Chromatin hydrodynamics.

Area of Science:

• Cell Biology
• Biophysics
• Soft Matter Physics

Background:

• Recent observations show large-scale correlated motion of chromatin within live cell nuclei.
• Understanding these dynamics is crucial for nuclear organization and function.

Purpose of the Study:

• To develop a hydrodynamic theory describing chromatin motion within the cell nucleus.
• To connect theoretical predictions with experimental data on chromatin dynamics.

Main Methods:

• Development of a two-fluid hydrodynamic model treating nucleus content as a chromatin-nucleoplasm solution.
• Application of linear response methods to derive chromatin density and velocity correlation functions.
• Analysis of experimental data using the derived theoretical framework and viscoelastic models.

Main Results:

• The two-fluid model successfully explains chromatin dynamics, differentiating between passive thermal fluctuations and active events (e.g., ATP hydrolysis).
• Experimental data for both native and ATP-depleted chromatin are well-fitted by a Maxwell fluid model for viscoelastic moduli.
• ATP-depleted chromatin shows predominantly longitudinal fluctuations, while active chromatin exhibits transverse, long-wavelength velocity fluctuations.

Conclusions:

• The hydrodynamic two-fluid model provides a robust framework for understanding nuclear chromatin dynamics.
• Active cellular processes, particularly those involving ATP hydrolysis, significantly influence chromatin motion, generating distinct fluctuation patterns.
• The model's ability to fit experimental data highlights the interplay between passive and active forces in shaping nuclear organization.