Dnmt1 deficiency promotes CAG repeat expansion in the mouse germline

Area of Science:

• Genetics
• Epigenetics
• Neuroscience

Background:

• Expanded CAG repeat tracts are responsible for numerous neurodegenerative disorders.
• These repeats often expand across generations, leading to earlier disease onset and increased severity.

Purpose of the Study:

• To investigate the role of DNA methyltransferase Dnmt1 in the instability of expanded CAG triplet repeats.
• To determine if Dnmt1 deficiency affects intergenerational CAG repeat expansion in mice.

Main Methods:

• siRNA knockdown of Dnmt1 in human cells.
• Analysis of CAG repeat instability in Dnmt1-deficient mice and their germlines.
• Examination of DNA and histone methylation patterns in affected mice.

Main Results:

• Dnmt1 knockdown destabilized CAG triplet repeats in human cells.
• Dnmt1 deficiency in mice promoted intergenerational expansion of CAG repeats at the Sca1 locus.
• Dnmt1-deficient mice models mimicked human intergenerational instability patterns, with aberrant methylation observed.

Conclusions:

• Dnmt1 plays a critical role in maintaining CAG repeat stability.
• Aberrant DNA and histone methylation in Dnmt1-deficient mice suggest a role for local chromatin structure in repeat instability.
• Epigenetic changes during germline development contribute to intergenerational CAG repeat instability in both mice and humans.