Cohesin is required for chromatin loop formation. However, its precise role in regulating gene transcription remains largely debated. Here we investigated the relationship between cohesin and RNA polymerase II (RNAPII) using single-molecule mapping and live-cell imaging methods in human cells. Cohesin-mediated transcriptional loops were highly correlated with those of RNA polymerase II and followed the direction of gene transcription. Depleting RAD21, a subunit of cohesin, resulted in the loss of long-range (>100 kb) loops between distal (super-)enhancers and promoters of cell-type-specific downregulated genes. By contrast, short-range (<50 kb) loops were insensitive to RAD21 depletion and connected genes that are mostly constitutively expressed. This result explains why only a small fraction of genes are affected by the loss of long-range chromatin interactions in cohesin-depleted cells. Remarkably, RAD21 depletion appeared to upregulate genes that were involved in initiating DNA replication and disrupted DNA replication timing. Our results elucidate the multifaceted roles of cohesin in establishing transcriptional loops, preserving long-range chromatin interactions for cell-specific genes and maintaining timely DNA replication.
Mj et al. (Tue,) studied this question.