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Hromowyk KJ, Talbot JC, Martin BL, Janssen PML, Amacher SL. Cell fusion is differentially regulated in zebrafish post-embryonic slow and fast muscle. Dev Biol 2020; 462:85-100. [PMID: 32165147 PMCID: PMC7225055 DOI: 10.1016/j.ydbio.2020.03.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Revised: 02/08/2020] [Accepted: 03/03/2020] [Indexed: 12/13/2022]
Abstract
Skeletal muscle fusion occurs during development, growth, and regeneration. To investigate how muscle fusion compares among different muscle cell types and developmental stages, we studied muscle cell fusion over time in wild-type, myomaker (mymk), and jam2a mutant zebrafish. Using live imaging, we show that embryonic myoblast elongation and fusion correlate tightly with slow muscle cell migration. In wild-type embryos, only fast muscle fibers are multinucleate, consistent with previous work showing that the cell fusion regulator gene mymk is specifically expressed throughout the embryonic fast muscle domain. However, by 3 weeks post-fertilization, slow muscle fibers also become multinucleate. At this late-larval stage, mymk is not expressed in muscle fibers, but is expressed in small cells near muscle fibers. Although previous work showed that both mymk and jam2a are required for embryonic fast muscle cell fusion, we observe that muscle force and function is almost normal in mymk and jam2a mutant embryos, despite the lack of fast muscle multinucleation. We show that genetic requirements change post-embryonically, with jam2a becoming much less important by late-larval stages and mymk now required for muscle fusion and growth in both fast and slow muscle cell types. Correspondingly, adult mymk mutants perform poorly in sprint and endurance tests compared to wild-type and jam2a mutants. We show that adult mymk mutant muscle contains small mononucleate myofibers with average myonuclear domain size equivalent to that in wild type adults. The mymk mutant fibers have decreased Laminin expression and increased numbers of Pax7-positive cells, suggesting that impaired fiber growth and active regeneration contribute to the muscle phenotype. Our findings identify several aspects of muscle fusion that change with time in slow and fast fibers as zebrafish develop beyond embryonic stages.
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Affiliation(s)
- Kimberly J Hromowyk
- Department of Molecular Genetics and Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, 43210, USA; Center for Muscle Health and Neuromuscular Disorders, The Ohio State University and Nationwide Children's Hospital, Columbus, OH, 43210, USA; Molecular, Cellular, and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH, 43210, USA
| | - Jared C Talbot
- Department of Molecular Genetics and Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, 43210, USA; Center for Muscle Health and Neuromuscular Disorders, The Ohio State University and Nationwide Children's Hospital, Columbus, OH, 43210, USA.
| | - Brit L Martin
- Center for Muscle Health and Neuromuscular Disorders, The Ohio State University and Nationwide Children's Hospital, Columbus, OH, 43210, USA; Molecular, Cellular, and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH, 43210, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210, USA
| | - Paul M L Janssen
- Center for Muscle Health and Neuromuscular Disorders, The Ohio State University and Nationwide Children's Hospital, Columbus, OH, 43210, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, 43210, USA; Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, 43210, USA
| | - Sharon L Amacher
- Department of Molecular Genetics and Biological Chemistry and Pharmacology, The Ohio State University, Columbus, OH, 43210, USA; Center for Muscle Health and Neuromuscular Disorders, The Ohio State University and Nationwide Children's Hospital, Columbus, OH, 43210, USA; Center for RNA Biology, The Ohio State University, Columbus, OH, 43210, USA.
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Thomas JD, Oliveira R, Sznajder ŁJ, Swanson MS. Myotonic Dystrophy and Developmental Regulation of RNA Processing. Compr Physiol 2018; 8:509-553. [PMID: 29687899 PMCID: PMC11323716 DOI: 10.1002/cphy.c170002] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Myotonic dystrophy (DM) is a multisystemic disorder caused by microsatellite expansion mutations in two unrelated genes leading to similar, yet distinct, diseases. DM disease presentation is highly variable and distinguished by differences in age-of-onset and symptom severity. In the most severe form, DM presents with congenital onset and profound developmental defects. At the molecular level, DM pathogenesis is characterized by a toxic RNA gain-of-function mechanism that involves the transcription of noncoding microsatellite expansions. These mutant RNAs disrupt key cellular pathways, including RNA processing, localization, and translation. In DM, these toxic RNA effects are predominantly mediated through the modulation of the muscleblind-like and CUGBP and ETR-3-like factor families of RNA binding proteins (RBPs). Dysfunction of these RBPs results in widespread RNA processing defects culminating in the expression of developmentally inappropriate protein isoforms in adult tissues. The tissue that is the focus of this review, skeletal muscle, is particularly sensitive to mutant RNA-responsive perturbations, as patients display a variety of developmental, structural, and functional defects in muscle. Here, we provide a comprehensive overview of DM1 and DM2 clinical presentation and pathology as well as the underlying cellular and molecular defects associated with DM disease onset and progression. Additionally, fundamental aspects of skeletal muscle development altered in DM are highlighted together with ongoing and potential therapeutic avenues to treat this muscular dystrophy. © 2018 American Physiological Society. Compr Physiol 8:509-553, 2018.
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Affiliation(s)
- James D. Thomas
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, University of Florida, College of Medicine, Gainesville, Florida, USA
| | - Ruan Oliveira
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, University of Florida, College of Medicine, Gainesville, Florida, USA
| | - Łukasz J. Sznajder
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, University of Florida, College of Medicine, Gainesville, Florida, USA
| | - Maurice S. Swanson
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics and the Genetics Institute, University of Florida, College of Medicine, Gainesville, Florida, USA
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Goody MF, Sher RB, Henry CA. Hanging on for the ride: adhesion to the extracellular matrix mediates cellular responses in skeletal muscle morphogenesis and disease. Dev Biol 2015; 401:75-91. [PMID: 25592225 DOI: 10.1016/j.ydbio.2015.01.002] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Revised: 12/31/2014] [Accepted: 01/02/2015] [Indexed: 10/24/2022]
Abstract
Skeletal muscle specification and morphogenesis during early development are critical for normal physiology. In addition to mediating locomotion, skeletal muscle is a secretory organ that contributes to metabolic homeostasis. Muscle is a highly adaptable tissue, as evidenced by the ability to increase muscle cell size and/or number in response to weight bearing exercise. Conversely, muscle wasting can occur during aging (sarcopenia), cancer (cancer cachexia), extended hospital stays (disuse atrophy), and in many genetic diseases collectively known as the muscular dystrophies and myopathies. It is therefore of great interest to understand the cellular and molecular mechanisms that mediate skeletal muscle development and adaptation. Muscle morphogenesis transforms short muscle precursor cells into long, multinucleate myotubes that anchor to tendons via the myotendinous junction. This process requires carefully orchestrated interactions between cells and their extracellular matrix microenvironment. These interactions are dynamic, allowing muscle cells to sense biophysical, structural, organizational, and/or signaling changes within their microenvironment and respond appropriately. In many musculoskeletal diseases, these cell adhesion interactions are disrupted to such a degree that normal cellular adaptive responses are not sufficient to compensate for accumulating damage. Thus, one major focus of current research is to identify the cell adhesion mechanisms that drive muscle morphogenesis, with the hope that understanding how muscle cell adhesion promotes the intrinsic adaptability of muscle tissue during development may provide insight into potential therapeutic approaches for muscle diseases. Our objectives in this review are to highlight recent studies suggesting conserved roles for cell-extracellular matrix adhesion in vertebrate muscle morphogenesis and cellular adaptive responses in animal models of muscle diseases.
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Affiliation(s)
- Michelle F Goody
- School of Biology and Ecology, University of Maine, Orono, ME 04469, United States
| | - Roger B Sher
- Department of Molecular and Biomedical Sciences, University of Maine, Orono, ME 04469, United States; Graduate School of Biomedical Sciences and Engineering, University of Maine, Orono, ME 04469, United States
| | - Clarissa A Henry
- School of Biology and Ecology, University of Maine, Orono, ME 04469, United States; Graduate School of Biomedical Sciences and Engineering, University of Maine, Orono, ME 04469, United States; Institute for Molecular Biophysics, University of Maine, Orono, ME 04469, United States.
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Abstract
Muscle fibers form as a result of myoblast fusion, yet the cell surface receptors regulating this process are unknown in vertebrates. In Drosophila, myoblast fusion involves the activation of the Rac pathway by the guanine nucleotide exchange factor Myoblast City and its scaffolding protein ELMO, downstream of cell-surface cell-adhesion receptors. We previously showed that the mammalian ortholog of Myoblast City, DOCK1, functions in an evolutionarily conserved manner to promote myoblast fusion in mice. In search for regulators of myoblast fusion, we identified the G-protein coupled receptor brain-specific angiogenesis inhibitor (BAI3) as a cell surface protein that interacts with ELMO. In cultured cells, BAI3 or ELMO1/2 loss of function severely impaired myoblast fusion without affecting differentiation and cannot be rescued by reexpression of BAI3 mutants deficient in ELMO binding. The related BAI protein family member, BAI1, is functionally distinct from BAI3, because it cannot rescue the myoblast fusion defects caused by the loss of BAI3 function. Finally, embryonic muscle precursor expression of a BAI3 mutant unable to bind ELMO was sufficient to block myoblast fusion in vivo. Collectively, our findings provide a role for BAI3 in the relay of extracellular fusion signals to their intracellular effectors, identifying it as an essential transmembrane protein for embryonic vertebrate myoblast fusion.
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