Trinucleotide repeat instability during double-strand break repair: from mechanisms to gene therapy

  title={Trinucleotide repeat instability during double-strand break repair: from mechanisms to gene therapy},
  author={Valentine Mosbach and Lucie Poggi and Guy-Franck Richard},
  journal={Current Genetics},
Trinucleotide repeats are a particular class of microsatellites whose large expansions are responsible for at least two dozen human neurological and developmental disorders. Slippage of the two complementary DNA strands during replication, homologous recombination or DNA repair is generally accepted as a mechanism leading to repeat length changes, creating expansions and contractions of the repeat tract. The present review focuses on recent developments on double-strand break repair involving… 

Slipped-CAG DNA binding small molecule induces trinucleotide repeat contractions in vivo

A compound, naphthyridine-azaquinolone (NA), is reported that specifically binds slipped-CAG DNA intermediates of expansion mutations, a previously unsuspected target, and induces contractions of expanded repeats and reduces mutant HTT protein aggregates in cell and animal models of Huntington's disease.

Structure-forming repeats and their impact on genome stability.

Experimenting with Trinucleotide Repeats: Facts and Technical Issues.

  • G. Richard
  • Biology, Chemistry
    Methods in molecular biology
  • 2020
Known technical issues linked to trinucleotide repeat secondary structures, such as slippage during polymerase chain reaction and aberrant migration of long trin nucleotide repeats during agarose gel electrophoresis are reviewed.

THO and TRAMP complexes prevent transcription-replication conflicts, DNA breaks, and CAG repeat contractions

It is discovered that Thp2, an RNA export factor and member of the THO complex, and Trf4, a key component of the TRAMP complex involved in nuclear RNA degradation, are necessary to prevent CAG fragility and repeat contractions in a S. cerevisiae model system.

Gene Therapy for Huntington's Disease Using Targeted Endonucleases.

A protocol for HTT gene knock out using a modified Cas9 protein (nickase, Cas9n) and a pair of sgRNAs flanking the repeats is described and efficient HTT inactivation independent of the CAG tract length was confirmed by Western blotting.

Quantifying Replication Fork Progression at CTG Repeats by 2D Gel Electrophoresis.

Although two-dimensional agarose gel electrophoresis theoretically allows to resolve a mixture of structured DNA molecules and quantify them by radioactive hybridization, its practical application to trinucleotide repeats faces some serious technical challenges.

Single-cell microfluidic analysis unravels individual cellular fates during Double-Strand Break Repair

DSBR is characterized with an interdisciplinary approach, linking large population dynamics and individual cells, and three different categories of repair are identified: high-efficacy error-free, low-efficency error- free and low-efficiency error-prone.

Defects in the GINS complex increase the instability of repetitive sequences via a recombination-dependent mechanism

It is proposed that defective functioning of the CMG-E complex in psf1-1 cells impairs the progression of DNA replication what increases the contribution of repair mechanisms such as template switch and break-induced replication.

Defining the Properties and Toxicity Mechanisms of Non-Canonical Translation Products Associated with ALS and Huntington’s Disease Using C. elegans

These studies are the first to model codon-varied CAG RAN polypeptides in a multicellular animal and suggest that polyLeu toxicity occurs via disrupted folding of transmembrane proteins.

Recent progress in genome editing for gene therapy applications: the French perspective.

Improvements developed today are proposed to overcome the editing related genotoxicity and improve editing precision by the use of novel recombinant nuclease-based systems such as nickases, base editors and prime editors.



Double-strand break repair can lead to high frequencies of deletions within short CAG/CTG trinucleotide repeats

It is shown that deletion of RAD27, a gene involved in the processing of Okazaki fragments, increases the frequency of contractions tenfold and suggests that both gene conversion and single-strand annealing are major sources of trinucleotide repeat rearrangements.

Meiotic instability of CAG repeat tracts occurs by double-strand break repair in yeast.

It is shown here that meiotic instability of the CAG/CTG repeat tract in yeast is associated with double-strand break (DSB) formation within the repeated sequences, and that the DSB formation is dependent on the meiotic recombination machinery.

Highly Specific Contractions of a Single CAG/CTG Trinucleotide Repeat by TALEN in Yeast

It is the first demonstration that induction of a TALEN in an eukaryotic cell leads to shortening of trinucleotide repeat tracts to lengths below pathological thresholds in humans, with 100% efficacy and very high specificity.

Double-Strand Break Repair Pathways Protect against CAG/CTG Repeat Expansions, Contractions and Repeat-Mediated Chromosomal Fragility in Saccharomyces cerevisiae

It is concluded that failure of principal DSB repair pathways to repair breaks that occur within the repeats can result in the accumulation of atypical intermediates, whose aberrant resolution will then lead to CAG expansions, contractions, and repeat-mediated chromosomal fragility.

DNA tandem repeat instability in the Escherichia coli chromosome is stimulated by mismatch repair at an adjacent CAG·CTG trinucleotide repeat

It is shown that a CAG·CTG TNR array stimulates instability at a 275-bp tandem repeat located 6.3 kb away on the Escherichia coli chromosome, a demonstration, in a simple model system, that MMR at one type of repetitive DNA has the potential to influence the stability of another.

Replication dependent instability at (CTG)•(CAG) repeat hairpins in human cells

Targeted recombination is used to create a series of isogenic HeLa cell lines in which (CTG)•(CAG) repeats are replicated from an ectopic copy of the c-myc replication origin and hairpin cleavage by synthetic zinc finger nucleases in these cells has provided the first direct evidence for the formation of hairpin structures during replication in vivo.

Nanopore sequencing of complex genomic rearrangements in yeast reveals mechanisms of repeat-mediated double-strand break repair.

Using whole-genome Nanopore sequencing to characterize several CGRs that originated from naturally occurring DSBs at (GAA)n microsatellites in Saccharomyces cerevisiae gave important insights into the mechanisms of DSB repair leading to C GRs.