Recurrent DNA nicks drive massive expansions of (GAA)n repeats

• 成果类型: Article
• 署名作者: Li, Liangzi; Scott, W. Shem; Khristich, Alexandra N.; Armenia, Jillian F.; Mirkin, Sergei M.
• 署名单位: Tufts University; Stanford University; Vanderbilt University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-11800
• DOI: 10.1073/pnas.2413298121
• 发表日期: 2024-12-03
• 关键词: double-strand breaks; fragile-x premutation; excision-repair gene; homologous recombination; saccharomyces-cerevisiae; friedreich ataxia; cag repeat; triplet repeats; trinucleotide expansion; postreplication repair

摘要

Over 50 hereditary degenerative disorders are caused by expansions of short tandem DNA repeats (STRs). (GAA)n repeat expansions are responsible for Friedreich's ataxia as well as late- onset cerebellar ataxias (LOCAs). Thus, the mechanisms of (GAA)n repeat expansions attract broad scientific attention. To investigate the role of DNA nicks in this process, we utilized a CRISPR-Cas9 nickase system to introduce targeted nicks adjacent to the (GAA)n repeat tract. We found that DNA nicks 5 ' of the (GAA)100 run led to a dramatic increase in both the rate and scale of its expansion in dividing cells. Strikingly, they also promoted large- scale expansions of carrier- and large normal- size (GAA)n repeats, recreating, in a model system, the expansion events that occur in human pedigrees. DNA nicks 3 ' of the (GAA)100 repeat led to a smaller but significant increase in the expansion rate as well. Our genetic analysis implies that in dividing cells, conversion of nicks into double- strand breaks (DSBs) during DNA replication followed by DSB or fork repair leads to repeat expansions. Finally, we showed that 5 ' GAA-strand nicks increase expansion frequency in nondividing yeast cells, albeit to a lesser extent than in dividing cells.