Cohesin Reshapes Replication Fork Contacts for Genome Stability

Cohesin, a protein complex crucial for sister chromatid cohesion, plays a significant role in managing replication fork dynamics during periods of replication stress, according to research published online in Nature on September 16, 2026. The study details how cohesin's loop extrusion activity limits the coupling of sister replication forks and anchors nearby forks. This tethering action is instrumental in promoting replication fork reversal and slowing down fork progression, thereby safeguarding genome stability. The findings elucidate a novel mechanism by which cohesin contributes to the cellular response to DNA replication challenges.

Replication forks are the Y-shaped structures where DNA is unwound and copied during replication. When cells encounter obstacles, such as DNA damage or limited nucleotide pools, replication can stall. This stalling can lead to fork collapse, resulting in DNA breaks and genomic instability. Cells have evolved intricate mechanisms to cope with stalled forks, including fork slowing, reversal, and restart. Fork reversal involves the nascent DNA strands folding back on themselves, forming a chicken-foot structure that can protect the fork from degradation and facilitate repair.

The research highlights that cohesin's ability to form and maintain DNA loops is central to its function in this context. By extruding DNA into loops, cohesin can physically bring distant DNA regions together. In the context of replication, this loop extrusion activity can effectively tether sister replication forks that are located in proximity. This tethering prevents the forks from moving too far apart or becoming uncoupled, which could otherwise exacerbate problems arising from replication stress. The physical constraint imposed by cohesin-mediated loops helps to maintain a coordinated fork structure.

Furthermore, the study demonstrates that this tethering and coordination mechanism directly contributes to fork slowing and reversal. When replication forks are held together by cohesin, their independent progression is hindered. This constraint can lead to a reduction in the overall speed of replication fork movement. More critically, it promotes the reversal of the fork, a protective response that allows the cell to manage the stalled replication machinery. The research provides molecular insights into how cohesin's architectural role in the genome extends to the dynamic processes of DNA replication, offering a deeper understanding of genome maintenance pathways.