Arokium Hubert, Kamata Masakazu, Kim Sanggu, Kim Namshin, Liang Min, Presson Angela P, Chen Irvin S
Department of Microbiology, Immunology and Molecular Genetics, University of California Los Angeles, David Geffen School of Medicine, Los Angeles, California, United States of America.
Korean Bioinformation Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, South Korea.
PLoS One. 2014 Oct 7;9(10):e108682. doi: 10.1371/journal.pone.0108682. eCollection 2014.
Long interspersed element-1 (LINE-1 or L1) retrotransposition induces insertional mutations that can result in diseases. It was recently shown that the copy number of L1 and other retroelements is stable in induced pluripotent stem cells (iPSCs). However, by using an engineered reporter construct over-expressing L1, another study suggests that reprogramming activates L1 mobility in iPSCs. Given the potential of human iPSCs in therapeutic applications, it is important to clarify whether these cells harbor somatic insertions resulting from endogenous L1 retrotransposition. Here, we verified L1 expression during and after reprogramming as well as potential somatic insertions driven by the most active human endogenous L1 subfamily (L1Hs). Our results indicate that L1 over-expression is initiated during the reprogramming process and is subsequently sustained in isolated clones. To detect potential somatic insertions in iPSCs caused by L1Hs retotransposition, we used a novel sequencing strategy. As opposed to conventional sequencing direction, we sequenced from the 3' end of L1Hs to the genomic DNA, thus enabling the direct detection of the polyA tail signature of retrotransposition for verification of true insertions. Deep coverage sequencing thus allowed us to detect seven potential somatic insertions with low read counts from two iPSC clones. Negative PCR amplification in parental cells, presence of a polyA tail and absence from seven L1 germline insertion databases highly suggested true somatic insertions in iPSCs. Furthermore, these insertions could not be detected in iPSCs by PCR, likely due to low abundance. We conclude that L1Hs retrotransposes at low levels in iPSCs and therefore warrants careful analyses for genotoxic effects.
长散在重复序列1(LINE-1或L1)逆转录转座会引发插入突变,进而可能导致疾病。最近有研究表明,L1及其他逆转录元件的拷贝数在诱导多能干细胞(iPSC)中是稳定的。然而,另一项研究通过使用一个过表达L1的工程报告构建体,提示重编程会激活iPSC中L1的移动性。鉴于人iPSC在治疗应用中的潜力,明确这些细胞是否含有由内源性L1逆转录转座导致的体细胞插入至关重要。在此,我们验证了重编程期间及之后的L1表达,以及由最活跃的人类内源性L1亚家族(L1Hs)驱动的潜在体细胞插入情况。我们的结果表明,L1过表达在重编程过程中启动,并在分离的克隆中持续存在。为了检测由L1Hs逆转录转座在iPSC中引起的潜在体细胞插入,我们使用了一种新颖的测序策略。与传统测序方向相反,我们从L1Hs的3'端向基因组DNA进行测序,从而能够直接检测逆转录转座的多聚腺苷酸尾特征以验证真正的插入。深度覆盖测序使我们能够从两个iPSC克隆中检测到七个低读数计数的潜在体细胞插入。亲代细胞中的阴性PCR扩增、多聚腺苷酸尾的存在以及七个L1种系插入数据库中未出现,强烈提示iPSC中存在真正的体细胞插入。此外,这些插入在iPSC中通过PCR无法检测到,可能是由于丰度较低。我们得出结论,L1Hs在iPSC中以低水平逆转录转座,因此有必要对其遗传毒性效应进行仔细分析。
Hum Mol Genet. 2011-10-11
Mol Cell Biol. 2019-3-19
Genome Res. 2018-4-11
Biochem Soc Trans. 2024-6-26
Reprod Biol Endocrinol. 2020-1-21
Mob DNA. 2016-8-11
Genome Res. 2012-9-11
Science. 2012-6-28
Curr Opin Genet Dev. 2012-3-8
Nat Rev Genet. 2011-11-29
Hum Mol Genet. 2011-10-11