The role of ESRG in human pluripotency IV

Human pluripotent stem cells (PSCs) express human endogenous retroviruses type-H (HERV-Hs), which exist more than a thousand copies on the human genome and frequently produce chimeric transcripts as long-non-coding RNAs (lncRNAs) fused with downstream neighbor genes. Previous studies showed that HERV-H expression is required for the maintenance of PSC identity, and the aberrant HERV-H expression attenuated neural differentiation potentials, but little is known what their roles are. In this study, therefore, we focused on ESRG, which is known as a PSC-related HERV-H-driven lncRNA. The global transcriptome data of various tissues and cell lines and quantitative expression analysis showed that ESRG expression is much higher than other HERV-Hs and tightly silenced after differentiation, letting us hypothesize its crucial role in human pluripotency. However, the loss of function by the complete excision of the entire ESRG gene body using a CRISPR/Cas9 platform revealed that ESRG is dispensable for the maintenance of primed and naïve pluripotent states. The loss of ESRG hardly affects the global gene expression of PSCs and differentiation potentials toward trilineage. Differentiated cells derived from ESRG knockout PSCs retained the potential to be reprogrammed into induced PSC (iPSC) by the forced expression of OCT3/4, SOX2, and KLF4. In conclusion, ESRG is dispensable for the maintenance and the recapturing of human pluripotency.

人类多能干细胞（human pluripotent stem cells, PSCs）可表达人类内源性逆转录病毒H型（human endogenous retroviruses type-H, HERV-Hs）。该病毒家族在人类基因组中存在千余拷贝，且常可生成与下游邻近基因融合的长链非编码RNA（long non-coding RNAs, lncRNAs）型嵌合转录本。既往研究证实，HERV-H的表达是维持PSC身份所必需的，而异常的HERV-H表达会削弱神经分化潜能，但目前对其具体作用仍知之甚少。为此，本研究聚焦于ESRG——一种已被明确为PSC相关的HERV-H驱动型lncRNA。针对多种组织与细胞系的全局转录组数据及定量表达分析显示，ESRG的表达水平显著高于其他HERV-H成员，且在细胞分化后会被严格沉默，据此我们推测其在人类多能性维持中发挥关键作用。然而，通过CRISPR/Cas9平台完全切除整个ESRG基因体以实现功能敲除后，实验结果表明ESRG并非维持始发态与原始态多能状态所必需。ESRG的缺失几乎不会影响PSC的全局基因表达谱，也不会干扰其向三胚层的分化潜能。由ESRG敲除PSC分化得到的细胞，仍可通过强制表达OCT3/4、SOX2及KLF4被重编程为诱导多能干细胞（induced pluripotent stem cells, iPSCs）。综上，ESRG对于人类多能性的维持与重捕获均非必需。