Physics Colloquium

Chromatin structure and dynamics control all aspects of DNA biology yet are poorly understood. In interphase,
time between two cell divisions, chromatin fills the cell nucleus in its minimally condensed polymeric state.
Chromatin serves as substrate to a number of biological processes, e.g. gene expression and DNA replication,
which require it to become locally restructured. These are energy-consuming processes giving rise to nonequilibrium
dynamics. Chromatin dynamics has been traditionally studied by imaging of fluorescently labeled
nuclear proteins and single DNA-sites, thus focusing only on a small number of tracer particles. Recently, we
developed an approach, displacement correlation spectroscopy (DCS) based on time-resolved image
correlation analysis, to map chromatin dynamics simultaneously across the whole nucleus in cultured human
cells [1]. DCS revealed that chromatin movement was coherent across large regions (4–5μm) for several
seconds. Regions of coherent motion extended beyond the boundaries of single-chromosome territories,
suggesting elastic coupling of motion over length scales much larger than those of genes [1]. These largescale,
coupled motions were ATP-dependent and unidirectional for several seconds. Following these
observations, we developed a hydrodynamic theory of active chromatin dynamics, using the two-fluid model
and describing the content of cell nucleus as a chromatin solution, which is subject to both passive thermal
fluctuations and active (ATP-consuming) scalar and vector events [2]. In this work we continue in our efforts to
elucidate the mechanism and function of the chromatin dynamics in interphase. We investigate the chromatin
interactions with the nuclear envelope and compare the surface dynamics of the chromatin globule with its bulk
dynamics [3]. Furthermore, we explore the rheology of the chromatin inside the cell nucleus using the native
subnuclear structures [4].
[1] Zidovska A, Weitz DA, Mitchi