Loss of the muscle-specific chloride channel in type 1 myotonic dystrophy due to misregulated alternative splicing

Myotonic dystrophy type 1 (DM1) is a dominant multi-systemic disorder caused by a CTG expansion in the 3' untranslated region of the DMPK gene. A predominant characteristic of DM1 is myotonia resulting from skeletal muscle membrane hyperexcitability. Here we demonstrate loss of the muscle-specific chloride channel (CIC-1) mRNA and protein in DM1 skeletal muscle tissue due to aberrant splicing of the CIC-1 pre-mRNA. The splicing regulator, CUG binding protein (CUG-BP), which is elevated in DM1 striated muscle, binds to the CIC-1 pre-mRNA, and overexpression of CUG-BP in normal cells reproduces the aberrant pattern of CIC-1 splicing observed in DM1 skeletal muscle. We propose that disruption of alternative splicing regulation causes a predominant pathological feature of DM1.