Tissue- and age-specific DNA replication patterns at the CTG/CAG-expanded human myotonic dystrophy type 1 locus

Area of Science:

• Genetics
• Molecular Biology
• Epigenetics

Background:

• Myotonic dystrophy is caused by CTG/CAG repeat expansions at the DM1 locus.
• Repeat instability varies significantly between different tissues and at different ages within patients.
• Understanding the mechanisms driving this instability is crucial for therapeutic development.

Purpose of the Study:

• To investigate DNA replication profiles at the DM1 locus in patient-derived cells and transgenic mouse models.
• To correlate replication dynamics with the observed tissue- and age-specific repeat instability in myotonic dystrophy.

Main Methods:

• Analysis of DNA replication origins and fork progression at the DM1 locus in human fibroblasts and mouse tissues.
• Examination of the role of CTCF sites and CpG methylation in regulating replication at the DM1 locus.
• Comparison of replication patterns across different ages in mouse models exhibiting varying repeat instability.

Main Results:

• Replication origins near the DM1 repeat were identified, with diminished replication observed at the expansion in patient cells.
• In mice, the DM1 expansion replicated using the downstream origin with CAG as the lagging template.
• Replication pausing and subsequent relief in mouse testes correlated with age-dependent instability.
• CpG methylation at DM1 CTCF sites influenced replication in brain, pancreas, and thymus.
• CTCF sites impeded replication progression depending on chromatin context.

Conclusions:

• Replication progression dynamics at the DM1 locus are a key determinant of tissue- and age-specific repeat instability.
• Epigenetic modifications, such as CpG methylation, and CTCF site interactions modulate replication and instability.
• These findings provide insights into the molecular mechanisms underlying myotonic dystrophy pathogenesis.