Loop extrusion provides mechanical robustness to chromatin

Chromosomes are complex biopolymers folded into dynamic loops via a loop extrusion process and may experience various mechanical forces in vivo . We develop a force-dependent model of chromatin loop extrusion and investigate its mechanical consequences on chromosome organization using simulations and analytical theory. We show that loop extrusion alters the force–extension behavior of DNA in a non-monotonic manner: extrusion stiffens the chain at low forces but softens it at intermediate and high forces. Our model predicts hysteresis in pulling–recoiling cycles and out-of-equilibrium responses, consistent with recent single-chromosome stretching experiments. We further find that loop extrusion provides mechanical robustness to chromatin by promoting compaction while enabling rapid structural recovery after stress. These results establish loop extrusion as a key regulator of chromatin mechanics.