title: Expansions, contractions, and fragility of the spinocerebellar ataxia type 10 pentanucleotide repeat in yeast.
abstract: Spinocerebellar ataxia 10 (SCA10) is an autosomal dominant disease caused by large-scale expansions of the (ATTCT)(n) repeat within an intron of the human ATXN10 gene. In contrast to other expandable repeats, this pentanucleotide repeat does not form stable intra- or interstranded DNA structures, being a DNA unwinding element instead. We analyzed the instability of the (ATTCT)(n) repeat in a yeast experimental system, where its expansions led to inactivation of the URA3 reporter gene. The inactivation was due to a dramatic decrease in the mRNA levels owing to premature transcription termination and RNA polyadenylation at the repeat. The rates of expansions strongly increased with the repeat's length, mimicking genetic anticipation in human pedigrees. A first round of genetic analysis showed that a functional TOF1 gene precludes, whereas a functional RAD5 gene promotes, expansions of the (ATTCT)(n) repeat. We hypothesize that repeat expansions could occur upon fortuitous template switching during DNA replication. The rate of repeat contractions was elevated in the Tof1 knockout strain, but it was not affected by the RAD5 gene. Supporting the notion of replication irregularities, we found that (ATTCT)(n) repeats also cause length-dependent chromosomal fragility in yeast. Repeat-mediated fragility was also affected by the Tof1 and Rad5 proteins, being reduced in their absence.
authors.affiliation: Department of Biology, Tufts University, Medford, MA 02155, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Cherng
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Shishkin
authors.forename: Lucas I
authors.initials: LI
authors.lastname: Schlager
authors.forename: Ryan H
authors.initials: RH
authors.lastname: Tuck
authors.forename: Laura
authors.initials: L
authors.lastname: Sloan
authors.forename: Robert
authors.initials: R
authors.lastname: Matera
authors.forename: Partha S
authors.initials: PS
authors.lastname: Sarkar
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Ashizawa
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Freudenreich
authors.forename: Sergei M
authors.initials: SM
authors.lastname: Mirkin
mesh_terms: D000067736:Ataxin-10; D001483:Base Sequence; D001938:Brazil; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases / Q000235:genetics; D042622:DNA Repeat Expansion / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D020868:Gene Silencing; D017930:Genes, Reporter / Q000235:genetics; D006801:Humans; D018895:Microsatellite Repeats / Q000235:genetics*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D014170:Transformation, Genetic
chemical_list: C503889:ATXN10 protein, human; D000067736:Ataxin-10; D004268:DNA-Binding Proteins; D009419:Nerve Tissue Proteins; D029701:Saccharomyces cerevisiae Proteins; C119636:TOF1 protein, S cerevisiae; C554167:URA3 protein, S cerevisiae; D004247:DNA; C076225:RAD5 protein, S cerevisiae; D004265:DNA Helicases