Abstract
The histone chaperone FACT is essential for chromatin organization and stem cell identity, yet the sequence of events through which FACT maintains chromatin integrity remains unclear. We generate a high-resolution temporal map of events leading to chromatin destabilization and cell identity loss in murine embryonic stem cells following dTAG-mediated depletion of FACT. Loss of FACT initiates a rapid cascade, with nucleosome phasing disruption and reduced H3K4me3 beginning within 10 minutes in a transcription-dependent manner. This architectural destabilization enables pluripotency transcription factors to ectopically occupy gene bodies. FACT loss results in RNA Polymerase II accumulation within 30 minutes and altered H3K36me3 deposition preceding a global transcriptional collapse at 2 hours of FACT depletion. FACT restoration fails to rescue these defects, demonstrating they are largely irreversible. Our findings define a temporal hierarchy in which FACT loss drives progressive deterioration of chromatin architecture, leading to transcriptional collapse in stem cells.