Myotonic Dystrophy: The Structure of Cug Repeats in Solution

Abstract

Myotonic dystrophy (DM), a genetic and neuromuscular disorder, is the most common form of adult-onset muscular dystrophy and results in symptoms such as proximal muscle weakness, myotonia, iridescent cataracts and cardiac arrhythmia. Myotonic dystrophy type 1 (DM1), the most prevalent type of DM, is caused by a (CTG)0 expansion in the 3' untranslated region of the dystrophin myotonin protein kinase gene. At the RNA level, the CUG repeats form a stem-loop that is thought to be the pathogenic element. We determined that the crystal structure of CUG repeats and found that the repeats form a structure similar to standard double-stranded A-form nucleic acid. Since crystal structures may be misleading, however, we will verify A-form conformation using a solution-based assay. A-form double-stranded RNA (dsRNA) is known to be cleaved into small RNA molecules in cells. Therefore, we predict that the cellular machinery recognizing and cleaving these dsRNA should degrade expanded CUG repeats. To test this hypothesis, we will monitor the cleavage of CUG repeats in solution using an enzyme that recognizes and cleaves A-form dsRNA.