Confinement-Induced Glassy Dynamics in a Model for Chromosome Organization

Recent experiments showing scaling of the intrachromosomal contact probability, P(s)~s^-1 with the genomic distance s, are interpreted to mean a self-similar fractal-like chromosome organization. However, scaling of $P(s)$ varies across organisms, requiring an explanation. We illustrate dynamical arrest in a highly confined space as a discriminating marker for genome organization, by modeling chromosomes inside a nucleus as a homopolymer confined to a sphere of varying sizes. Brownian dynamics simulations show that the chain dynamics slows down as the polymer volume fraction (φ) inside the confinement approaches a critical value φc. The universal value of φc^∞≈0.44 for a sufficiently long polymer (N1) allows us to discuss genome dynamics using φ as the sole parameter. Our study shows that the onset of glassy dynamics is the reason for the segregated chromosome organization in humans (N≈3×10⁹, φφc^∞), whereas chromosomes of budding yeast (N≈10⁸, φ<φc^∞) are equilibrated with no clear signature of such organization.