[Misregulation of alternative splicing and microRNA processing in DM1 pathogenesis].

Myotonic dystrophy of type I (DM1) is an autosomal dominant inherited disease caused by an unstable CTG expansion in the 3' non-coding region of the DMPK gene that confers to the mutant transcript a toxic RNA gain-of-function. Nuclear accumulation of DMPK transcripts containing expanded CUG repeats alters the activities of the splicing regulators MBNL1 and CUGBP1 resulting in alternative splicing misregulation of a numerous of transcripts in DM1 tissues. In collaboration with N. Charlet we identified a new mis-splicing event in the muscles of DM1 patients: BIN1 exon11 splicing mis-regulation due to MBNL1 loss-of-function results in the expression of an inactive form of BIN1. Reproducing similar BIN1 mis-splicing defect in the muscles of wild type mice is sufficient to promote T-tubule alterations and muscle strength decrease, suggesting that alteration of BIN1 splicing contributes to DM1 muscle weakness. Interestingly, the RNA binding protein MBNL1 regulates also the processing of the microRNA miR-1 that was found mis-regulated in the heart of DM1 patients. The consequences of miR-1 mis-regulation on DM1 heart conduction defects are not fully understood yet, however this work may shed light on the alteration of this class of non-coding RNA as an additional molecular mechanisms involved in DM1 pathophysiology.