Tasor, a component of the human silencing hub (HUSH) complex, is crucial for maintaining genome integrity. It plays a key role in epigenetic repression of retroviruses, transposons like LINE-1 (L1), and genes. The HUSH complex, with Tasor as a central subunit, recruits histone methyl-transferase SETDB1 to deposit H3K9me3 repressive marks, leading to heterochromatin formation and gene silencing [2,3,4].

In naive pluripotent stem cells (PSCs), loss of Tasor triggers replication stress, disrupts H3K9me3 heterochromatin, and impairs L1 silencing, with more severe effects in primed PSCs. The survival of Tasor knockout PSCs during the transition from naive to primed pluripotency can be restored by inhibiting caspase or deleting the mitochondrial antiviral signaling protein (MAVS), suggesting unscheduled L1 expression activates an innate immune response causing cell death in cells exiting naive pluripotency [1]. Also, in the context of HIV, Tasor silencing or its degradation by HIV-2 Vpx increases HIV-1 LTR-derived transcripts at a post-transcriptional level, and Tasor interacts with RNA-related proteins like CNOT1 to repress HIV expression [2].

In summary, Tasor is essential for epigenetic regulation, especially in silencing transposable elements and maintaining cell viability during pluripotency transitions. Studies using Tasor knockout models have revealed its role in safeguarding the developmental potential of naive embryonic stem cells and in controlling viral expression, which may have implications for understanding stem cell-related disorders and viral-associated diseases.