Time-controlled and muscle-specific CRISPR/Cas9-mediated deletion of CTG-repeat expansion in the gene.

CRISPR/Cas9-mediated therapeutic gene editing is a promising technology for durable treatment of incurable monogenic diseases such as myotonic dystrophies. Gene-editing approaches have been recently applied to and models of myotonic dystrophy type 1 (DM1) to delete the pathogenic CTG-repeat expansion located in the 3' untranslated region of the gene. In DM1-patient-derived cells removal of the expanded repeats induced beneficial effects on major hallmarks of the disease with reduction in transcript-containing ribonuclear foci and reversal of aberrant splicing patterns. Here, we set out to excise the triplet expansion in a time-restricted and cell-specific fashion to minimize the potential occurrence of unintended events in off-target genomic loci and select for the target cell type. To this aim, we employed either a ubiquitous promoter-driven or a muscle-specific promoter-driven Cas9 nuclease and tetracycline repressor-based guide RNAs. A dual-vector approach was used to deliver the CRISPR/Cas9 components into DM1 patient-derived cells and in skeletal muscle of a DM1 mouse model. In this way, we obtained efficient and inducible gene editing both in proliferating cells and differentiated post-mitotic myocytes as well as in skeletal muscle tissue .