RNA splicing is responsive to MBNL1 dose

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• Myotonic dystrophy type 1 (DM1) is a multisystem disorder caused by expanded CTG repeats in the DMPK gene.
• Expanded CUG repeat RNAs sequester the RNA splice regulator MBNL1, leading to splice defects and DM1 pathology.
• While CTG repeat length correlates with DM1 severity, significant phenotype variability exists among patients.

Purpose of the Study:

• To investigate the relationship between MBNL1 levels and the number/severity of RNA splice defects in DM1.
• To explore how MBNL1 depletion contributes to the observed variability in DM1 patient phenotypes.

Main Methods:

• Analysis of MBNL1 levels in relation to splice defect repertoire and severity.
• Assessment of the impact of gradual MBNL1 decrease on RNA splicing.
• Correlation of MBNL1 dose variations with DM1 phenotype variability.

Main Results:

• A gradual decrease in MBNL1 levels expands the range of splice defects and increases their severity.
• MBNL1 loss has a graded effect on splice defects, not an all-or-none outcome.
• Small variations in free MBNL1 levels, influenced by CUG tract size and hairpin formation, significantly alter splice abnormalities.

Conclusions:

• MBNL1 depletion's impact on RNA splicing is dose-dependent, contributing to DM1 phenotype variability.
• Modest changes in MBNL1 levels, beyond a critical threshold, significantly affect splice defect severity and number.
• Understanding MBNL1's graded effect is crucial for explaining DM1 patient variability and potential therapeutic strategies.