The distribution of SMN protein complex in human fetal tissues and its alteration in spinal muscular atrophy

Burlet, Philippe; Huber, Céline; Bertrandy, Solange; Ludosky, Marie-Aline; Zwaenepoel, Ingrid; Clermont, Olivier; Roume, J.; Delezoïde, Anne Lise; Cartaud, Jean; Münnich, Arnold; Lefebvre, Suzie

doi:10.1093/hmg/7.12.1927

Cited by 131 publications

(115 citation statements)

References 26 publications

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“…Our morphological and immunophenotyping findings agree with studies characterizing the "Taiwanese" mouse model of SMA (25), and other reports on SMN expression dynamics over the course of development in human and mouse tissues (36,62,63). Other aspects of our results show similarities and differences compared with data on other mouse models of SMA.…”

Section: Fayzullina Andsupporting

confidence: 90%

DNA Damage Response and DNA Repair in Skeletal Myocytes From a Mouse Model of Spinal Muscular Atrophy

Fayzullina

Martin

2016

J Neuropathol Exp Neurol

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We studied DNA damage response (DDR) and DNA repair capacities of skeletal muscle cells from a mouse model of infantile spinal muscular atrophy (SMA) caused by loss-of-function mutation of survival of motor neuron (Smn). Primary myocyte cultures derived from skeletal muscle satellite cells of neonatal control and mutant SMN mice had similar myotube length, myonuclei, satellite cell marker Pax7 and differentiated myotube marker myosin, and acetylcholine receptor clustering. DNA damage was induced in differentiated skeletal myotubes by c-irradiation, etoposide, and methyl methanesulfonate (MMS). Unexposed control and SMA myotubes had stable genome integrity. After c-irradiation and etoposide, myotubes repaired most DNA damage equally. Control and mutant myotubes exposed to MMS exhibited equivalent DNA damage without repair. Control and SMA myotube nuclei contained DDR proteins phosphop53 and phospho-H2AX foci that, with DNA damage, dispersed and then re-formed similarly after recovery. We conclude that mouse primary satellite cell-derived myotubes effectively respond to and repair DNA strand-breaks, while DNA alkylation repair is underrepresented. Morphological differentiation, genome stability, genome sensor, and DNA strand-break repair potential are preserved in mouse SMA myocytes; thus, reduced SMN does not interfere with myocyte differentiation, genome integrity, and DNA repair, and faulty DNA repair is unlikely pathogenic in SMA.

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Section: Fayzullina Andsupporting

confidence: 90%

DNA Damage Response and DNA Repair in Skeletal Myocytes From a Mouse Model of Spinal Muscular Atrophy

Fayzullina

Martin

2016

J Neuropathol Exp Neurol

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“…9 In the nucleus, the SMN complex participates in the regeneration of spliceosomes. [10][11][12] The expression of SMN was studied in several control and SMA tissue and a decrease of SMN protein in fetal spinal cord 13,14 and in fetal muscle 15 of SMA I patients was demonstrated. A reduction in SMN protein level during postnatal development and a lack of SMN in skeletal muscles of SMA fetuses might be correlated with defects of muscle fibers.…”

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confidence: 99%

“…These observations suggest that SMA is a prenatal rather than a postnatal disease. 15 The molecular mechanism leading to SMA is still unknown. The SMN protein is ubiquitously expressed and the deficiency in SMN expression is observed not only in motor neurons but also in other tissues from SMA patients.…”

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confidence: 99%

Reduced expression of nicotinic AChRs in myotubes from spinal muscular atrophy I patients

Arnold¹,

Gueye²,

Guettier‐Sigrist³

et al. 2004

Laboratory Investigation

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Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by degeneration of motoneurons and skeletal muscle atrophy. In its most severe form, it leads to death before the age of 2 years. While primary degeneration of motor neurons is well established in this disease, and this results in neurogenic atrophy of skeletal muscle, we have previously reported evidence for a primary muscle defect. In this study, we used primary cultures of embryonic human skeletal muscle cells from patients with SMA and from controls to examine the effects of muscle fiber differentiation in the absence of a nerve component. Cultured SMA skeletal muscle cells are unable to fuse correctly to form multinuclear myotubes, the precursors of the myofibers. We also show that agrin-induced aggregates of nicotinic acetylcholine receptors, one of the earliest steps of neuromuscular junction formation, cannot be visualized by confocal microscopy on cells from SMA patients. In binding experiments, we demonstrate that this lack of clustering is due to defective expression of the nicotinic acetylcholine receptors in the myotubes of SMA patients whereas the affinity of a-bungarotoxin for its receptor remains unchanged regardless of muscle cell type (SMA or control). These observations suggest that muscle cells from SMA patients have intrinsic abnormalities that may affect proper formation of the neuromuscular junction. Keywords: spinal muscular atrophy; myotubes; neuromuscular junction; nicotinic acetylcholine receptors; aggregation; binding Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by degeneration of spinal motor neurons leading to a muscle weakness and paralysis. SMA is traditionally classified into three types based on the age of onset and the severity of symptoms. 1 The SMA I or Werdnig-Hoffmann disease is the most severe form. Patients never attain the ability to sit, and their lifespan does not exceed infancy in most cases. SMA II is the intermediate form. Patients are unable to stand or walk unaided, and death usually occurs in adulthood. SMA III or Kugelberg-Welander disease presents a milder phenotype. Patients are able to stand and walk and present a near-normal life expectancy. The gene responsible for all three types of SMA was mapped to the region 5q11.2-13.3 by linkage analysis. [2][3][4][5] This gene, named SMN for 'survival of motor neurons', is mutated in 98% of the SMA patients, and the majority of mutations occur in exon 7. 6 It encodes a ubiquitously expressed SMN protein present in both the cytoplasm and the nucleus. In this last compartment, the SMN protein is concentrated in structures called gems (for 'gemini of coiled bodies') located in the close proximity of Cajal bodies (previously named coiled bodies). 7,8 The SMN protein participates in the formation of the SMN complex, which is associated with small nuclear ribonucleoproteins (snRNP) in the cytoplasm and plays a crucial role in the spliceosomal snRNP assembly. 9 In the nucleus, the SMN complex participates in the regener...

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“…The SMN protein is subject to both temporal and spatial regulation: the highest SMN levels have been reported in brain, spinal cord, kidney and heart [Lefebvre et al, 1997;Coovert et al, 1997;Burlet et al, 1998] and SMN is especially abundant throughout embryonic development [Battaglia et al, 1997;Burlet et al, 1998; La Bella et al, 1998]. The levels of SMN protein diminish during the early postnatal period; however, the timing of this repression varies among tissues [Kernochan et al, 2005].…”

Section: Are Smn1 and Smn2 As Identical As They Appear To Be?mentioning

confidence: 99%

Solving the puzzle of spinal muscular atrophy: What are the missing pieces?

Tiziano

Melki

Simard

2013

American J of Med Genetics Pt A

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Spinal muscular atrophy (SMA) is an autosomal recessive, lower motor neuron disease. Clinical heterogeneity is pervasive: three infantile (type I-III) and one adult-onset (type IV) forms are recognized. Type I SMA is the most common genetic cause of death in infancy and accounts for about 50% of all patients with SMA. Most forms of SMA are caused by mutations of the survival motor neuron (SMN1) gene. A second gene that is 99% identical to SMN1 (SMN2) is located in the same region. The only functionally relevant difference between the two genes identified to date is a C ! T transition in exon 7 of SMN2, which determines an alternative spliced isoform that predominantly excludes exon 7. Thus, SMN2 genes do not produce sufficient full length SMN protein to prevent the onset of the disease. Since the identification of the causative mutation, biomedical research of SMA has progressed by leaps and bounds: from clues on the function of SMN protein, to the development of different models of the disease, to the identification of potential treatments, some of which are currently in human trials. The aim of this review is to elucidate the current state of knowledge, emphasizing how close we are to the solution of the puzzle that is SMA, and, more importantly, to highlight the missing pieces of this puzzle. Filling in these gaps in our knowledge will likely accelerate the development and delivery of efficient treatments for SMA patients and be a prerequisite towards achieving our final goal, the cure of SMA. Ó 2013 Wiley Periodicals, Inc. Key words: spinal muscular atrophy; SMN INTRODUCTIONSpinal muscular atrophy (SMA) is a lower motor neuron disease that predominantly affects spinal cord anterior horn cells and brain stem nuclei [Dubowitz, 1995; reviewed in Hamilton and Gillingwater, 2013]. Alpha-motor neuron cell degeneration results in progressive, symmetrical skeletal muscle atrophy of limbs and trunk, spreading proximal to distal [Crawford and Pardo, 1996]. Clinical heterogeneity is pervasive: based on the age of onset and on the maximum motor achievement of patients, three infantile (type I-III) and one adult-onset (type IV) forms are commonly recognized. Classification criteria are summarized in Table I. However, this rigid classification does not accurately depict the range of SMA clinical phenotypes, which display a more continuous spectrum, ranging from prenatal onset to almost asymptomatic patients. SMA is a common autosomal recessive disorder (incidence is $1 in 6,000 in most ethnicities). Type I SMA is the most common genetic cause of death in infancy and accounts for about 50% of all patients with SMA [Crawford and Pardo, 1996;Prior, 2010].Most forms of SMA are caused by mutations in the survival motor neuron (SMN) gene, which was isolated in 1995 in chromosome 5q13 harboring a segmental duplication [Lefebvre et al., 1995]. Mutations in SMN1 are responsible for the four forms of SMA [Wirth, 2000;Alías et al., 2009]. A second gene that is 99% identical to SMN1, the SMN2 gene, is located in the same region [Le...

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The distribution of SMN protein complex in human fetal tissues and its alteration in spinal muscular atrophy

Cited by 131 publications

References 26 publications

DNA Damage Response and DNA Repair in Skeletal Myocytes From a Mouse Model of Spinal Muscular Atrophy

DNA Damage Response and DNA Repair in Skeletal Myocytes From a Mouse Model of Spinal Muscular Atrophy

Reduced expression of nicotinic AChRs in myotubes from spinal muscular atrophy I patients

Solving the puzzle of spinal muscular atrophy: What are the missing pieces?

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