Condensed Chromatin Behaves like a Solid on the Mesoscale In Vitro and in Living Cells

Area of Science:

• Molecular Biology
• Genomics
• Biophysics

Background:

• Chromatin structure, formed by DNA and histones, is crucial for eukaryotic genome regulation.
• Understanding the physical state of condensed chromatin is key to deciphering genome organization and function.

Purpose of the Study:

• To investigate the physical properties of condensed chromatin in vitro and in vivo.
• To determine if condensed chromatin exhibits solid-like or liquid-like behavior.
• To explore the relationship between chromatin state and the behavior of associated proteins.

Main Methods:

• In vitro studies of nucleosomal array self-association under various solution conditions.
• In vivo measurements of DNA mobility in living cells.
• Observation of heterochromatin and euchromatin behavior.

Main Results:

• In vitro, nucleosomal arrays formed solid-like supramolecular condensates.
• In vivo, condensed chromatin demonstrated solid-like behavior, restricting DNA mobility.
• Heterochromatin proteins exhibited liquid-like behavior, coalescing around the solid chromatin scaffold.

Conclusions:

• Condensed chromatin exists in a solid-like state, acting as an elastic gel that resists external forces.
• This solid chromatin scaffold facilitates liquid-liquid phase separation of chromatin-binding proteins.
• The solid nature of chromatin is maintained even with limited inter-fiber interactions.