We propose a dual function of cohesin in homology search:

🔹Loop-forming cohesin defines search space, limited by TADs
🔹Cohesive cohesin tethers the break to its sister, to favour productive interactions

This ensures efficient & accurate homology search!

Cohesion directs homology search towards sister chromatid

What happens if we disrupt sister cohesion? Upon sororin depletion (cohesion stabilizer):
✅ Loops remain intact
❌ Contacts between sister chromatids are lost

DSBs remodel sister chromatids in cis and trans

Sister-pore-C allows us to track how DNA architecture changes before and after DSBs. We found that DSBs locally increase loops and interactions between the broken ends and the intact sister chromatid.

A new tool: sister-pore-C

Homology-directed repair normally uses the sister chromatid as a template, but how does a DSB find its sister locus in 3D space? We developed sister-pore-C, a high-resolution method to map chromatin interactions within & between sister chromatids.

Cohesin-mediated loops control search range

When we disrupted cohesin regulators, search dynamics changed:
🔹 Reducing loops by NIPBL depletion narrowed homology search
🔹 Expanding loops by WAPL depletion made the search broader

Cohesin loops regulate homology search range!

RAD51 filaments sample local TADs

By mapping RAD51, a key repair protein, we found that homology search occurs within topologically associated domains near the breakrather than across the entire genome.
How does chromosome organization influence the search range?

Site-specific induction of homology-directed repair

To study how chromosome architecture influences homology search, we induced DSBs at specific genomic sites in S/G2-synchronized human cells. Most breaks were repaired by homologous recombination.