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 favor productive interactions This ensures efficient & accurate homology search! 10/12

DSBs recruit two cohesin pools to distinct domains 🔹Loop-forming cohesin accumulates across ~1 Mb, controlling homology sampling range. 🔹Cohesive cohesin accumulates at DSBs, tethering the broken DNA ends to the intact sister chromatid. 9/12

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 8/12

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. 7/12

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. 6/12

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! 5/12

RAD51 filaments sample local TADs By mapping RAD51, a key repair protein, we found that homology search occurs within topologically associated domains near the break rather than across the entire genome. How does chromosome organization influence the search range? 4/12

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. 3/12

Just had our annual lab christmas dinner, featuring curry and Schrottwichteln (a not-quite-secret-santa, rules here: geschenke.de/blogs/wichteln/…). Wishing you a festive end to 2024!

A great big congratulations to Sofia, who successfully defended her PhD thesis @IMBA_Vienna yesterday. Here’s one happy graduate complete with traditional lab-made defense hat 🎩 Well done Sofia! @SofiaKolesni29 @viennabiocenter @TrainingVbc