MBNL Sequestration by Toxic RNAs and RNA Misprocessing in the Myotonic Dystrophy Brain

Area of Science:

• Neurology
• Molecular Biology
• Genetics

Background:

• Some neurological disorders are RNA-mediated due to non-coding repeat expansion RNAs (RNA(exp)).
• Disease toxicity is hypothesized to stem from protein sequestration by these expansions, depleting normal cellular targets.
• Experimental evidence for this RNA sequestration model has been limited.

Purpose of the Study:

• To provide experimental evidence for the RNA sequestration model of toxicity in myotonic dystrophy (DM).
• To investigate the role of MBNL proteins in DM-associated RNA toxicity.
• To establish a tool for evaluating RNA-mediated toxicity in other expansion diseases.

Main Methods:

• HITS-CLIP (High-Throughput Sequencing of RNA with Crosslinking and Immunoprecipitation) was used on human control and DM brain samples.
• Analysis of pre-mRNA processing was performed in human brain samples and Mbnl compound-knockout mice.
• Investigated MBNL2 binding to DM repeat expansions and its downstream effects.

Main Results:

• MBNL2 directly binds to DM repeat expansions in the brain, leading to its depletion from normal RNA targets.
• Downstream effects include altered alternative splicing and polyadenylation.
• Similar RNA processing defects, including Mapt splicing dysregulation and fetal tau isoform expression, were observed in Mbnl knockout mice.

Conclusions:

• MBNL proteins are directly sequestered by repeat expansion RNAs in the DM brain, supporting the RNA toxicity model.
• This sequestration causes significant downstream RNA processing defects.
• The study introduces a valuable experimental approach for studying RNA-mediated toxicity in other genetic expansion disorders.