LIN28 Promotes Nucleolar/Ribosomal Functions to Repress the 2C-like Transcriptional Program in Pluripotent Stem Cells [ChIP-seq]

LIN28 is an RNA binding protein with important roles in early embryo development by interaction with let-7 microRNA precursors or mRNAs in cytoplasm. Here, we showed novel roles of LIN28 within the nucleolus in cultured pluripotent stem cells (PSCs). We found Lin28 deficiency led to activation of the 2-cell (2C)-like transcriptional program and repression of the ES cell program. Mechanistically, LIN28 maintains a peri-nucleolar heterochromatin-residing complex to repress 2C activator Dux via association with NCL and TRIM28. Meanwhile, it promotes liquid-liquid phase separation (LLPS) of nucleolar proteins FBL and NCL to support nucleolar function through its RNA binding domains and intrinsic disordered regions. These findings elucidate novel roles for nucleolar LIN28 in coordinately regulating the ES/2C state homeostasis, and shed light on RNA binding protein-mediated nucleolar phase separation mechanisms in PSCs and early embryo development. Overall design: Examination of histone modifications in wide-type and Lin28a/b double knockout iPS cells by ChIP-seq.