SRA

Nucleolus is the organelle for ribosome biogenesis and sensing various types of stress. Its role in regulating stem cell fate is unclear. Here, we present multiple lines of evidence that nucleolar stress induced by interfering rRNA biogenesis can drive two-cell stage embryo-like (2C-like) transcriptional program and induce an expanded 2C-like cell population in mouse embryonic stem (mES) cells. Mechanistically, the liquid-liquid phase separation (LLPS) mediated by rRNA and nucleolar proteins maintains the formation of peri-nucleolar heterochromatin (PNH). When mES cells undergo rRNA biogenesis defect, the normal LLPS of nucleolus is disrupted, causing deconjugation of NCL/TRIM28 complex on PNH and changes of epigenetic state and 3D structure of PNH, which leads to Dux, a conserved multicopy retrogene defining the cleavage-specific transcriptional program in placental mammals, to be released from the PNH region, activation of 2C-like program and transition of mES cells to 2C-like cells. Embryos with rRNA biogenesis defect are incompatible to develop from 2-cell (2C) to blastocyte (BC) and appear to skew from the blastocyst to earlier cleavage embryo signatures. Our results highlight that nucleolar LLPS-mediated 3D chromatin structure reshaping of PNH compartment regulates the fate transition of mES cells to 2C-like cells. Our findings for the first time elucidate the novel roles of rRNA biogenesis in regulating the 2C-like and ES state homeostasis in cultured cells and suggest that rRNA biogenesis is a new molecular switch from nucleolus-unmatured 2C stage to nucleolus-matured BC stage during murine pre-implantation embryo development. Overall design: Examination of histone modifications and NCL/TRIM28 binding in control and CX-5461 treated ES cells by ChIP-seq.