Coordinated action of Stag1 and Stag2 in post-mitotic chromatin reconfiguration

As its nuclear concentration increases in late-G1, Stag2 progressively suppresses large loops, likely by competing with Stag1, which constitutes more stable cohesin on chromatin. Mechanistically, we found that intermediate CTCF roadblocks and long traveling distances both attenuate Stag2’s chromatin retention, with the former playing a more prominent role, eventually preventing large loop formation. Concurrently, Stag2’s recruitment to heterochromatin is delayed until late-G1 compared to its rapid association with euchromatin.

Finally, the combined loss of both Stag proteins led to a synergistic ablation of nearly all structural loops. In concordance, transcription reactivation was more severely affected than deleting each Stag protein. These results establish Stag2-associated cohesin as the principal architect of post-mitotic genome refolding, orchestrating intricate size, context, and temporal regulation, with Stag1 providing crucial functional compensation.