Confinement-Induced Glassy Dynamics in a Model for Chromosome Organization

Recent experiments showing scaling of the intrachromosomal contact probability, P(s) similar to 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 (.) inside the confinement approaches a critical value phi(c). The universal value of phi(infinity)(c) approximate to 0.44 for a sufficiently long polymer (N >> 1) allows us to discuss genome dynamics using. as the sole parameter. Our study shows that the onset of glassy dynamics is the reason for the segregated chromosome organization in humans (N approximate to 3 x 10(9), phi greater than or similar to phi(infinity)(c) c), whereas chromosomes of budding yeast (N approximate to 10(8), phi greater than or similar to phi(infinity)(c) c) are equilibrated with no clear signature of such organization.