Abstract：
TDP1 removes transcription-blocking topoisomerase I cleavage complexes (TOP1ccs), and its inactivating H493R mutation causes the neurodegenerative syndrome SCAN1. However, the molecular mechanism underlying the SCAN1 phenotype is unclear. Here, we generate human SCAN1 cell models using CRISPR-Cas9 and show that they accumulate TOP1ccs along with changes in gene expression and genomic distribution of R-loops. SCAN1 cells also accumulate transcriptional DNA double-strand breaks (DSBs) specifically in the G1 cell population due to increased DSB formation and lack of repair, both resulting from abortive removal of transcription-blocking TOP1ccs. Deficient TDP1 activity causes increased DSB production, and the presence of mutated TDP1 protein hampers DSB repair by a TDP2-dependent backup pathway. This study provides powerful models to study TDP1 functions under physiological and pathological conditions and unravels that a gain of function of the mutated TDP1 protein, which prevents DSB repair, rather than a loss of TDP1 activity itself, could contribute to SCAN1 pathogenesis.
摘要：
TDP1去除转录阻断拓扑异构酶I切割复合物（TOP1ccs），其失活的H493R突变导致神经退行性综合征SCAN1。然而,SCAN1表型的分子机制尚不清楚.这里,我们使用CRISPR-Cas9生成人类SCAN1细胞模型，并显示它们随着基因表达和R环基因组分布的变化而积累TOP1ccs。由于增加的DSB形成和缺乏修复，SCAN1细胞还会在G1细胞群体中积累转录DNA双链断裂（DSB），两者都是由于转录阻断TOP1ccs的失败去除。TDP1活性不足导致DSB产量增加，并且突变的TDP1蛋白的存在通过TDP2依赖性备份途径阻碍DSB修复。这项研究为研究TDP1在生理和病理条件下的功能提供了强大的模型，并揭示了突变的TDP1蛋白的功能获得，这阻止了DSB修复，而不是TDP1活性本身的损失，可能有助于SCAN1的发病机制。
