SS18/BAFs regulate chromatin accessibility dynamics during pluripotent-somatic transition

The exit from pluripotency or pluripotent-somatic transition (PST) landmarks an event of mammalian development, and is also a representative cell-fate transition model, but remains largely unresolved. Recently, we reported construction of robust JUN-induced PST completed in one cell cycle and whose dominant regulator SS18/BAFs (Brg1/Brahma-associated factors). However, the transition process in the chromatin architecture and the roles played by BAF are still unknown. Here we report the dynamic changes of chromatin accessibility during JUN-induced PST. Meanwhile, SS18/BAFs mediates PST process by relocating from pluripotent loci to AP-1 associated ones and once compromised, JUN fails to open chromatin and PST will be delayed. Furthermore, we show that the relocation of SS18/BAF partially relays on histone modification H3K27ac, instead of JUN-centric protein-protein interaction. These results reveal the orchestration of master transcription factor, epigenetic machine, and histone modification in the cell fate transition. Overall design: We analyzed the transcriptome expression profiles (RNA-seq) in WT and bromodomain inhibitors treatment mESCs during the process of JUN triggered differentiation