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Gleneadie HJ, Fernandez-Ruiz B, Sardini A, Van de Pette M, Dimond A, Prinjha RK, McGinty J, French PMW, Bagci H, Merkenschlager M, Fisher AG. Endogenous bioluminescent reporters reveal a sustained increase in utrophin gene expression upon EZH2 and ERK1/2 inhibition. Commun Biol 2023; 6:318. [PMID: 36966198 PMCID: PMC10039851 DOI: 10.1038/s42003-023-04666-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Accepted: 03/06/2023] [Indexed: 03/27/2023] Open
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked disorder caused by loss of function mutations in the dystrophin gene (Dmd), resulting in progressive muscle weakening. Here we modelled the longitudinal expression of endogenous Dmd, and its paralogue Utrn, in mice and in myoblasts by generating bespoke bioluminescent gene reporters. As utrophin can partially compensate for Dmd-deficiency, these reporters were used as tools to ask whether chromatin-modifying drugs can enhance Utrn expression in developing muscle. Myoblasts treated with different PRC2 inhibitors showed significant increases in Utrn transcripts and bioluminescent signals, and these responses were independently verified by conditional Ezh2 deletion. Inhibition of ERK1/2 signalling provoked an additional increase in Utrn expression that was also seen in Dmd-mutant cells, and maintained as myoblasts differentiate. These data reveal PRC2 and ERK1/2 to be negative regulators of Utrn expression and provide specialised molecular imaging tools to monitor utrophin expression as a therapeutic strategy for DMD.
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Affiliation(s)
- Hannah J Gleneadie
- Epigenetic Memory Group, MRC London Institute of Medical Sciences (LMS), Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Beatriz Fernandez-Ruiz
- Epigenetic Memory Group, MRC London Institute of Medical Sciences (LMS), Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Alessandro Sardini
- Whole Animal Physiology and Imaging Facility, MRC LMS, Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Mathew Van de Pette
- Epigenetic Memory Group, MRC London Institute of Medical Sciences (LMS), Imperial College London, Du Cane Road, London, W12 0NN, UK
- MRC Toxicology Unit, Gleeson Building, Tennis Court Road, Cambridge, CB2 1QR, UK
| | - Andrew Dimond
- Epigenetic Memory Group, MRC London Institute of Medical Sciences (LMS), Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Rab K Prinjha
- Immunology and Epigenetics Research Unit, Research, GlaxoSmithKline, Gunnels Wood Road, Stevenage, Herts, SG1 2NY, UK
| | - James McGinty
- Photonics Group, Department of Physics, Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
| | - Paul M W French
- Photonics Group, Department of Physics, Blackett Laboratory, Imperial College London, London, SW7 2AZ, UK
| | - Hakan Bagci
- Lymphocyte Development Group, MRC LMS, Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Matthias Merkenschlager
- Lymphocyte Development Group, MRC LMS, Imperial College London, Du Cane Road, London, W12 0NN, UK
| | - Amanda G Fisher
- Epigenetic Memory Group, MRC London Institute of Medical Sciences (LMS), Imperial College London, Du Cane Road, London, W12 0NN, UK.
- Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU, Oxford, UK.
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Dystrophin Dp71 Isoforms Are Differentially Expressed in the Mouse Brain and Retina: Report of New Alternative Splicing and a Novel Nomenclature for Dp71 Isoforms. Mol Neurobiol 2017; 55:1376-1386. [PMID: 28127699 DOI: 10.1007/s12035-017-0405-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2016] [Accepted: 01/12/2017] [Indexed: 12/27/2022]
Abstract
Multiple dystrophin Dp71 isoforms have been identified in rats, mice, and humans and in several cell line models. These Dp71 isoforms are produced by the alternative splicing of exons 71 to 74 and 78 and intron 77. Three main groups of Dp71 proteins are defined based on their C-terminal specificities: Dp71d, Dp71f, and Dp71e. Dp71 is highly expressed in the brain and retina; however, the specific isoforms present in these tissues have not been determined to date. In this work, we explored the expression of Dp71 isoforms in the mouse brain and retina using RT-PCR assays followed by the cloning of PCR products into the pGEM-T Easy vector, which was used to transform DH5α cells. Dp71-positive colonies were later analyzed by PCR multiplex and DNA sequencing to determine the alternative splicing. We thus demonstrated the expression of Dp71 transcripts corresponding to Dp71, Dp71a, Dp71c, Dp71b, Dp71ab, Dp71 Δ110, and novel Dp71 isoforms spliced in exon 74; 71 and 74; 71, 73 and 74; and 74 and 78, which we named Dp71d Δ74 , Dp71d Δ71,74 , Dp71d Δ71,73-74 , and Dp71f Δ74 , respectively. Additionally, we demonstrated that the Dp71d group of isoforms is highly expressed in the brain, while the Dp71f group predominates in the retina, at both the cDNA and protein levels. These findings suggest that distinct Dp71 isoforms may play different roles in the brain and retina.
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Dystrophins, utrophins, and associated scaffolding complexes: role in mammalian brain and implications for therapeutic strategies. J Biomed Biotechnol 2010; 2010:849426. [PMID: 20625423 PMCID: PMC2896903 DOI: 10.1155/2010/849426] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 03/14/2010] [Indexed: 12/23/2022] Open
Abstract
Two decades of molecular, cellular, and functional studies considerably increased our understanding of dystrophins function and unveiled the complex etiology of the cognitive deficits in Duchenne muscular dystrophy (DMD), which involves altered expression of several dystrophin-gene products in brain. Dystrophins are normally part of critical cytoskeleton-associated membrane-bound molecular scaffolds involved in the clustering of receptors, ion channels, and signaling proteins that contribute to synapse physiology and blood-brain barrier function. The utrophin gene also drives brain expression of several paralogs proteins, which cellular expression and biological roles remain to be elucidated. Here we review the structural and functional properties of dystrophins and utrophins in brain, the consequences of dystrophins loss-of-function as revealed by numerous studies in mouse models of DMD, and we discuss future challenges and putative therapeutic strategies that may compensate for the cognitive impairment in DMD based on experimental manipulation of dystrophins and/or utrophins brain expression.
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Dystrophin Dp71 is critical for stability of the DAPs in the nucleus of PC12 cells. Neurochem Res 2009; 35:366-73. [PMID: 19784870 DOI: 10.1007/s11064-009-0064-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2009] [Indexed: 10/20/2022]
Abstract
We have adopted the PC12 cell line as in vitro cell model for studying Dp71 function in neuronal cells. These cells express a cytoplasmic (Dp71f) and a nuclear (Dp71d) isoform of Dp71 as well as various dystrophin-associated proteins (DAPs). In this study, we revealed by confocal microscopy analysis and Western blotting evaluation of cell fractions the presence of different DAPs (beta-dystroglycan, beta-dystrobrevin, epsilon-sarcoglycan and gamma1-syntrophin) in the nucleus of PC12 cells. Furthermore, we established by immunoprecipitation assays that Dp71d and the DAPs form a dystrophin-associated protein complex (DAPC) in the nucleus. Interestingly, depletion of Dp71 by antisense treatment (antisense-Dp71 cells) provoked a drastic reduction of nuclear DAPs, which indicates that Dp71d is critical for DAPs stability within the nucleus. Although Up71, the utrophin gene product homologous to Dp71, exhibited increased expression in the antisense-Dp71 cells, its scarce nuclear levels makes unlikely that could compensate for Dp71 nuclear deficiency.
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Fort PE, Sene A, Pannicke T, Roux MJ, Forster V, Mornet D, Nudel U, Yaffe D, Reichenbach A, Sahel JA, Rendon A. Kir4.1 and AQP4 associate with Dp71- and utrophin-DAPs complexes in specific and defined microdomains of Müller retinal glial cell membrane. Glia 2008; 56:597-610. [DOI: 10.1002/glia.20633] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Dp71, utrophin and beta-dystroglycan expression and distribution in PC12/L6 cell cocultures. Neuroreport 2008; 18:1657-61. [PMID: 17921863 DOI: 10.1097/wnr.0b013e3282f0e42d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Function of dystrophin Dp71 isoforms is unknown but seems related to neurite outgrowth and synapse formation. To evaluate Dp71 role in myoneural synapses, we established a coculture model using PC12 cells and L6 myotubes and analyzed expression and localization of Dp71 and related proteins, utrophin and beta-dystroglycan, in PC12 cells. Confocal microscopy showed Dp71d isoform in PC12 nuclei, golgi-complex-like and endoplasmic reticulum-like structures, whereas Dp71ab concentrates at neurite tips and cytoplasm, colocalizing with beta-dystroglycan, utrophin, synaptophysin and acetylcholine receptors. Evidences suggest that Dp71ab isoform, unlike Dp71d, may take part in neurite-related processes. This is the first work on Dp and members of Dp-associated protein complex roles in a cell-line based coculturing system, which may be useful in determining Dp71 isoforms associations.
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Odom GL, Gregorevic P, Chamberlain JS. Viral-mediated gene therapy for the muscular dystrophies: successes, limitations and recent advances. BIOCHIMICA ET BIOPHYSICA ACTA 2007; 1772:243-62. [PMID: 17064882 PMCID: PMC1894910 DOI: 10.1016/j.bbadis.2006.09.007] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 09/16/2006] [Accepted: 09/20/2006] [Indexed: 02/07/2023]
Abstract
Much progress has been made over the past decade elucidating the molecular basis for a variety of muscular dystrophies (MDs). Accordingly, there are examples of mouse models of MD whose disease progression has been halted in large part with the use of viral vector technology. Even so, we must acknowledge significant limitations of present vector systems that must be overcome prior to successful treatment of humans with such approaches. This review will present a variety of viral-mediated therapeutic strategies aimed at counteracting the muscle-wasting symptoms associated with muscular dystrophy. We include viral vector systems used for muscle gene transfer, with a particular emphasis on adeno-associated virus. Findings of several encouraging studies focusing on repair of the mutant dystrophin gene are also included. Lastly, we present a discussion of muscle compensatory therapeutics being considered that include pathways involved in the up-regulation of utrophin, promotion of cellular adhesion, enhancement of muscle mass, and antagonism of the inflammatory response. Considering the complexity of the muscular dystrophies, it appears likely that a multilayered approach tailored to a patient sub-group may be warranted in order to effectively contest the progression of this devastating disease.
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Affiliation(s)
- Guy L. Odom
- Department of Neurology Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington School of Medicine, 1959 NE Pacific Street, Seattle, WA, 98195-7720, USA
| | - Paul Gregorevic
- Department of Neurology Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington School of Medicine, 1959 NE Pacific Street, Seattle, WA, 98195-7720, USA
| | - Jeffrey S. Chamberlain
- Department of Neurology Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington School of Medicine, 1959 NE Pacific Street, Seattle, WA, 98195-7720, USA
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The dystrotelin, dystrophin and dystrobrevin superfamily: new paralogues and old isoforms. BMC Genomics 2007; 8:19. [PMID: 17233888 PMCID: PMC1790709 DOI: 10.1186/1471-2164-8-19] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2006] [Accepted: 01/17/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Dystrophins and dystrobrevins are distantly related proteins with important but poorly understood roles in the function of metazoan muscular and neuronal tissues. Defects in them and their associated proteins cause a range of neuromuscular disorders. Members of this superfamily have been discovered in a relatively serendipitous way; we set out to compile a comprehensive description of dystrophin- and dystrobrevin-related sequences from available metazoan genome sequences, validated in representative organisms by RT-PCR, or acquired de novo from key species. RESULTS Features of the superfamily revealed by our survey include: a) Dystrotelin, an entirely novel branch of the superfamily, present in most vertebrates examined. Dystrotelin is expressed in the central nervous system, and is a possible orthologue of Drosophila DAH. We describe the preliminary characterisation of its function, evolution and expression. b) A novel vertebrate member of the dystrobrevin family, gamma-dystrobrevin, an ancient branch now extant only in fish, but probably present in our own ancestors. Like dystrophin, zebrafish gamma-dystrobrevin mRNA is localised to myosepta. c) The extent of conservation of alternative splicing and alternative promoter use in the dystrophin and dystrobrevin genes; alternative splicing of dystrophin exons 73 and 78 and alpha-dystrobrevin exon 13 are conserved across vertebrates, as are the use of the Dp116, Dp71 and G-utrophin promoters; the Dp260 and Dp140 promoters are tetrapod innovations. d) The evolution of the unique N-terminus of DRP2 and its relationship to Dp116 and G-utrophin. e) A C-terminally truncated common ancestor of dystrophin and utrophin in cyclostomes. f) A severely restricted repertoire of dystrophin complex components in ascidians. CONCLUSION We have refined our understanding of the evolutionary history and isoform diversity of the five previously reported vertebrate superfamily members and describe two novel members, dystrotelin and gamma-dystrobrevin. Dystrotelins, dystrophins and dystrobrevins are roughly equally related to each other. Vertebrates therefore have a repertoire of seven superfamily members (three dystrophins, three dystrobevins, and one dystrotelin), with one lost in tetrapods. Most invertebrates studied have one member from each branch. Although the basic shared function which is implied by the common architecture of these distantly related proteins remains unclear, it clearly permeates metazoan biology.
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Weir AP, Morgan JE, Davies KE. A-utrophin up-regulation in mdx skeletal muscle is independent of regeneration. Neuromuscul Disord 2004; 14:19-23. [PMID: 14659408 DOI: 10.1016/j.nmd.2003.09.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Duchenne muscular dystrophy is a fatal childhood disease caused by mutations that abolish the expression of dystrophin in muscle. Utrophin is a paralogue of dystrophin and can functionally replace it in skeletal muscle. A method to induce utrophin up-regulation in muscle should therefore be therapeutically useful in Duchenne muscular dystrophy. The search for such a method needs to be informed by an understanding of the mechanisms controlling utrophin expression in muscle. Two full length utrophin isoforms are expressed: A and B. A-utrophin is up-regulated in dystrophin deficient skeletal muscle and we sought to test the hypothesis that this up-regulation occurs as a consequence of ongoing regeneration. We measured utrophin expression by immunohistochemistry and immunoblotting in the oesophageal outer muscular layer and in gamma-irradiated limb muscle from mdx mice. Skeletal muscle in these tissues is dystrophin deficient but not regenerating; we found that A-utrophin up-regulation still occurred. We conclude that utrophin up-regulation in skeletal muscle does not depend on regeneration. An alternative hypothesis involving competition for binding sites between utrophin and dystrophin is discussed. These results have important implications for future studies aiming to effect therapeutic utrophin up-regulation in Duchenne muscular dystrophy patients.
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Affiliation(s)
- Andrew P Weir
- Department of Human Anatomy and Genetics, University of Oxford, South Parks Rd, Oxford, UK
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10
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Scott JM, Li S, Harper SQ, Welikson R, Bourque D, DelloRusso C, Hauschka SD, Chamberlain JS. Viral vectors for gene transfer of micro-, mini-, or full-length dystrophin. Neuromuscul Disord 2002; 12 Suppl 1:S23-9. [PMID: 12206791 DOI: 10.1016/s0960-8966(02)00078-0] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Gene therapy for Duchenne muscular dystrophy will require methods to deliver gene constructs encoding functional versions of dystrophin to the vast majority of a patient's musculature. Obstacles to achieving these goals include identifying which forms of dystrophin would be effective in a clinical setting and developing gene delivery shuttles capable of carrying and expressing dystrophin cassettes without toxic or adverse immunologic consequences. We review here recent work from our laboratory to identify sequences within dystrophin that are required to prevent development of dystrophic changes in muscle or which might be able to correct pre-existing damage. We also describe work aimed at developing viral shuttle vectors able to carry and express these dystrophin cassettes at high levels and in a muscle-specific fashion. While great challenges remain in developing methods for systemic gene delivery, we show that a variety of viral vectors are able to carry and express therapeutic levels of dystrophin when delivered directly to mouse skeletal muscle.
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Affiliation(s)
- Jeannine M Scott
- Department of Neurology, University of Washington School of Medicine, Seattle, WA 98195, USA
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Rybakova IN, Patel JR, Davies KE, Yurchenco PD, Ervasti JM. Utrophin binds laterally along actin filaments and can couple costameric actin with sarcolemma when overexpressed in dystrophin-deficient muscle. Mol Biol Cell 2002; 13:1512-21. [PMID: 12006649 PMCID: PMC111123 DOI: 10.1091/mbc.01-09-0446] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2001] [Revised: 12/21/2001] [Accepted: 01/28/2002] [Indexed: 11/11/2022] Open
Abstract
Dystrophin is widely thought to mechanically link the cortical cytoskeleton with the muscle sarcolemma. Although the dystrophin homolog utrophin can functionally compensate for dystrophin in mice, recent studies question whether utrophin can bind laterally along actin filaments and anchor filaments to the sarcolemma. Herein, we have expressed full-length recombinant utrophin and show that the purified protein is fully soluble with a native molecular weight and molecular dimensions indicative of monomers. We demonstrate that like dystrophin, utrophin can form an extensive lateral association with actin filaments and protect actin filaments from depolymerization in vitro. However, utrophin binds laterally along actin filaments through contribution of acidic spectrin-like repeats rather than the cluster of basic repeats used by dystrophin. We also show that the defective linkage between costameric actin filaments and the sarcolemma in dystrophin-deficient mdx muscle is rescued by overexpression of utrophin. Our results demonstrate that utrophin and dystrophin are functionally interchangeable actin binding proteins, but that the molecular epitopes important for filament binding differ between the two proteins. More generally, our results raise the possibility that spectrin-like repeats may enable some members of the plakin family of cytolinkers to laterally bind and stabilize actin filaments.
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Affiliation(s)
- Inna N Rybakova
- Department of Physiology, University of Wisconsin Medical School, Madison 53706, USA
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Blake DJ, Weir A, Newey SE, Davies KE. Function and genetics of dystrophin and dystrophin-related proteins in muscle. Physiol Rev 2002; 82:291-329. [PMID: 11917091 DOI: 10.1152/physrev.00028.2001] [Citation(s) in RCA: 813] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The X-linked muscle-wasting disease Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. There is currently no effective treatment for the disease; however, the complex molecular pathology of this disorder is now being unravelled. Dystrophin is located at the muscle sarcolemma in a membrane-spanning protein complex that connects the cytoskeleton to the basal lamina. Mutations in many components of the dystrophin protein complex cause other forms of autosomally inherited muscular dystrophy, indicating the importance of this complex in normal muscle function. Although the precise function of dystrophin is unknown, the lack of protein causes membrane destabilization and the activation of multiple pathophysiological processes, many of which converge on alterations in intracellular calcium handling. Dystrophin is also the prototype of a family of dystrophin-related proteins, many of which are found in muscle. This family includes utrophin and alpha-dystrobrevin, which are involved in the maintenance of the neuromuscular junction architecture and in muscle homeostasis. New insights into the pathophysiology of dystrophic muscle, the identification of compensating proteins, and the discovery of new binding partners are paving the way for novel therapeutic strategies to treat this fatal muscle disease. This review discusses the role of the dystrophin complex and protein family in muscle and describes the physiological processes that are affected in Duchenne muscular dystrophy.
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Affiliation(s)
- Derek J Blake
- Medical Research Council, Functional Genetics Unit, Department of Human Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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Garcia-Tovar CG, Perez A, Luna J, Mena R, Osorio B, Aleman V, Mondragon R, Mornet D, Rendón A, Hernandez JM. Biochemical and histochemical analysis of 71 kDa dystrophin isoform (Dp71f) in rat brain. Acta Histochem 2001; 103:209-24. [PMID: 11368101 DOI: 10.1078/0065-1281-00591] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Dp71 is a member of the dystrophin family and the most abundant dmd gene product in the brain. In the present study, we focused on a short dystrophin transcript named Dp71f, which is alternatively spliced when exon 78 is absent The topographic localization of this protein in the encephalon has not been properly described yet, nor its cellular or subcellular localization, and even less its functions. Dp71f was found to be a cytoplasmic 70 kDa protein and localized in all encephalon regions studied. Double labeling using specific markers for various cell types confirmed Dp71f distribution in the cytoplasm of all cell types studied. Labeling was more conspicuous near the nucleus and diminished towards the periphery of cells. In some cases, we observed cells that were positive for actin and Dp71f in regions corresponding to lamellipodia-like structures. Dp71f and Dp71d isoforms were differently distributed. Our study is the first specific and unambiguous description of the topography and cellular localization patterns of Dp71f in brain, suggesting that Dp71f is a ubiquitous protein.
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Crawford GE, Faulkner JA, Crosbie RH, Campbell KP, Froehner SC, Chamberlain JS. Assembly of the dystrophin-associated protein complex does not require the dystrophin COOH-terminal domain. J Cell Biol 2000; 150:1399-410. [PMID: 10995444 PMCID: PMC2150715 DOI: 10.1083/jcb.150.6.1399] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dystrophin is a multidomain protein that links the actin cytoskeleton to laminin in the extracellular matrix through the dystrophin associated protein (DAP) complex. The COOH-terminal domain of dystrophin binds to two components of the DAP complex, syntrophin and dystrobrevin. To understand the role of syntrophin and dystrobrevin, we previously generated a series of transgenic mouse lines expressing dystrophins with deletions throughout the COOH-terminal domain. Each of these mice had normal muscle function and displayed normal localization of syntrophin and dystrobrevin. Since syntrophin and dystrobrevin bind to each other as well as to dystrophin, we have now generated a transgenic mouse deleted for the entire dystrophin COOH-terminal domain. Unexpectedly, this truncated dystrophin supported normal muscle function and assembly of the DAP complex. These results demonstrate that syntrophin and dystrobrevin functionally associate with the DAP complex in the absence of a direct link to dystrophin. We also observed that the DAP complexes in these different transgenic mouse strains were not identical. Instead, the DAP complexes contained varying ratios of syntrophin and dystrobrevin isoforms. These results suggest that alternative splicing of the dystrophin gene, which naturally generates COOH-terminal deletions in dystrophin, may function to regulate the isoform composition of the DAP complex.
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Affiliation(s)
- G E Crawford
- Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan 48109-0618, USA
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15
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Knuesel I, Bornhauser BC, Zuellig RA, Heller F, Schaub MC, Fritschy JM. Differential expression of utrophin and dystrophin in CNS neurons: an in situ hybridization and immunohistochemical study. J Comp Neurol 2000; 422:594-611. [PMID: 10861528 DOI: 10.1002/1096-9861(20000710)422:4<594::aid-cne8>3.0.co;2-q] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The cellular distribution of utrophin, the autosomal homologue of dystrophin, was investigated in developing and adult rat and mouse brain by in situ hybridization and immunohistochemistry. Digoxigenin-labeled cRNA probes complementary to N-terminal, rod-domain, and C-terminal encoding sequences of utrophin were used to differentiate between full-length and short C-terminal isoforms. Largely overlapping distribution patterns were seen for the three probes in neurons of cerebral cortex, accessory olfactory bulb, and several sensory and motor brainstem nuclei as well as in blood vessels, pia mater, and choroid plexus. The C-terminal probe was detected in addition in the main olfactory bulb, striatum, thalamic reticular nucleus, and hypothalamus, suggesting a selective expression of G-utrophin in these neurons. Western blot analysis with isoform-specific antisera confirmed the expression of both full-length and G-utrophin in brain. Immunohistochemically, only full-length utrophin was detected in neurons, in close association with the plasma membrane. In addition, intense staining was seen in blood vessels, meninges, and choroid plexus, selectively localized in the basolateral membrane of immunopositive epithelial cells. The expression pattern of utrophin was already established at early postnatal stages and did not change thereafter. Double-labeling analysis revealed that utrophin and dystrophin are differentially expressed on the cellular and subcellular levels in juvenile and adult brain. Likewise, in mice lacking full-length dystrophin isoforms (mdx mice), no change in utrophin expression and distribution could be detected in brain, although utrophin was markedly up-regulated in muscle cells. These results suggest that utrophin and dystrophin are independently regulated and have distinct functional roles in CNS neurons.
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Affiliation(s)
- I Knuesel
- Institute of Pharmacology, University of Zurich, CH-8057 Zurich, Switzerland
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16
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Gramolini AO, Wu J, Jasmin BJ. Regulation and functional significance of utrophin expression at the mammalian neuromuscular synapse. Microsc Res Tech 2000; 49:90-100. [PMID: 10757882 DOI: 10.1002/(sici)1097-0029(20000401)49:1<90::aid-jemt10>3.0.co;2-l] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Duchenne muscular dystrophy (DMD) is caused by the absence of full-length dystrophin molecules in skeletal muscle fibers. In normal muscle, dystrophin is found along the length of the sarcolemma where it links the intracellular actin cytoskeleton to the extracellular matrix, via the dystrophin-associated protein (DAP) complex. Several years ago, an autosomal homologue to dystrophin, termed utrophin, was identified and shown to be expressed in a variety of tissues, including skeletal muscle. However, in contrast to the localization of dystrophin in extrajunctional regions of muscle fibers, utrophin preferentially accumulates at the postsynaptic membrane of the neuromuscular junction in both normal and DMD adult muscle fibers. Since it has recently been suggested that the upregulation of utrophin might functionally compensate for the lack of dystrophin in DMD, considerable interest is now directed toward the elucidation of the various regulatory mechanisms presiding over expression of utrophin in normal and dystrophic skeletal muscle fibers. In this review, we discuss some of the most recent data relevant to our understanding of the impact of myogenic differentiation and innervation on the expression and localization of utrophin in skeletal muscle fibers.
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Affiliation(s)
- A O Gramolini
- Department of Cellular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Canada K1H 8M5
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17
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Zuellig RA, Bornhauser BC, Knuesel I, Heller F, Fritschy JM, Schaub MC. Identification and characterisation of transcript and protein of a new short N-terminal utrophin isoform. J Cell Biochem 2000; 77:418-31. [PMID: 10760950 DOI: 10.1002/(sici)1097-4644(20000601)77:3<418::aid-jcb7>3.0.co;2-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Dystrophin and utrophin are known to link the intracellular cytoskeleton to the extracellular matrix via a transmembraneous glycoprotein complex. Four short C-terminal isoforms (Dp71, Dp116, Dp140, and Dp260) are described for dystrophin and three for utrophin (Up71, Up113, and Up140). We describe here for the first time the existence of a 3.7-kb transcript and a 62-kDa protein in C6 glioma cells representing a short N-terminal isoform unique for utrophin (N-utrophin). More than 20 clones covering the entire coding region of utrophin were isolated from a rat C6 glioma cell cDNA library. Two clones were found to code for a protein with 539 amino acids. Its sequence is identical to that of the full-length utrophin, except for the last residue where Cys is replaced by Val. This isoform contains the actin binding domain (consisting of two calponin homology subdomains), followed by two spectrin-like repeats. A recombinant fragment corresponding to N-utrophin binds to F-actin in vitro with an equilibrium constant (affinity) K of 4.5 x 10(5) M(-1) and a stoichiometry of one fragment per around five actin monomers. Immunocytochemical staining of C6 glioma cells with antisera specific for different utrophin regions localised full-length utrophin in the submembraneous cortical actin layer as revealed by confocal microscopy. A distinct staining pattern for the N-utrophin was not detectable, although it was expected to localise at the actin stress fibers. It is assumed that it co-localises via the two spectrin-like repeats with the full-length utrophin at the cell membrane.
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Affiliation(s)
- R A Zuellig
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland
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18
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Mehler MF. Brain dystrophin, neurogenetics and mental retardation. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 2000; 32:277-307. [PMID: 10751678 DOI: 10.1016/s0165-0173(99)00090-9] [Citation(s) in RCA: 134] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Duchenne muscular dystrophy (DMD) and the allelic disorder Becker muscular dystrophy (BMD) are common X-linked recessive neuromuscular disorders that are associated with a spectrum of genetically based developmental cognitive and behavioral disabilities. Seven promoters scattered throughout the huge DMD/BMD gene locus normally code for distinct isoforms of the gene product, dystrophin, that exhibit nervous system developmental, regional and cell-type specificity. Dystrophin is a complex plasmalemmal-cytoskeletal linker protein that possesses multiple functional domains, autosomal and X-linked homologs and associated binding proteins that form multiunit signaling complexes whose composition is unique to each cellular and developmental context. Through additional interactions with a variety of proteins of the extracellular matrix, plasma membrane, cytoskeleton and distinct intracellular compartments, brain dystrophin acquires the capability to participate in the modulatory actions of a large number of cellular signaling pathways. During neural development, dystrophin is expressed within the neural tube and selected areas of the embryonic and postnatal neuraxis, and may regulate distinct aspects of neurogenesis, neuronal migration and cellular differentiation. By contrast, in the mature brain, dystrophin is preferentially expressed by specific regional neuronal subpopulations within proximal somadendritic microdomains associated with synaptic terminal membranes. Increasing experimental evidence suggests that in adult life, dystrophin normally modulates synaptic terminal integrity, distinct forms of synaptic plasticity and regional cellular signal integration. At a systems level, dystrophin may regulate essential components of an integrated sensorimotor attentional network. Dystrophin deficiency in DMD/BMD patients and in the mdx mouse model appears to impair intracellular calcium homeostasis and to disrupt multiple protein-protein interactions that normally promote information transfer and signal integration from the extracellular environment to the nucleus within regulated microdomains. In DMD/BMD, the individual profiles of cognitive and behavioral deficits, mental retardation and other phenotypic variations appear to depend on complex profiles of transcriptional regulation associated with individual dystrophin mutations that result in the corresponding presence or absence of individual brain dystrophin isoforms that normally exhibit developmental, regional and cell-type-specific expression and functional regulation. This composite experimental model will allow fine-level mapping of cognitive-neurogenetic associations that encompass the interrelationships between molecular, cellular and systems levels of signal integration, and will further our understanding of complex gene-environmental interactions and the pathogenetic basis of developmental disorders associated with mental retardation.
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Affiliation(s)
- M F Mehler
- Departments of Neurology, Neuroscience and Psychiatry, the Einstein Comprehensive Cancer Center, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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19
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Austin RC, Morris GE, Howard PL, Klamut HJ, Ray PN. Expression and synthesis of alternatively spliced variants of Dp71 in adult human brain. Neuromuscul Disord 2000; 10:187-93. [PMID: 10734266 DOI: 10.1016/s0960-8966(99)00105-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Transcripts encoding the 70-75 kDa C-terminal protein product of the dystrophin gene (Dp71) are alternatively spliced to generate multiple protein products in a number of adult human tissues. In this report, reverse transcriptase-polymerase chain reaction was used to clone and characterize a subpopulation of truncated Dp71 transcripts in adult human brain tissue which did not contain exons 71-74, resulting in an in-frame deletion of 330 bp encoding the syntrophin-binding domain. These truncated Dp71 transcripts are also alternatively spliced for exon 78. Immunoblot analysis, using dystrophin-specific C-terminal antibodies directed against epitopes in either exon 77 (MANDRA1), or 78 (1461), identified full-length dystrophin, Dp140 and Dp71, in total protein lysates from adult human brain tissue. In addition, a minor immunoreactive protein of approximately 58 kDa was also identified (designated Dp71 big up tri, open(110)). The observation that a monoclonal antibody directed against epitopes within exons 73-74 (MANEX7374A) failed to detect this 58 kDa protein provides definitive evidence that Dp71 big up tri, open(110) is derived from Dp71 transcripts deleted for the syntrophin-binding domain. These results, as well as previous findings, demonstrate that alternative splicing of Dp71 in the human brain generates a variety of mRNA transcripts encoding distinct protein variants of Dp71, and further supports the use of exon-specific antibodies in characterizing these variants. The presence of these Dp71 protein variants in brain tissue points to their interaction with various cellular proteins and their involvement in different cellular functions.
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Affiliation(s)
- R C Austin
- Department of Pathology and Molecular Medicine, McMaster University and the Hamilton Civic Hospitals Research Centre, 711 Concession Street, Hamilton, Ontario, Canada.
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20
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Amann KJ, Guo AW, Ervasti JM. Utrophin lacks the rod domain actin binding activity of dystrophin. J Biol Chem 1999; 274:35375-80. [PMID: 10585405 DOI: 10.1074/jbc.274.50.35375] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously identified a cluster of basic spectrin-like repeats in the dystrophin rod domain that binds F-actin through electrostatic interactions (Amann, K. J., Renley, B. A., and Ervasti, J. M. (1998) J. Biol. Chem. 273, 28419-28423). Because of the importance of actin binding to the presumed physiological role of dystrophin, we sought to determine whether the autosomal homologue of dystrophin, utrophin, shared this rod domain actin binding activity. We therefore produced recombinant proteins representing the cluster of basic repeats of the dystrophin rod domain (DYSR11-17) or the homologous region of the utrophin rod domain (UTROR11-16). Although UTROR11-16 is 64% similar and 41% identical to DYSR11-17, UTROR11-16 (pI = 4. 86) lacks the basic character of the repeats found in DYSR11-17 (pI = 7.44). By circular dichroism, gel filtration, and sedimentation velocity analysis, we determined that each purified recombinant protein had adopted a stable, predominantly alpha-helical fold and existed as a highly soluble monomer. DYSR11-17 bound F-actin with an apparent K(d) of 7.3 +/- 1.3 microM and a molar stoichiometry of 1:5. Significantly, UTROR11-16 failed to bind F-actin at concentrations as high as 100 microM. We present these findings as further support for the electrostatic nature of the interaction of the dystrophin rod domain with F-actin and suggest that utrophin interacts with the cytoskeleton in a manner distinct from dystrophin.
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Affiliation(s)
- K J Amann
- Graduate Program in Cellular and Molecular Biology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
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21
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Lumeng C, Phelps S, Crawford GE, Walden PD, Barald K, Chamberlain JS. Interactions between beta 2-syntrophin and a family of microtubule-associated serine/threonine kinases. Nat Neurosci 1999; 2:611-7. [PMID: 10404183 DOI: 10.1038/10165] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A screen for proteins that interact with beta 2-syntrophin led to the isolation of MAST205 (microtubule-associated serine/threonine kinase-205 kD) and a newly identified homologue, SAST (syntrophin-associated serine/threonine kinase). Binding studies showed that beta 2-syntrophin and MAST205/SAST associated via a PDZ-PDZ domain interaction. MAST205 colocalized with beta 2-syntrophin and utrophin at neuromuscular junctions. SAST colocalized with syntrophin in cerebral vasculature, spermatic acrosomes and neuronal processes. SAST and syntrophin were highly associated with purified microtubules and microtubule-associated proteins, whereas utrophin and dystrophin were only partially associated with microtubules. Our data suggest that MAST205 and SAST link the dystrophin/utrophin network with microtubule filaments via the syntrophins.
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Affiliation(s)
- C Lumeng
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor 48109-0618, USA
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