Transcripts containing expanded CNG repeats, which are found in several neuromuscular diseases, are not exported from the nucleus and aggregate as ribonuclear inclusions by an unknown mechanism. Using the MS2-GFP system, which tethers fluorescent proteins to a specific mRNA, we followed the dynamics of single CUG-repeat transcripts and RNA aggregation in living cells. Single transcripts with 145 CUG repeats from the dystrophia myotonica-protein kinase (DMPK) gene had reduced diffusion kinetics compared with transcripts containing only five CUG repeats. Fluorescence recovery after photobleaching (FRAP) experiments showed that CUG-repeat RNAs display a stochastic aggregation behaviour, because individual RNA foci formed at different rates and displayed different recoveries. Spontaneous clustering of CUG-repeat RNAs was also observed, confirming the stochastic aggregation revealed by FRAP. The splicing factor Mbnl1 colocalized with individual CUG-repeat transcripts and its aggregation with RNA foci displayed the same stochastic behaviour as CUG-repeat mRNAs. Moreover, depletion of Mbnl1 by RNAi resulted in decreased aggregation of CUG-repeat transcripts after FRAP, supporting a direct role for Mbnl1 in CUG-rich RNA foci formation. Our data reveal that nuclear CUG-repeat RNA aggregates are labile, constantly forming and disaggregating structures, and that the Mbnl1 splicing factor is directly involved in the aggregation process.
Download full-text PDF |
Source |
---|---|
http://dx.doi.org/10.1242/jcs.073270 | DOI Listing |
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!