Form Of Emery-Dreifuss Muscular Dystrophy Research Articles

Effect of genetic background on the cardiac phenotype in a mouse model of Emery-Dreifuss muscular dystrophy

A-type lamins gene (LMNA) mutations cause an autosomal dominant inherited form of Emery-Dreifuss muscular dystrophy (EDMD). EDMD is characterized by slowly progressive muscle weakness and wasting and dilated cardiomyopathy, often leading to heart failure-related disability. EDMD is highly penetrant with poor prognosis and there is currently no specific therapy available. Clinical variability ranges from early onset with severe presentation in childhood to late onset with slow progression in adulthood. Genetic background is a well-known factor that significantly affects phenotype in several mouse models of human diseases. This phenotypic variability is attributed, at least in part, to genetic modifiers that regulate the disease process. To characterize the phenotype of A-type lamins mutation on different genetic background, we created and phenotyped C57BL/6JRj-LmnaH222P/H222P mice (C57Lmnap.H222P) and compared them with the 129S2/SvPasCrl-LmnaH222P/H222P mice (129Lmnap.H222P). These mouse strains were compared with their respective control strains at multiple time points between 3 and 10 months of age. Both contractile and electrical cardiac muscle functions, as well as survival were characterized. We found that 129Lmnap.H222P mice showed significantly reduced body weight and reduced cardiac function earlier than in the C57Lmnap.H222P mice. We also revealed that only 129Lmnap.H222P mice developed heart arrhythmias. The 129Lmnap.H222P model with an earlier onset and more pronounced cardiac phenotype may be more useful for evaluating therapies that target cardiac muscle function, and heart arrhythmias.

Semaphorin 3A promotes activation of Pax7, Myf5, and MyoD through inhibition of emerin expression in activated satellite cells.

We previously showed that Semaphorin 3A (Sema3A) expression was induced when quiescent muscle satellite cells were stimulated by hepatocyte growth factor and became activated satellite cells (ASCs). However, how Sema3A regulates genes in the early phase of ASCs remains unclear. In this study, we investigated whether Sema3A signaling can regulate the early phase of ASCs, an important satellite cell stage for postnatal growth, repair, and maintenance of skeletal muscle. We showed that expression of the myogenic proliferation regulatory factors Pax7 and Myf5 was decreased in myoblasts transfected with Sema3A siRNA. These cells failed to activate expression MyoD, another myogenic proliferation regulatory factor, during differentiation. Interestingly, some of the Sema3A‐depleted cells did not express Pax7 and MyoD and had enlarged nuclei and very large cytoplasmic areas. We also observed that Pax7 and Myf5 expression was increased in Myc‐Sema3A overexpressing myoblasts. BrdU analysis indicated that Sema3A regulated proliferation of ASCs. These findings suggest that Sema3A signaling can modulate expression of Pax7, Myf5, and MyoD. Moreover, we found that expression of emerin, an inner nuclear membrane protein, was regulated by Sema3A signaling. Emerin was identified by positional cloning as the gene responsible for the X‐linked form of Emery–Dreifuss muscular dystrophy (X‐EDMD). In conclusion, our results support a role for Sema3A in maintaining ASCs through regulation, via emerin, of Pax7, Myf5, and MyoD expression.

Advances in muscle imaging for Emery-Dreifuss muscular dystrophy

Laminopathies are a heterogeneous group of disorders related to alterations on genes coding for proteins of the nuclear envelope. Among these clinical entities, there are several diseases affecting mainly the cardiac and skeletal muscles. These disorders include forms with a selective cardiac compromise and muscular dystrophies (autosomal and X-linked forms of Emery-Dreifuss muscular dystrophy, Limb girdle muscular dystrophy 1B, LMNA-related congenital muscular dystrophy and other rare clinical entities). We performed imaging studies on a large cohort of subjects bearing either LMNA or EMD gene mutations; each patient enrolled displayed variable compromise on posterior legs’ muscles, ranging from mild compromise on soleus and medial head of gastrocnemius to overt alterations on soleus, medial head of gastrocnemius [1,3]. Of note, we saw that even subjects presenting with clinically selective cardiac compromise displayed, on imaging studies, variable alterations on skeletal muscles. This findings showed a continuum in skeletal muscles compromise among different phenotypes related to LMNA or EMD gene mutations and lead to hypothesize a common mechanism in the process of damage of skeletal muscles fibers.

P.5.17 LMNA-associated myopathies: The Italian Laminopathies Network experience in a large cohort of patients

LMNA gene mutations have been associated with several diseases. Some of them are muscle disorders, including the autosomal dominant and recessive forms of Emery-Dreifuss muscular dystrophy (EDMD2 and EDMD3), limb-girdle muscular dystrophy 1B (LGMD1B) and congenital muscular dystrophy (MDCL). With few exceptions, most of the studies are focused on one of these phenotypes and data on large cohorts of myopathic patients are lacking. The aim of our study was to evaluate clinical, neurophysiologic, histological and molecular features of 77 myopathic patients mutated in LMNA gene and followed in different Italian neuromuscular centres. Patients with predominant or exclusively progeroid/lipodystrophic or cardiac phenotype were excluded. The cohort included 36 (46.8%) patients with LGMD1B phenotype, 30 (39%) with EDMD2 and 11 with MDCL (14.3%). Mean age at onset was 10.3±12.3years in patients with EDMD2, 29.5±17.6 in LGMD1B and 0.4±0.5 in MDCL. Independent walking was reached in all patients, with the exception of 4 (5.2%) MDCL, who never acquired the ability to stand up. Another 4 (5.2%) patients (3 LGMD1B and 1 EDMD2) lost ambulation, and 3 EDMD2 (3.9%), required monolateral support to walk. Cardiac involvement was found in 57 (74%) patients. Pacemaker or ICD were implanted in 42 (54.5%) patients (21 EDMD2, 18 LGMD1B and 3 MDCL), while heart transplant was performed in 5 (6.5%) patients (3 EDMD2 and 2 with LGMD1B). Six (7.8%) patients died due to cardiac problems (3 EDMD2 and 3 MDCL). Only 5 (6.5%) patients required non-invasive ventilation (4 EDMD2 and 1 CMD), confirming that respiratory problems are not a major issue in LMNA-associated myopathies. Ten novel mutations were detected. Despite EDMD2, LGMD1B and MDCL phenotypes are part of a continuum spectrum, their identification is clinically and prognostically relevant.

An EDMD Mutation in C. elegans Lamin Blocks Muscle-Specific Gene Relocation and Compromises Muscle Integrity

In worms, as in other organisms, many tissue-specific promoters are sequestered at the nuclear periphery when repressed and shift inward when activated. It has remained unresolved, however, whether the association of facultative heterochromatin with the nuclear periphery, or its release, has functional relevance for cell or tissue integrity. Using ablation of the unique lamin gene in C.elegans, we show that lamin is necessary for the perinuclear positioning of heterochromatin. We then express at low levels in otherwise wild-type worms a lamin carrying a point mutation, Y59C, which in humans is linked to an autosomal-dominant form of Emery-Dreifuss muscular dystrophy. Using embryos and differentiated tissues, we track the subnuclear position of integrated heterochromatic arrays and their expression. In LMN-1 Y59C-expressing worms, we see abnormal retention at the nuclear envelope of a gene array bearing a muscle-specific promoter. This correlates with impaired activation of the array-borne myo-3 promoter and altered expression of a number of muscle-specific genes. However, an equivalent array carrying the intestine-specific pha-4 promoter is expressed normally and shifts inward when activated in gut cells of LMN-1 Y59C worms. Remarkably, adult LMN-1 Y59C animals have selectively perturbed body muscle ultrastructure and reduced muscle function. Lamin helps sequester heterochromatin at the nuclear envelope, and wild-type lamin permits promoter release following tissue-specific activation. A disease-linked point mutation in lamin impairs muscle-specific reorganization of a heterochromatic array during tissue-specific promoter activation in a dominant manner. This dominance and the correlated muscle dysfunction in LMN-1 Y59C worms phenocopies Emery-Dreifuss muscular dystrophy.

Matrix metalloproteinases in serum of Emery-Dreifuss muscular dystrophy patients.

In the pathogenesis of dilated cardiomyopathy (DCM) in Emery-Dreifuss muscular dystrophy (EDMD) matrix metalloproteinases (MMPs) are supposed to be involved and may have diagnostic/prognostic value. Serum levels of MT1-MMP, MMP-2 and MMP-9 were quantified by ELISA and zymography in 22 EDMD patients and 15 age-matched controls. In the autosomal-dominant EDMD MMP-2 and MT1-MMP were increased in all cases, and MMP-9 was increased in two of the eight examined patients. In the X-linked EDMD MMP-2 expression was increased in all the cases, MMP-9 level was elevated in 3 of the 14 cases, and MT1-MMP was decreased in eight of these patients. There was no evident correlation between the MMPs level and the different cardiac parameters including left-ventricular end-diastolic diameter, left atrial diameter and left ventricular ejection fraction in either form of EDMD. The presented results indicate that a changed level of matrix metalloproteinases, especially that of MMP-2 in serum, may be of value for detection of cardiac involvement in EDMD patients, especially in those patients with no evident subjective cardiac symptoms. Further follow-up studies of MMPs are needed to check if their determination is of value for monitoring of the progression of atrial/ventricular dilatation. MMPs determinations may also be useful for monitoring DCM treatment by synthetic MMPs inhibitors.

NET37, a Nuclear Envelope Transmembrane Protein with Glycosidase Homology, Is Involved in Myoblast Differentiation

The nuclear lamina and its associated proteins are important for nuclear structure and chromatin organization and also have been implicated in the regulation of cell signaling and gene expression. In this study we demonstrate that the lamina-associated nuclear envelope transmembrane protein NET37 is required for myogenic differentiation of C2C12 cells. NET37, a member of glycosidase family 31, is highly expressed in mouse skeletal muscle and is strongly up-regulated during C2C12 differentiation. By protease mapping we show that its glycosidase homology domain is located in the lumen of the nuclear envelope/endoplasmic reticulum. When NET37 is depleted from proliferating myoblasts by RNAi, myogenic differentiation is significantly impaired, and there is a concomitant delay in up-regulation of the late myogenic transcription factor myogenin. We expressed silencing-resistant NET37 mutated at a conserved residue in the glycosidase domain and found that this predicted catalytically inactive protein is unable to support myogenesis in cells depleted of wild type NET37. Therefore, the enzymatic function of NET37 appears to be important for myogenic differentiation. C2C12 cells depleted of NET37 have reduced activation of Akt after shifting to differentiation medium and are defective in insulin like growth factor-II (IGF-II) secretion, an autocrine/paracrine factor involved in Akt activation. We also observed that pro-IGF-II co-immunoprecipitates with NET37. Based on our results, we propose that NET37 has a role in IGF-II maturation in the secretory pathway during myoblast differentiation. The localization of NET37 at the nuclear envelope raises the possibility that it may coordinate myogenic events between the nuclear interior and the endoplasmic reticulum lumen via transmembrane communication.

Prevalence of genetic muscle disease in Northern England: in-depth analysis of a muscle clinic population.

We have performed a detailed population study of patients with genetic muscle disease in the northern region of England. Our current clinic population comprises over 1100 patients in whom we have molecularly characterized 31 separate muscle disease entities. Diagnostic clarity achieved through careful delineation of clinical features supported by histological, immunological and genetic analysis has allowed us to reach a definitive diagnosis in 75.7% of our patients. We have compared our case profile with that from Walton and Nattrass' seminal study from 1954, also of the northern region, together with data from other more recent studies from around the world. Point prevalence figures for each of the five major disease categories are comparable with those from other recent studies. Myotonic dystrophies are the most common, comprising 28.6% of our clinic population with a point prevalence of 10.6/100,000. Next most frequent are the dystrophinopathies and facioscapulohumeral muscular dystrophy making up 22.9% (8.46/100,000) and 10.7% (3.95/100,000) of the clinic population, respectively. Spinal muscular atrophy patients account for 5.1% or 1.87/100,000 patients. Limb girdle muscular dystrophy, which was described for the first time in the paper by Walton and Nattrass (1954) and comprised 17% of their clinic population, comprises 6.2% of our clinic population at a combined prevalence of 2.27/100,000. The clinic population included patients with 12 other muscle disorders. These disorders ranged from a point prevalence of 0.89/100 000 for the group of congenital muscular dystrophies to conditions with only two affected individuals in a population of three million. For the first time our study provides epidemiological information for X-linked Emery-Dreifuss muscular dystrophy and the collagen VI disorders. Each of the X-linked form of Emery-Dreifuss muscular dystrophy and Ullrich muscular dystrophy has a prevalence of 0.13/100,000, making both very rare. Bethlem myopathy was relatively more common with a prevalence of 0.77/100,000. Overall our study provides comprehensive epidemiological information on individually rare inherited neuromuscular conditions in Northern England. Despite the deliberate exclusion of relatively common groups such as hereditary motor and sensory neuropathy (40/100,000) and mitochondrial disorders (9.2/100,000), the combined prevalence is 37.0/100,000, demonstrating that these disorders, taken as a group, encompass a significant proportion of patients with chronic disease. The study also illustrates the immense diagnostic progress since the first regional survey over 50 years ago by Walton and Nattrass.

Emery-Dreifuss Muscular Dystrophy: A Novel Mutation in the LMNA Gene

Described here is the phenotypical expression of a novel LMNA mutation c.1157 G>T in a Czech patient with an early-onset form of Emery-Dreifuss muscular dystrophy. The mutation predicts aberrant splicing. Now 21 years old, the patient has had slowly progressing muscle dystrophy since the age of one and early contractures of elbows. He is the only family member affected. Even though the dystrophy typically affects the heart as well, in the present case these signs are not yet expressed.

Nuclear changes in skeletal muscle extend to satellite cells in autosomal dominant Emery-Dreifuss muscular dystrophy/limb-girdle muscular dystrophy 1B

Autosomal forms of Emery-Dreifuss muscular dystrophy (AD-/AR-EDMD) and limb-girdle muscular dystrophy type 1B (LGMD1B) are caused by mutations in the gene encoding A-type lamins ( LMNA). A-type lamins are major components of nuclear lamina and known to have important roles in maintaining nuclear integrity. LMNA mutations are also suggested to cause reduced myogenic differentiation potentials, implying that satellite cell nuclei in AD-EDMD/LGMD1B are likewise affected. We examined nuclear changes of skeletal muscles including satellite cells from four patients with AD-EDMD/LGMD1B by light and electron microscopy. We found that 92.5 ± 5.0% of myonuclei had structural abnormalities, including shape irregularity and/or chromatin disorganization, and the presence of peri-/intranuclear vacuoles. Chromatin changes were also observed in 50% of the satellite cell nuclei. Increased number of Pax7-positive nuclei, but fewer number of MyoD-positive nuclei were seen on immunohistochemical analyses, suggesting functional alteration of satellite cells in addition to the nuclear morphological changes in AD-EDMD/LGMD1B.

Nesprin-2 Giant (NUANCE) maintains nuclear envelope architecture and composition in skin

Giant isoforms, encoded by Nesprin-1 (Syne1) and Nesprin-2 (Syne2), are multifunctional actin-binding and nuclear-envelope-associated proteins belonging to the spectrin superfamily. Here, we investigate the function of Nesprin-2 Giant (NUANCE) in skin by generating mice lacking the actin-binding domain of Nesprin-2 (Nesprin-2DeltaABD). This loss results in a slight but significant thickening of the epidermis, which is a consequence of the increased epithelial nuclear size. Nonetheless, epidermal proliferation and differentiation appear normal in the knockout epidermis. Surprisingly, Nesprin-2 C-terminal-isoform expression and nuclear envelope localization were affected in certain tissues. Nuclei of primary dermal knockout fibroblasts and keratinocytes were heavily misshapen, displaying a striking similarity to nuclear deformations characteristic of laminopathies. Furthermore, emerin, the protein involved in the X-linked form of Emery-Dreifuss muscular dystrophy (EDMD), was unevenly distributed along the nuclear envelope in mutant fibroblasts, often forming aggregates in the deformed nuclear envelope areas. Thus, Nesprin-2 is an important scaffold protein implicated in the maintenance of nuclear envelope architecture. Aged knockout fibroblasts readily generated, by alternative splicing and alternative translation initiation, aberrant Nesprin-2 Giant isoforms that lacked an ABD but that were sufficient to restore nuclear shape and emerin localization; this suggests that other regions of Nesprin-2 Giant, potentially including its spectrin repeats, are crucial for these functions.

Multitissular involvement in a family with LMNA and EMD mutations

Mutations in the EMD and LMNA genes, encoding emerin and lamins A and C, are responsible for the X-linked and autosomal dominant and recessive forms of Emery-Dreifuss muscular dystrophy (EDMD). LMNA mutations can also lead to several other disorders, collectively termed laminopathies, involving heart, fat, nerve, bone, and skin tissues, and some premature ageing syndromes. Fourteen members of a single family underwent neurologic, electromyographic, and cardiologic assessment. Gene mutation and protein expression analyses were performed for lamins A/C and emerin. Clinical investigations showed various phenotypes, including isolated cardiac disease (seven patients), axonal neuropathy (one patient), and a combination of EDMD with axonal neuropathy (two patients), whereas five subjects remained asymptomatic. Genetic analyses identified the coincidence of a previously described homozygous LMNA mutation (c.892C-->T, p. R298C) and a new in-frame EMD deletion (c.110-112delAGA, p. delK37), which segregate independently. Analyses of the contribution of these mutations showed 1) the EMD codon deletion acts in X-linked dominant fashion and was sufficient to induce the cardiac disease, 2) the combination of both the hemizygous EMD and the homozygous LMNA mutations was necessary to induce the EDMD phenotype, 3) emerin was present in reduced amount in EMD-mutated cells, and 4) lamin A/C and emerin expression was most dramatically affected in the doubly mutated fibroblasts. This highlights the crucial role of lamin A/C-emerin interactions, with evidence for synergistic effects of these mutations that lead to Emery-Dreifuss muscular dystrophy as the worsened result of digenic mechanism in this family.

Primary Myocardial Dysfunction in Autosomal Dominant EDMD. A Tissue Doppler and Cardiovascular Magnetic Resonance Study

Emery-Dreifuss muscular dystrophy is a genetically heterogeneous form of muscular dystrophy. One form is inherited in an X-linked fashion and is secondary to mutations in the gene encoding the nuclear protein emerin. A more common variant is inherited in an autosomal dominant way (EDMD2) due to mutations affecting the nuclear lamina protein lamin A/C. Typical features of both conditions are relatively mild skeletal muscle weakness, but cardiac involvement develops almost invariably by adult age, including conduction defects, arrhythmias and cardiomyopathy. Thus, early detection of cardiac abnormalities may be important for planning early therapeutic intervention. In this study, we hypothesized that early myocardial dysfunction can be detected by tissue Doppler echocardiography and CMR in unselected patients with the autosomal dominant form of Emery-Dreifuss muscular dystrophy. This would suggest that fibrosis could be implicated in the pathogenesis of cardiac dysfunction in EDMD2. Eight consecutive patients with genetically proven EDMD2 without pacemakers were enrolled in the study and compared to eight age-matched controls. All patients and controls first underwent a comprehensive echocardiographic-Doppler examination, followed by measurement of mitral annular velocities using pulsed tissue Doppler. Color M-mode tissue images were recorded from the parasternal long axis projections to derive Myocardial Velocity Gradients (MVG). Subsequently, all subjects underwent cardiovascular magnetic resonance (CMR) imaging for function, intrinsic myocardial tissue contrast using T1 and T2 weighted spin echo (TSE) for fat deposition and extrinsic contrast (Gadolinium-DTPA late fibrosis imaging). Strain measurements, using harmonic phase imaging (HARP) tagging were also derived. Cavity dimensions LV mass and fractional shortening were similar between patients and controls. The overall body mass index was less in patients than in controls (14.5 +/- 1.4 vs. 18.1 +/- 2.4 g/m2, p < 0.002). While systolic MVG were similar between groups, the early diastolic MVG was lower in patients than in controls (4 +/- 1.2 s-1 vs. 7.1 +/- 2.7, p < 0.02). On CMR, LA and LV, RV volumes were similar between patients and controls. CMR strain patterns, however, showed a significant reduction in inferior wall contractility in patients compared to controls (-0.06 +/- 0.02 vs -0.09 +/- 0.03, p < 0.05). No patient showed late gadolinium enhancement. Patients with EDMD2 have abnormal left ventricular function prior to developing any cardiac symptoms. The absence of myocardial fibrosis, however, by CMR suggests that this functional abnormality may not be secondary to scarring but could precede it. Tissue Doppler echocardiography and CMR are sensitive methods of assessing the presence of myocardial dysfunction prior to the development of any cardiovascular symptoms.

Emery–Dreifuss muscular dystrophy with cardiac manifestations

An asymptomatic 40-year-old man attended clinic for cardiology assessment before cataract surgery. He had been diagnosed 9 years earlier with a ‘non specified limb-girdle muscular dystrophy’ following investigation for lower limb muscle weakness. Earlier electrocardiograms (ECGs) showed a bradycardic, junctional escape rhythm of 30–40 beats per minute (BPM). He had previously refused pacemaker insertion. He denied any syncope, shortness of breath or palpitations. He had muscle wasting to his upper arms and calves plus mild elbow contractures. He was normotensive, resting regular heart rate = 42 BPM and cardiorespiratory examination was unremarkable. His ECG showed atrial fibrillation, with a slow junctional escape rhythm of approximately 40 BPM and normal QRS width (Figure 1). Blood tests showed no haematological, electrolyte or thyroid dysfunction and no impaired glucose tolerance. Echocardiography showed good left ventricular function and 24-hour ECG Holter monitoring showed 8 pauses (longest 2.13s), with a heart rate varying between 29 and 79 BPM. He was commenced on clopidogrel to prevent thromboembolic complications and then he agreed for a VVIR system to be implanted to avoid bradyarrhythmic death. No complications ensued and he remains well at present. The patient also had two brothers, one died suddenly and the cause of death was not clearly determined. His elder brother was 52 years old and was diagnosed with a non-specific muscular dystrophy also associated with a junctional rhythm. He had a VVIR permanent pacemaker inserted in April 2003 following recurrent episodes of dizziness. An hereditary skeletal myopathy in association with pathognomic cardiac abnormalities suggested a diagnosis of Emery–Dreifuss muscular dystrophy (EDMD). Prognostically and therapeutically a definitive genetic diagnosis was required. Genetic testing confirmed that both siblings had inherited the X-linked form of EDMD involving a single base change of the emerin gene.

Alfred Hauptmann, Siegfried Thannhauser, and an endangered muscular disorder.

Alfred Hauptmann (Figure 1), a German neurologist who initially introduced phenobarbital in epilepsy therapy, and Siegfried Thannhauser (Figure 2), an outstanding German metabolism specialist, left Germany during the Nazi regime because of their Jewish origin. Both scientists emigrated to the United States and, in 1941, described a new myopathic entity, 1 later called Hauptmann-Thannhauser muscular dystrophy. Recently, this eponym has largely disappeared from the literature and has been replaced with the term autosomal dominant form of Emery-Dreifuss muscular dystrophy. However, molecular biology as well as more in-depth clinical studies argue that Hauptmann-Thannhauser muscular dystrophy is a distinct entity. On the basis of their discovery and their important contributions in other neurological spheres, we suggest a reinstatement of the term Hauptmann-Thannhauser muscular dystrophy in modern neurological nosology.

Expression and localization of nuclear proteins in autosomal-dominant Emery-Dreifuss muscular dystrophy with LMNA R377H mutation

BackgroundThe autosomal dominant form of Emery-Dreifuss muscular dystrophy (AD-EDMD) is caused by mutations in the gene encoding for the lamins A and C (LMNA). Lamins are intermediate filament proteins which form the nuclear lamina underlying the inner nuclear membrane. We have studied the expression and the localization of nuclear envelope proteins in three different cell types and muscle tissue of an AD-EDMD patient carrying a point mutation R377H in the lamin A/C gene.ResultsLymphoblastoid cells, skin fibroblasts, primary myoblasts and muscle thin sections were studied by immunocytochemistry and electron microscopy. Cellular levels of A-type lamins were reduced compared to control cells. In contrast, the amount of emerin and lamin B appeared unaltered. Cell synchronization experiments showed that the reduction of the cellular level of A-type lamin was due to instability of lamin A. By electron microscopy, we identified a proportion of nuclei with morphological alterations in lymphoblastoid cells, fibroblasts and mature muscle fibres. Immunofluorescence microscopy showed that a major population of the lamin B receptor (LBR), an inner nuclear membrane protein, was recovered in the cytoplasm in association with the ER. In addition, the intranuclear organization of the active form of RNA polymerase II was markedly different in cells of this AD-EDMD patient. This aberrant intranuclear distribution was specifically observed in muscle cells where the pathology of EDMD predominates.ConclusionsFrom our results we conclude: Firstly, that structural alterations of the nuclei which are found only in a minor fraction of lymphoblastoid cells and mature muscle fibres are not sufficient to explain the clinical pathology of EDMD; Secondly, that wild type lamin A is required not only for the retention of LBR in the inner nuclear membrane but also for a correct localization of the transcriptionally active RNA pol II in muscle cells. We speculate that a rearrangement of the internal chromatin could lead to muscle-specific disease symptoms by interference with proper mRNA transcription.

Effects of expressing lamin A mutant protein causing Emery-Dreifuss muscular dystrophy and familial partial lipodystrophy in Hela cells

Patients with the autosomal dominant form of Emery-Dreifuss muscular dystrophy (EDMD) or familial partial lipodystrophy (FPLD) have specific mutations in the lamin A gene. Three such point mutations, G465D (FPLD), R482L, (FPLD), or R527P (EDMD), were introduced by site-specific mutagenesis in the C-terminal tail domain of a FLAG-tagged full-length lamin A construct. HeLa cells were transfected with mutant and wild-type constructs. Lamin A accumulated in nuclear aggregates and the number of cells with aggregates increased with time after transfection. At 72 h post transfection 60–80% of cells transfected with the mutant lamin A constructs had aggregates, while only 35% of the cells transfected with wild-type lamin A revealed aggregates. Mutant transfected cells expressed 10–24×, and wild-type transfected cells 20×, the normal levels of lamin A. Lamins C, B1 and B2, Nup153, LAP2, and emerin were recruited into aggregates, resulting in a decrease of these proteins at the nuclear rim. Aggregates were also characterized by electron microscopy and found to be preferentially associated with the inner nuclear membrane. Aggregates from mutant constructs were larger than those formed by the wild-type constructs, both in immunofluorescence and electron microscopy. The combined results suggest that aggregate formation is in part due to overexpression, but that there are also mutant-specific effects.

The expression, lamin-dependent localization and RNAi depletion phenotype for emerin in C. elegans.

Emerin belongs to the LEM-domain family of nuclear membrane proteins, which are conserved in metazoans from C. elegans to humans. Loss of emerin in humans causes the X-linked form of Emery-Dreifuss muscular dystrophy (EDMD), but the disease mechanism is not understood. We have begun to address the function of emerin in C. elegans, a genetically tractable nematode. The emerin gene (emr-1) is conserved in C. elegans. We detect Ce-emerin protein in the nuclear envelopes of all cell types except sperm, and find that Ce-emerin co-immunoprecipitates with Ce-lamin from embryo lysates. We show for the first time in any organism that nuclear lamins are essential for the nuclear envelope localization of emerin during early development. We further show that four other types of nuclear envelope proteins, including fellow LEM-domain protein Ce-MAN1, as well as Ce-lamin, UNC-84 and nucleoporins do not depend on Ce-emerin for their localization. This result suggests that emerin is not essential to organize or localize the only lamin (B-type) expressed in C. elegans. We also analyzed the RNAi phenotype resulting from the loss of emerin function in C. elegans under laboratory growth conditions, and found no detectable phenotype throughout development. We propose that C. elegans is an appropriate system in which to study the molecular mechanisms of emerin function in vivo.

Selective muscle involvement on magnetic resonance imaging in autosomal dominant Emery-Dreifuss muscular dystrophy.

The aim of this study was to evaluate the spectrum of muscle involvement on MRI in patients with autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD2) due to mutations in the lamin A/C gene and to compare it to the pattern found in other conditions with similar phenotype. Nine patients with a diagnosis of EDMD2 had MRI scanning of their leg muscles. Seven other patients, four with the X-linked form of Emery-Dreifuss muscular dystrophy (EDMD) and three with an Emery-Dreifuss-like phenotype but no detectable mutations in either the emerin or the lamin A/C gene were also scanned as disease controls. All patients with EDMD2 showed a characteristic involvement of the posterior calf muscles. The medial head of the gastrocnemius was always predominantly involved while the lateral head was relatively spared. This pattern was more obvious in mildly affected patients in whom the other calf muscles were spared or only mildly involved but was also recognisable in the patients with more advanced disease. In contrast, none of the patients with the X-linked EDMD or with Emery-Dreifuss-like phenotype but no mutation in either genes showed this pattern of muscle involvement. Our results suggest that patients with EDMD2 have a specific pattern of muscle involvement and that muscle MRI can be used, in combination with other techniques, to distinguish various genetic forms of Emery-Dreifuss muscular dystrophy.

BAF is required for emerin assembly into the reforming nuclear envelope.

Mutations in emerin cause the X-linked recessive form of Emery-Dreifuss muscular dystrophy (EDMD). Emerin localizes at the inner membrane of the nuclear envelope (NE) during interphase, and diffuses into the ER when the NE disassembles during mitosis. We analyzed the recruitment of wildtype and mutant GFP-tagged emerin proteins during nuclear envelope assembly in living HeLa cells. During telophase, emerin accumulates briefly at the 'core' region of telophase chromosomes, and later distributes over the entire nuclear rim. Barrier-to-autointegration factor (BAF), a protein that binds nonspecifically to double-stranded DNA in vitro, co-localized with emerin at the 'core' region of chromosomes during telophase. An emerin mutant defective for binding to BAF in vitro failed to localize at the 'core' in vivo, and subsequently failed to localize at the reformed NE. In HeLa cells that expressed BAF mutant G25E, which did not show 'core' localization, the endogenous emerin proteins failed to localize at the 'core' region during telophase, and did not assemble into the NE during the subsequent interphase. BAF mutant G25E also dominantly dislocalized LAP2beta and lamin A from the NE, but had no effect on the localization of lamin B. We conclude that BAF is required for the assembly of emerin and A-type lamins at the reforming NE during telophase, and may mediate their stability in the subsequent interphase.