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Abstract：
Cohesin is required for chromatin loop formation. However, its precise role in regulating gene transcription remains largely unknown. 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 RNAPII 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 genes. By contrast, the short-range (<50 kb) loops were insensitive to RAD21 depletion and connected genes that are mostly housekeeping. This result explains why only a small fraction of genes are affected by the loss of long-range chromatin interactions due to cohesin depletion. Remarkably, RAD21 depletion appeared to up-regulate genes located in early initiation zones (EIZ) of DNA replication, and the EIZ signals were amplified drastically without RAD21. Our results revealed new mechanistic insights of cohesin\'s multifaceted roles in establishing transcriptional loops, preserving long-range chromatin interactions for cell-specific genes, and maintaining timely order of DNA replication.
摘要：
染色质环形成需要凝聚素。然而,它在调节基因转录中的确切作用仍在很大程度上未知。我们使用单分子作图和人细胞中的活细胞成像方法研究了粘附蛋白和RNA聚合酶II（RNAPII）之间的关系。Cohesin介导的转录环与RNAPII的转录环高度相关，并遵循基因转录的方向。消耗RAD21，粘附分子的一个亚基，导致远端（超）增强子和细胞类型特异性基因启动子之间的远程（>100kb）环丢失。相比之下,短程（<50kb）环对RAD21耗竭和连接的基因不敏感，这些基因主要是内务。这个结果解释了为什么只有一小部分基因受到长程染色质相互作用的损失的影响。值得注意的是,RAD21耗竭似乎上调了位于DNA复制早期起始区（EIZ）的基因，EIZ信号在没有RAD21的情况下急剧放大。我们的研究结果揭示了新的机制见解，在建立转录环中的多方面作用，保留细胞特异性基因的长程染色质相互作用，保持DNA复制的及时顺序。
