Extensile motor activity drives coherent flows in a model of interphase chromatin

The 3D spatiotemporal organization of genetic material inside the cell nucleus remains an open question in cellular biology. During the time between two cell divisions, chromatin – the functional form of DNA in cells – fills the nucleus in its uncondensed polymeric form. Recent in-vivo imaging experiments have revealed the existence of coherent motions inside the nucleus, with correlated displacements on the scale of microns and lasting for seconds. To elucidate the mechanisms behind these motions, we develop a novel coarse-grained model where chromatin is represented as a confined flexible chain acted upon by active molecular motors that perform work by exerting dipolar stresses on the system. Numerical simulations of this model account for steric and hydrodynamic interactions as well as internal chain mechanics, and demonstrate the emergence of coherent motions in systems involving extensile dipoles, which are accompanied by large-scale chain reconfigurations and local nematic ordering. Comparisons with experiments show good qualitative agreement and support the hypothesis that long-ranged hydrodynamic couplings between chromatin-associated active motor proteins are responsible for the observed dynamics.