Interplay between cohesin kinetics and polymer relaxation modulates chromatin-domain structure and dynamics

Abstract

The three-dimensional organization of chromatin into domains and compartments leads to specific scaling of contact probability and compaction with genomic distance. However, chromatin is also dynamic, with active loop extrusion playing a crucial role. While extrusion ensures a specific spatial organization, how it affects the dynamic scaling of measurable quantities is an open question. In this work, using polymer simulations with active loop extrusion, we demonstrate that the interplay between the timescales of extrusion processes and polymer relaxation can influence the 3D organization of chromatin polymer. We point out this as a factor contributing to the experimentally observed non-trivial scaling of relaxation time with genomic separation and mean-square displacement with time. We show that the dynamic scaling exponents with loop extrusion are consistent with the experimental observations and can be very different from those predicted by existing fractal-globule models for chromatin.