Expansions, contractions, and fragility of the spinocerebellar ataxia type 10 pentanucleotide repeat in yeast
Expansions, contractions, and fragility of the spinocerebellar ataxia type 10 pentanucleotide repeat in yeast
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DOI：
10.1073/pnas.1009409108
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发表时间：
2011-02-15
影响因子：
11.1
通讯作者：
Mirkin, Sergei M.
中科院分区：
文献类型：
--
作者：
Cherng, Nicole;Shishkin, Alexander A.;Mirkin, Sergei M.
脊髓小脑性共济失调10（SCA10）是一种常染色体显性遗传疾病，由人类ATXN10基因内含子内（ATTCT）（n）重复序列的大规模扩增引起。与其他可扩展重复序列相比，这种五核苷酸重复序列不形成稳定的链内或链间DNA结构，而是DNA解旋元件。我们在酵母实验系统中分析了（ATTCT）（n）重复序列的不稳定性，其中其扩增导致URA3报告基因的失活。失活是由于mRNA水平的急剧下降，由于过早的转录终止和RNA多聚腺苷酸化的重复。扩增率随着重复序列的长度而显著增加，这与人类谱系中的遗传预测相似。第一轮遗传分析表明，功能性TOF1基因排除了（ATTCT）（n）重复序列的扩增，而功能性RAD5基因促进了（ATTCT）（n）重复序列的扩增。我们假设重复扩增可能发生在DNA复制过程中偶然的模板转换。Tof1基因敲除株的重复收缩率升高，但不受RAD5基因的影响。支持复制不规则性的概念，我们发现（ATTCT）（n）重复也会导致酵母中长度依赖性染色体脆性。重复介导的脆性也受到Tof1和Rad5蛋白的影响，在它们不存在的情况下减少。
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.