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1.  Genetic and clinical specificity of 26 symptomatic carriers for dystrophinopathies at pediatric age 
The molecular basis underlying the clinical variability in symptomatic Duchenne muscular dystrophy (DMD) carriers are still to be precised. We report 26 cases of early symptomatic DMD carriers followed in the French neuromuscular network. Clinical presentation, muscular histological analysis and type of gene mutation, as well as X-chromosome inactivation (XCI) patterns using DNA extracted from peripheral blood or muscle are detailed. The initial symptoms were significant weakness (88%) or exercise intolerance (27%). Clinical severity varied from a Duchenne-like progression to a very mild Becker-like phenotype. Cardiac dysfunction was present in 19% of the cases. Cognitive impairment was worthy of notice, as 27% of the carriers are concerned. The muscular analysis was always contributive, revealing muscular dystrophy (83%), mosaic in immunostaining (81%) and dystrophin abnormalities in western blot analysis (84%). In all, 73% had exonic deletions or duplications and 27% had point mutations. XCI pattern was biased in 62% of the cases. In conclusion, we report the largest series of manifesting DMD carriers at pediatric age and show that exercise intolerance and cognitive impairment may reveal symptomatic DMD carriers. The complete histological and immunohistological study of the muscle is the key of the diagnosis leading to the dystrophin gene analysis. Our study shows also that cognitive impairment in symptomatic DMD carriers is associated with mutations in the distal part of the DMD gene. XCI study does not fully explain the mechanisms as well as the wide spectrum of clinical phenotype, though a clear correlation between the severity of the phenotype and inactivation bias was observed.
PMCID: PMC3722679  PMID: 23299919
dystrophin; female carrier; X inactivation
2.  P2RX7 Purinoceptor: A Therapeutic Target for Ameliorating the Symptoms of Duchenne Muscular Dystrophy 
PLoS Medicine  2015;12(10):e1001888.
Duchenne muscular dystrophy (DMD) is the most common inherited muscle disease, leading to severe disability and death in young men. Death is caused by the progressive degeneration of striated muscles aggravated by sterile inflammation. The pleiotropic effects of the mutant gene also include cognitive and behavioral impairments and low bone density.
Current interventions in DMD are palliative only as no treatment improves the long-term outcome. Therefore, approaches with a translational potential should be investigated, and key abnormalities downstream from the absence of the DMD product, dystrophin, appear to be strong therapeutic targets. We and others have demonstrated that DMD mutations alter ATP signaling and have identified P2RX7 purinoceptor up-regulation as being responsible for the death of muscles in the mdx mouse model of DMD and human DMD lymphoblasts. Moreover, the ATP–P2RX7 axis, being a crucial activator of innate immune responses, can contribute to DMD pathology by stimulating chronic inflammation. We investigated whether ablation of P2RX7 attenuates the DMD model mouse phenotype to assess receptor suitability as a therapeutic target.
Methods and Findings
Using a combination of molecular, histological, and biochemical methods and behavioral analyses in vivo we demonstrate, to our knowledge for the first time, that genetic ablation of P2RX7 in the DMD model mouse produces a widespread functional attenuation of both muscle and non-muscle symptoms. In dystrophic muscles at 4 wk there was an evident recovery in key functional and molecular parameters such as improved muscle structure (minimum Feret diameter, p < 0.001), increased muscle strength in vitro (p < 0.001) and in vivo (p = 0.012), and pro-fibrotic molecular signatures. Serum creatine kinase (CK) levels were lower (p = 0.025), and reduced cognitive impairment (p = 0.006) and bone structure alterations (p < 0.001) were also apparent. Reduction of inflammation and fibrosis persisted at 20 mo in leg (p = 0.038), diaphragm (p = 0.042), and heart muscles (p < 0.001). We show that the amelioration of symptoms was proportional to the extent of receptor depletion and that improvements were observed following administration of two P2RX7 antagonists (CK, p = 0.030 and p = 0.050) without any detectable side effects. However, approaches successful in animal models still need to be proved effective in clinical practice.
These results are, to our knowledge, the first to establish that a single treatment can improve muscle function both short and long term and also correct cognitive impairment and bone loss in DMD model mice. The wide-ranging improvements reflect the convergence of P2RX7 ablation on multiple disease mechanisms affecting skeletal and cardiac muscles, inflammatory cells, brain, and bone. Given the impact of P2RX7 blockade in the DMD mouse model, this receptor is an attractive target for translational research: existing drugs with established safety records could potentially be repurposed for treatment of this lethal disease.
Dariusz Gorecki and colleagues investigate the effect of P2RX7 ablation on muscle, brain, and bone pathology in a DMD model mouse.
Editors' Summary
Muscular dystrophies are inherited diseases in which the body’s muscles gradually weaken and waste away. The most common and severe muscular dystrophy—Duchenne muscular dystrophy (DMD)—also includes cognitive (thinking) and behavioral impairments and low bone density as well as chronic inflammation. DMD affects about 1 in 3,500 boys; girls can be carriers of DMD but rarely have any symptoms. At birth, boys who carry a mutation (genetic change) in the gene that makes the protein dystrophin seem normal, but the symptoms of DMD soon begin to appear. Affected children may initially have difficulty walking or may find it hard to sit or stand independently. As they age, their muscle strength progressively declines, a process that is aggravated by sterile inflammation (an immune system response to tissue damage that occurs in the absence of an infectious agent), and most affected boys are confined to a wheelchair by the time they are 12 years old. The diaphragm and other muscles involved in breathing also weaken, and the heart muscle becomes enlarged. Consequently, few boys with DMD live beyond their early 20s, usually dying from breathing or heart problems. At present, there is no cure for DMD. However, physical therapy and treatment with steroids (intended to reduce sterile inflammation) can prolong the ability of patients to walk, and assisted ventilation can help with their breathing.
Why Was This Study Done?
One way to treat DMD under investigation is replacement of the defective dystrophin in muscles using gene therapy. Dystrophin normally forms structural scaffolds that sit in the membranes that surround muscle fibers and protect the fibers from damage during muscle contraction. In DMD, the loss of dystrophin, dystrophin-associated proteins, and specific signaling processes causes progressive muscle loss. Although gene therapy approaches that target dystrophin hold some promise, achieving sufficient dystrophin expression in all the crucial muscle groups to prevent progressive muscle damage is hard. Moreover, gene therapy targeted at muscles will not treat the non-muscle-related characteristics of DMD. Targeting an abnormality downstream of dystrophin might therefore be a better approach to the treatment of DMD. One such target is P2RX7. This purinoceptor was originally identified as a sensor of ATP released from damaged cells and is an activator of innate immune responses. Because upregulation of P2RX7 is responsible for muscle death in the mdx mouse model of DMD and for the death of human DMD lymphoblasts, in this study, the researchers investigate whether genetic ablation of P2RX7 can attenuate the DMD symptoms of the mdx mouse model.
What Did the Researchers Do and Find?
The researchers mated mdx mice and mice that lack the gene for P2RX7 to obtain Pf-mdx/P2RX7−/− mice, which make no functional dystrophin or P2RX7. They then compared the structure and function of the muscles (dystrophic pathology) in these mice with those in mdx mice. They also examined specific aspects of the behavior of the mice. At four weeks, there was improved muscle structure and strength, decreased inflammation, and decreased fibrosis (thickening and scarring of the connective tissue covering the muscles) in the Pf-mdx/P2RX7−/− mice compared to the mdx mice. P2RX7 ablation also reduced blood levels of creatinine kinase (a marker of muscle, heart, and brain injury), cognitive impairment, and bone structure alterations. Importantly, the reduction in inflammation and fibrosis was still evident at 20 months in the leg, diaphragm, and heart muscles of the Pf-mdx/P2RX7−/− mice compared to the mdx mice. Finally, the dystrophic pathology in mdx mice could also be reduced by treating these mice with P2RX7 antagonists (molecules that bind to P2RX7 and prevent its function).
What Do These Findings Mean?
These findings show that genetic ablation of P2RX7 can improve muscle function in the short and long term and can also correct cognitive impairment and bone loss in a mouse model of DMD. Thus, in mdx mice, P2RX7 ablation affects multiple disease mechanisms that affect skeletal and heart muscles, inflammatory cells, brain, and bone. Other preliminary findings suggest that P2RX7 blockade in mdx mice also improves DMD symptoms. These are promising results, but results in animals do not necessarily translate into effective clinical treatments. Nevertheless, these findings identify P2RX7 as an attractive target for the treatment of DMD, particularly since it might be possible to repurpose P2RX7 antagonists originally developed for the treatment of chronic pain for the treatment of DMD.
Additional Information
This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at
The US National Institute of Neurological Disorders and Stroke provides information on muscular dystrophy (in English and Spanish)
The US National Human Genome Research Institute also provides basic information on Duchenne muscular dystrophy and links to additional resources
The US Centers for Disease Control and Prevention has information about muscular dystrophy
The not-for-profit Nemours Foundation provides information about muscular dystrophy for parents, children, and teenagers (in English and Spanish)
The US not-for-profit organization Parent Project Muscular Dystrophy provides detailed information about all aspects of Duchenne muscular dystrophy and parents’ stories about Duchenne muscular dystrophy
MedlinePlus provides links to further resources on muscular dystrophy and an encyclopedia page on Duchenne muscular dystrophy (in English and Spanish)
Wikipedia has pages about Duchenne muscular dystrophy and P2RX7 (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
TREAT-NMD is a network for the neuromuscular field that provides an infrastructure to ensure that the most promising new therapies reach patients as quickly as possible
PMCID: PMC4604078  PMID: 26461208
3.  Prognostic value of X-chromosome inactivation in symptomatic female carriers of dystrophinopathy 
Between 8% and 22% of female carriers of DMD mutations exhibit clinical symptoms of variable severity. Development of symptoms in DMD mutation carriers without chromosomal rearrangements has been attributed to skewed X-chromosome inactivation (XCI) favouring predominant expression of the DMD mutant allele. However the prognostic use of XCI analysis is controversial. We aimed to evaluate the correlation between X-chromosome inactivation and development of clinical symptoms in a series of symptomatic female carriers of dystrophinopathy.
We reviewed the clinical, pathological and genetic features of twenty-four symptomatic carriers covering a wide spectrum of clinical phenotypes. DMD gene analysis was performed using MLPA and whole gene sequencing in blood DNA and muscle cDNA. Blood and muscle DNA was used for X-chromosome inactivation (XCI) analysis thought the AR methylation assay in symptomatic carriers and their female relatives, asymptomatic carriers as well as non-carrier females.
Symptomatic carriers exhibited 49.2% more skewed XCI profiles than asymptomatic carriers. The extent of XCI skewing in blood tended to increase in line with the severity of muscle symptoms. Skewed XCI patterns were found in at least one first-degree female relative in 78.6% of symptomatic carrier families. No mutations altering XCI in the XIST gene promoter were found.
Skewed XCI is in many cases familial inherited. The extent of XCI skewing is related to phenotype severity. However, the assessment of XCI by means of the AR methylation assay has a poor prognostic value, probably because the methylation status of the AR gene in muscle may not reflect in all cases the methylation status of the DMD gene.
PMCID: PMC3492175  PMID: 23092449
Dystrophin; DMD; Symptomatic carrier; Duchenne muscular dystrophy; Becker muscular dystrophy; X-chromosome inactivation
4.  Clinical and Genetic Characterization of Manifesting Carriers of DMD Mutations 
Neuromuscular disorders : NMD  2010;20(8):499-504.
Manifesting carriers of DMD gene mutations may present diagnostic challenges, particularly in the absence of a family history of dystrophinopathy. We review the clinical and genetic features in fifteen manifesting carriers identified among 860 subjects within the United Dystrophinopathy Project, a large clinical dystrophinopathy cohort whose members undergo comprehensive DMD mutation analysis. We defined manifesting carriers as females with significant weakness, excluding those with only myalgias/cramps. DNA extracted from peripheral blood was used to study X chromosome inactivation patterns. Among these manifesting carriers, age at symptom onset ranged from 2 to 47 years. Seven had no family history and eight had male relatives with Duchene muscular dystrophy (DMD). Clinical severity among the manifesting carriers varied from a DMD-like progression to a very mild Becker muscular dystrophy-like phenotype. Eight had exonic deletions or duplications and six had point mutations. One patient had two mutations (an exonic deletion and a splice site mutation), consistent with a heterozygous compound state. The X chromosome inactivation pattern was skewed toward nonrandom in four out of seven informative deletions or duplications but was random in all cases with nonsense mutations. We present the results of DMD mutation analysis in this manifesting carrier cohort, including the first example of a presumably compound heterozygous DMD mutation. Our results demonstrate that improved molecular diagnostic methods facilitate the identification of DMD mutations in manifesting carriers, and confirm the heterogeneity of mutational mechanisms as well as the wide spectrum of phenotypes.
PMCID: PMC2944769  PMID: 20630757
manifesting carriers; dystrophinopathy; DMD; dystrophin; X-chromosome inactivation; Duchenne muscular dystrophy; Becker muscular dystrophy
5.  Clinical and Genetic Characterization of Female Dystrophinopathy 
Background and Purpose
Duchenne and Becker muscular dystrophies are the most common X-linked recessive muscular dystrophies. Dystrophin gene mutations usually affect men, but reportedly 2.5-7.8% of women are affected and are classified as symptomatic carriers. The aim of this study was to clinically and genetically characterize symptomatic female dystrophinopathy carriers.
The clinical and genetic data of 11 female dystrophinopathy carriers among 285 patients who underwent multiplex ligation-dependent probe amplification (MLPA) analysis for the dystrophin gene were reviewed. Women with muscle weakness and/or dilated cardiomyopathy were classified as symptomatic carriers, while subjects with high serum creatine kinase (CK) levels and/or minor myopathic signs such as muscle cramps and myalgia were classified as asymptomatic.
Twelve female carriers were identified, but 1 symptomatic carrier who also had Turner syndrome was excluded from the study. Of the 11 included female carriers, 4 were symptomatic and 7 were asymptomatic. The age at symptom onset in the symptomatic female carriers ranged from 15 to 31 years (mean, 30.6 years), and the age at diagnosis for asymptomatic carriers ranged from 4 to 38 years (mean, 24.5 years). Serum CK levels were markedly elevated (mean, 1,301 IU/mL) in three of the four (75%) symptomatic female carriers, and mildly elevated in three of the seven (42%) asymptomatic female carriers. Symptomatic female carriers typically presented with asymmetric bilateral leg weakness as the initial symptom, with aggravated symptoms after labor.
Female dystrophinopathy is not uncommon, and it is an important factor with respect to males with dystrophinopathy who may be born to such patients. Screening with MLPA is useful because it can aid in early diagnosis and appropriate management.
PMCID: PMC4507379  PMID: 26022459
dystrophinopathy; female; multiplex ligation-dependent probe amplification
6.  Microarray-based mutation detection in the dystrophin gene 
Human mutation  2008;29(9):1091-1099.
Duchenne and Becker muscular dystrophies (DMD and BMD) are X-linked recessive neuromuscular disorders caused by mutations in the dystrophin gene affecting approximately 1 in 3,500 males. The human dystrophin gene spans > 2,200 kb, or roughly 0.1% of the genome, and is composed of 79 exons. The mutational spectrum of disease-causing alleles, including exonic copy number variations (CNVs), is complex. Deletions account for approximately 65% of DMD mutations and 85% of BMD mutations. Duplications occur in approximately 6–10% of males with either DMD or BMD. The remaining 30–35% of mutations consist of small deletions, insertions, point mutations, or splicing mutations, most of which introduce a premature stop codon. Laboratory analysis of dystrophin can be used to confirm a clinical diagnosis of DMD, characterize the type of dystrophin mutation, and perform prenatal testing and carrier testing for females. Current dystrophin diagnostic assays involve a variety of methodologies, including multiplex PCR, Southern blot analysis, MLPA, DOVAM-S, and SCAIP; however, these methods are time-consuming, laborious, and do not accurately detect duplication mutations in the dystrophin gene. Furthermore, carrier testing in females is often difficult when a related affected male is unavailable. Here we describe the development, design, validation, and implementation of a high-resolution CGH microarray-based approach capable of accurately detecting both deletions and duplications in the dystrophin gene. This assay can be readily adopted by clinical molecular testing laboratories and represents a rapid, cost-effective approach for screening a large gene, such as dystrophin.
PMCID: PMC2574813  PMID: 18663755
dystrophin; microarray; CGH array; Duchenne Muscular Dystrophy; DMD; Becker Muscular Dystrophy; BMD; exonic-copy number variation; CNV
7.  Modeling and study of the mechanism of dilated cardiomyopathy using induced pluripotent stem cells derived from individuals with Duchenne muscular dystrophy 
Disease Models & Mechanisms  2015;8(5):457-466.
Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene (DMD), and is characterized by progressive weakness in skeletal and cardiac muscles. Currently, dilated cardiomyopathy due to cardiac muscle loss is one of the major causes of lethality in late-stage DMD patients. To study the molecular mechanisms underlying dilated cardiomyopathy in DMD heart, we generated cardiomyocytes (CMs) from DMD and healthy control induced pluripotent stem cells (iPSCs). DMD iPSC-derived CMs (iPSC-CMs) displayed dystrophin deficiency, as well as the elevated levels of resting Ca2+, mitochondrial damage and cell apoptosis. Additionally, we found an activated mitochondria-mediated signaling network underlying the enhanced apoptosis in DMD iPSC-CMs. Furthermore, when we treated DMD iPSC-CMs with the membrane sealant Poloxamer 188, it significantly decreased the resting cytosolic Ca2+ level, repressed caspase-3 (CASP3) activation and consequently suppressed apoptosis in DMD iPSC-CMs. Taken together, using DMD patient-derived iPSC-CMs, we established an in vitro model that manifests the major phenotypes of dilated cardiomyopathy in DMD patients, and uncovered a potential new disease mechanism. Our model could be used for the mechanistic study of human muscular dystrophy, as well as future preclinical testing of novel therapeutic compounds for dilated cardiomyopathy in DMD patients.
Highlighted Article: Patient-derived induced pluripotent stem cells are used to establish an in vitro model of DMD-associated cardiomyopathy that could be used for future preclinical testing.
PMCID: PMC4415895  PMID: 25791035
Dilated cardiomyopathy; Duchenne muscular dystrophy; Induced pluripotent stem cells
8.  Porcine Zygote Injection with Cas9/sgRNA Results in DMD-Modified Pig with Muscle Dystrophy 
Dystrophinopathy, including Duchenne muscle dystrophy (DMD) and Becker muscle dystrophy (BMD) is an incurable X-linked hereditary muscle dystrophy caused by a mutation in the DMD gene in coding dystrophin. Advances in further understanding DMD/BMD for therapy are expected. Studies on mdx mice and dogs with muscle dystrophy provide limited insight into DMD disease mechanisms and therapeutic testing because of the different pathological manifestations. Miniature pigs share similar physiology and anatomy with humans and are thus an excellent animal model of human disease. Here, we successfully achieved precise DMD targeting in Chinese Diannan miniature pigs by co-injecting zygotes with Cas9 mRNA and sgRNA targeting DMD. Two piglets were obtained after embryo transfer, one of piglets was identified as DMD-modified individual via traditional cloning, sequencing and T7EN1 cleavage assay. An examination of targeting rates in the DMD-modified piglet revealed that sgRNA:Cas9-mediated on-target mosaic mutations were 70% and 60% of dystrophin alleles in skeletal and smooth muscle, respectively. Meanwhile, no detectable off-target mutations were found, highlighting the high specificity of genetic modification using CRISPR/Cas9. The DMD-modified piglet exhibited degenerative and disordered phenotypes in skeletal and cardiac muscle, and declining thickness of smooth muscle in the stomach and intestine. In conclusion, we successfully generated myopathy animal model by modifying the DMD via CRISPR/Cas9 system in a miniature pig.
PMCID: PMC5085701  PMID: 27735844
CRISPR/Cas9; DMD; pig; disease model; gene editing
9.  The Effects of Low Levels of Dystrophin on Mouse Muscle Function and Pathology 
PLoS ONE  2012;7(2):e31937.
Duchenne muscular dystrophy (DMD) is a severe progressive muscular disorder caused by reading frame disrupting mutations in the DMD gene, preventing the synthesis of functional dystrophin. As dystrophin provides muscle fiber stability during contractions, dystrophin negative fibers are prone to exercise-induced damage. Upon exhaustion of the regenerative capacity, fibers will be replaced by fibrotic and fat tissue resulting in a progressive loss of function eventually leading to death in the early thirties. With several promising approaches for the treatment of DMD aiming at dystrophin restoration in clinical trials, there is an increasing need to determine more precisely which dystrophin levels are sufficient to restore muscle fiber integrity, protect against muscle damage and improve muscle function.
To address this we generated a new mouse model (mdx-XistΔhs) with varying, low dystrophin levels (3–47%, mean 22.7%, stdev 12.1, n = 24) due to skewed X-inactivation. Longitudinal sections revealed that within individual fibers, some nuclei did and some did not express dystrophin, resulting in a random, mosaic pattern of dystrophin expression within fibers.
Mdx-XistΔhs, mdx and wild type females underwent a 12 week functional test regime consisting of different tests to assess muscle function at base line, or after chronic treadmill running exercise. Overall, mdx-XistΔhs mice with 3–14% dystrophin outperformed mdx mice in the functional tests. Improved histopathology was observed in mice with 15–29% dystrophin and these levels also resulted in normalized expression of pro-inflammatory biomarker genes, while for other parameters >30% of dystrophin was needed. Chronic exercise clearly worsened pathology, which needed dystrophin levels >20% for protection. Based on these findings, we conclude that while even dystrophin levels below 15% can improve pathology and performance, levels of >20% are needed to fully protect muscle fibers from exercise-induced damage.
PMCID: PMC3281102  PMID: 22359642
10.  The DMD Locus Harbours Multiple Long Non-Coding RNAs Which Orchestrate and Control Transcription of Muscle Dystrophin mRNA Isoforms 
PLoS ONE  2012;7(9):e45328.
The 2.2 Mb long dystrophin (DMD) gene, the largest gene in the human genome, corresponds to roughly 0.1% of the entire human DNA sequence. Mutations in this gene cause Duchenne muscular dystrophy and other milder X-linked, recessive dystrophinopathies. Using a custom-made tiling array, specifically designed for the DMD locus, we identified a variety of novel long non-coding RNAs (lncRNAs), both sense and antisense oriented, whose expression profiles mirror that of DMD gene. Importantly, these transcripts are intronic in origin and specifically localized to the nucleus and are transcribed contextually with dystrophin isoforms or primed by MyoD-induced myogenic differentiation. Furthermore, their forced ectopic expression in both human muscle and neuronal cells causes a specific and negative regulation of endogenous dystrophin full length isoforms and significantly down-regulate the activity of a luciferase reporter construct carrying the minimal promoter regions of the muscle dystrophin isoform. Consistent with this apparently repressive role, we found that, in muscle samples of dystrophinopathic female carriers, lncRNAs expression levels inversely correlate with those of muscle full length DMD isoforms. Overall these findings unveil an unprecedented complexity of the transcriptional pattern of the DMD locus and reveal that DMD lncRNAs may contribute to the orchestration and homeostasis of the muscle dystrophin expression pattern by either selective targeting and down-modulating the dystrophin promoter transcriptional activity.
PMCID: PMC3448672  PMID: 23028937
11.  Dysfunctional Muscle and Liver Glycogen Metabolism in mdx Dystrophic Mice 
PLoS ONE  2014;9(3):e91514.
Duchenne muscular dystrophy (DMD) is a severe, genetic muscle wasting disorder characterised by progressive muscle weakness. DMD is caused by mutations in the dystrophin (dmd) gene resulting in very low levels or a complete absence of the dystrophin protein, a key structural element of muscle fibres which is responsible for the proper transmission of force. In the absence of dystrophin, muscle fibres become damaged easily during contraction resulting in their degeneration. DMD patients and mdx mice (an animal model of DMD) exhibit altered metabolic disturbances that cannot be attributed to the loss of dystrophin directly. We tested the hypothesis that glycogen metabolism is defective in mdx dystrophic mice.
Dystrophic mdx mice had increased skeletal muscle glycogen (79%, (P<0.01)). Skeletal muscle glycogen synthesis is initiated by glycogenin, the expression of which was increased by 50% in mdx mice (P<0.0001). Glycogen synthase activity was 12% higher (P<0.05) but glycogen branching enzyme activity was 70% lower (P<0.01) in mdx compared with wild-type mice. The rate-limiting enzyme for glycogen breakdown, glycogen phosphorylase, had 62% lower activity (P<0.01) in mdx mice resulting from a 24% reduction in PKA activity (P<0.01). In mdx mice glycogen debranching enzyme expression was 50% higher (P<0.001) together with starch-binding domain protein 1 (219% higher; P<0.01). In addition, mdx mice were glucose intolerant (P<0.01) and had 30% less liver glycogen (P<0.05) compared with control mice. Subsequent analysis of the enzymes dysregulated in skeletal muscle glycogen metabolism in mdx mice identified reduced glycogenin protein expression (46% less; P<0.05) as a possible cause of this phenotype.
We identified that mdx mice were glucose intolerant, and had increased skeletal muscle glycogen but reduced amounts of liver glycogen.
PMCID: PMC3953428  PMID: 24626262
12.  Three Cases of Manifesting Female Carriers in Patients with Duchenne Muscular Dystrophy 
Yonsei Medical Journal  2010;52(1):192-195.
Duchenne muscular dystrophy usually affects males. However, females are also affected in rare instances. Approximately 8% of female Duchenne muscular dystrophy (DMD) carriers are manifesting carriers and have muscle weakness to some extent. We investigated the clinical features of 3 female patients with dystrophinopathy diagnosed by clinical, pathological, and genetic studies at our neuromuscular disease clinic. The onset age of manifesting symptoms varied (8-28 years). Muscle weakness grade varied as follows: patient 1 showed asymmetrical bilateral proximal upper and lower extremities weakness, patient 2 showed asymmetrical bilateral upper extremities weakness similar to scapulohumoral muscular dystrophy, and patient 3 had only bilateral asymmetric proximal lower extremities weakness. Two patients had familial histories of DMD (their sons were diagnosed with DMD), but the 1 remaining patient had no familial history of DMD. The serum creatine kinase level was elevated in all patients, but it was not correlated with muscular weakness. An electromyography study showed findings of myopathy in all patients. One patient was diagnosed with a DMD carrier by a muscle biopsy with an immunohistochemical stain (dystrophin). The remaining 2 patients with familial history of DMD were diagnosed by multiplex ligation-dependent probe amplification (MLPA). There were inconsistent clinical features in the female carriers. An immunohistochemical analysis of dystrophin could be useful for female carrier patients. Also, multiplex ligation-dependent probe amplification is essential for the diagnosis of a manifesting female carrier DMD in female myopathic patients because conventional multiplex PCR could not detect the duplication and is less accurate compared to MLPA.
PMCID: PMC3017697  PMID: 21155054
Dystrophinopathy; female carrier; multiplex ligation-dependent probe amplification
13.  Genetic Analysis of Dystrophin Gene for Affected Male and Female Carriers with Duchenne/Becker Muscular Dystrophy in Korea 
Journal of Korean Medical Science  2012;27(3):274-280.
Duchenne and Becker muscular dystrophy (DMD/BMD) are X-linked recessive disorders caused by mutation in dystrophin gene. We analyzed the results of a genetic test in 29 DMD/BMD patients, their six female relatives, and two myopathic female patients in Korea. As the methods developed, we applied different procedures for dystrophin gene analysis; initially, multiplex polymerase chain reaction was used, followed by multiplex ligation-dependent probe amplification (MLPA). Additionally, we used direct DNA sequencing for some patients who had negative results using the above methods. The overall mutation detection rate was 72.4% (21/29) in DMD/BMD patients, identifying deletions in 58.6% (17/29). Most of the deletions were confined to the central hot spot region between exons 44 and 55 (52.9%, 7/19). The percentage of deletions and duplications revealed by MLPA was 45.5% (5/11) and 27.2% (3/11), respectively. Using the MLPA method, we detected mutations confirming their carrier status in all female relatives and symptomatic female patients. In one patient in whom MLPA revealed a single exon deletion of the dystrophin gene, subsequent DNA sequencing analysis identified a novel nonsense mutation (c.4558G > T; Gln1520X). The MLPA assay is a useful quantitative method for detecting mutation in asymptomatic or symptomatic carriers as well as DMD/BMD patients.
PMCID: PMC3286774  PMID: 22379338
Gene Amplification; Duchenne/Becker Muscular Dystrophy; Deletion; Duplication
14.  Complex genomic rearrangements in the dystrophin gene due to replication-based mechanisms 
Genomic rearrangements such as intragenic deletions and duplications are the most prevalent type of mutations in the dystrophin gene resulting in Duchenne and Becker muscular dystrophy (D/BMD). These copy number variations (CNVs) are nonrecurrent and can result from either nonhomologous end joining (NHEJ) or microhomology-mediated replication-dependent recombination (MMRDR). We characterized five DMD patients with complex genomic rearrangements using a combination of MLPA/mRNA transcript analysis/custom array comparative hybridization arrays (CGH) and breakpoint sequence analysis to investigate the mechanisms for these rearrangements. Two patients had complex rearrangements that involved microhomologies at breakpoints. One patient had a noncontiguous insertion of 89.7 kb chromosome 4 into intron 43 of DMD involving three breakpoints with 2–5 bp microhomology at the junctions. A second patient had an inversion of exon 44 flanked by intronic deletions with two breakpoint junctions each showing 2 bp microhomology. The third patient was a female with an inherited deletion of exon 47 in DMD on the maternal allele and a de novo noncontiguous duplication of exons 45–49 in DMD and MID1 on the paternal allele. The other two patients harbored complex noncontiguous duplications within the dystrophin gene. We propose a replication-based mechanisms for all five complex DMD rearrangements. This study identifies additional underlying mechanisms in DMD, and provides insight into the molecular bases of these genomic rearrangements.
PMCID: PMC4303224  PMID: 25614876
Duchenne muscular dystrophy; dystrophin; MMRDR; mRNA; rearrangement; replication
15.  Clinical and molecular characterization of a cohort of patients with novel nucleotide alterations of the Dystrophin gene detected by direct sequencing 
BMC Medical Genetics  2011;12:37.
Duchenne and Becker Muscular dystrophies (DMD/BMD) are allelic disorders caused by mutations in the dystrophin gene, which encodes a sarcolemmal protein responsible for muscle integrity. Deletions and duplications account for approximately 75% of mutations in DMD and 85% in BMD. The implementation of techniques allowing complete gene sequencing has focused attention on small point mutations and other mechanisms underlying complex rearrangements.
We selected 47 patients (41 families; 35 DMD, 6 BMD) without deletions and duplications in DMD gene (excluded by multiplex ligation-dependent probe amplification and multiplex polymerase chain reaction analysis). This cohort was investigated by systematic direct sequence analysis to study sequence variation. We focused our attention on rare mutational events which were further studied through transcript analysis.
We identified 40 different nucleotide alterations in DMD gene and their clinical correlates; altogether, 16 mutations were novel. DMD probands carried 9 microinsertions/microdeletions, 19 nonsense mutations, and 7 splice-site mutations. BMD patients carried 2 nonsense mutations, 2 splice-site mutations, 1 missense substitution, and 1 single base insertion. The most frequent stop codon was TGA (n = 10 patients), followed by TAG (n = 7) and TAA (n = 4). We also analyzed the molecular mechanisms of five rare mutational events. They are two frame-shifting mutations in the DMD gene 3'end in BMD and three novel splicing defects: IVS42: c.6118-3C>A, which causes a leaky splice-site; c.9560A>G, which determines a cryptic splice-site activation and c.9564-426 T>G, which creates pseudoexon retention within IVS65.
The analysis of our patients' sample, carrying point mutations or complex rearrangements in DMD gene, contributes to the knowledge on phenotypic correlations in dystrophinopatic patients and can provide a better understanding of pre-mRNA maturation defects and dystrophin functional domains. These data can have a prognostic relevance and can be useful in directing new therapeutic approaches, which rely on a precise definition of the genetic defects as well as their molecular consequences.
PMCID: PMC3061890  PMID: 21396098
16.  Genetic correction of dystrophin deficiency and skeletal muscle remodeling in adult MDX mouse via transplantation of retroviral producer cells. 
Journal of Clinical Investigation  1997;100(3):620-628.
Duchenne muscular dystrophy (DMD) is an X-linked, lethal disease caused by mutations of the dystrophin gene. No effective therapy is available, but dystrophin gene transfer to skeletal muscle has been proposed as a treatment for DMD. We have developed a strategy for efficient in vivo gene transfer of dystrophin cDNA into regenerating skeletal muscle. Retroviral producer cells, which release a vector carrying the therapeutically active dystrophin minigene, were mitotically inactivated and transplanted in adult nude/mdx mice. Transplantation of 3 x 10(6) producer cells in a single site of the tibialis anterior muscle resulted in the transduction of between 5.5 and 18% total muscle fibers. The same procedure proved also feasible in immunocompetent mdx mice under short-term pharmacological immunosuppression. Minidystrophin expression was stable for up to 6 mo and led to alpha-sarcoglycan reexpression. Muscle stem cells could be transduced in vivo using this procedure. Transduced dystrophic skeletal muscle showed evidence of active remodeling reminiscent of the genetic normalization process which takes place in female DMD carriers. Overall, these results demonstrate that retroviral-mediated dystrophin gene transfer via transplantation of producer cells is a valid approach towards the long-term goal of gene therapy of DMD.
PMCID: PMC508230  PMID: 9239410
17.  Functional significance of dystrophin positive fibres in Duchenne muscular dystrophy. 
Archives of Disease in Childhood  1993;68(5):632-636.
The age when boys lose the ability to walk independently is one of the milestones in the progression of Duchenne muscular dystrophy (DMD). We have used this as a measure of disease severity in a group of 30 patients with DMD and six patients with intermediate Duchenne/Becker dystrophy (D/BMD). Dystrophin analysis was performed on tissue sections and western blots of muscle biopsy specimens from these patients and the relationships that were found between clinical severity and abundance of dystrophin labelling are reported. All patients with intermediate D/BMD had dystrophin labelling that was detected on sections and blots. Weak dystrophin labelling was found in sections from 21/30 DMD cases and on blots in 18/30 cases. Two non-exclusive patterns of dystrophin labelling were observed on sections: very clear labelling on a small percentage of fibres (usually < 1%) or very weak labelling on a much higher proportion (about 25%). The mean age at loss of mobility among the DMD patients with no dystrophin labelling on tissue sections was 7.9 years (range 6.3-9.5) while the mean age among those with some labelling was 9.9 years (range 8.0-11.9); this is a significant difference. Quantitative estimates of dystrophin abundance were obtained from densitometric analysis of dystrophin bands on blots. In the whole group of 36 patients, a significant positive relationship was found between the abundance of dystrophin and the age at loss of independent mobility. It is concluded that even the very low concentrations of dystrophin found in DMD patients may have some functional significance.
PMCID: PMC1029331  PMID: 8323331
18.  Enhanced currents through L-type calcium channels in cardiomyocytes disturb the electrophysiology of the dystrophic heart 
Duchenne muscular dystrophy (DMD), induced by mutations in the gene encoding for the cytoskeletal protein dystrophin, is an inherited disease characterized by progressive muscle weakness. Besides the relatively well characterized skeletal muscle degenerative processes, DMD is also associated with cardiac complications. These include cardiomyopathy development and cardiac arrhythmias. The current understanding of the pathomechanisms in the heart is very limited, but recent research indicates that dysfunctional ion channels in dystrophic cardiomyocytes play a role. The aim of the present study was to characterize abnormalities in L-type calcium channel function in adult dystrophic ventricular cardiomyocytes. By using the whole cell patch clamp technique, the properties of currents through calcium channels in ventricular cardiomyocytes isolated from the hearts of normal and dystrophic adult mice were compared. Besides the commonly used dystrophin-deficient mdx mouse model for human DMD, we also used mdx-utr mice which are both dystrophin- and utrophin-deficient. We found that calcium channel currents were significantly increased, and channel inactivation was reduced in dystrophic cardiomyocytes. Both effects enhance the calcium influx during an action potential (AP). Whereas the AP in dystrophic mouse cardiomyocytes was nearly normal, implementation of the enhanced dystrophic calcium conductance in a computer model of a human ventricular cardiomyocyte considerably prolonged the AP. Finally, the described dystrophic calcium channel abnormalities entailed alterations in the electrocardiograms of dystrophic mice. We conclude that gain of function in cardiac L-type calcium channels may disturb the electrophysiology of the dystrophic heart and thereby cause arrhythmias.
PMCID: PMC4892346  PMID: 24337461
cardiac action potential; Duchenne muscular dystrophy; L-type calcium channels; dystrophin-deficient mouse models; ventricular cardiomyocytes
19.  Assessment of the structural and functional impact of in-frame mutations of the DMD gene, using the tools included in the eDystrophin online database 
Dystrophin is a large essential protein of skeletal and heart muscle. It is a filamentous scaffolding protein with numerous binding domains. Mutations in the DMD gene, which encodes dystrophin, mostly result in the deletion of one or several exons and cause Duchenne (DMD) and Becker (BMD) muscular dystrophies. The most common DMD mutations are frameshift mutations resulting in an absence of dystrophin from tissues. In-frame DMD mutations are less frequent and result in a protein with partial wild-type dystrophin function. The aim of this study was to highlight structural and functional modifications of dystrophin caused by in-frame mutations.
Methods and results
We developed a dedicated database for dystrophin, the eDystrophin database. It contains 209 different non frame-shifting mutations found in 945 patients from a French cohort and previous studies. Bioinformatics tools provide models of the three-dimensional structure of the protein at deletion sites, making it possible to determine whether the mutated protein retains the typical filamentous structure of dystrophin. An analysis of the structure of mutated dystrophin molecules showed that hybrid repeats were reconstituted at the deletion site in some cases. These hybrid repeats harbored the typical triple coiled-coil structure of native repeats, which may be correlated with better function in muscle cells.
This new database focuses on the dystrophin protein and its modification due to in-frame deletions in BMD patients. The observation of hybrid repeat reconstitution in some cases provides insight into phenotype-genotype correlations in dystrophin diseases and possible strategies for gene therapy. The eDystrophin database is freely available:
PMCID: PMC3748829  PMID: 22776072
Dystrophin; DMD gene mutations; Spectrin-like repeats; Duchenne muscular dystrophy; Becker muscular dystrophy; Phenotype-genotype correlation
20.  Two novel missense mutations in the myostatin gene identified in Japanese patients with Duchenne muscular dystrophy 
BMC Medical Genetics  2007;8:19.
Myostatin is a negative regulator of skeletal muscle growth. Truncating mutations in the myostatin gene have been reported to result in gross muscle hypertrophy. Duchenne muscular dystrophy (DMD), the most common lethal muscle wasting disease, is a result of an absence of muscle dystrophin. Although this disorder causes a rather uniform pattern of muscle wasting, afflicted patients display phenotypic variability. We hypothesized that genetic variation in myostatin is a modifier of the DMD phenotype.
We analyzed 102 Japanese DMD patients for mutations in the myostatin gene.
Two polymorphisms that are commonly observed in Western countries, p.55A>T and p.153K>R, were not observed in these Japanese patients. An uncommon polymorphism of p.164E>K was uncovered in four cases; each patient was found to be heterozygous for this polymorphism, which had the highest frequency of the polymorphism observed in the Japanese patients. Remarkably, two patients were found to be heterozygous for one of two novel missense mutations (p.95D>H and p.156L>I). One DMD patient carrying a novel missense mutation of p.95D>H was not phenotypically different from the non-carriers. The other DMD patient was found to carry both a novel mutation (p.156L>I) and a known polymorphism (p.164E>K) in one allele, although his phenotype was not significantly modified. Any nucleotide change creating a target site for micro RNAs was not disclosed in the 3' untranslated region.
Our results indicate that heterozygous missense mutations including two novel mutations did not produce an apparent increase in muscle strength in Japanese DMD cases, even in a patient carrying two missense mutations.
PMCID: PMC1855920  PMID: 17428346
21.  Integrated study of 100 patients with Xp21 linked muscular dystrophy using clinical, genetic, immunochemical, and histopathological data. Part 3. Differential diagnosis and prognosis. 
Journal of Medical Genetics  1993;30(9):745-751.
This report is the third part of a trilogy from a multidisciplinary study which was undertaken to investigate gene and protein expression in a large cohort of patients with well defined and diverse clinical phenotypes. The aim of part 3 was to review which of the analytical techniques that we had used would be the most useful for differential diagnosis, and which would provide the most accurate indication of disease severity. Careful clinical appraisal is very important and every DMD patient was correctly diagnosed on this basis. In contrast, half of the sporadic BMD patients and all of the sporadic female patients had received different tentative diagnoses based on clinical assessments alone. Sequential observations of quantitative parameters (such as the time taken to run a fixed distance) were found to be useful clinical indicators for prognosis. Intellectual problems might modify the impression of physical ability in patients presenting at a young age. Histopathological assessment was accurate for DMD but differentiation between BMD and other disorders was more difficult, as was the identification of manifesting carriers. Our data on a small number of women with symptoms of muscle disease indicate that abnormal patterns of dystrophin labelling on sections may be an effective way of differentiating between female patients with a form of limb girdle dystrophy and those carrying a defective Xp21 gene. Dystrophin gene analysis detects deletions/duplications in 50 to 90% of male patients and is the most effective non-invasive technique for diagnosis. Quantitative Western blotting, however, would differentiate between all Xp21 and non-Xp21 male patients. In this study we found a clear relationship between increased dystrophin abundance (determined by densitometric analysis of blots) and clinical condition, with a correlation between dystrophin abundance and the age at loss of independent mobility among boys with DMD and intermediate D/BMD. This indicates that blotting is the most sensitive and accurate technique for diagnosis and prognosis.
PMCID: PMC1016531  PMID: 8411069
22.  The Polyproline Site in Hinge 2 Influences the Functional Capacity of Truncated Dystrophins 
PLoS Genetics  2010;6(5):e1000958.
Mutations in dystrophin can lead to Duchenne muscular dystrophy or the more mild form of the disease, Becker muscular dystrophy. The hinge 3 region in the rod domain of dystrophin is particularly prone to deletion mutations. In-frame deletions of hinge 3 are predicted to lead to BMD, however the severity of disease can vary considerably. Here we performed extensive structure-function analyses of truncated dystrophins with modified hinges and spectrin-like repeats in mdx mice. We found that the polyproline site in hinge 2 profoundly influences the functional capacity of a microdystrophinΔR4-R23/ΔCT with a large deletion in the hinge 3 region. Inclusion of polyproline in microdystrophinΔR4-R23/ΔCT led to small myofibers (12% smaller than wild-type), Achilles myotendinous disruption, ringed fibers, and aberrant neuromuscular junctions in the mdx gastrocnemius muscles. Replacing hinge 2 of microdystrophinΔR4-R23/ΔCT with hinge 3 significantly improved the functional capacity to prevent muscle degeneration, increase muscle fiber area, and maintain the junctions. We conclude that the rigid α-helical structure of the polyproline site significantly impairs the functional capacity of truncated dystrophins to maintain appropriate connections between the cytoskeleton and extracellular matrix.
Author Summary
Dystrophin functions like a large molecular spring between the muscle cytoskeleton and the extracellular matrix in order to protect the membrane from contraction-induced injury. Mutations in dystrophin can lead to a severe muscle wasting disease called Duchenne muscular dystrophy (DMD) in young boys. DMD patients are typically wheelchair bound by 9–13 years of age and die at approximately 30 years. There are also mutations within the dystrophin gene that lead to internal truncations of non-essential regions, such as the internal rod domain that leads to a mild form of the disease called Becker Muscular Dystrophy. However, these internal truncations frequently occur at a “hot spot” within the rod domain where the resulting disease severity is difficult to predict. Here we found that consecutive proline residues, that function much like a molecular ruler, can dramatically influence the function of these internally truncated dystrophins within skeletal muscles. Using this information, we designed a dystrophin mini-gene that can accommodate the limited packaging size of recombinant adeno-associated virus. This virus can deliver the dystrophin mini-gene to most muscles throughout a dystrophic mouse to prevent muscle degeneration and partially restore muscle function.
PMCID: PMC2873924  PMID: 20502633
23.  Muscle Structure Influences Utrophin Expression in mdx Mice 
PLoS Genetics  2014;10(6):e1004431.
Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by mutations in the dystrophin gene. To examine the influence of muscle structure on the pathogenesis of DMD we generated mdx4cv:desmin double knockout (dko) mice. The dko male mice died of apparent cardiorespiratory failure at a median age of 76 days compared to 609 days for the desmin−/− mice. An ∼2.5 fold increase in utrophin expression in the dko skeletal muscles prevented necrosis in ∼91% of 1a, 2a and 2d/x fiber-types. In contrast, utrophin expression was reduced in the extrasynaptic sarcolemma of the dko fast 2b fibers leading to increased membrane fragility and dystrophic pathology. Despite lacking extrasynaptic utrophin, the dko fast 2b fibers were less dystrophic than the mdx4cv fast 2b fibers suggesting utrophin-independent mechanisms were also contributing to the reduced dystrophic pathology. We found no overt change in the regenerative capacity of muscle stem cells when comparing the wild-type, desmin−/−, mdx4cv and dko gastrocnemius muscles injured with notexin. Utrophin could form costameric striations with α-sarcomeric actin in the dko to maintain the integrity of the membrane, but the lack of restoration of the NODS (nNOS, α-dystrobrevin 1 and 2, α1-syntrophin) complex and desmin coincided with profound changes to the sarcomere alignment in the diaphragm, deposition of collagen between the myofibers, and impaired diaphragm function. We conclude that the dko mice may provide new insights into the structural mechanisms that influence endogenous utrophin expression that are pertinent for developing a therapy for DMD.
Author Summary
Duchenne muscular dystrophy (DMD) is a severe muscle wasting disorder caused by mutations in the dystrophin gene. Utrophin is structurally similar to dystrophin and improving its expression can prevent skeletal muscle necrosis in the mdx mouse model of DMD. Consequently, improving utrophin expression is a primary therapeutic target for treating DMD. While the downstream mechanisms that influence utrophin expression and stability are well described, the upstream mechanisms are less clear. Here, we found that perturbing the highly ordered structure of striated muscle by genetically deleting desmin from mdx mice increased utrophin expression to levels that prevented skeletal muscle necrosis. Thus, the mdx:desmin double knockout mice may prove valuable in determining the upstream mechanisms that influence utrophin expression to develop a therapy for DMD.
PMCID: PMC4055409  PMID: 24922526
24.  Dystromirs as Serum Biomarkers for Monitoring the Disease Severity in Duchenne Muscular Dystrophy 
PLoS ONE  2013;8(11):e80263.
Duchenne muscular Dystrophy (DMD) is an inherited disease caused by mutations in the dystrophin gene that disrupt the open reading frame, while in frame mutations result in Becker muscular dystrophy (BMD). Ullrich congenital muscular dystrophy (UCMD) is due to mutations affecting collagen VI genes. Specific muscle miRNAs (dystromirs) are potential non-invasive biomarkers for monitoring the outcome of therapeutic interventions and disease progression. We quantified miR-1, miR-133a,b, miR-206 and miR-31 in serum from patients with DMD, BMD, UCMD and healthy controls. MiR-1, miR-133a,b and miR-206 were upregulated in DMD, but unchanged in UCMD compared to controls. Milder DMD patients had higher levels of dystromirs than more severely affected patients. Patients with low forced vital capacity (FVC) values, indicating respiratory muscle weakness, had low levels of serum miR-1 and miR-133b. There was no significant difference in the level of the dystromirs in BMD compared to controls.
We also assessed the effect of dystrophin restoration on the expression of the five dystromirs in serum of DMD patients treated systemically for 12 weeks with antisense oligomer eteplirsen that induces skipping of exon 51 in the dystrophin gene. The dystromirs were also analysed in muscle biopsies of DMD patients included in a single dose intramuscular eteplirsen clinical trial. Our analysis detected a trend towards normalization of these miRNA between the pre- and post-treatment samples of the systemic trial, which however failed to reach statistical significance. This could possibly be due to the small number of patients and the short duration of these clinical trials.
Although longer term studies are needed to clarify the relationship between dystrophin restoration following therapeutic intervention and the level of circulating miRNAs, our results indicate that miR-1 and miR-133 can be considered as exploratory biomarkers for monitoring the progression of muscle weakness and indirectly the remaining muscle mass in DMD.
PMCID: PMC3840009  PMID: 24282529
25.  Spatio-Temporal Differences in Dystrophin Dynamics at mRNA and Protein Levels Revealed by a Novel FlipTrap Line 
PLoS ONE  2015;10(6):e0128944.
Dystrophin (Dmd) is a structural protein that links the extracellular matrix to actin filaments in muscle fibers and is required for the maintenance of muscles integrity. Mutations in Dmd lead to muscular dystrophies in humans and other vertebrates. Here, we report the characterization of a zebrafish gene trap line that fluorescently labels the endogenous Dmd protein (Dmd-citrine, Gt(dmd-citrine) ct90a). We show that the Dmd-citrine line recapitulates endogenous dmd transcript expression and Dmd protein localization. Using this Dmd-citrine line, we follow Dmd localization to the myosepta in real-time using time-lapse microscopy, and find that the accumulation of Dmd protein at the transverse myosepta coincides with the onset of myotome formation, a critical stage in muscle maturation. We observed that Dmd protein localizes specifically to the myosepta prior to dmd mRNA localization. Additionally, we demonstrate that the Dmd-citrine line can be used to assess muscular dystrophy following both genetic and physical disruptions of the muscle.
PMCID: PMC4471274  PMID: 26083378

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