Postmitotic transcription and 3D regulation show locus-specific and differentiation-specific sensitivity to cohesin depletion.

Acute cohesin loss causes widespread reorganization of three-dimensional (3D) chromatin architecture but has relatively minor effects on steady-state transcription. It remains unclear whether its role in gene regulation becomes more critical during mitotic exit, when 3D chromatin architecture and transcription are globally re-established. To address this, we acutely depleted RAD21 in mouse embryonic stem cells during mitotic exit under self-renewal or differentiation conditions. Here we show that, although most loops failed to reform without cohesin, the few cohesin-independent loops were linked to active promoters, strong enhancers and H3K27ac mitotic bookmarking. Transcriptional changes were only modest, indicating that gene reactivation largely bypasses cohesin. Sensitive genes showed RAD21 promoter binding, a higher number of structural loops and positioning within well-insulated, gene-poor topologically associating domains. During differentiation, cohesin loss impaired activation of a broader set of developmental genes, partly due to defective de novo regulatory interactions. Together, these findings demonstrate context-specific requirements for cohesin in gene activation.