Role of Setdb1 in cell fate transitions between 2C-like state and pluripotent state

Setdb1 is known as a histone H3K9 methyltransferase which is essential for embryo development. Although several studies have shown that Setdb1 is required for pluripotency maintenance of mouse embryonic stem cells (ESCs) cultured in serum/LIF (SL) condition, the function of Setdb1 on cell fate decisions is widely unknown. Here we reported that under the “ground state” of pluripotency induced by two inhibitors (2i) of the MEK and GSK3 pathways, Setdb1 knockout do not induce trophectoderm (TE) differentiation as in SL condition. In both conditions, Setdb1 deficiency reactivates 2C-like state genes such as Zscan4 and Dux, which are repressed by Setdb1-dependent H3K9me3. Interestingly, Setdb1 deficiency only induces 2C-like totipotency in SL condition. In ground state, Setdb1-null ESCs maintain expression of pluripotent markers such as Nanog, resulted in a distinct stage with 2C-like totipotency. Furthermore, we found that in ground state, Setdb1 deficiency induced a rapid cell death by upregulating Ripk3 and then activating RIPK1/RIPK3 dependent necroptosis.