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Korb A, Tajbakhsh S, Comai GE. Functional specialisation and coordination of myonuclei. Biol Rev Camb Philos Soc 2024. [PMID: 38477382 DOI: 10.1111/brv.13063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2023] [Revised: 01/30/2024] [Accepted: 02/02/2024] [Indexed: 03/14/2024]
Abstract
Myofibres serve as the functional unit for locomotion, with the sarcomere as fundamental subunit. Running the entire length of this structure are hundreds of myonuclei, located at the periphery of the myofibre, juxtaposed to the plasma membrane. Myonuclear specialisation and clustering at the centre and ends of the fibre are known to be essential for muscle contraction, yet the molecular basis of this regionalisation has remained unclear. While the 'myonuclear domain hypothesis' helped explain how myonuclei can independently govern large cytoplasmic territories, novel technologies have provided granularity on the diverse transcriptional programs running simultaneously within the syncytia and added a new perspective on how myonuclei communicate. Building upon this, we explore the critical cellular and molecular sources of transcriptional and functional heterogeneity within myofibres, discussing the impact of intrinsic and extrinsic factors on myonuclear programs. This knowledge provides new insights for understanding muscle development, repair, and disease, but also opens avenues for the development of novel and precise therapeutic approaches.
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Affiliation(s)
- Amaury Korb
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Shahragim Tajbakhsh
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
| | - Glenda E Comai
- Institut Pasteur, Université Paris Cité, CNRS UMR 3738, Stem Cells & Development Unit, 25 rue du Dr. Roux, Institut Pasteur, Paris, F-75015, France
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2
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Eguchi T, Tezuka T, Watanabe Y, Inoue-Yamauchi A, Sagara H, Ozawa M, Yamanashi Y. Calcium-binding protein 7 expressed in muscle negatively regulates age-related degeneration of neuromuscular junctions in mice. iScience 2024; 27:108997. [PMID: 38327785 PMCID: PMC10847746 DOI: 10.1016/j.isci.2024.108997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 12/05/2023] [Accepted: 01/19/2024] [Indexed: 02/09/2024] Open
Abstract
The neuromuscular junction (NMJ) forms centrally in myotubes and, as the only synapse between motor neuron and myotube, are indispensable for motor activity. The midmuscle formation of NMJs, including midmuscle-restricted expression of NMJ-related genes, is governed by the muscle-specific kinase (MuSK). However, mechanisms underlying MuSK-mediated signaling are unclear. Here, we find that the Calcium-binding protein 7 (Cabp7) gene shows midmuscle-restricted expression, and muscle-specific depletion of Cabp7 in mice accelerated age-related NMJ degeneration, muscle weakness/atrophy, and motor dysfunction. Surprisingly, forced expression in muscle of CIP, an inhibitory peptide of the negative regulator of NMJ formation cyclin-dependent kinase 5 (Cdk5), restored NMJ integrity and muscle strength, and healed muscle atrophy in muscle-specific Cabp7-deficient mice, which showed increased muscle expression of the Cdk5 activator p25. These findings together demonstrate that MuSK-mediated signaling induces muscle expression of Cabp7, which suppresses age-related NMJ degeneration likely by attenuating p25 expression, providing insights into prophylactic/therapeutic intervention against age-related motor dysfunction.
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Affiliation(s)
- Takahiro Eguchi
- Division of Genetics, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Tohru Tezuka
- Division of Genetics, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Yuji Watanabe
- Medical Proteomics Laboratory, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Akane Inoue-Yamauchi
- Division of Genetics, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Hiroshi Sagara
- Medical Proteomics Laboratory, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Manabu Ozawa
- Laboratory of Reproductive Systems Biology, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
- Core Laboratory for Developing Advanced Animal Models, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Yuji Yamanashi
- Division of Genetics, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
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3
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Bagley JR, Denes LT, McCarthy JJ, Wang ET, Murach KA. The myonuclear domain in adult skeletal muscle fibres: past, present and future. J Physiol 2023; 601:723-741. [PMID: 36629254 PMCID: PMC9931674 DOI: 10.1113/jp283658] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 01/06/2023] [Indexed: 01/12/2023] Open
Abstract
Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined 'domains' to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA-sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease.
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Affiliation(s)
- James R. Bagley
- Muscle Physiology Laboratory, Department of Kinesiology, San Francisco State University, San Francisco, California
| | | | - John J. McCarthy
- The Center for Muscle Biology, University of Kentucky, Lexington, Kentucky
- Department of Physiology, College of Medicine, University of Kentucky
| | - Eric T. Wang
- Department of Molecular Genetics and Microbiology, Center for NeuroGenetics, University of Florida, Gainesville, Florida
- Myology Institute, University of Florida
- Genetics Institute, University of Florida
| | - Kevin A. Murach
- Exercise Science Research Center, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas
- Cell and Molecular Biology Graduate Program, University of Arkansas
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4
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Padilla JR, Ferreira LM, Folker ES. Nuclear movement in multinucleated cells. Development 2022; 149:dev200749. [PMID: 36305464 PMCID: PMC10655921 DOI: 10.1242/dev.200749] [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] [Indexed: 06/16/2023]
Abstract
Nuclear movement is crucial for the development of many cell types and organisms. Nuclear movement is highly conserved, indicating its necessity for cellular function and development. In addition to mononucleated cells, there are several examples of cells in which multiple nuclei exist within a shared cytoplasm. These multinucleated cells and syncytia have important functions for development and homeostasis. Here, we review a subset of the developmental contexts in which the regulation of the movement and positioning of multiple nuclei are well understood, including pronuclear migration, the Drosophila syncytial blastoderm, the Caenorhabditis elegans hypodermis, skeletal muscle and filamentous fungi. We apply the principles learned from these models to other systems.
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Affiliation(s)
- Jorel R. Padilla
- Biology Department, Boston College, Chestnut Hill, MA 02467, USA
| | | | - Eric S. Folker
- Biology Department, Boston College, Chestnut Hill, MA 02467, USA
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5
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Jing H, Chen P, Hui T, Yu Z, Zhou J, Fei E, Wang S, Ren D, Lai X, Li B. Synapse-specific Lrp4 mRNA enrichment requires Lrp4/MuSK signaling, muscle activity and Wnt non-canonical pathway. Cell Biosci 2021; 11:105. [PMID: 34090516 PMCID: PMC8180081 DOI: 10.1186/s13578-021-00619-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 05/25/2021] [Indexed: 11/10/2022] Open
Abstract
Background The neuromuscular junction (NMJ) is a peripheral synapse critical to muscle contraction. Like acetylcholine receptors (AChRs), many essential proteins of NMJ are extremely concentrated at the postjunctional membrane. However, the mechanisms of synapse-specific concentration are not well understood; furthermore, it is unclear whether signaling molecules critical to NMJ formation and maintenance are also locally transcribed. Results We studied the β-gal activity encoded by a lacZ cassette driven by the promoter of the Lrp4 gene. As reported for Lrp4 mRNA, β-gal was in the central region in embryonic muscles and at the NMJ after its formation. However, β-gal was no longer in the central areas of muscle fibers in Lrp4 or MuSK mutant mice, indicating a requirement of Lrp4/MuSK signaling. This phenotype could be rescued by transgenic expression of LRP4 with a transmembrane domain but not soluble ECD in Lrp4 mutant mice. β-gal and AChR clusters were distributed in a broader region in lacZ/ECD than that of heterozygous lacZ/+ mice, indicating an important role of the transmembrane domain in Lrp4 signaling. Synaptic β-gal activity became diffused after denervation or treatment with µ-conotoxin, despite its mRNA was increased, indicating synaptic Lrp4 mRNA enrichment requires muscle activity. β-gal was also diffused in aged mice but became re-concentrated after muscle stimulation. Finally, Lrp4 mRNA was increased in C2C12 myotubes by Wnt ligands in a manner that could be inhibited by RKI-1447, an inhibitor of ROCK in Wnt non-canonical signaling. Injecting RKI-1447 into muscles of adult mice diminished Lrp4 synaptic expression. Conclusions This study demonstrates that synapse-specific enrichment of Lrp4 mRNA requires a coordinated interaction between Lrp4/MuSK signaling, muscle activity, and Wnt non-canonical signaling. Thus, the study provides a new mechanism for Lrp4 mRNA enrichment. It also provides a potential target for the treatment of NMJ aging and other NMJ-related diseases. Supplementary Information The online version contains supplementary material available at 10.1186/s13578-021-00619-z.
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Affiliation(s)
- Hongyang Jing
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Peng Chen
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Tiankun Hui
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Zheng Yu
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Jin Zhou
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Human Aging Research Institute, Nanchang University, Nanchang, 330031, China
| | - Erkang Fei
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Shunqi Wang
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Dongyan Ren
- School of Life Science, Nanchang University, Nanchang, 330031, China.,Institute of Life Science, Nanchang University, Nanchang, 330031, China
| | - Xinsheng Lai
- School of Life Science, Nanchang University, Nanchang, 330031, China. .,Institute of Life Science, Nanchang University, Nanchang, 330031, China.
| | - Baoming Li
- School of Life Science, Nanchang University, Nanchang, 330031, China. .,Institute of Life Science, Nanchang University, Nanchang, 330031, China. .,Department of Psychology and Institute of Brain Science, School of Education, Hangzhou Normal University, Hangzhou, 311121, China.
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6
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Computational Assessment of Transport Distances in Living Skeletal Muscle Fibers Studied In Situ. Biophys J 2020; 119:2166-2178. [PMID: 33121941 DOI: 10.1016/j.bpj.2020.10.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/10/2020] [Accepted: 10/07/2020] [Indexed: 11/22/2022] Open
Abstract
Transport distances in skeletal muscle fibers are mitigated by these cells having multiple nuclei. We have studied mouse living slow (soleus) and fast (extensor digitorum longus) muscle fibers in situ and determined cellular dimensions and the positions of all the nuclei within fiber segments. We modeled the effect of placing nuclei optimally and randomly using the nuclei as the origin of a transportation network. It appeared that an equidistant positioning of nuclei minimizes transport distances along the surface for both muscles. In the soleus muscle, however, which were richer in nuclei, positioning of nuclei to reduce transport distances to the cytoplasm were of less importance, and these fibers exhibit a pattern not statistically different from a random positioning of nuclei. We also simulated transport times for myoglobin and found that they were remarkably similar between the two muscles despite differences in nuclear patterning and distances. Together, these results highlight the importance of spatially distributed nuclei to minimize transport distances to the surface when nuclear density is low, whereas it appears that the distribution are of less importance at higher nuclear densities.
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7
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Kann AP, Krauss RS. Multiplexed RNAscope and immunofluorescence on whole-mount skeletal myofibers and their associated stem cells. Development 2019; 146:dev.179259. [PMID: 31519691 DOI: 10.1242/dev.179259] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 09/05/2019] [Indexed: 12/11/2022]
Abstract
Skeletal muscle myofibers are large syncytial cells comprising hundreds of myonuclei, and in situ hybridization experiments have reported a range of transcript localization patterns within them. Although some transcripts are uniformly distributed throughout myofibers, proximity to specialized regions can affect the programming of myonuclei and functional compartmentalization of transcripts. Established techniques are limited by a lack of both sensitivity and spatial resolution, restricting the ability to identify different patterns of gene expression. In this study, we adapted RNAscope fluorescent in situ hybridization technology for use on whole-mount mouse primary myofibers, a preparation that isolates single myofibers with their associated muscle stem cells remaining in their niche. This method can be combined with immunofluorescence, enabling an unparalleled ability to visualize and quantify transcripts and proteins across the length and depth of skeletal myofibers and their associated stem cells. Using this approach, we demonstrate a range of potential uses, including the visualization of specialized transcriptional programming within myofibers, tracking activation-induced transcriptional changes, quantification of stem cell heterogeneity and evaluation of stem cell niche factor transcription patterns.
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Affiliation(s)
- Allison P Kann
- Department of Cell, Developmental, and Regenerative Biology, 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
| | - Robert S Krauss
- Department of Cell, Developmental, and Regenerative Biology, 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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8
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Abstract
This article discusses antibodies associated with immune-mediated myasthenia gravis and the pathologic action of these antibodies at the neuromuscular junctions of skeletal muscle. To explain how these antibodies act, we consider the physiology of neuromuscular transmission with emphasis on 4 features: the structure of the neuromuscular junction; the roles of postsynaptic acetylcholine receptors and voltage-gated Na+ channels and in converting the chemical signal from the nerve terminal into a propagated action potential on the muscle fiber that triggers muscle contraction; the safety factor for neuromuscular transmission; and how the safety factor is reduced in different forms of autoimmune myasthenia gravis.
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Affiliation(s)
- Robert L Ruff
- Department of Neurology, Case Western University School of Medicine, The Metro Health System, 2500 Metro Health Drive, Cleveland, OH 44109, USA; Department of Neurosciences, Case Western Reserve University, Cleveland, OH, USA
| | - Robert P Lisak
- Department of Neurology, Wayne State University School of Medicine, 8D University Health Center, 4201 St Antoine, Detroit, MI 48201, USA; Department of Biochemistry, Microbiology and Immunology, Wayne State University, Detroit, MI, USA.
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9
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Halievski K, Nath SR, Katsuno M, Adachi H, Sobue G, Breedlove SM, Lieberman AP, Jordan CL. Disease Affects Bdnf Expression in Synaptic and Extrasynaptic Regions of Skeletal Muscle of Three SBMA Mouse Models. Int J Mol Sci 2019; 20:ijms20061314. [PMID: 30875922 PMCID: PMC6470984 DOI: 10.3390/ijms20061314] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 03/08/2019] [Accepted: 03/09/2019] [Indexed: 01/01/2023] Open
Abstract
Spinal bulbar muscular atrophy (SBMA) is a slowly progressive, androgen-dependent neuromuscular disease in men that is characterized by both muscle and synaptic dysfunction. Because gene expression in muscle is heterogeneous, with synaptic myonuclei expressing genes that regulate synaptic function and extrasynaptic myonuclei expressing genes to regulate contractile function, we used quantitative PCR to compare gene expression in these two domains of muscle from three different mouse models of SBMA: the "97Q" model that ubiquitously expresses mutant human androgen receptor (AR), the 113Q knock-in (KI) model that expresses humanized mouse AR with an expanded glutamine tract, and the "myogenic" model that overexpresses wild-type rat AR only in skeletal muscle. We were particularly interested in neurotrophic factors because of their role in maintaining neuromuscular function via effects on both muscle and synaptic function, and their implicated role in SBMA. We confirmed previous reports of the enriched expression of select genes (e.g., the acetylcholine receptor) in the synaptic region of muscle, and are the first to report the synaptic enrichment of others (e.g., glial cell line-derived neurotrophic factor). Interestingly, all three models displayed comparably dysregulated expression of most genes examined in both the synaptic and extrasynaptic domains of muscle, with only modest differences between regions and models. These findings of comprehensive gene dysregulation in muscle support the emerging view that skeletal muscle may be a prime therapeutic target for restoring function of both muscles and motoneurons in SBMA.
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Affiliation(s)
- Katherine Halievski
- Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824-1115, USA.
| | - Samir R Nath
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
| | - Masahisa Katsuno
- Department of Neurology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
| | - Hiroaki Adachi
- Department of Neurology, University of Occupational and Environment Health School of Medicine, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu Fukuoka 807-8555, Japan.
| | - Gen Sobue
- Department of Neurology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan.
| | - S Marc Breedlove
- Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824-1115, USA.
| | - Andrew P Lieberman
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
| | - Cynthia L Jordan
- Neuroscience Program, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824-1115, USA.
- Physiology Department, 108 Giltner Hall, Michigan State University, East Lansing, MI 48824-1115, USA.
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10
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Gerwin L, Haupt C, Wilkinson KA, Kröger S. Acetylcholine receptors in the equatorial region of intrafusal muscle fibres modulate mouse muscle spindle sensitivity. J Physiol 2019; 597:1993-2006. [PMID: 30673133 DOI: 10.1113/jp277139] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Accepted: 01/22/2019] [Indexed: 01/08/2023] Open
Abstract
KEY POINTS Acetylcholine receptors are aggregated in the central regions of intrafusal muscle fibres. Single unit muscle spindle afferent responses from isolated mouse extensor digitorum longus muscle were recorded in the absence of fusimotor input to ramp and hold stretches as well as to sinusoidal vibrations in the presence and absence of the acetylcholine receptor blockers d-tubocurarine and α-bungarotoxin. Proprioceptive afferent responses to both types of stretch were enhanced in the presence of either blocker. Blocking acetylcholine uptake and vesicular acetylcholine release by hemicholinium-3 also enhanced stretch-evoked responses. These results represent the first evidence that acetylcholine receptors negatively modulate muscle spindle responses to stretch. The data support the hypothesis that the sensory nerve terminal is able to release vesicles to fine-tune proprioceptive afferent sensitivity. ABSTRACT Muscle spindles are complex stretch-sensitive mechanoreceptors. They consist of specialized skeletal muscle fibres, called intrafusal fibres, which are innervated in the central (equatorial) region by afferent sensory axons and in both polar regions by efferent γ-motoneurons. Previously it was shown that acetylcholine receptors (AChR) are concentrated in the equatorial region at the contact site between the sensory neuron and the intrafusal muscle fibre. To address the function of these AChRs, single unit sensory afferents were recorded from an isolated mouse extensor digitorum longus muscle in the absence of γ-motoneuron activity. Specifically, we investigated the responses of individual sensory neurons to ramp-and-hold stretches and sinusoidal vibrations before and after the addition of the competitive and non-competitive AChR blockers d-tubocurarine and α-bungarotoxin, respectively. The presence of either drug did not affect the resting action potential discharge frequency. However, the action potential frequencies in response to stretch were increased. In particular, frequencies of the dynamic peak and dynamic index to ramp-and-hold stretches were significantly higher in the presence of either drug. Treatment of muscle spindle afferents with the high-affinity choline transporter antagonist hemicholinium-3 similarly increased muscle spindle afferent firing frequencies during stretch. Moreover, the firing rate during sinusoidal vibration stimuli at low amplitudes was higher in the presence of α-bungarotoxin compared to control spindles also indicating an increased sensitivity to stretch. Collectively these data suggest a modulation of the muscle spindle afferent response to stretch by AChRs in the central region of intrafusal fibres possibly fine-tuning muscle spindle sensitivity.
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Affiliation(s)
- Laura Gerwin
- Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University, Großhaderner Str. 9, D-82152, Planegg-Martinsried, Germany.,Institute for Stem Cell Research, German Research Center for Environmental Health, Helmholtz Centre Munich, Ingolstädter Landstraße 1, D-85764, Neuherberg, Germany
| | - Corinna Haupt
- Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University, Großhaderner Str. 9, D-82152, Planegg-Martinsried, Germany
| | - Katherine A Wilkinson
- Department of Biological Sciences, San Jose State University, One Washington Square, San Jose, CA, 95192, USA
| | - Stephan Kröger
- Department of Physiological Genomics, Biomedical Center, Ludwig-Maximilians-University, Großhaderner Str. 9, D-82152, Planegg-Martinsried, Germany
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11
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Larsson L, Degens H, Li M, Salviati L, Lee YI, Thompson W, Kirkland JL, Sandri M. Sarcopenia: Aging-Related Loss of Muscle Mass and Function. Physiol Rev 2019; 99:427-511. [PMID: 30427277 DOI: 10.1152/physrev.00061.2017] [Citation(s) in RCA: 700] [Impact Index Per Article: 140.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Sarcopenia is a loss of muscle mass and function in the elderly that reduces mobility, diminishes quality of life, and can lead to fall-related injuries, which require costly hospitalization and extended rehabilitation. This review focuses on the aging-related structural changes and mechanisms at cellular and subcellular levels underlying changes in the individual motor unit: specifically, the perikaryon of the α-motoneuron, its neuromuscular junction(s), and the muscle fibers that it innervates. Loss of muscle mass with aging, which is largely due to the progressive loss of motoneurons, is associated with reduced muscle fiber number and size. Muscle function progressively declines because motoneuron loss is not adequately compensated by reinnervation of muscle fibers by the remaining motoneurons. At the intracellular level, key factors are qualitative changes in posttranslational modifications of muscle proteins and the loss of coordinated control between contractile, mitochondrial, and sarcoplasmic reticulum protein expression. Quantitative and qualitative changes in skeletal muscle during the process of aging also have been implicated in the pathogenesis of acquired and hereditary neuromuscular disorders. In experimental models, specific intervention strategies have shown encouraging results on limiting deterioration of motor unit structure and function under conditions of impaired innervation. Translated to the clinic, if these or similar interventions, by saving muscle and improving mobility, could help alleviate sarcopenia in the elderly, there would be both great humanitarian benefits and large cost savings for health care systems.
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Affiliation(s)
- Lars Larsson
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Hans Degens
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Meishan Li
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Leonardo Salviati
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Young Il Lee
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Wesley Thompson
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - James L Kirkland
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
| | - Marco Sandri
- Department of Physiology and Pharmacology, Basic and Clinical Muscle Biology Group, Karolinska Institutet , Stockholm , Sweden ; Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet , Stockholm , Sweden ; Department of Biobehavioral Health, The Pennsylvania State University , University Park, Pennsylvania ; School of Healthcare Science, Metropolitan University , Manchester , United Kingdom ; Institute of Sport Science and Innovations, Lithuanian Sports University , Kaunas , Lithuania ; Clinical Genetics Unit, Department of Woman and Child Health, University of Padova , Padova , Italy ; IRP Città della Speranza, Padova , Italy ; Department of Biology, Texas A&M University , College Station, Texas ; Robert and Arlene Kogod Center on Aging, Mayo Clinic , Rochester, Minnesota ; Department of Biomedical Science, Venetian Institute of Molecular Medicine, University of Padova , Padova , Italy
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12
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Egner IM, Bruusgaard JC, Gundersen K. Satellite cell depletion prevents fiber hypertrophy in skeletal muscle. Development 2017; 143:2898-906. [PMID: 27531949 DOI: 10.1242/dev.134411] [Citation(s) in RCA: 135] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Accepted: 06/28/2016] [Indexed: 12/18/2022]
Abstract
The largest mammalian cells are the muscle fibers, and they have multiple nuclei to support their large cytoplasmic volumes. During hypertrophic growth, new myonuclei are recruited from satellite stem cells into the fiber syncytia, but it was recently suggested that such recruitment is not obligatory: overload hypertrophy after synergist ablation of the plantaris muscle appeared normal in transgenic mice in which most of the satellite cells were abolished. When we essentially repeated these experiments analyzing the muscles by immunohistochemistry and in vivo and ex vivo imaging, we found that overload hypertrophy was prevented in the satellite cell-deficient mice, in both the plantaris and the extensor digitorum longus muscles. We attribute the previous findings to a reliance on muscle mass as a proxy for fiber hypertrophy, and to the inclusion of a significant number of regenerating fibers in the analysis. We discuss that there is currently no model in which functional, sustainable hypertrophy has been unequivocally demonstrated in the absence of satellite cells; an exception is re-growth, which can occur using previously recruited myonuclei without addition of new myonuclei.
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Affiliation(s)
- Ingrid M Egner
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway
| | - Jo C Bruusgaard
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway Department of Health Sciences, Kristiania University College, P.O. Box 1190, Sentrum, Oslo N-0107, Norway
| | - Kristian Gundersen
- Department of Biosciences, University of Oslo, Blindern, Oslo N-0316, Norway
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13
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Gundersen K. Muscle memory and a new cellular model for muscle atrophy and hypertrophy. ACTA ACUST UNITED AC 2016; 219:235-42. [PMID: 26792335 DOI: 10.1242/jeb.124495] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Memory is a process in which information is encoded, stored, and retrieved. For vertebrates, the modern view has been that it occurs only in the brain. This review describes a cellular memory in skeletal muscle in which hypertrophy is 'remembered' such that a fibre that has previously been large, but subsequently lost its mass, can regain mass faster than naive fibres. A new cell biological model based on the literature, with the most reliable methods for identifying myonuclei, can explain this phenomenon. According to this model, previously untrained fibres recruit myonuclei from activated satellite cells before hypertrophic growth. Even if subsequently subjected to grave atrophy, the higher number of myonuclei is retained, and the myonuclei seem to be protected against the elevated apoptotic activity observed in atrophying muscle tissue. Fibres that have acquired a higher number of myonuclei grow faster when subjected to overload exercise, thus the nuclei represent a functionally important 'memory' of previous strength. This memory might be very long lasting in humans, as myonuclei are stable for at least 15 years and might even be permanent. However, myonuclei are harder to recruit in the elderly, and if the long-lasting muscle memory also exists in humans, one should consider early strength training as a public health advice. In addition, myonuclei are recruited during steroid use and encode a muscle memory, at least in rodents. Thus, extending the exclusion time for doping offenders should be considered.
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Affiliation(s)
- Kristian Gundersen
- Department of Biosciences, University of Oslo, Blindernveien 31, Oslo N0316, Norway
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14
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López-Leal R, Alvarez J, Court FA. Origin of axonal proteins: Is the axon-schwann cell unit a functional syncytium? Cytoskeleton (Hoboken) 2016; 73:629-639. [DOI: 10.1002/cm.21319] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Revised: 07/28/2016] [Accepted: 08/02/2016] [Indexed: 12/31/2022]
Affiliation(s)
- Rodrigo López-Leal
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Geroscience Center for Brain Health and Metabolism; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
| | - Jaime Alvarez
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
| | - Felipe A. Court
- Faculty of Sciences, Center for Integrative Biology; Universidad Mayor; Santiago Chile
- Geroscience Center for Brain Health and Metabolism; Santiago Chile
- Millenium Nucleus for Regenerative Biology; Santiago Chile
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15
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Formation of cholinergic synapse-like specializations at developing murine muscle spindles. Dev Biol 2014; 393:227-235. [DOI: 10.1016/j.ydbio.2014.07.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/14/2014] [Accepted: 07/15/2014] [Indexed: 12/30/2022]
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16
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IJIRI D, SAEGUSA A, MATSUBARA T, KANAI Y, HIRABAYASHI M. In vivo gene transfer into skeletal muscle of neonatal chicks by electroporation. Anim Sci J 2011; 83:504-9. [DOI: 10.1111/j.1740-0929.2011.00983.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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17
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Hall MN, Corbett AH, Pavlath GK. Regulation of nucleocytoplasmic transport in skeletal muscle. Curr Top Dev Biol 2011; 96:273-302. [PMID: 21621074 DOI: 10.1016/b978-0-12-385940-2.00010-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Proper skeletal muscle function is dependent on spatial and temporal control of gene expression in multinucleated myofibers. In addition, satellite cells, which are tissue-specific stem cells that contribute critically to repair and maintenance of skeletal muscle, are also required for normal muscle physiology. Gene expression in both myofibers and satellite cells is dependent upon nuclear proteins that require facilitated nuclear transport. A unique challenge for myofibers is controlling the transcriptional activity of hundreds of nuclei in a common cytoplasm yet achieving nuclear selectivity in transcription at specific locations such as neuromuscular synapses and myotendinous junctions. Nucleocytoplasmic transport of macromolecular cargoes is regulated by a complex interplay among various components of the nuclear transport machinery, namely nuclear pore complexes, nuclear envelope proteins, and various soluble transport receptors. The focus of this review is to highlight what is known about the nuclear transport machinery and its regulation in skeletal muscle and to consider the unique challenges that multinucleated muscle cells as well as satellite cells encounter in regulating nucleocytoplasmic transport during cell differentiation and tissue adaptation. Understanding how regulated nucleocytoplasmic transport controls gene expression in skeletal muscle may lead to further insights into the mechanisms contributing to muscle growth and maintenance throughout the lifespan of an individual.
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Affiliation(s)
- Monica N Hall
- Graduate Program in Genetics and Molecular Biology, Emory University, Atlanta, Georgia, USA
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18
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Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining. Proc Natl Acad Sci U S A 2010; 107:15111-6. [PMID: 20713720 DOI: 10.1073/pnas.0913935107] [Citation(s) in RCA: 201] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Effects of previous strength training can be long-lived, even after prolonged subsequent inactivity, and retraining is facilitated by a previous training episode. Traditionally, such "muscle memory" has been attributed to neural factors in the absence of any identified local memory mechanism in the muscle tissue. We have used in vivo imaging techniques to study live myonuclei belonging to distinct muscle fibers and observe that new myonuclei are added before any major increase in size during overload. The old and newly acquired nuclei are retained during severe atrophy caused by subsequent denervation lasting for a considerable period of the animal's lifespan. The myonuclei seem to be protected from the high apoptotic activity found in inactive muscle tissue. A hypertrophy episode leading to a lasting elevated number of myonuclei retarded disuse atrophy, and the nuclei could serve as a cell biological substrate for such memory. Because the ability to create myonuclei is impaired in the elderly, individuals may benefit from strength training at an early age, and because anabolic steroids facilitate more myonuclei, nuclear permanency may also have implications for exclusion periods after a doping offense.
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19
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Affiliation(s)
- Andrew G Engel
- Department of Neurology, Mayo Clinic, Rochester, MN, USA.
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20
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Liu J, Burkin DJ, Kaufman SJ. Increasing alpha 7 beta 1-integrin promotes muscle cell proliferation, adhesion, and resistance to apoptosis without changing gene expression. Am J Physiol Cell Physiol 2007; 294:C627-40. [PMID: 18045857 DOI: 10.1152/ajpcell.00329.2007] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The dystrophin-glycoprotein complex maintains the integrity of skeletal muscle by associating laminin in the extracellular matrix with the actin cytoskeleton. Several human muscular dystrophies arise from defects in the components of this complex. The alpha(7)beta(1)-integrin also binds laminin and links the extracellular matrix with the cytoskeleton. Enhancement of alpha(7)-integrin levels alleviates pathology in mdx/utrn(-/-) mice, a model of Duchenne muscular dystrophy, and thus the integrin may functionally compensate for the absence of dystrophin. To test whether increasing alpha(7)-integrin levels affects transcription and cellular functions, we generated alpha(7)-integrin-inducible C2C12 cells and transgenic mice that overexpress the integrin in skeletal muscle. C2C12 myoblasts with elevated levels of integrin exhibited increased adhesion to laminin, faster proliferation when serum was limited, resistance to staurosporine-induced apoptosis, and normal differentiation. Transgenic expression of eightfold more integrin in skeletal muscle did not result in notable toxic effects in vivo. Moreover, high levels of alpha(7)-integrin in both myoblasts and in skeletal muscle did not disrupt global gene expression profiles. Thus increasing integrin levels can compensate for defects in the extracellular matrix and cytoskeleton linkage caused by compromises in the dystrophin-glycoprotein complex without triggering apparent overt negative side effects. These results support the use of integrin enhancement as a therapy for muscular dystrophy.
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Affiliation(s)
- Jianming Liu
- Department of Cell and Developmental Biology, University of Illinois, 601 S. Goodwin Ave., B107 Chemical and Life Sciences Laboratory, Urbana, IL 61801, USA
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21
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Kalamida D, Poulas K, Avramopoulou V, Fostieri E, Lagoumintzis G, Lazaridis K, Sideri A, Zouridakis M, Tzartos SJ. Muscle and neuronal nicotinic acetylcholine receptors. FEBS J 2007; 274:3799-845. [PMID: 17651090 DOI: 10.1111/j.1742-4658.2007.05935.x] [Citation(s) in RCA: 216] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are integral membrane proteins and prototypic members of the ligand-gated ion-channel superfamily, which has precursors in the prokaryotic world. They are formed by the assembly of five transmembrane subunits, selected from a pool of 17 homologous polypeptides (alpha1-10, beta1-4, gamma, delta, and epsilon). There are many nAChR subtypes, each consisting of a specific combination of subunits, which mediate diverse physiological functions. They are widely expressed in the central nervous system, while, in the periphery, they mediate synaptic transmission at the neuromuscular junction and ganglia. nAChRs are also found in non-neuronal/nonmuscle cells (keratinocytes, epithelia, macrophages, etc.). Extensive research has determined the specific function of several nAChR subtypes. nAChRs are now important therapeutic targets for various diseases, including myasthenia gravis, Alzheimer's and Parkinson's diseases, and schizophrenia, as well as for the cessation of smoking. However, knowledge is still incomplete, largely because of a lack of high-resolution X-ray structures for these molecules. Nevertheless, electron microscopy studies on 2D crystals of nAChR from fish electric organs and the determination of the high-resolution X-ray structure of the acetylcholine binding protein (AChBP) from snails, a homolog of the extracellular domain of the nAChR, have been major steps forward and the data obtained have important implications for the design of subtype-specific drugs. Here, we review some of the latest advances in our understanding of nAChRs and their involvement in physiology and pathology.
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Affiliation(s)
- Dimitra Kalamida
- Department of Pharmacy, University of Patras, Rio Patras, Greece
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22
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Abstract
At the developing vertebrate neuromuscular junction, neuregulins are growth/differentiation factors essential for terminal Schwann cell survival. Neuregulins have also been thought as the critical signals responsible for the increased transcription of acetylcholine receptor subunit genes at the neuromuscular synapse. This latter role is now highly controversial. This article reviews the evidence that has shaped the views of the neuregulins and how these views have been challenged. The most recent experiments indicate that neuregulin signaling to postsynaptic muscle fibers may modulate, rather than determine, acetylcholine receptor expression at the neuromuscular junction. Based on findings from my lab and those of others, I propose that this modulation might involve novel posttranscriptional molecular mechanisms. Finally, I also suggest that neuregulin signaling may have an important role to play in mediating the response of adult terminal Schwann cells to denervation.
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Affiliation(s)
- Mendell Rimer
- Section of Neurobiology, Institute for Neuroscience and Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas 78712-0248, USA.
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23
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Lunde IG, Ekmark M, Rana ZA, Buonanno A, Gundersen K. PPARdelta expression is influenced by muscle activity and induces slow muscle properties in adult rat muscles after somatic gene transfer. J Physiol 2007; 582:1277-87. [PMID: 17463039 PMCID: PMC2075258 DOI: 10.1113/jphysiol.2007.133025] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The effects of exercise on skeletal muscle are mediated by a coupling between muscle electrical activity and gene expression. Several activity correlates, such as intracellular Ca(2+), hypoxia and metabolites like free fatty acids (FFAs), might initiate signalling pathways regulating fibre-type-specific genes. FFAs can be sensed by lipid-dependent transcription factors of the peroxisome proliferator-activated receptor (PPAR) family. We found that the mRNA for the predominant muscle isoform, PPARdelta, was three-fold higher in the slow/oxidative soleus compared to the fast/glycolytic extensor digitorum longus (EDL) muscle. In histological sections of the soleus, the most oxidative fibres display the highest levels of PPARdelta protein. When the soleus muscle was stimulated electrically by a pattern mimicking fast/glycolytic IIb motor units, the mRNA level of PPARdelta was reduced to less than half within 24 h. In the EDL, a three-fold increase was observed after slow type I-like electrical stimulation. When a constitutively active form of PPARdelta was overexpressed for 14 days in normally active adult fibres after somatic gene transfer, the number of I/IIa hybrids in the EDL more than tripled, IIa fibres increased from 14% to 25%, and IIb fibres decreased from 55% to 45%. The level of succinate dehydrogenase activity increased and size decreased, also when compared to normal fibres of the same type. Thus PPARdelta can change myosin heavy chain, oxidative enzymes and size locally in muscle cells in the absence of general exercise. Previous studies on PPARdelta in muscle have been performed in transgenic animals where the transgene has been present during muscle development. Our data suggest that PPARdelta can mediate activity effects acutely in pre-existing adult fibres, and thus is an important link in excitation-transcription coupling.
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Affiliation(s)
- Ida G Lunde
- Department of Molecular Biosciences, University of Oslo, PO Box 1041, Blindern, N-0316 Oslo, Norway
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24
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Kummer TT, Misgeld T, Sanes JR. Assembly of the postsynaptic membrane at the neuromuscular junction: paradigm lost. Curr Opin Neurobiol 2006; 16:74-82. [PMID: 16386415 DOI: 10.1016/j.conb.2005.12.003] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Accepted: 12/15/2005] [Indexed: 11/28/2022]
Abstract
Studies of the vertebrate skeletal neuromuscular junction led to an influential model of how neurotransmitter receptors accumulate in the postsynaptic membrane. In this model, motor axons organize postsynaptic development by secreting neuregulin to induce acetylcholine receptor gene transcription in specialized subsynaptic nuclei, agrin to cluster diffuse receptors in the postsynaptic membrane, and acetylcholine to evoke electrical activity that promotes synaptic maturation. However, new studies in this area have first, demonstrated that axons sometimes innervate pre-existing receptor clusters; second, recast the roles of agrin and neuregulin; third, revealed early effects of neurotransmission; fourth, questioned the role of subsynaptic myonuclei; fifth, shown that elaborately-branched postsynaptic structures can form aneurally; and sixth, raised the possibility that neurotransmitter affects receptor type as well as distribution. These recent studies challenge the widely-held paradigms, although not the results that led to them, and suggest a new model for neuromuscular synaptogenesis.
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Affiliation(s)
- Terrance T Kummer
- Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, USA
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25
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Perreault MC, Pastor-Bernier A, Renaud JS, Roux S, Glover JC. C fragment of tetanus toxin hybrid proteins evaluated for muscle-specific transsynaptic mapping of spinal motor circuitry in the newborn mouse. Neuroscience 2006; 141:803-816. [PMID: 16713105 DOI: 10.1016/j.neuroscience.2006.04.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 03/08/2006] [Accepted: 04/02/2006] [Indexed: 11/17/2022]
Abstract
We investigated whether the non-toxic C fragment of tetanus toxin (TTC) fused to either beta-galactosidase or green fluorescent protein could be utilized to transsynaptically trace muscle-specific spinal circuitry in the neonatal mouse after i.m. injection into a single hindlimb muscle. We found that even with careful low volume injection (0.2-1.0 microl) into a single muscle (medial gastrocnemius), the TTC hybrid proteins spread rapidly to many other hindlimb muscles and to trunk musculature such that retrograde labeling of motoneurons could not be constrained to a single motoneuron pool. Retrogradely labeled motoneurons in the lower lumbar segments harboring the medial gastrocnemius motoneuron pool were first observed two hours after the medial gastrocnemius injection. Within the next 10 h, additional lumbar and lower thoracic motoneurons became labeled, and punctate labeling in the neuropil surrounding the motoneurons appeared. Many of the TTC hybrid protein-labeled puncta in the neuropil co-localized synaptotagmin, indicating that they represent presynaptic axon terminals onto motoneurons. Although this is consistent with retrograde transsynaptic passage, we found no evidence that the TTC hybrid proteins were transported further along premotor axons to label interneuron somata. The i.m. TTC injection procedure described here therefore provides an important tool for the study of presynaptic terminals onto motoneurons. However, additional technical modifications will be required to utilize TTC tracers for transsynaptic mapping of muscle-specific spinal motor circuitry in the neonatal mouse. We provide here a set of criteria for assessing the i.m. delivery of TTC tracers as a basis for future improvements in this technique.
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Affiliation(s)
- M-C Perreault
- Department of Physiology, University of Oslo, Domus Medica, Sognsvannsveien 9, POB 1103 Blindern, N-0317 Oslo, Norway.
| | - A Pastor-Bernier
- Department of Physiology, University of Oslo, Domus Medica, Sognsvannsveien 9, POB 1103 Blindern, N-0317 Oslo, Norway
| | - J-S Renaud
- Department of Physiology, University of Oslo, Domus Medica, Sognsvannsveien 9, POB 1103 Blindern, N-0317 Oslo, Norway
| | - S Roux
- Unité d'Embryologie Moléculaire, Institut Pasteur, Unités de Recherche Associées 2578, Centre National de la Recherche Scientifique, 25 rue du Dr roux, 75724 Paris, France
| | - J C Glover
- Department of Physiology, University of Oslo, Domus Medica, Sognsvannsveien 9, POB 1103 Blindern, N-0317 Oslo, Norway
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26
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Kishi M, Kummer TT, Eglen SJ, Sanes JR. LL5beta: a regulator of postsynaptic differentiation identified in a screen for synaptically enriched transcripts at the neuromuscular junction. ACTA ACUST UNITED AC 2005; 169:355-66. [PMID: 15851520 PMCID: PMC2171857 DOI: 10.1083/jcb.200411012] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
In both neurons and muscle fibers, specific mRNAs are concentrated beneath and locally translated at synaptic sites. At the skeletal neuromuscular junction, all synaptic RNAs identified to date encode synaptic components. Using microarrays, we compared RNAs in synapse-rich and -free regions of muscles, thereby identifying transcripts that are enriched near synapses and that encode soluble membrane and nuclear proteins. One gene product, LL5β, binds to both phosphoinositides and a cytoskeletal protein, filamin, one form of which is concentrated at synaptic sites. LL5β is itself associated with the cytoplasmic face of the postsynaptic membrane; its highest levels border regions of highest acetylcholine receptor (AChR) density, which suggests a role in “corraling” AChRs. Consistent with this idea, perturbing LL5β expression in myotubes inhibits AChR aggregation. Thus, a strategy designed to identify novel synaptic components led to identification of a protein required for assembly of the postsynaptic apparatus.
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Affiliation(s)
- Masashi Kishi
- Department of Anatomy and Neurobiology, Washington University Medical Center, St. Louis, MO 63110, USA
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27
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Cossins J, Webster R, Maxwell S, Burke G, Vincent A, Beeson D. A mouse model of AChR deficiency syndrome with a phenotype reflecting the human condition. Hum Mol Genet 2004; 13:2947-57. [PMID: 15471888 DOI: 10.1093/hmg/ddh320] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The two subtypes of mammalian muscle nicotinic acetylcholine receptors (AChR) are generated by the substitution of the epsilon (adult) subunit for the gamma (fetal) subunit within the AChR pentamer. Null mutations of the adult AChR epsilon-subunit gene are the most common cause of the AChR deficiency syndrome. This is a disorder of neuromuscular transmission characterized by non-progressive fatigable muscle weakness present throughout life. In contrast with the human disorder, mice with AChR epsilon-subunit null mutations die between 10 and 14 weeks of age. We generated transgenic mice that constitutively express the human AChR gamma-subunit in an AChR epsilon-subunit 'knock-out' background. These mice, in which neuromuscular transmission is mediated by fetal AChR, live well into adult life but show striking similarities to human AChR deficiency syndrome. They display fatigable muscle weakness, reduced miniature endplate potentials and endplate potentials, reduced motor endplate AChR number and altered endplate morphology. Our results illustrate how species differences in the control of ion-channel gene expression may affect disease phenotype, demonstrate that expression of adult AChR subtype is not essential for long-term survival, and suggest that in patients with AChR deficiency syndrome, up-regulation of the gamma-subunit could be a beneficial therapeutic strategy.
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Affiliation(s)
- Judy Cossins
- Neuroscience Group, Weatherall Institute of Molecular Medicine, The John Radcliffe, Oxford, UK
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28
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Rana ZA, Ekmark M, Gundersen K. Coexpression after electroporation of plasmid mixtures into muscle in vivo. ACTA ACUST UNITED AC 2004; 181:233-8. [PMID: 15180796 DOI: 10.1111/j.1365-201x.2004.01282.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AIM Muscle is perhaps the most frequently considered tissue for non-viral gene therapy, in particular after gene transfer by electroporation. Expression in muscle is stable, but since the cell turnover is so slow incorporation in the host genome is not required. This raises interesting practical and theoretical questions related to the behaviour of the transgenic DNA under such conditions. METHODS We have investigated expression of reporter genes from plasmid mixtures electroporated into the extensor digitorum longus (EDL) muscle in mice in order to assess the degree of coexpression. RESULTS Under conditions where the reporter is easily identified the coexpression rate was 100%, as none of 287 fibres from five different muscles expressing blue fluorescent protein (BFP) failed to express green fluorescent protein (GFP). With other reporter combinations the rate was lower, but this we attribute to marginal sensitivity for fluorescent proteins, or from reporter protein degradation for beta-galactosidase. CONCLUSIONS The high degree of coexpression suggests that a large copy number takes part in the final transcription with this system. The finding also enhances the usefulness of muscle and electroporation for gene therapy and experimental biology.
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Affiliation(s)
- Z A Rana
- Department of Molecular Biosciences, University of Oslo, Blindern, Oslo, Norway
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Ngô-Muller V, Bertrand A, Concordet JP, Daegelen D. Mouse muscle identity: the position-dependent and fast fiber-specific expression of a transgene in limb muscles is methylation-independent and cell-autonomous. Dev Dyn 2004; 228:594-605. [PMID: 14648836 DOI: 10.1002/dvdy.10402] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We previously characterised transgenic mice in which fast-muscle-specific regulatory sequences from the human aldolase A pM promoter drive the chloramphenicol acetyltransferase gene expression. Mutation of a NF1/MEF2 binding site (M2 motif) in this promoter does not affect fibre-type specificity of the transgene but modifies its expression in a subset of fast-twitch fibres at the limb level, preferentially affecting distal limb muscles. We investigated the molecular and cellular bases of this peculiar expression pattern that provided an adequate model to characterise the mechanisms responsible for muscle positional information. By direct electrotransfer of mutated M2 construct in adult muscle, we demonstrate that positional differences in mutated M2 transgene expression are not observed when the transgene is not integrated into chromatin. Also, this transgene expression pattern does not seem to be correlated with the extent of CpG methylation in its promoter sequence. Finally, we show that positional values reflected by CAT levels are maintained in primary cultures established from different adult limb muscles, as well as in heterotopically transplanted muscles. Our results suggest that mutation of the M2 site contributes to reveal a molecular memory of fibre fate that would be set up on pM promoter during development and persist into adulthood possibly through a chromatin imprint maintained in satellite cells associated with various limb muscles.
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Affiliation(s)
- Valerie Ngô-Muller
- Département de Génétique, Développement et Pathologie Moléculaire, Institut Cochin-INSERM U 567, CNRS UMR 8104, and Université René Descartes Paris V, 24 rue du Faubourg St-Jacques, Paris, France
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Fromm L, Rhode M. Neuregulin-1 induces expression of Egr-1 and activates acetylcholine receptor transcription through an Egr-1-binding site. J Mol Biol 2004; 339:483-94. [PMID: 15147836 DOI: 10.1016/j.jmb.2004.04.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2003] [Revised: 02/23/2004] [Accepted: 04/05/2004] [Indexed: 10/26/2022]
Abstract
Localization of acetylcholine receptors (AChRs) to neuromuscular synapses is mediated, in part, through selective transcription of AChR genes in myofiber synaptic nuclei. Neuregulin-1 (NRG-1) and its receptors, ErbBs, are concentrated at synaptic sites, and NRG-1 activates AChR synthesis in cultured muscle cells, suggesting that NRG-1-ErbB signaling functions to activate synapse-specific transcription. Previous studies have demonstrated that NRG-1-induced transcription is conferred by cis-acting elements located within 100 bp of 5' flanking DNA from the AChR epsilon subunit gene, and that it requires a GABP binding site within this region. To determine whether additional regulatory elements have a role in NRG-1 responsiveness, we used transcriptional reporter assays in a muscle cell line, and we identified an element that is required for NRG-1-induced transcription (neuregulin response element, NRE). Proteins from myotube extracts bind the NRE and NRG-1 treatment of the cells stimulates this binding. The ability of NRG-1 to stimulate formation of a protein-DNA complex with the NRE requires induction of protein expression. The complex contains early growth response-1 (Egr-1), a member of the Egr family of transcription factors, because proteins in the complex bind specifically to an Egr consensus site, and formation of the complex is inhibited by antibodies to Egr-1. NRG-1 induces expression of Egr-1 in myotubes, which presumably is responsible for the ability of NRG-1 to stimulate protein binding to the NRE. These results suggest that NRG-1 signaling in myotubes involves induction of Egr-1 expression, which in turn serves to activate transcription of the AChR epsilon subunit gene.
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Affiliation(s)
- Larry Fromm
- Center for Medical Education, Ball State University and Indiana University School of Medicine, Muncie, IN 47306, USA.
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31
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Monks DA, O'Bryant EL, Jordan CL. Androgen receptor immunoreactivity in skeletal muscle: enrichment at the neuromuscular junction. J Comp Neurol 2004; 473:59-72. [PMID: 15067718 DOI: 10.1002/cne.20088] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Potential cellular targets of androgen action within skeletal muscle of the rat were determined by comparing the cellular distribution of androgen receptor (AR)-positive nuclei in the highly androgen-responsive levator ani (LA) muscle with that of the relatively androgen-unresponsive extensor digitorum longus (EDL) muscle. We found that androgen responsiveness correlates with AR expression in muscle fibers and not in fibroblasts. Results indicate that a much higher percentage of myonuclei in the LA are AR(+) than in the EDL (74% vs. 7%), correlating with differences in androgen responsiveness. Both muscles contain an equivalent proportion of AR(+) fibroblasts (approximately 62%). AR(+) nuclei were not observed in terminal Schwann cells in either muscle. These results suggest that ARs within LA muscle fibers mediate the androgen-dependent survival and growth of the LA muscle and its motoneurons. We also observed an unexpected enrichment of AR(+) myonuclei and fibroblasts proximate to neuromuscular junctions, suggesting that ARs at muscle synapses may selectively regulate synapse-specific genes important for the survival and growth of motoneurons. Although castration reduced the proportion of AR(+) fibroblasts in both muscles, the proportion of AR(+) myonuclei was reduced only in the LA. As expected, testosterone treatment prevented these effects of castration but, unexpectedly, increased the proportion of AR(+) myonuclei in the EDL to above normal. These results suggest that how AR expression in skeletal muscle is influenced by androgens depends not only on the particular muscle but on the particular cell type within that muscle.
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Affiliation(s)
- Douglas Ashley Monks
- Neuroscience Program and Department of Psychology, Michigan State University, East Lansing, Michigan 48824-1101, USA
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Ballestar E, Paz MF, Valle L, Wei S, Fraga MF, Espada J, Cigudosa JC, Huang THM, Esteller M. Methyl-CpG binding proteins identify novel sites of epigenetic inactivation in human cancer. EMBO J 2004; 22:6335-45. [PMID: 14633992 PMCID: PMC291845 DOI: 10.1093/emboj/cdg604] [Citation(s) in RCA: 265] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Methyl-CpG binding proteins (MBDs) mediate histone deacetylase-dependent transcriptional silencing at methylated CpG islands. Using chromatin immunoprecitation (ChIP) we have found that gene-specific profiles of MBDs exist for hypermethylated promoters of breast cancer cells, whilst a common pattern of histone modifications is shared. This unique distribution of MBDs is also characterized in chromosomes by comparative genomic hybridization of immunoprecipitated DNA and immunolocalization. Most importantly, we demonstrate that MBD association to methylated DNA serves to identify novel targets of epigenetic inactivation in human cancer. We combined the ChIP assay of MBDs with a CpG island microarray (ChIP on chip). The scenario revealed shows that, while many genes are regulated by multiple MBDs, others are associated with a single MBD. These target genes displayed methylation- associated transcriptional silencing in breast cancer cells and primary tumours. The candidates include the homeobox gene PAX6, the prolactin hormone receptor, and dipeptidylpeptidase IV among others. Our results support an essential role for MBDs in gene silencing and, when combined with genomic strategies, their potential to 'catch' new hypermethylated genes in cancer.
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Affiliation(s)
- Esteban Ballestar
- Epigenetics Laboratory, Molecular Pathology Programme, Spanish National Cancer Centre (CNIO), Melchor Fernández Almagro 3, 28029 Madrid, Spain
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Bruusgaard JC, Liestøl K, Ekmark M, Kollstad K, Gundersen K. Number and spatial distribution of nuclei in the muscle fibres of normal mice studied in vivo. J Physiol 2003; 551:467-78. [PMID: 12813146 PMCID: PMC2343230 DOI: 10.1113/jphysiol.2003.045328] [Citation(s) in RCA: 173] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
We present here a new technique with which to visualize nuclei in living muscle fibres in the intact animal, involving injection of labelled DNA into single cells. This approach allowed us to determine the position of all of nuclei within a sarcolemma without labelling satellite cells. In contrast to what has been reported in tissue culture, we found that the nuclei were immobile, even when observed over several days. Nucleic density was uniform along the fibre except for the endplate and some myotendinous junctions, where the density was higher. The perijunctional region had the same number of nuclei as the rest of the fibre. In the extensor digitorum longus (EDL) muscle, the extrajunctional nuclei were elongated and precisely aligned to the long axis of the fibre. In the soleus, the nuclei were rounder and not well aligned. When comparing small and large fibres in the soleus, the number of nuclei varied approximately in proportion to cytoplasmic volume, while in the EDL the number was proportional to surface area. Statistical analysis revealed that the nuclei were not randomly distributed in either the EDL or the soleus. For each fibre, actual distributions were compared with computer simulations in which nuclei were assumed to repel each other, which optimizes the distribution of nuclei with respect to minimizing transport distances. The simulated patterns were regular, with clear row-like structures when the density of nuclei was low. The non-random and often row-like distribution of nuclei observed in muscle fibres may thus reflect regulatory mechanisms whereby nuclei repel each other in order to minimize transport distances.
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Affiliation(s)
- J C Bruusgaard
- Department of Biology, University of Oslo, Blindern, Norway
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35
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Lacazette E, Le Calvez S, Gajendran N, Brenner HR. A novel pathway for MuSK to induce key genes in neuromuscular synapse formation. J Cell Biol 2003; 161:727-36. [PMID: 12756238 PMCID: PMC2199368 DOI: 10.1083/jcb.200210156] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
At the developing neuromuscular junction the Agrin receptor MuSK is the central organizer of subsynaptic differentiation induced by Agrin from the nerve. The expression of musk itself is also regulated by the nerve, but the mechanisms involved are not known. Here, we analyzed the activation of a musk promoter reporter construct in muscle fibers in vivo and in cultured myotubes, using transfection of multiple combinations of expression vectors for potential signaling components. We show that neuronal Agrin by activating MuSK regulates the expression of musk via two pathways: the Agrin-induced assembly of muscle-derived neuregulin (NRG)-1/ErbB, the pathway thought to regulate acetylcholine receptor (AChR) expression at the synapse, and via a direct shunt involving Agrin-induced activation of Rac. Both pathways converge onto the same regulatory element in the musk promoter that is also thought to confer synapse-specific expression to AChR subunit genes. In this way, a positive feedback signaling loop is established that maintains musk expression at the synapse when impulse transmission becomes functional. The same pathways are used to regulate synaptic expression of AChR epsilon. We propose that the novel pathway stabilizes the synapse early in development, whereas the NRG/ErbB pathway supports maintenance of the mature synapse.
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Affiliation(s)
- Eric Lacazette
- Department of Physiology, University of Basel, CH-4056 Basel, Switzerland
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36
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Hippenmeyer S, Shneider NA, Birchmeier C, Burden SJ, Jessell TM, Arber S. A role for neuregulin1 signaling in muscle spindle differentiation. Neuron 2002; 36:1035-49. [PMID: 12495620 DOI: 10.1016/s0896-6273(02)01101-7] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The maturation of synaptic structures depends on inductive interactions between axons and their prospective targets. One example of such an interaction is the influence of proprioceptive sensory axons on the differentiation of muscle spindles. We have monitored the expression of three transcription factors, Egr3, Pea3, and Erm, that delineate early muscle spindle development in an assay of muscle spindle-inducing signals. We provide genetic evidence that Neuregulin1 (Nrg1) is required for proprioceptive afferent-evoked induction of muscle spindle differentiation in the mouse. Ig-Nrg1 isoforms are preferentially expressed by proprioceptive sensory neurons and are sufficient to induce muscle spindle differentiation in vivo, whereas CRD-Nrg1 isoforms are broadly expressed in sensory and motor neurons but are not required for muscle spindle induction.
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MESH Headings
- Animals
- Cell Differentiation/genetics
- DNA-Binding Proteins/genetics
- DNA-Binding Proteins/metabolism
- Early Growth Response Protein 3
- Female
- Fetus
- Ganglia, Spinal/cytology
- Ganglia, Spinal/embryology
- Ganglia, Spinal/metabolism
- Gene Expression Regulation, Developmental/genetics
- Male
- Mice
- Mice, Knockout
- Motor Neurons/cytology
- Motor Neurons/metabolism
- Muscle Spindles/cytology
- Muscle Spindles/embryology
- Muscle Spindles/metabolism
- Muscle, Skeletal/cytology
- Muscle, Skeletal/embryology
- Muscle, Skeletal/innervation
- Mutation/genetics
- Neuregulin-1/deficiency
- Neuregulin-1/genetics
- Neurons, Afferent/cytology
- Neurons, Afferent/metabolism
- Proprioception/genetics
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- Signal Transduction/genetics
- Transcription Factors/genetics
- Transcription Factors/metabolism
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Affiliation(s)
- Simon Hippenmeyer
- Biozentrum, Department of Cell Biology, University of Basel, Klingelbergstrasse 70, 4056-, Basel, Switzerland
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37
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Stacy S, Gelb BE, Koop BA, Windle JJ, Wall KA, Krolick KA, Infante AJ, Kraig E. Split tolerance in a novel transgenic model of autoimmune myasthenia gravis. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 169:6570-9. [PMID: 12444169 DOI: 10.4049/jimmunol.169.11.6570] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Because it is one of the few autoimmune disorders in which the target autoantigen has been definitively identified, myasthenia gravis (MG) provides a unique opportunity for testing basic concepts of immune tolerance. In most MG patients, Abs against the acetylcholine receptors (AChR) at the neuromuscular junction can be readily identified and have been directly shown to cause muscle weakness. T cells have also been implicated and appear to play a role in regulating the pathogenic B cells. A murine MG model, generated by immunizing mice with heterologous AChR from the electric fish Torpedo californica, has been used extensively. In these animals, Abs cross-react with murine AChR; however, the T cells do not. Thus, to study tolerance to AChR, a transgenic mouse model was generated in which the immunodominant Torpedo AChR (T-AChR) alpha subunit is expressed in appropriate tissues. Upon immunization, these mice showed greatly reduced T cell responses to T-AChR and the immunodominant alpha-chain peptide. Limiting dilution assays suggest the likely mechanism of tolerance is deletion or anergy. Despite this tolerance, immunization with intact T-AChR induced anti-AChR Abs, including Abs against the alpha subunit, and the incidence of MG-like symptoms was similar to that of wild-type animals. Furthermore, evidence suggests that this B cell response to the alpha-chain receives help from T cells directed against the other AChR polypeptides (beta, gamma, or delta). This model offers a novel opportunity to elucidate mechanisms of tolerance regulation to muscle AChR and to clarify the role of T cells in MG.
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Affiliation(s)
- Sue Stacy
- Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78229, USA
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38
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Huang YZ, Wang Q, Won S, Luo ZG, Xiong WC, Mei L. Compartmentalized NRG signaling and PDZ domain-containing proteins in synapse structure and function. Int J Dev Neurosci 2002; 20:173-85. [PMID: 12175853 DOI: 10.1016/s0736-5748(02)00011-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
The synapse-specific synthesis of the acetylcholine receptor (AChR) is mediated by multiple mechanisms including compartmentalized signaling induced by neuregulin (NRG). This paper presents evidence that NRG receptors--ErbB receptor tyrosine kinases interact with distinct PDZ domain-containing proteins that are localized at the neuromuscular junction (NMJ). ErbB4 associates with the PSD-95 (also known as SAP90)-family members including PSD-95, SAP97, and SAP102 whereas ErbB2 interacts with Erbin and PICK1. Although, ErbB kinases are concentrated at the NMJ, they are not colocalized with the AChR in cultured muscle cells even in the presence of agrin. Co-expression of PSD-95 causes ErbB4 to form clusters in COS cells. We propose that PDZ domain-containing proteins play a role in anchoring ErbB proteins at the neuromuscular junction, and/or mediating downstream signaling pathways. Such mechanisms could be important for the maintenance and function of the synapse.
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Affiliation(s)
- Yang Z Huang
- Department of Neurobiology, Pathology, Physical Medicine and Rehabilitation, University of Alabama at Birmingham, 35294-0021, USA
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39
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Abicht A, Stucka R, Schmidt C, Briguet A, Höpfner S, Song IH, Pongratz D, Müller-Felber W, Ruegg MA, Lochmüller H. A newly identified chromosomal microdeletion and an N-box mutation of the AChR epsilon gene cause a congenital myasthenic syndrome. Brain 2002; 125:1005-13. [PMID: 11960891 DOI: 10.1093/brain/awf095] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Congenital myasthenic syndromes (CMSs) are frequently caused by mutations of the coding region of the acetylcholine receptor epsilon subunit (AChRepsilon) gene leading to a reduced expression of the acetylcholine receptor (AChR) at the postsynaptic membrane. Two recent observations have linked two different N-box mutations of the human AChRepsilon promoter to a clinical CMS phenotype. N-boxes are regulatory sequence elements of mammalian promoters that confer synapse-specific expression of several genes, including the AChR subunit genes. Here, we report on a novel point mutation (epsilon-154G-->A) in the N-box of the AChRepsilon promoter in a German CMS pedigree. Semiquantitative analysis of AChRepsilon mRNA levels in the patient's muscle indicated significantly impaired AChRepsilon expression. We provide additional evidence of a pathogenic role for this mutation using the mutated promoter (epsilon-154G-->A) driving a heterologous gene (luciferase) in rat skeletal muscle. We show that agrin-induced gene expression is significantly reduced by the N-box mutant (mt) compared with the wild-type (wt) promoter. Refined haplotype analysis and direct sequencing revealed maternal inheritance of the mutant AChRepsilon promoter (epsilon-154G-->A) together with paternal inheritance of a chromosomal microdeletion (Delta1290 bp) encompassing the promoter and the first two exons of the AChRepsilon gene in the index patient. In conclusion, we provide genetic and functional evidence that a mutation of the AChRepsilon subunit promoter (epsilon-154G-->A) causes CMS due to the reduction of gene expression in skeletal muscle. Moreover, this is the first report of a chromosomal microdeletion affecting an AChR gene. This type of mutation may be missed in standard screening techniques of CMS patients.
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Affiliation(s)
- Angela Abicht
- Genzentrum and Friedrich-Baur-Institut, Ludwig-Maximilians-University Munich, Germany
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40
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Jasmin BJ, Angus LM, Bélanger G, Chakkalakal JV, Gramolini AO, Lunde JA, Stocksley MA, Thompson J. Multiple regulatory events controlling the expression and localization of utrophin in skeletal muscle fibers: insights into a therapeutic strategy for Duchenne muscular dystrophy. JOURNAL OF PHYSIOLOGY, PARIS 2002; 96:31-42. [PMID: 11755781 DOI: 10.1016/s0928-4257(01)00078-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Duchenne muscular dystrophy (DMD) is the most prevalent inherited muscle disease and results from mutations/deletions in the X-linked dystrophin gene. Although several approaches have been envisaged to counteract the effects of this progressive disease, there is currently no cure available. One strategy consists in utilizing a protein normally expressed in DMD muscle which, once expressed at appropriate levels and at the correct subcellular location, could compensate for the lack of dystrophin. A candidate for such a role is the dystrophin-related protein now referred to as utrophin. In contrast to dystrophin, which is expressed along the length of healthy muscle fibers, utrophin accumulates at the neuromuscular junction in both normal and DMD fibers. Several years ago, we began a series of experiments to determine the mechanisms responsible for the expression of utrophin at the neuromuscular synapse. Initially, we showed that utrophin transcripts accumulate preferentially within the postsynaptic sarcoplasm. To determine whether selective transcription of the utrophin gene accounts for this synaptic accumulation of utrophin mRNAs, we injected several utrophin promoter-reporter constructs directly into mouse muscle and demonstrated the preferential synaptic expression of the reporter gene. These results suggested that local transcriptional activation of the utrophin gene is responsible for the accumulation of utrophin mRNAs at the neuromuscular junction. In these studies, we also demonstrated that an N-box motif contained within the utrophin promoter plays a critical role in directing the synapse-specific expression of the utrophin gene. Additionally, our studies have shown that the ets-factors GABP alpha and beta are part of a protein complex that can bind to the N-box motif to transactivate the gene in muscle cells in culture and in vivo. In these experiments, we also noted that the nerve-derived trophic factors agrin and ARIA/heregulin regulate expression of utrophin via the activation of GABP alpha and beta which in turn, transactivate the utrophin gene via the N-box motif. Although these studies demonstrate that transcriptional activation can regulate utrophin mRNA levels, it is possible that additional mechanisms are also involved. In particular, the association of mRNAs with cytoskeletal elements and RNA-binding proteins may contribute to the accumulation of utrophin transcripts within the postsynaptic sarcoplasm. In recent studies, we have begun to examine this and we have now identified specific regions within the 3' untranslated region that are necessary for targeting and stabilizing utrophin mRNAs in skeletal muscle cells. A series of in vivo studies have also led us to conclude that post-transcriptional mechanisms are indeed important in regulating the abundance of utrophin transcripts in muscle. Together, these studies should lead to the identification of cis- and trans-acting elements regulating transcription of the utrophin gene as well as the stability and targeting of its mRNA in muscle cells. The results should therefore, identify specific targets that may become important in designing specific pharmacological interventions directed at increasing the expression of utrophin into extrasynaptic regions of DMD muscle fibers. In addition, these findings will contribute to our basic understanding of the cellular and molecular events involved in the formation, maintenance and plasticity of the neuromuscular synapse.
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Affiliation(s)
- Bernard J Jasmin
- Department of Cellular and Molecular Medicine and Centre for Neuromuscular Disease, Faculty of Medicine, University of Ottawa, and Ottawa Health Research Institute, Ottawa, Ontario, Canada K1H 8M5.
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Sanes JR, Lichtman JW. Induction, assembly, maturation and maintenance of a postsynaptic apparatus. Nat Rev Neurosci 2001; 2:791-805. [PMID: 11715056 DOI: 10.1038/35097557] [Citation(s) in RCA: 747] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- J R Sanes
- Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 South Euclid, Campus Box 8108, St Louis, Missouri 63110-1093, USA.
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42
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Keller P, Payne JL, Tremml G, Greer PA, Gaboli M, Pandolfi PP, Bessler M. FES-Cre targets phosphatidylinositol glycan class A (PIGA) inactivation to hematopoietic stem cells in the bone marrow. J Exp Med 2001; 194:581-9. [PMID: 11535627 PMCID: PMC2195941 DOI: 10.1084/jem.194.5.581] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A somatic mutation in the X-linked phosphatidylinositol glycan class A (PIGA) gene causes the loss of glycosyl phosphatidylinositol (GPI)-linked proteins on blood cells from patients with paroxysmal nocturnal hemoglobinuria. Because all blood cell lineages may be affected it is thought that the mutation occurs in a hematopoietic stem cell. In transgenic mice, germline transmission of an inactive Piga gene is embryonic lethal. To inactivate the murine Piga gene in early hematopoiesis we therefore chose conditional gene inactivation using the Cre/loxP system. We expressed Cre recombinase under the transcription regulatory sequences of the human c-fes gene. FES-Cre inactivated PIGA in hematopoietic cells of mice carrying a floxed Piga allele (LF mice). PIGA(-) cells were found in all hematopoietic lineages of definitive but not primitive hematopoiesis. Their proportions were low in newborn mice but subsequently increased continuously to produce for the first time mice that have almost exclusively PIGA(-) blood cells. The loss of GPI-linked proteins occurred mainly in c-kit(+)CD34(+)Lin(-) progenitor cells before the CFU-GEMM stage. Using bone marrow reconstitution experiments with purified PIGA(-) cells we demonstrate that LF mice have long-term bone marrow repopulating cells that lack GPI-linked proteins, indicating that recombination of the floxed Piga allele occurs in the hematopoietic stem cell.
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Affiliation(s)
- Peter Keller
- Division of Hematology, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110
| | - Jennifer L. Payne
- Division of Hematology, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110
| | - Gabi Tremml
- Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021
| | - Peter A. Greer
- Cancer Research Laboratories, Departments of Biochemistry and Pathology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Mirella Gaboli
- Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021
| | - Pier P. Pandolfi
- Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021
| | - Monica Bessler
- Division of Hematology, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110
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43
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Feng G, Mellor RH, Bernstein M, Keller-Peck C, Nguyen QT, Wallace M, Nerbonne JM, Lichtman JW, Sanes JR. Imaging neuronal subsets in transgenic mice expressing multiple spectral variants of GFP. Neuron 2000; 28:41-51. [PMID: 11086982 DOI: 10.1016/s0896-6273(00)00084-2] [Citation(s) in RCA: 2370] [Impact Index Per Article: 98.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We generated transgenic mice in which red, green, yellow, or cyan fluorescent proteins (together termed XFPs) were selectively expressed in neurons. All four XFPs labeled neurons in their entirety, including axons, nerve terminals, dendrites, and dendritic spines. Remarkably, each of 25 independently generated transgenic lines expressed XFP in a unique pattern, even though all incorporated identical regulatory elements (from the thyl gene). For example, all retinal ganglion cells or many cortical neurons were XFP positive in some lines, whereas only a few ganglion cells or only layer 5 cortical pyramids were labeled in others. In some lines, intense labeling of small neuronal subsets provided a Golgi-like vital stain. In double transgenic mice expressing two different XFPs, it was possible to differentially label 3 neuronal subsets in a single animal.
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Affiliation(s)
- G Feng
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St Louis, Missouri 63110, USA
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44
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Dupuis M, Denis-Mize K, Woo C, Goldbeck C, Selby MJ, Chen M, Otten GR, Ulmer JB, Donnelly JJ, Ott G, McDonald DM. Distribution of DNA vaccines determines their immunogenicity after intramuscular injection in mice. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 165:2850-8. [PMID: 10946318 DOI: 10.4049/jimmunol.165.5.2850] [Citation(s) in RCA: 236] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Intramuscular injection of DNA vaccines elicits potent humoral and cellular immune responses in mice. However, DNA vaccines are less efficient in larger animal models and humans. To gain a better understanding of the factors limiting the efficacy of DNA vaccines, we used fluorescence-labeled plasmid DNA in mice to 1) define the macroscopic and microscopic distribution of DNA after injection into the tibialis anterior muscle, 2) characterize cellular uptake and expression of DNA in muscle and draining lymph nodes, and 3) determine the effect of modifying DNA distribution and cellular uptake by volume changes or electroporation on the magnitude of the immune response. Injection of a standard 50-microl dose resulted in the rapid dispersion of labeled DNA throughout the muscle. DNA was internalized within 5 min by muscle cells near the injection site and over several hours by cells that were located along muscle fibers and in the draining lymph nodes. Histochemical staining and analysis of mRNA expression in isolated cells by RT-PCR showed that the transgene was detectably expressed only by muscle cells, despite substantial DNA uptake by non-muscle cells. Reduction of the injection volume to 5 microl resulted in substantially less uptake and expression of DNA by muscle cells, and correspondingly lower immune responses against the transgene product. However, expression and immunogenicity were restored when the 5-microl injection was followed by electroporation in vivo. These findings indicate that distribution and cellular uptake significantly affect the immunogenicity of DNA vaccines.
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MESH Headings
- AIDS Vaccines/administration & dosage
- AIDS Vaccines/genetics
- AIDS Vaccines/immunology
- AIDS Vaccines/pharmacokinetics
- Animals
- Antigens, Viral/administration & dosage
- Antigens, Viral/immunology
- DNA, Viral/metabolism
- Electroporation
- Gene Expression Regulation
- Gene Products, gag/biosynthesis
- Gene Products, gag/genetics
- Gene Products, gag/immunology
- HIV Antibodies/biosynthesis
- HIV Antibodies/blood
- Injections, Intramuscular
- Luciferases/genetics
- Luciferases/metabolism
- Lymph Nodes/cytology
- Lymph Nodes/metabolism
- Mice
- Mice, Inbred BALB C
- Mice, Transgenic
- Muscle, Skeletal/cytology
- Muscle, Skeletal/enzymology
- Muscle, Skeletal/metabolism
- Plasmids/administration & dosage
- Plasmids/immunology
- Transgenes/immunology
- Vaccines, DNA/administration & dosage
- Vaccines, DNA/genetics
- Vaccines, DNA/immunology
- Vaccines, DNA/pharmacokinetics
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Affiliation(s)
- M Dupuis
- Cardiovascular Research Institute and Department of Anatomy, University of California, San Francisco, CA 94143, USA
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Yang JF, Zhou H, Choi RC, Ip NY, Peng HB, Tsim KW. A cysteine-rich form of Xenopus neuregulin induces the expression of acetylcholine receptors in cultured myotubes. Mol Cell Neurosci 1999; 13:415-29. [PMID: 10383827 DOI: 10.1006/mcne.1999.0759] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Neuregulin-1 (NRG-1) has diverse functions in neural development, and one of them is to up regulate the expression of acetylcholine receptors (AChRs) at muscle fibers during the formation of neuromuscular junctions. NRG-1 has two prominent alternative splicing sites at the N-terminus; it could be an immunoglobulin (Ig)-like domain named Ig-NRG-1 or an apolar cysteine-rich domain (CRD) named CRD-NRG-1. cDNAs encoding Xenopus CRD-NRG-1 were isolated by cross-hybridization with Xenopus Ig-NRG-1 cDNA fragment. The amino acid sequence of Xenopus CRD-NRG-1 is 45 to 70% identical to the human, rat, and chick homologs. Similar to Ig-NRG-1, two variation sites within CRD-NRG-1 were identified at the spacer domain with 0 or 43 amino acids inserted and at the C-terminus of the EGF-like domain to derive either alpha or beta isoform. Two transcripts encoding CRD-NRG-1, approximately 7.5 and approximately 9.0 kb, were revealed in adult brain and spinal cord, but the expression in muscle was below the detectable level. The recombinant Xenopus CRD-NRG-1 when applied onto cultured myotubes was able to induce the tyrosine phosphorylation of ErbB receptors and the expression of AChR. The AChR-inducing activity of CRD-NRG-1 was precipitated by anti-NRG-1 antibody but not by heparin. In situ hybridization showed a strong expression of CRD-NRG-1 mRNA in developing brain, spinal cord, and myotomal muscles of Xenopus embryo. Similar to the results in other species, both CRD-NRG-1 and Ig-NRG-1 may play a role in the developing Xenopus neuromuscular junctions.
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Affiliation(s)
- J F Yang
- Department of Biology and Biotechnology Research Institute, The Hong Kong University of Science and Technology, Clear Water Bay Road, Hong Kong, China
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Abstract
We describe the formation, maturation, elimination, maintenance, and regeneration of vertebrate neuromuscular junctions (NMJs), the best studied of all synapses. The NMJ forms in a series of steps that involve the exchange of signals among its three cellular components--nerve terminal, muscle fiber, and Schwann cell. Although essentially any motor axon can form NMJs with any muscle fiber, an additional set of cues biases synapse formation in favor of appropriate partners. The NMJ is functional at birth but undergoes numerous alterations postnatally. One step in maturation is the elimination of excess inputs, a competitive process in which the muscle is an intermediary. Once elimination is complete, the NMJ is maintained stably in a dynamic equilibrium that can be perturbed to initiate remodeling. NMJs regenerate following damage to nerve or muscle, but this process differs in fundamental ways from embryonic synaptogenesis. Finally, we consider the extent to which the NMJ is a suitable model for development of neuron-neuron synapses.
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Affiliation(s)
- J R Sanes
- Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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Si J, Mei L. ERK MAP kinase activation is required for acetylcholine receptor inducing activity-induced increase in all five acetylcholine receptor subunit mRNAs as well as synapse-specific expression of acetylcholine receptor epsilon-transgene. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 67:18-27. [PMID: 10101228 DOI: 10.1016/s0169-328x(99)00028-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The AChR is a pentamer of four different subunits in a stoichiometry of alpha2betagammadelta in embryonic and alpha2betaepsilondelta in adult animals. Transcription of AChR subunit genes is most active in synaptic nuclei in adult skeletal muscle cells, and is regulated by neural factors such as ARIA. We report here that ARIA up-regulated specifically the expression of all five AChR subunits in C2C12 cells. The mRNA level of erbB2, erbB3, rapsyn, MuSK, SHP-2 and beta-actin remained unchanged in response to ARIA stimulation in C2C12 cells. The ARIA-induced increase in AChR subunit expression in C2C12 cells was inhibited by the erbB kinase inhibitor tyrphostin AG1478 and the MEK inhibitor PD98059, but not by the PI3 kinase inhibitor wortmannin, suggesting an important role of the erbB protein tyrosine kinases and MAP kinase in the regulation of the expression of the five different AChR subunits. To determine the signaling pathways in vivo, we studied the expression of reporter genes driven by the epsilon-promoter in injected muscles. The in vivo expression of the epsilon-transgene was inhibited by co-expression of dominant negative mutants of key components in the MAP kinase pathway including ras, raf and MEK, but not the dominant negative mutant of PI3 kinase. These results suggest that ERK MAP kinase activation is required for ARIA-induced increase in all five AChR subunit mRNAs as well as synapse-specific expression of AChR epsilon-transgene.
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MESH Headings
- Androstadienes/pharmacology
- Animals
- Antibiotics, Antineoplastic/pharmacology
- Blotting, Northern
- Blotting, Western
- Calcium-Calmodulin-Dependent Protein Kinases/antagonists & inhibitors
- Calcium-Calmodulin-Dependent Protein Kinases/metabolism
- Cells, Cultured
- Enzyme Activation/drug effects
- Enzyme Activation/physiology
- Enzyme Inhibitors/pharmacology
- Gene Expression/drug effects
- Gene Expression/physiology
- Lac Operon
- Mice
- Muscle Fibers, Skeletal/cytology
- Phosphatidylinositol 3-Kinases/metabolism
- Quinazolines
- RNA, Messenger/metabolism
- Receptors, Cholinergic/analysis
- Receptors, Cholinergic/genetics
- Receptors, Cholinergic/metabolism
- Sirolimus/pharmacology
- Synapses/chemistry
- Synapses/enzymology
- Transcription, Genetic/physiology
- Transgenes/physiology
- Tyrphostins/pharmacology
- Up-Regulation/physiology
- Wortmannin
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Affiliation(s)
- J Si
- Department of Pharmacology, University of Virginia School of Medicine, Box 448, Jordan Hall 515, 1300 Jefferson Park Ave., Charlottesville, VA 22908, USA
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48
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Abstract
This work demonstrates that electrical muscle stimulation markedly increases the transfection efficiency of an intramuscular injection of plasmid DNA. In soleus or extensor digitorum longus muscles of adult rats the percentage of transfected fibers increased from about 1 to more than 10. The number of transfected fibers and the amount of foreign protein produced could be graded by varying the number or duration of the electrical pulses applied to the muscle. The stimulation had to be applied when DNA was present in the muscle. When dextran was injected together with the plasmid DNA, it was also taken up by the transfected fibers. Stimulation-induced membrane permeabilization and increased DNA uptake were therefore probably responsible for the improved transfection. The stimulation caused some muscle damage but the fibers regenerated rapidly. The described method, which is simple, efficient, and reproducible, should become valuable for basic research, gene therapy and DNA vaccination.
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Affiliation(s)
- I Mathiesen
- Department of Physiology, University of Oslo, Norway
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Bennett MR. Synapse formation molecules in muscle and autonomic ganglia: the dual constraint hypothesis. Prog Neurobiol 1999; 57:225-87. [PMID: 9987806 DOI: 10.1016/s0301-0082(98)00043-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In 1970 it was thought that if the motor-nerve supply to a muscle was interrupted and then allowed to regenerate into the muscle, motor-synaptic terminals most often formed presynaptic specializations at random positions over the surface of the constituent muscle fibres, so that the original spatial pattern of synapses was not restored. However, in the early 1970s a systematic series of experiments were carried out showing that if injury to muscles was avoided then either reinnervation or cross-reinnervation reconstituted the pattern of synapses on the muscle fibres according to an analysis using the combined techniques of electrophysiology, electronmicroscopy and histology on the muscles. It was thus shown that motor-synaptic terminals are uniquely restored to their original synaptic positions. This led to the concept of the synaptic site, defined as that region on a muscle fibre that contains molecules for triggering synaptic terminal formation. However, nerves in developing muscles were found to form connections at random positions on the surface of the very short muscle cells, indicating that these molecules are not generated by the muscle but imprinted by the nerves themselves; growth in length of the cells on either side of the imprint creates the mature synaptic site in the approximate middle of the muscle fibres. This process is accompanied at first by the differentiation of an excess number of terminals at the synaptic site, and then the elimination of all but one of the terminals. In the succeeding 25 years, identification of the synaptic site molecules has been a major task of molecular neurobiology. This review presents an historical account of the developments this century of the idea that synaptic-site formation molecules exist in muscle. The properties that these molecules must possess if they are to guide the differentiation and elimination of synaptic terminals is considered in the context of a quantitative model of this process termed the dual-constraint hypothesis. It is suggested that the molecules agrin, ARIA, MuSK and S-laminin have suitable properties according to the dual-constraint hypothesis to subserve this purpose. The extent to which there is evidence for similar molecules at neuronal synapses such as those in autonomic ganglia is also considered.
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Affiliation(s)
- M R Bennett
- Neurobiology Laboratory, University of Sydney, NSW, Australia.
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50
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Abstract
We describe a technique wherein single muscle fibers of intact mice are made transgenic by intracellular injection of DNA expression vectors for the reporter genes lacZ and green fluorescent protein (GFP). Application of in vivo imaging techniques allowed identification of single cells during the injections, and of the same single cells when the muscle was reexposed days or weeks later. DNA concentration by itself had little effect on fiber survival or expression efficacy, but it seemed crucial to exceed a threshold of about 10(6) injected plasmid molecules in order to obtain expression. On the other hand, experiments with coinjection of two different plasmids suggested that relatively few individual molecules were eventually transcribed in expressing cells. Plasmid DNA remained localized to the injection site, and expression was confined to nuclei in the vicinity. Expression was stable, as reporter was detected 2-61 days after injection.
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Affiliation(s)
- J K Utvik
- Department of Neurophysiology, University of Oslo, Norway
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