Data from: The replication of Frataxin gene is assured by activation of dormant origins in the presence of a GAA-repeat expansion

It is well known that DNA replication affects the stability of several trinucleotide repeats, but whether replication profiles of human loci carrying an expanded repeat differ from those of normal alleles is poorly understood in the endogenous context. We investigated this issue using cell lines from Friedreich’s ataxia patients, homozygous for a GAA-repeat expansion in intron 1 of the Frataxin gene. By interphase, FISH we found that in comparison to the normal Frataxin sequence the replication of expanded alleles is slowed or delayed. According to molecular combing, origins never fired within the normal Frataxin allele. In contrast, in mutant alleles dormant origins are recruited within the gene, causing a switch of the prevalent fork direction through the expanded repeat. Furthermore, a global modification of the replication profile, involving origin choice and a differential distribution of unidirectional forks, was observed in the surrounding 850 kb region. These data provide a wide-view of the interplay of events occurring during replication of genes carrying an expanded repeat.

众所周知，DNA复制（DNA replication）会影响多种三核苷酸重复序列（trinucleotide repeats）的稳定性，但在内源生理环境中，携带扩张型重复序列的人类基因座（human loci）的复制特征与正常等位基因（normal alleles）是否存在差异，这一问题仍未得到充分阐释。本研究针对该问题展开探究，使用了来自弗里德赖希共济失调（Friedreich’s ataxia）患者的细胞系，该类细胞系的frataxin（Frataxin）基因内含子1区域存在纯合的GAA重复序列扩张。通过间期荧光原位杂交（interphase FISH）实验，我们发现相较于正常frataxin基因序列，扩张型等位基因的复制进程出现减慢或延迟。分子梳（molecular combing）分析结果显示，正常frataxin基因座内从未有复制起始位点激活。与之相反，突变型等位基因的基因区域内会募集处于休眠状态的复制起始位点，进而导致复制叉的主流行进方向在扩张型重复序列区域发生切换。此外，在该基因周围850kb的区域内，我们还观察到了复制特征的全局性改变，包括复制起始位点选择的变化以及单向复制叉（unidirectional forks）的差异化分布。本研究数据为携带扩张型重复序列的基因复制过程中各类事件的相互作用提供了全面的研究视角。