Trinucleotide repeat expansions catalyzed by human cell-free extracts.

Area of Science:

• Genetics
• Molecular Biology
• Neuroscience

Background:

• Trinucleotide repeat expansions are responsible for numerous heritable neurological disorders.
• Somatic expansions occur in non-proliferating tissues, suggesting replication-independent mechanisms.
• The DNA repair protein MutSβ (Msh2-Msh3 complex) is implicated in somatic expansions, but its biochemical role is debated.

Purpose of the Study:

• To develop a novel in vitro assay to study replication-independent trinucleotide repeat expansions.
• To investigate the biochemical role of MutSβ in trinucleotide repeat expansions.
• To establish a system that recapitulates key features of in vivo somatic expansions.

Main Methods:

• Utilized human cell-free extracts in a novel in vitro assay.
• Assessed expansions and contractions of trinucleotide repeats.
• Investigated the role of MutSβ in the observed repeat dynamics.

Main Results:

• Human cell-free extracts catalyze trinucleotide repeat expansions and contractions without DNA replication.
• The in vitro expansions mimic the size range observed in human diseases.
• Triplet repeat length and sequence influence expansion in vitro, mirroring in vivo observations.
• MutSβ significantly stimulates expansions in the cell-free system.

Conclusions:

• Aberrant DNA repair, particularly involving MutSβ, is a key driver of somatic trinucleotide repeat expansions.
• The developed in vitro system accurately models replication-independent somatic expansions.
• This system provides a powerful tool for studying the molecular mechanisms underlying trinucleotide repeat expansion disorders.