Viscoelasticity of model interphase chromosomes

TL;DR

This study explores the viscoelastic properties of interphase chromosomes by tracking particle motion, revealing deviations from classical diffusion theories and providing insights into chromatin's mechanical behavior.

Contribution

It introduces a novel analysis of particle diffusion in chromatin, linking microscopic motion to macroscopic viscoelastic properties of chromosomes.

Findings

Large particles are temporarily caged by chromatin constraints.

Diffusion behavior deviates from Stokes-Einstein relation.

Calculated elastic and viscous moduli match experimental data.

Abstract

We investigated the viscoelastic response of model interphase chromosomes by tracking the three-dimensional motion of hundreds of dispersed Brownian particles of sizes ranging from the thickness of the chromatin fiber up to slightly above the mesh size of the chromatin solution. In agreement with previous computational studies on polymer solutions and melts, we found that the large-time behaviour of diffusion coefficient and the experienced viscosity of moving particles as functions of particle size deviate from the traditional Stokes-Einstein relation, and agree with a recent scaling theory of diffusion of non-sticky particles in polymer solutions. Interestingly, we found that at short times large particles are temporary "caged" by chromatin spatial constraints, which thus form effective domains whose size match remarkably well recent experimental results for micro-tracers inside interphase nuclei. Finally, by employing a known mathematical relation between the time mean-square displacement of tracked particles and the complex shear modulus of the surrounding solution, we calculated the elastic and viscous moduli of interphase chromosomes.