Replication Stalling and Heteroduplex Formation within CAG/CTG Trinucleotide Repeats by Mismatch Repair
Permanent link to this recordhttp://hdl.handle.net/10754/602087
MetadataShow full item record
AbstractTrinucleotide repeat expansions are responsible for at least two dozen neurological disorders. Mechanisms leading to these large expansions of repeated DNA are still poorly understood. It was proposed that transient stalling of the replication fork by the repeat tract might trigger slippage of the newly-synthesized strand over its template, leading to expansions or contractions of the triplet repeat. However, such mechanism was never formally proven. Here we show that replication fork pausing and CAG/CTG trinucleotide repeat instability are not linked, stable and unstable repeats exhibiting the same propensity to stall replication forks when integrated in a yeast natural chromosome. We found that replication fork stalling was dependent on the integrity of the mismatch-repair system, especially the Msh2p-Msh6p complex, suggesting that direct interaction of MMR proteins with secondary structures formed by trinucleotide repeats in vivo, triggers replication fork pauses. We also show by chromatin immunoprecipitation that Msh2p is enriched at trinucleotide repeat tracts, in both stable and unstable orientations, this enrichment being dependent on MSH3 and MSH6. Finally, we show that overexpressing MSH2 favors the formation of heteroduplex regions, leading to an increase in contractions and expansions of CAG/CTG repeat tracts during replication, these heteroduplexes being dependent on both MSH3 and MSH6. These heteroduplex regions were not detected when a mutant msh2-E768A gene in which the ATPase domain was mutated was overexpressed. Our results unravel two new roles for mismatch-repair proteins: stabilization of heteroduplex regions and transient blocking of replication forks passing through such repeats. Both roles may involve direct interactions between MMR proteins and secondary structures formed by trinucleotide repeat tracts, although indirect interactions may not be formally excluded.
CitationReplication Stalling and Heteroduplex Formation within CAG/CTG Trinucleotide Repeats by Mismatch Repair 2016 DNA Repair
SponsorsG.-F. R. thanks C. Saveanu and F. Feuerbach for the use of the TAP-tag library and advices on ChIP.
- Absence of MutSβ leads to the formation of slipped-DNA for CTG/CAG contractions at primate replication forks.
- Authors: Slean MM, Panigrahi GB, Castel AL, Pearson AB, Tomkinson AE, Pearson CE
- Issue date: 2016 Jun
- Instability of CAG and CTG trinucleotide repeats in Saccharomyces cerevisiae.
- Authors: Miret JJ, Pessoa-Brandão L, Lahue RS
- Issue date: 1997 Jun
- MSH2 ATPase domain mutation affects CTG*CAG repeat instability in transgenic mice.
- Authors: Tomé S, Holt I, Edelmann W, Morris GE, Munnich A, Pearson CE, Gourdon G
- Issue date: 2009 May
- In vitro repair of DNA hairpins containing various numbers of CAG/CTG trinucleotide repeats.
- Authors: Zhang T, Huang J, Gu L, Li GM
- Issue date: 2012 Feb 1
- Replication and expansion of trinucleotide repeats in yeast.
- Authors: Pelletier R, Krasilnikova MM, Samadashwily GM, Lahue R, Mirkin SM
- Issue date: 2003 Feb