A low absolute number of expanded transcripts is involved in myotonic dystrophy type 1 manifestation in muscle
SourceHuman Molecular Genetics, 25, 8, (2016), pp. 1648-1662
Article / Letter to editor
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Cell Biology (UMC)
Human Molecular Genetics
SubjectRadboudumc 0: Other Research RIMLS: Radboud Institute for Molecular Life Sciences; Radboudumc 19: Nanomedicine RIMLS: Radboud Institute for Molecular Life Sciences
Muscular manifestation of myotonic dystrophy type 1 (DM1), a common inheritable degenerative multisystem disorder, is mainly caused by expression of RNA from a (CTG.CAG)n-expanded DM1 locus. Here, we report on comparative profiling of expression of normal and expanded endogenous or transgenic transcripts in skeletal muscle cells and biopsies from DM1 mouse models and patients in order to help us in understanding the role of this RNA-mediated toxicity. In tissue ofHSA(LR)mice, the most intensely used 'muscle-only' model in the DM1 field, RNA from the alpha-actin (CTG)250 transgene was at least 1000-fold more abundant than that from theDmpkgene, or theDMPKgene in humans. Conversely, theDMPKtransgene in another line, DM500/DMSXL mice, was expressed approximately 10-fold lower than the endogenous gene. Temporal regulation of expanded RNA expression differed between models. Onset of expression occurred remarkably late inHSA(LR)myoblasts duringin vitromyogenesis whereasDmpkorDMPK(trans)genes were expressed throughout proliferation and differentiation phases. Importantly, quantification of absolute transcript numbers revealed that normal and expandedDmpk/DMPKtranscripts in mouse models and DM1 patients are low-abundance RNA species. Northern blotting, reverse transcriptase-quantitative polymerase chain reaction, RNA-sequencing and fluorescentin situhybridization analyses showed that they occur at an absolute number between one and a few dozen molecules per cell. Our findings refine the current RNA dominance theory for DM1 pathophysiology, as anomalous factor binding to expanded transcripts and formation of soluble or insoluble ribonucleoprotein aggregates must be nucleated by only few expandedDMPKtranscripts and therefore be a small numbers game.
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