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

ABSTRACT: The eukaryotic genome's 3D structure is organized by the cohesin complex, containing either Stag1 or Stag2 subunits. While both organize chromatin, their distinct roles in de novo loop establishment during post-mitotic refolding remain unknown. We leveraged the mitosis-to-G1 transition to dissect their independent functions. Our findings reveal that Stag1 depletion has minimal effect on post-mitotic genome refolding or transcription reactivation. In contrast, Stag2 mediates chromatin remodeling in a multifaceted, chromatin context-dependent, and cell cycle stage-specific manner. In early-G1, it rapidly engages with euchromatin, extruding small structural loops, which may account for the timely reactivation of transcription. 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.

ORGANISM(S): Mus musculus

PROVIDER: GSE306128 | GEO | 2026/08/19

REPOSITORIES: GEO