Coupling transcriptional state to large-scale repeat expansions in yeast

Area of Science:

• Genetics
• Molecular Biology
• Human Hereditary Disorders

Background:

• Expansions of simple DNA repeats are the root cause of numerous human hereditary disorders.
• Replication, DNA repair, and transcription are all implicated in repeat expansion, but their distinct roles remain unclear.

Purpose of the Study:

• To differentiate the roles of replication and transcription in the expansion of Friedreich's ataxia (GAA)n repeats.
• To investigate how transcriptional state and replication affect large-scale repeat expansions.

Main Methods:

• Developed two yeast genetic systems with (GAA)n repeats in transcribed or nontranscribed regions under a galactose-inducible promoter.
• Assessed large-scale repeat expansions under varying conditions of transcription and replication.
• Utilized a selectable cassette for repeat analysis.

Main Results:

• Large-scale repeat expansions occurred even without transcription.
• Transcriptional induction significantly increased expansion rates in both systems.
• Replication defects elevated expansion rates regardless of the transcriptional state.
• Findings suggest active transcriptional state, not transcription itself, modulates expansions.

Conclusions:

• Transcriptional state, potentially via nucleosomal density, acts as a key modulator of large-scale DNA repeat expansions.
• Replication stress also significantly contributes to repeat instability.
• This research provides insights into the mechanisms underlying hereditary repeat expansion disorders.