Misregulated alternative splicing of BIN1 is associated with T tubule alterations and muscle weakness in myotonic dystrophy

Abstract

Myotonic dystrophy is the most common muscular dystrophy in adults and the first recognized example of an RNA-mediated disease. Congenital myotonic dystrophy (CDM1) and myotonic dystrophy of type 1 (DM1) or of type 2 (DM2) are caused by the expression of mutant RNAs containing expanded CUG or CCUG repeats, respectively. These mutant RNAs sequester the splicing regulator Muscleblind-like-1 (MBNL1), resulting in specific misregulation of the alternative splicing of other pre-mRNAs. We found that alternative splicing of the bridging integrator-1 (BIN1) pre-mRNA is altered in skeletal muscle samples of people with CDM1, DM1 and DM2. BIN1 is involved in tubular invaginations of membranes and is required for the biogenesis of muscle T tubules, which are specialized skeletal muscle membrane structures essential for excitation-contraction coupling. Mutations in the BIN1 gene cause centronuclear myopathy, which shares some histopathological features with myotonic dystrophy. We found that MBNL1 binds the BIN1 pre-mRNA and regulates its alternative splicing. BIN1 missplicing results in expression of an inactive form of BIN1 lacking phosphatidylinositol 5-phosphate-binding and membrane-tubulating activities. Consistent with a defect of BIN1, muscle T tubules are altered in people with myotonic dystrophy, and membrane structures are restored upon expression of the normal splicing form of BIN1 in muscle cells of such individuals. Finally, reproducing BIN1 splicing alteration in mice is sufficient to promote T tubule alterations and muscle weakness, a predominant feature of myotonic dystrophy.

Four parameters increase the sensitivity and specificity of the exon array analysis and disclose 25 novel aberrantly spliced exons in myotonic dystrophy

“…To prove this, we analyzed four human exon arrays of GSE21795, 23 GSE28672, 24 GSE24581 25 and GSE21840 26 in the Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/). Each data set was comprised of a pair of three to five samples, and aberrant and alternative splicing events of a total of 23 exons were validated by RT-PCR in the original papers.…”

MBNL1 and RBFOX2 cooperate to establish a splicing programme involved in pluripotent stem cell differentiation

“…One normal function of Muscleblind is to modulate splicing during muscle and heart development [29][30][31][32][33][34] . The second most correlated knockdown was RBFOX2, which is a well-characterized splicing factor that we and others have implicated in epithelial-tomesenchymal transition and invasion 22,23,34,35 .…”

Triadopathies: An Emerging Class of Skeletal Muscle Diseases

“…Altered splicing of the DHPR leads to changes in L-type Ca 2+ channel conductance [86]. Missplicing of BIN1 results in enrichment of an inactive form of the gene product, which, in turn, disrupts T-tubule formation and maintenance, as determined by targeted alteration of the spliced exon in the mouse [87]. The BIN1 splicing alteration is proposed to be responsible for the central nucleation pattern commonly observed in muscle from patients with DM1 and to contribute to the muscle weakness observed in this disease.…”