Premium
The Effects of Replication Fork Restart on CAG Repeat Instability in S. pombe
Author(s) -
Gold Michaela,
Freon Karine,
Su Allen,
Lambert Sarah,
Freudenreich Catherine
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.591.5
Subject(s) - biology , msh2 , trinucleotide repeat expansion , genetics , dna replication , spinocerebellar ataxia , schizosaccharomyces pombe , dna , dna repair , microbiology and biotechnology , mutant , gene , dna mismatch repair , allele
Trinucleotide repeats are a category of repetitive DNA elements that can form secondary structures and cause many diseases. Expansions of CAG repeats in particular can lead to numerous neurodegenerative polyglutamine diseases, including Huntington's disease and some spinocerebellar ataxias. These expansions could occur because the secondary structures the repeats form can stall DNA replicative polymerases, and fork restart may be prone to repeat instability. In order to test this idea, we have used the Schizosaccharomyces pombe fission yeast Replication Fork Barrier (RFB) system to induce fork restart through a CAG repeat tract and study the effects on CAG repeat instability (expansions and contractions). We created constructs with 70 CAG repeats inserted at different locations relative to the RFB. With the repeats either 1.9 kb or 6.7 kb after the RFB, increased CAG repeat instability was detected after RFB induction, indicating that fork restart can be a source of repeat instability. In order to test the mechanism of repeat instability during fork restart, key proteins potentially involved in the process were deleted. In contrast to wild‐type, in cells missing the Rad52 protein, which is involved with homologous recombination (HR) and required for restart in this system, induction of the RFB did not further increase repeat instability. This suggests that HR could be a leading cause of RFB‐induced repeat instability. Msh2 has been shown to bind CAG repeats and cause repeat expansions in mouse models. In S. pombe strains without Msh2, expansions decreased irrespective of RFB status. These results suggest that Msh2 is involved in the CAG expansion mechanism as in vertebrates, but likely not during fork restart, and S. pombe can be used to study this phenomenon. In summary, we have identified two mechanisms of CAG instability in S. pombe : expansions caused by presence of the Msh2 protein unrelated to fork restart, and a second novel mechanism of HR‐dependent fork restart that causes both expansions and contractions of this unstable repeat. Support or Funding Information This research was funded by National Institutes of Health grant P01‐GM105473/402373 and the Curie Institute Rothschild‐Yvette Mayent Award to C.H.F., ANR 14‐CE10‐0010‐01 and FRM label funds to S.L., and Tufts University Sandler and Undergraduate Research Funds to C.H.F. and M.A.G..