Colocalization of muscleblind with RNA foci is separable from mis-regulation of alternative splicing in myotonic dystrophy

J Cell Sci. 2005 Jul 1;118(Pt 13):2923-33. doi: 10.1242/jcs.02404. Epub 2005 Jun 16.


Myotonic dystrophy type I (DM1), which is caused by a non-coding CTG-repeat expansion in the dystrophia myotonica-protein kinase (DMPK) gene, is an RNA-mediated disease. Expanded CUG repeats in transcripts of mutant DMPK form nuclear foci that recruit muscleblind-like (MBNL) proteins, a family of alternative splicing factors. Although transcripts of mutant DMPK and MBNL proteins accumulate in nuclear RNA foci, it is not clear whether foci formation is required for splicing mis-regulation. Here, we use a co-transfection strategy to show that both CUG and CAG repeats form RNA foci that colocalize with green fluorescent protein (GFP)-MBNL1 and endogenous MBNL1. However, only CUG repeats alter splicing of the two tested pre-mRNAs, cardiac troponin T (cTNT) and insulin receptor (IR). Using FRAP, we demonstrate that GFP-MBNL1 in CUG and CAG foci have similar half-times of recovery and fractions of immobile molecules, suggesting that GFP-MBNL1 is bound by both CUG and CAG repeats. We also find an immobile fraction of GFP-MBNL1 in DM1 fibroblasts and a similar rapid exchange in endogenous CUG RNA foci. Therefore, formation of RNA foci and disruption of MBNL1-regulated splicing are separable events.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Alternative Splicing*
  • Cell Line
  • Cell Nucleus / genetics*
  • Cell Nucleus / metabolism
  • Exons
  • Fibroblasts / metabolism
  • Fibroblasts / ultrastructure
  • Gene Expression
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Humans
  • In Situ Hybridization, Fluorescence
  • Myotonic Dystrophy / classification
  • Myotonic Dystrophy / genetics*
  • Myotonic Dystrophy / metabolism*
  • RNA / genetics*
  • RNA / metabolism
  • RNA-Binding Proteins / genetics*
  • RNA-Binding Proteins / metabolism
  • Time Factors
  • Trinucleotide Repeat Expansion / genetics


  • MBNL1 protein, human
  • RNA-Binding Proteins
  • Green Fluorescent Proteins
  • RNA