Peripheral heterochromatin tethering is required for chromatin-based nuclear mechanical response

Area of Science:

• Cell Biology
• Biophysics
• Polymer Physics

Background:

• The cell nucleus is mechanically responsive, influencing chromosome behavior.
• Chromatin's mechanical response, including heterochromatin's resistance to deformation, is crucial for nuclear elasticity.
• Chromatin's liquid-like properties create ambiguity in understanding nuclear elasticity mechanisms.

Purpose of the Study:

• To determine how heterochromatin enhances the nuclear mechanical response.
• To elucidate the physical mechanisms underlying chromatin-based nuclear elasticity.

Main Methods:

• Polymer physics simulations of a nucleus model.
• Validation using micromechanical measurements.
• Analysis of chromosome conformation capture data.

Main Results:

• Peripheral heterochromatin attachment to the nuclear lamina is essential for transmitting forces and eliciting chromatin's elastic response.
• Increased heterochromatin levels enhance nuclear rigidity by strengthening chromatin-lamina linkages.
• Internal heterochromatin crosslinks (e.g., HP1α) stiffen nuclei only when chromatin is peripherally tethered.
• Heterochromatin affinity interactions driving liquid-liquid phase separation do not contribute to nuclear rigidity.

Conclusions:

• Heterochromatin's mechanical properties regulate nuclear mechanics through peripheral attachment to the lamina.
• This mechanism enables nuclear mechanosensing of external forces and internal architecture.
• Gel-like peripheral heterochromatin bears stress during stretching, while fluid-like euchromatin is less affected.