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Nikonova E, DeCata J, Canela M, Barz C, Esser A, Bouterwek J, Roy A, Gensler H, Heß M, Straub T, Forne I, Spletter ML. Bruno 1/CELF regulates splicing and cytoskeleton dynamics to ensure correct sarcomere assembly in Drosophila flight muscles. PLoS Biol 2024; 22:e3002575. [PMID: 38683844 PMCID: PMC11081514 DOI: 10.1371/journal.pbio.3002575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Revised: 05/09/2024] [Accepted: 03/04/2024] [Indexed: 05/02/2024] Open
Abstract
Muscles undergo developmental transitions in gene expression and alternative splicing that are necessary to refine sarcomere structure and contractility. CUG-BP and ETR-3-like (CELF) family RNA-binding proteins are important regulators of RNA processing during myogenesis that are misregulated in diseases such as Myotonic Dystrophy Type I (DM1). Here, we report a conserved function for Bruno 1 (Bru1, Arrest), a CELF1/2 family homolog in Drosophila, during early muscle myogenesis. Loss of Bru1 in flight muscles results in disorganization of the actin cytoskeleton leading to aberrant myofiber compaction and defects in pre-myofibril formation. Temporally restricted rescue and RNAi knockdown demonstrate that early cytoskeletal defects interfere with subsequent steps in sarcomere growth and maturation. Early defects are distinct from a later requirement for bru1 to regulate sarcomere assembly dynamics during myofiber maturation. We identify an imbalance in growth in sarcomere length and width during later stages of development as the mechanism driving abnormal radial growth, myofibril fusion, and the formation of hollow myofibrils in bru1 mutant muscle. Molecularly, we characterize a genome-wide transition from immature to mature sarcomere gene isoform expression in flight muscle development that is blocked in bru1 mutants. We further demonstrate that temporally restricted Bru1 rescue can partially alleviate hypercontraction in late pupal and adult stages, but it cannot restore myofiber function or correct structural deficits. Our results reveal the conserved nature of CELF function in regulating cytoskeletal dynamics in muscle development and demonstrate that defective RNA processing due to misexpression of CELF proteins causes wide-reaching structural defects and progressive malfunction of affected muscles that cannot be rescued by late-stage gene replacement.
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Affiliation(s)
- Elena Nikonova
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Jenna DeCata
- School of Science and Engineering, Division of Biological and Biomedical Systems, Kansas City, Missouri, United States of America
| | - Marc Canela
- Faculty of Biology, Universitat de Barcelona, Barcelona, Spain
| | - Christiane Barz
- Muscle Dynamics Group, Max Planck Institute of Biochemistry, München, Germany
| | - Alexandra Esser
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Jessica Bouterwek
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Akanksha Roy
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, München, Germany
| | - Heidemarie Gensler
- Department of Systematic Zoology, Biocenter, Faculty of Biology, Ludwig-Maximilians-Universität München, München, Germany
| | - Martin Heß
- Department of Systematic Zoology, Biocenter, Faculty of Biology, Ludwig-Maximilians-Universität München, München, Germany
| | - Tobias Straub
- Biomedical Center, Bioinformatics Core Unit, Ludwig-Maximilians-Universität München, München, Germany
| | - Ignasi Forne
- Biomedical Center, Protein Analysis Unit, Ludwig-Maximilians-Universität München, München, Germany
| | - Maria L. Spletter
- Biomedical Center, Department of Physiological Chemistry, Ludwig-Maximilians-Universität München, München, Germany
- School of Science and Engineering, Division of Biological and Biomedical Systems, Kansas City, Missouri, United States of America
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Caremani M, Marcello M, Morotti I, Pertici I, Squarci C, Reconditi M, Bianco P, Piazzesi G, Lombardi V, Linari M. The force of the myosin motor sets cooperativity in thin filament activation of skeletal muscles. Commun Biol 2022; 5:1266. [DOI: 10.1038/s42003-022-04184-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Accepted: 10/28/2022] [Indexed: 11/19/2022] Open
Abstract
AbstractContraction of striated muscle is regulated by a dual mechanism involving both thin, actin-containing filament and thick, myosin-containing filament. Thin filament is activated by Ca2+ binding to troponin, leading to tropomyosin displacement that exposes actin sites for interaction with myosin motors, extending from the neighbouring stress-activated thick filaments. Motor attachment to actin contributes to spreading activation along the thin filament, through a cooperative mechanism, still unclear, that determines the slope of the sigmoidal relation between isometric force and pCa (−log[Ca2+]), estimated by Hill coefficient nH. We use sarcomere-level mechanics in demembranated fibres of rabbit skeletal muscle activated by Ca2+ at different temperatures (12–35 °C) to show that nH depends on the motor force at constant number of attached motors. The definition of the role of motor force provides fundamental constraints for modelling the dynamics of thin filament activation and defining the action of small molecules as possible therapeutic tools.
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McBride JM. Muscle Actuators, Not Springs, Drive Maximal Effort Human Locomotor Performance. J Sports Sci Med 2021; 20:766-777. [PMID: 35321123 PMCID: PMC8488820 DOI: 10.52082/jssm.2021.766] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 09/20/2021] [Indexed: 05/19/2023]
Abstract
The current investigation examined muscle-tendon unit kinematics and kinetics in human participants asked to perform a hopping task for maximal performance with variational preceding milieu. Twenty-four participants were allocated post-data collection into those participants with an average hop height of higher (HH) or lower (LH) than 0.1 m. Participants were placed on a customized sled at a 20º angle while standing on a force plate. Participants used their dominant ankle for all testing and their knee was immobilized and thus all movement involved only the ankle joint and corresponding propulsive unit (triceps surae muscle complex). Participants were asked to perform a maximal effort during a single dynamic countermovement hop (CMH) and drop hops from 10 cm (DH10) and 50 cm (DH50). Three-dimensional motion analysis was performed by utilizing an infrared camera VICON motion analysis system and a corresponding force plate. An ultrasound probe was placed on the triceps surae muscle complex for muscle fascicle imaging. HH hopped significantly higher in all hopping tasks in comparison to LH. In addition, the HH group concentric ankle work was significantly higher in comparison to LH during all of the hopping tasks. Active muscle work was significantly higher in HH in comparison to LH as well. Tendon work was not significantly different between HH and LH. Active muscle work was significantly correlated with hopping height (r = 0.97) across both groups and hopping tasks and contributed more than 50% of the total work. The data indicates that humans primarily use a motor-driven system and thus it is concluded that muscle actuators and not springs maximize performance in hopping locomotor tasks in humans.
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Affiliation(s)
- Jeffrey M McBride
- Neuromuscular & Biomechanics Laboratory, Beaver College of Health Sciences, Department of Health & Exercise Science, Appalachian State University, North Carolina, USA
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Powers JD, Malingen SA, Regnier M, Daniel TL. The Sliding Filament Theory Since Andrew Huxley: Multiscale and Multidisciplinary Muscle Research. Annu Rev Biophys 2021; 50:373-400. [PMID: 33637009 DOI: 10.1146/annurev-biophys-110320-062613] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Two groundbreaking papers published in 1954 laid out the theory of the mechanism of muscle contraction based on force-generating interactions between myofilaments in the sarcomere that cause filaments to slide past one another during muscle contraction. The succeeding decades of research in muscle physiology have revealed a unifying interest: to understand the multiscale processes-from atom to organ-that govern muscle function. Such an understanding would have profound consequences for a vast array of applications, from developing new biomimetic technologies to treating heart disease. However, connecting structural and functional properties that are relevant at one spatiotemporal scale to those that are relevant at other scales remains a great challenge. Through a lens of multiscale dynamics, we review in this article current and historical research in muscle physiology sparked by the sliding filament theory.
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Affiliation(s)
- Joseph D Powers
- Department of Bioengineering, University of California San Diego, La Jolla, California 92093, USA
| | - Sage A Malingen
- Department of Biology, University of Washington, Seattle, Washington 98195, USA;
| | - Michael Regnier
- Department of Bioengineering, University of Washington, Seattle, Washington 98185, USA
- Center for Translational Muscle Research, University of Washington, Seattle, Washington 98185, USA
| | - Thomas L Daniel
- Department of Biology, University of Washington, Seattle, Washington 98195, USA;
- Department of Bioengineering, University of Washington, Seattle, Washington 98185, USA
- Center for Translational Muscle Research, University of Washington, Seattle, Washington 98185, USA
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Powers JD, Bianco P, Pertici I, Reconditi M, Lombardi V, Piazzesi G. Contracting striated muscle has a dynamic I-band spring with an undamped stiffness 100 times larger than the passive stiffness. J Physiol 2020; 598:331-345. [PMID: 31786814 DOI: 10.1113/jp278713] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2019] [Accepted: 11/21/2019] [Indexed: 12/20/2022] Open
Abstract
KEY POINTS Fast sarcomere-level mechanics in contracting intact fibres from frog skeletal muscle reveal an I-band spring with an undamped stiffness 100 times larger than the known static stiffness. This undamped stiffness remains constant in the range of sarcomere length 2.7-3.1 µm, showing the ability of the I-band spring to adapt its length to the width of the I-band. The stiffness and tunability of the I-band spring implicate titin as a force contributor that, during contraction, allows weaker half-sarcomeres to equilibrate with in-series stronger half-sarcomeres, preventing the development of sarcomere length inhomogeneity. This work opens new possibilities for the detailed in situ description of the structural-functional basis of muscle dysfunctions related to mutations or site-directed mutagenesis in titin that alter the I-band stiffness. ABSTRACT Force and shortening in the muscle sarcomere are due to myosin motors from thick filaments pulling nearby actin filaments toward the sarcomere centre. Thousands of serially linked sarcomeres in muscle make the shortening (and the shortening speed) macroscopic, while the intrinsic instability of in-series force generators is likely prevented by the cytoskeletal protein titin that connects the thick filament with the sarcomere end, working as an I-band spring that accounts for the rise of passive force with sarcomere length (SL). However, current estimates of titin stiffness, deduced from the passive force-SL relation and single molecule mechanics, are much smaller than what is required to avoid the development of large inhomogeneities among sarcomeres. In this work, using 4 kHz stiffness measurements on a population of sarcomeres selected along an intact fibre isolated from frog skeletal muscle contracting at different SLs (temperature 4°C), we measure the undamped stiffness of an I-band spring that at SL > 2.7 µm attains a maximum constant value of ∼6 pN nm-1 per half-thick filament, two orders of magnitude larger than expected from titin-related passive force. We conclude that a titin-like dynamic spring in the I-band, made by an undamped elastic element in-series with damped elastic elements, adapts its length to the SL with kinetics that provide force balancing among serially linked sarcomeres during contraction. In this way, the I-band spring plays a fundamental role in preventing the development of SL inhomogeneity.
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Affiliation(s)
- Joseph D Powers
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
- Bioengineering, University of Washington, 3720 15th Ave NE, Seattle, WA, 98105, USA
| | - Pasquale Bianco
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Irene Pertici
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Massimo Reconditi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Vincenzo Lombardi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
| | - Gabriella Piazzesi
- PhysioLab, University of Florence, Via G. Sansone, 1, 50019 Sesto Fiorentino, Florence, Italy
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