Huh J-W, Ha H-S, Kim D-S, Kim H-S
Division of Biological Sciences, College of Natural Sciences, Pusan National University, Changjeon-dong, Busan, Republic of Korea.
Placenta. 2008 Jul;29(7):602-8. doi: 10.1016/j.placenta.2008.04.002. Epub 2008 May 13.
Domestication events of long terminal repeat (LTR) sequences of the human endogenous retrovirus (HERV) family have been considered to be a new mechanism for the generation of alternative splicing in the human genome. We investigated an LTR10A belonging to the HERV-I family at the human endothelial nitric oxide synthase (NOS3) gene locus. The LTR10A element was located upstream of the original promoter sequences of NOS3. Expression analysis using RT-PCR and reporter gene assays in HCT116 and COS7 cells indicated placenta-specific expression of NOS3 driven by the LTR10A-derived promoter. The placenta-restricted expression was also determined to be associated with hypomethylation of the LTR10A element by methylation analysis using sodium bisulfite DNA sequencing. Furthermore, treatment of brain-derived cell lines with demethylation reagents did not restore expression of the LTR-derived NOS3 gene transcript. Taken together, the integration event of an LTR10A element in the upstream region of NOS3 led to the generation of a placenta-specific alternative transcript governed by cooperative mechanisms of epigenetic control (DNA methylation) and transcriptional regulation (interaction between cis- and trans-acting elements).
人类内源性逆转录病毒（HERV）家族的长末端重复序列（LTR）的驯化事件被认为是人类基因组中产生可变剪接的一种新机制。我们研究了位于人类内皮型一氧化氮合酶（NOS3）基因位点的属于HERV-I家族的LTR10A。LTR10A元件位于NOS3原始启动子序列的上游。使用RT-PCR和报告基因分析在HCT116和COS7细胞中进行的表达分析表明，由LTR10A衍生的启动子驱动的NOS3具有胎盘特异性表达。通过使用亚硫酸氢钠DNA测序的甲基化分析确定，胎盘限制性表达也与LTR10A元件的低甲基化有关。此外，用去甲基化试剂处理脑源性细胞系并不能恢复LTR衍生的NOS3基因转录本的表达。综上所述，NOS3上游区域的LTR10A元件的整合事件导致了由表观遗传控制（DNA甲基化）和转录调控（顺式和反式作用元件之间的相互作用）的协同机制控制的胎盘特异性可变转录本的产生。
