Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.

Disease-associated trinucleotide repeats form secondary DNA structures that interfere with replication and repair. Replication has been implicated as a mechanism that can cause repeat expansions and contractions. However, because structure-forming repeats are also replication barriers, it has been u...

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Autores principales:	Michaela A Gold, Jenna M Whalen, Karine Freon, Zixin Hong, Ismail Iraqui, Sarah A E Lambert, Catherine H Freudenreich
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2021
Materias:	Genetics QH426-470
Acceso en línea:	https://doaj.org/article/217d60e344ba4718b05f2866338cb4b1
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spelling	oai:doaj.org-article:217d60e344ba4718b05f2866338cb4b12021-12-02T20:03:29ZRestarted replication forks are error-prone and cause CAG repeat expansions and contractions.1553-73901553-740410.1371/journal.pgen.1009863https://doaj.org/article/217d60e344ba4718b05f2866338cb4b12021-10-01T00:00:00Zhttps://doi.org/10.1371/journal.pgen.1009863https://doaj.org/toc/1553-7390https://doaj.org/toc/1553-7404Disease-associated trinucleotide repeats form secondary DNA structures that interfere with replication and repair. Replication has been implicated as a mechanism that can cause repeat expansions and contractions. However, because structure-forming repeats are also replication barriers, it has been unclear whether the instability occurs due to slippage during normal replication progression through the repeat, slippage or misalignment at a replication stall caused by the repeat, or during subsequent replication of the repeat by a restarted fork that has altered properties. In this study, we have specifically addressed the fidelity of a restarted fork as it replicates through a CAG/CTG repeat tract and its effect on repeat instability. To do this, we used a well-characterized site-specific replication fork barrier (RFB) system in fission yeast that creates an inducible and highly efficient stall that is known to restart by recombination-dependent replication (RDR), in combination with long CAG repeat tracts inserted at various distances and orientations with respect to the RFB. We find that replication by the restarted fork exhibits low fidelity through repeat sequences placed 2-7 kb from the RFB, exhibiting elevated levels of Rad52- and Rad8ScRad5/HsHLTF-dependent instability. CAG expansions and contractions are not elevated to the same degree when the tract is just in front or behind the barrier, suggesting that the long-traveling Polδ-Polδ restarted fork, rather than fork reversal or initial D-loop synthesis through the repeat during stalling and restart, is the greatest source of repeat instability. The switch in replication direction that occurs due to replication from a converging fork while the stalled fork is held at the barrier is also a significant contributor to the repeat instability profile. Our results shed light on a long-standing question of how fork stalling and RDR contribute to expansions and contractions of structure-forming trinucleotide repeats, and reveal that tolerance to replication stress by fork restart comes at the cost of increased instability of repetitive sequences.Michaela A GoldJenna M WhalenKarine FreonZixin HongIsmail IraquiSarah A E LambertCatherine H FreudenreichPublic Library of Science (PLoS)articleGeneticsQH426-470ENPLoS Genetics, Vol 17, Iss 10, p e1009863 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Genetics QH426-470
spellingShingle	Genetics QH426-470 Michaela A Gold Jenna M Whalen Karine Freon Zixin Hong Ismail Iraqui Sarah A E Lambert Catherine H Freudenreich Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
description	Disease-associated trinucleotide repeats form secondary DNA structures that interfere with replication and repair. Replication has been implicated as a mechanism that can cause repeat expansions and contractions. However, because structure-forming repeats are also replication barriers, it has been unclear whether the instability occurs due to slippage during normal replication progression through the repeat, slippage or misalignment at a replication stall caused by the repeat, or during subsequent replication of the repeat by a restarted fork that has altered properties. In this study, we have specifically addressed the fidelity of a restarted fork as it replicates through a CAG/CTG repeat tract and its effect on repeat instability. To do this, we used a well-characterized site-specific replication fork barrier (RFB) system in fission yeast that creates an inducible and highly efficient stall that is known to restart by recombination-dependent replication (RDR), in combination with long CAG repeat tracts inserted at various distances and orientations with respect to the RFB. We find that replication by the restarted fork exhibits low fidelity through repeat sequences placed 2-7 kb from the RFB, exhibiting elevated levels of Rad52- and Rad8ScRad5/HsHLTF-dependent instability. CAG expansions and contractions are not elevated to the same degree when the tract is just in front or behind the barrier, suggesting that the long-traveling Polδ-Polδ restarted fork, rather than fork reversal or initial D-loop synthesis through the repeat during stalling and restart, is the greatest source of repeat instability. The switch in replication direction that occurs due to replication from a converging fork while the stalled fork is held at the barrier is also a significant contributor to the repeat instability profile. Our results shed light on a long-standing question of how fork stalling and RDR contribute to expansions and contractions of structure-forming trinucleotide repeats, and reveal that tolerance to replication stress by fork restart comes at the cost of increased instability of repetitive sequences.
format	article
author	Michaela A Gold Jenna M Whalen Karine Freon Zixin Hong Ismail Iraqui Sarah A E Lambert Catherine H Freudenreich
author_facet	Michaela A Gold Jenna M Whalen Karine Freon Zixin Hong Ismail Iraqui Sarah A E Lambert Catherine H Freudenreich
author_sort	Michaela A Gold
title	Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
title_short	Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
title_full	Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
title_fullStr	Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
title_full_unstemmed	Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.
title_sort	restarted replication forks are error-prone and cause cag repeat expansions and contractions.
publisher	Public Library of Science (PLoS)
publishDate	2021
url	https://doaj.org/article/217d60e344ba4718b05f2866338cb4b1
work_keys_str_mv	AT michaelaagold restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT jennamwhalen restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT karinefreon restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT zixinhong restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT ismailiraqui restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT sarahaelambert restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions AT catherinehfreudenreich restartedreplicationforksareerrorproneandcausecagrepeatexpansionsandcontractions
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Restarted replication forks are error-prone and cause CAG repeat expansions and contractions.

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