Résumé :
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Myotonic dystrophy type 1 (DM1) is the most common adult-onset muscular dystrophy. This disease is characterized, among other symptoms, by progressive muscle atrophy and weakness, myotonia and cardiac defects. DM1 is an autosomal dominant disease and belongs to a group of RNA gain-of-function disorders. Mutation consists in the expansion of a CTG repeat in the 3'UTR of the DMPK gene. Mutated transcripts containing expanded CUG repeats accumulate as intranuclear foci and modify activities of splicing factors like MBNL1 and CUGBP1. These alterations induce splicing defects in several transcripts including deregulation of CLCN1, responsible for the myotonia observed in DM1 patients. Recently we have identified a new splicing mis-regulation of the BIN1/amphiphisin-II transcript in human congenital DM1 muscle cells. The abnormal exclusion of BIN1 exon-11 was confirmed in muscle biopsies of both congenital and adult DM1 patients. BIN1 protein is specialized in membrane curvature and inclusion of exon-11, which encodes a phosphoinositide-binding domain, in skeletal muscle generates muscle-specific isoforms of BIN1 involved in T-tubule organization.To test the contribution of BIN1 splicing to DM1 phenotype, we artificially forced the exclusion of Bin1 exon-11 in skeletal muscle using an exon-skipping strategy. We generated a modified U7-snRNA harboring a Bin1 exon-11 antisense sequence. The construction was cloned in an AAV vector and locally expressed in the tibialis anterior of healthy new-born or adult mice. Exclusion of the Bin1 exon-11 in mice induced perturbation of Bin1 localization and alteration of the T-tubules organization, both phenotypes observed in affected muscle of DM1 patients. Furthermore a 20% decrease in specific force was measured in the Bin1 exon-11 skipped muscles without any muscle mass loss. Altogether these results strongly suggest a role of the mis-regulation of BIN1 splicing in the muscle weakness observed in DM1 patients.
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