The protein factors MBNL1 and U2AF65 bind alternative RNA structures to regulate splicing

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by (CTG)(n) repeat expansions in the DMPK gene.
• Expanded CUG repeats form RNA structures that sequester the RNA-binding protein MBNL1.
• MBNL1 mis-regulation leads to aberrant alternative splicing and DM1 symptoms.

Purpose of the Study:

• To elucidate the mechanism by which MBNL1 binding regulates alternative splicing.
• To investigate the competition between MBNL1 and U2AF65 at the 3' end of intron 4 in cTNT pre-mRNA.

Main Methods:

• Investigated MBNL1 and U2AF65 binding to cTNT pre-mRNA.
• Analyzed RNA structures formed at intron 4.
• Assessed the impact of mutations on splicing and protein binding.

Main Results:

• MBNL1 directly competes with U2AF65 for binding at the 3' end of intron 4.
• MBNL1 binds a stem-loop structure, while U2AF65 binds a single-stranded region.
• Disruption of U2AF65 binding by MBNL1 or RNA structure stabilizes exon skipping.

Conclusions:

• MBNL1 controls cTNT exon 5 splicing by antagonizing U2AF65 binding.
• RNA secondary structure and MBNL1 binding mutually exclude U2AF65.
• This competition mechanism provides insight into DM1 pathogenesis.