Repeat expansion in a fragile X model is independent of double strand break repair mediated by Pol θ, RAD52, RAD54 or RAD54B.

Publisher: Nature Publishing Group Country of Publication: England NLM ID: 101563288 Publication Model: Electronic Cited Medium: Internet ISSN: 2045-2322 (Electronic) Linking ISSN: 20452322 NLM ISO Abbreviation: Sci Rep Subsets: MEDLINE

Original Publication: London : Nature Publishing Group, copyright 2011-

DNA-Directed DNA Polymerase*/metabolism ; DNA-Directed DNA Polymerase*/genetics ; DNA Polymerase theta* ; DNA Breaks, Double-Stranded* ; DNA End-Joining Repair* ; Rad52 DNA Repair and Recombination Protein*/metabolism ; Rad52 DNA Repair and Recombination Protein*/genetics ; DNA Helicases*/genetics ; DNA Helicases*/metabolism; Animals ; Mice ; Nuclear Proteins/genetics ; Nuclear Proteins/metabolism ; DNA-Binding Proteins/genetics ; DNA-Binding Proteins/metabolism ; DNA Repair ; Mouse Embryonic Stem Cells/metabolism ; Humans ; Disease Models, Animal

Microsatellite instability is responsible for the human repeat expansion diseases (REDs). The mutagenic process differs from classical cancer-associated microsatellite instability (MSI) in that it requires the mismatch repair proteins that normally protect against MSI. LIG4, an enzyme essential for non-homologous end-joining (NHEJ), the major pathway for double-strand break repair (DSBR) in mammalian cells, protects against expansion in mouse models. Thus, NHEJ may compete with the expansion pathway for access to a common intermediate. This raises the possibility that expansion involves an NHEJ-independent form of DSBR. Pol θ, a polymerase involved in the theta-mediated end joining (TMEJ) DSBR pathway, has been proposed to play a role in repeat expansion. Here we examine the effect of the loss of Pol θ on expansion in FXD mouse embryonic stem cells (mESCs), along with the effects of mutations in Rad52, Rad54l and Rad54b, genes important for multiple DSBR pathways. None of these mutations significantly affected repeat expansion. These observations put major constraints on what pathways are likely to drive expansion. Together with our previous demonstration of the protective effect of nucleases like EXO1 and FAN1, and the importance of Pol β, they suggest a plausible model for late steps in the expansion process.
Competing Interests: Declarations. Competing interests: The authors declare no competing interests.
(© 2025. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Update of: bioRxiv. 2024 Nov 06:2024.11.05.621911. doi: 10.1101/2024.11.05.621911.. (PMID: 39574643)

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Keywords: FMR1-related disorders (FMR1 disorders); Double-strand break repair; Fragile X-related disorders; Gap-filling model; Repeat expansion disease

EC 2.7.7.7 (DNA-Directed DNA Polymerase)
EC 2.7.7.- (DNA Polymerase theta)
0 (Rad52 DNA Repair and Recombination Protein)
EC 3.6.4.- (DNA Helicases)
0 (Rad52 protein, mouse)
EC 3.6.4.- (Rad54l protein, mouse)
0 (Nuclear Proteins)
0 (DNA-Binding Proteins)

Date Created: 20250211 Date Completed: 20250211 Latest Revision: 20250218

20250218

PMC11814403

10.1038/s41598-025-87541-3

39934227