Résumé :
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The autosomal dominant centronuclear myopathy (CNM) is a rare congenital myopathy characterized by delayed motor milestones, facial and muscular weakness often associated with bilateral ptosis. The typical muscle histopathology comprises central nuclei, predominance and hypotrophy of type 1 fibres, and radial arrangement of sarcoplasmic strands. Phenotypic variability has been observed ranging from mild forms, with slowly progressive myopathy occurring during adolescence or later, to more severe neonatal presentation. Since the identification of the first mutations in the DNM2 gene encoding the dynamin 2 (DNM2), sequencing of this gene led us to identify 13 heterozygous mutations in 39 CNM families covering the entire clinical spectrum. Four out of the 13 mutations cause severe neonatal CNM and are located in the ?-helix of the Pleckstrin Homology domain which is involved in targeting proteins to the plasma membrane. The severity of the phenotype associated with these mutations suggests that this region is particularly important for DNM2 function in muscle. DNM2 is a large GTPase involved in endocytosis, Mitogen-Activated Protein Kinase (MAPK) pathway activation, actin assembly and is a component of the centrosome, the main microtubule organizing center. We constructed vectors allowing in vitro and in vivo expression of GFP-tagged proteins. DNM2-mutants are able to impair the clathrin-mediated endocytosis and the EGF-induced ERK1/2 MAPK activation in transfected COS7 cells. Among these mutants, the p.R465W was expressed in the mouse tibialis anterior muscle by electrotransfer, showing a mislocalization compared to wild-type DNM2. Additionally, immunocytochemical analysis of muscle biopsies from DNM2-CNM patients demonstrate that the localisation of some proteins involved in nuclear positioning is modified. Our results suggest that the association in the muscle fibres of structural alterations and MAPK pathway impairment could be important in the pathophysiological processes of the DNM2-related CNM. 1. INSERM, U582, Institut de Myologie, Paris, F-75013, France. 2. Université Pierre et Marie Curie-Paris6, UMR S582, IFR14, Paris, F-75013, France. 3. Departamento de Neurología y Neurocirugía, HCUCH and Instituto de Ciencias Biomédicas Universidad de Chile, Santiago, Chile. 4. AP-HP, Groupe Hospitalier Pitié-Salpêtrière, Paris, F-75013, France.
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