Three-dimensional chromatin interactions remain stable upon CAG/CTG repeat expansion.

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Expanded CAG/CTG repeats are associated with over 13 neurological disorders, including myotonic dystrophy type 1 (DM1) and Huntington's disease (HD).
• Disease-associated repeat expansions often lead to heterochromatin formation, potentially altering chromatin structure, gene expression, and repeat instability.
• The precise role of chromatin conformation changes in the pathogenesis of these repeat expansion disorders remains unclear.

Purpose of the Study:

• To investigate whether expanded CAG/CTG repeats alter chromatin conformation in cis.
• To determine if changes in chromatin interactions contribute to repeat instability and altered gene expression in DM1 and HD.

Main Methods:

• Utilized 4C sequencing to analyze chromatin interactions at the DMPK (DM1) and HTT (HD) loci.
• Examined cells derived from DM1 and HD patients with varying repeat lengths and epigenetic modifications.
• Assessed the impact of ectopically inserted expanded CAG repeat tracts on surrounding chromatin structure.

Main Results:

• Chromatin interaction profiles were similar across a wide range of allele sizes (15 to 1700 repeats) for both the DMPK and HTT loci.
• These findings held true regardless of DNA methylation levels or CTCF binding status.
• Ectopic insertion of expanded CAG repeats did not alter the conformation of adjacent chromatin.

Conclusions:

• CAG/CTG repeat expansions alone are insufficient to induce changes in local chromatin conformation.
• Altered chromatin interactions are unlikely to be the primary driver of repeat instability or gene expression dysregulation in these neurological disorders.
• Further research is needed to elucidate the mechanisms underlying repeat expansion disorders.