TASOR expression in naive embryonic stem cells safeguards their developmental potential [CUT&TAG]. TASOR expression in naive embryonic stem cells safeguards their developmental potential [CUT&TAG]

The seamless transition through stages of pluripotency relies on a delicate balance between transcription factor networks and epigenetic silencing mechanisms that ensure proper regulation of the developmental program, critical for normal development. Here, we uncover the pivotal role of the transgene activation suppressor (TASOR), a component of the human silencing hub (HUSH) complex, in sustaining cell viability during the transition from naive to primed pluripotency, despite its rapid downregulation during this transition. Loss of TASOR in naive cells triggers replication stress, disrupts H3K9me3 heterochromatin formation, and compromise the transcriptional and post-transcriptional silencing of LINE-1 (L1) transposable elements (TEs), with these effects become more pronounced in primed cells. Remarkably, the survival of Tasor-knockout cells during naive to primed transition can be restored through the inhibition of cysteine-aspartic acid protease (Caspase) or deletion of mitochondrial antiviral signaling protein (MAVS). This suggests that unscheduled L1 expression activates an innate immune response, leading to programmed cell death, specifically in cells exiting naïve pluripotency. Additionally, we propose that HUSH-promoted H3K9me3 in naïve PSCs sets the stage for ensuing DNA methylation in primed cells, establishing long-term silencing during differentiation. Our findings shed insights on the crucial impact of epigenetic programs established in early developmental stages on subsequent phases, underscoring their significance in the developmental process. Overall design: CUT&TAG analysis in mouse embryonic stem cell lines and epiblast stem cell lines (WT, TASORKO, TASORKO+addback, TASORKO+MET)).

多能性各阶段的顺畅过渡，依赖于转录因子网络与表观遗传沉默机制间的精妙平衡——这一平衡可确保发育程序的精准调控，对正常发育至关重要。本研究揭示了转基因激活抑制因子（transgene activation suppressor, TASOR）——人类沉默枢纽（HUSH）复合物的组分之一——在原始态向始发态多能性过渡过程中维持细胞存活的关键作用，尽管该因子在此过渡阶段会快速下调。原始态多能细胞中TASOR的缺失会引发复制应激，破坏H3K9me3异染色质形成，并削弱长散在核元件1（LINE-1, L1）转座因子（TEs）的转录及转录后沉默，且这些效应在始发态多能细胞中更为显著。值得注意的是，在原始态向始发态多能性过渡过程中，Tasor基因敲除细胞的存活可通过抑制半胱天冬氨酸蛋白酶（Caspase）或敲除线粒体抗病毒信号蛋白（MAVS）得以恢复。这表明，异常表达的L1会激活先天免疫应答，进而引发程序性细胞死亡，这一现象特异性地发生在脱离原始态多能性的细胞中。此外，本研究提出，原始态多能干细胞中HUSH复合物介导的H3K9me3修饰，可为始发态多能细胞后续的DNA甲基化奠定基础，从而在分化过程中建立长期沉默状态。本研究结果阐明了早期发育阶段建立的表观遗传程序对后续发育阶段的关键影响，突显了其在发育进程中的重要意义。实验整体设计：对小鼠胚胎干细胞系及上胚层干细胞系（野生型WT、TASOR基因敲除型TASORKO、TASORKO+回补组、TASORKO+MET组）开展CUT&TAG分析。