2014-03-13
15:15 at HCI J 574

Chromatin Hydrodynamics

Yitzhak Rabin

Physics Departiment, Bar-Ilan University, Israel

Following recent observations of large scale cooperative motion of chromatin inside the nuclei of live cells, we present a hydrodynamic theory in which the nucleoplasm is described as a two-component fluid consisting of chromatin plus the surrounding solvent subject to active scalar and vector events associated with chromatin remodeling. Scalar events drive the longitudinal viscoelastic modes (where chromatin moves relative to solvent) while vector events generate the transverse modes (where chromatin moves together with solvent). Using linear response methods, we derive explicit expressions for the response functions that connect the chromatin density and velocity correlation functions to the corresponding correlation functions of the active sources in terms of the complex viscoelastic moduli of the nucleoplasmic medium. We then derive general expressions for the flow spectral density (FSD) of the chromatin velocity field and compare them to experimental results obtained by one of the present authors and her coworkers. We find that while the time dependence of the experimental data for both native and ATP-depleted chromatin can be well-fitted using a simple viscoelastic model (i.e., the Maxwell model), the observed wavelength dependence appears to be more complex than that of the Maxwell model, suggesting that a more complete theory may have to incorporate a length-scale dependent viscoelastic moduli and to account for spatial and temporal correlation between the active sources.