Human Molecular Genetics Advance Access originally published online on February 9, 2005
Human Molecular Genetics 2005 14(6):873-883; doi:10.1093/hmg/ddi080
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Myotonic dystrophy associated expanded CUG repeat muscleblind positive ribonuclear foci are not toxic to Drosophila
1Institute of Biomedical and Life Sciences, University of Glasgow, Anderson College Complex, 56 Dumbarton Road, Glasgow G11 6NU, UK and 2Department of Genetics, University of Valencia, Dr Moliner 50, 46100 Burjasot, Spain
* To whom correspondence should be addressed. Tel: +44 1413306213; Fax: +44 1413306871; Email: d.monckton{at}bio.gla.ac.uk
Received November 8, 2004; Revised January 21, 2005; Accepted February 1, 2005
Myotonic dystrophy type 1 is an autosomal dominant disorder associated with the expansion of a CTG repeat in the 3' untranslated region (UTR) of the DMPK gene. Recent data suggest that pathogenesis is predominantly mediated by a gain of function of the mutant transcript. In patients, these expanded CUG repeat-containing transcripts are sequestered into ribonuclear foci that also contain the muscleblind-like proteins. To provide further insights into muscleblind function and the pathogenesis of myotonic dystrophy, we generated Drosophila incorporating CTG repeats in the 3'-UTR of a reporter gene. As in patients, expanded CUG repeats form discrete ribonuclear foci in Drosophila muscle cells that co-localize with muscleblind. Unexpectedly, however, foci are not observed in all cell types and muscleblind is neither necessary nor sufficient for their formation. The foci are dynamic transient structures with short half-lifes that do not co-localize with the proteasome, suggesting they are unlikely to contain mis-folded proteins. However, they do co-localize with non-A, the human orthologs of which are implicated in both RNA splicing and attachment of dsRNA to the nuclear matrix. Muscleblind is also revealed as having a previously unrecognized role in stabilizing CUG transcripts. Most interestingly, Drosophila expressing (CUG)162 repeats has no detectable pathological phenotype suggesting that in contrast to expanded polyglutamine-containing proteins, neither the expanded CUG repeat RNA nor the ribonuclear foci are directly toxic.
Present address: The Wellcome Trust Centre for Cell Biology, Michael Swann Building, Mayfield Road, Edinburgh EH9 3JR, UK.
Present address: Target and Drug Discovery, Ordway Research Institute, 150 New Scotland Avenue, Albany, NY 12208, USA.
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