The DNA Replication Program Is Altered at the FMR1 Locus in Fragile X Embryonic Stem Cells
The DNA Replication Program Is Altered at the FMR1 Locus in Fragile X Embryonic Stem Cells
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DOI：
10.1016/j.molcel.2013.10.029
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发表时间：
2014-01-01
期刊：
影响因子：
16
通讯作者：
Schildkraut, Carl L.
中科院分区：
文献类型：
--
作者：
Gerhardt, Jeannine;Tomishima, Mark J.;Schildkraut, Carl L.
脆性X综合征（FXS）是由FMR 1基因中的CGG重复扩增引起的，该重复扩增似乎发生在卵子发生和早期胚胎发生期间。一个模型提出，重复序列的不稳定性取决于通过重复序列的复制叉方向，使得（CNG）（n）发夹样结构形成，导致DNA聚合酶停滞和滑动。在内源性FMR 1基因座处检查单个DNA分子上的DNA复制叉进展揭示了在人类细胞中复制叉在CGG重复处停滞。此外，与未受影响的hESC相比，FXS人胚胎干细胞（hESC）的复制谱表明，FXS hESC中FMR 1位点的重复序列的叉方向发生了改变，因此CCG链主要用作滞后链模板。这是由于缺乏复制起始，通常会发生在FMR 1的上游，这表明改变复制起点的使用结合叉停滞促进重复不稳定性在早期胚胎发育。
Fragile X syndrome (FXS) is caused by a CGG repeat expansion in the FMR1 gene that appears to occur during oogenesis and during early embryogenesis. One model proposes that repeat instability depends on the replication fork direction through the repeats such that (CNG)(n) hairpin-like structures form, causing DNA polymerase to stall and slip. Examining DNA replication fork progression on single DNA molecules at the endogenous FMR1 locus revealed that replication forks stall at CGG repeats in human cells. Furthermore, replication profiles of FXS human embryonic stem cells (hESCs) compared to nonaffected hESCs showed that fork direction through the repeats is altered at the FMR1 locus in FXS hESCs, such that predominantly the CCG strand serves as the lagging-strand template. This is due to the absence of replication initiation that would typically occur upstream of FMR1, suggesting that altered replication origin usage combined with fork stalling promotes repeat instability during early embryonic development.