Nested TAD hierarchy defines cohesion zones on replicated chromosomes.

Nested TAD hierarchy creates distinct cohesion zones on replicated chromosomes, balancing sister chromatid cohesion and loop extrusion.

• Why it matters: Understanding how genome architecture supports both gene regulation and DNA repair after replication is crucial for insights into genome stability and cell function.
• What they did: The study used high-resolution genomic analyses to reveal that cohesin accumulates at high-level TAD boundaries forming "cohesion zones," while loop-extruding cohesin is distributed across all hierarchical levels, influenced by CTCF barriers.
• The result: This segregation allows sister chromatids to remain tethered for repair and regulation while maintaining dynamic loop structures, advancing our understanding of chromosome organization during cell division.