Tropomodulin cDNA amplified from chicken muscle mRNA preparations by polymerase chain reaction closely matches clones selected by chicken muscle cDNA library screening. The novel immunolocalization we report raises new possibilities for the role of Tropomodulin in the organization of avian skeletal muscle at the Z-disc. We conclude that Tropomodulin is likely to be important in striated muscle biology as a structural component in the Z-disc region which participates in the process of thin filament organization and assembly.
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Lens Tropomodulin: developmental expression during differentiation.
Experimental Eye Research, 1996Co-Authors: Mark A Sussman, Larry Kedes, John W. Mcavoy, Michael Rudisill, Bradley J. Swanson, Gary E. Lyons, Janet C. BlanksAbstract:Lens epithelial cells undergo a dramatic transformation during the process of differentiation into elongated fiber cells. The membrane-associated actin cytoskeleton is likely to play a critical role in the stabilization and maintenance of the highly elongated fiber cell shape. Tropomodulin is a tropomyosin-binding protein associated with actin filaments in a variety of terminally differentiated cell types where stable actin filament organization is required for cell function. We now present results of studies to determine the temporal expression of Tropomodulin in the developing lens. In situ hybridization experiments detected expression of Tropomodulin mRNA in the developing mouse lens in elongating cells with a pattern similar to that of the fiber specific beta- and gamma-crystallins. Tropomodulin mRNA expression first appeared around 11.5 days post-coitum in elongating cells in the posterior part of the lens vesicle. At later stages the signal for Tropomodulin was present in the elongating cells at the lens equator and in cortical fiber cells; signal was absent from the epithelium. To investigate the possible link between Tropomodulin expression and fiber differentiation we used a well-established lens epithelial explant culture system in which fiber differentiation is induced by fibroblast growth factor (FGF). Tropomodulin expression was only observed in FGF-treated explants in conjunction with morphologic changes characteristic of lens fiber cell differentiation. The appearance of Tropomodulin during the process of fiber cell differentiation suggests that Tropomodulin may be important for stabilization and/or determination of actin filament length.
Shoichiro Ono - One of the best experts on this subject based on the ideXlab platform.
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Tropomodulin Protects α-Catenin-Dependent Junctional-Actin Networks under Stress during Epithelial Morphogenesis
Current Biology, 2012Co-Authors: Elisabeth Cox-paulson, Sawako Yamashiro, Shoichiro Ono, Elise Walck-shannon, Allison M. Lynch, Ronen Zaidel-bar, Celeste Eno, Jeff HardinAbstract: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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sarcomeric actin organization is synergistically promoted by Tropomodulin adf cofilin aip1 and profilin in c elegans
Journal of Cell Science, 2008Co-Authors: Sawako Yamashiro, Elisabeth A. Cox, David L. Baillie, Jeff Hardin, Shoichiro OnoAbstract: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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Sarcomeric actin organization is synergistically promoted by Tropomodulin, ADF/cofilin, AIP1 and profilin in C. elegans
Journal of Cell Science, 2008Co-Authors: Sawako Yamashiro, Elisabeth A. Cox, David L. Baillie, Jeff Hardin, Shoichiro OnoAbstract: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.