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 under external forces.
• Chromatin, especially heterochromatin, resists nuclear deformation, but its liquid-like properties create ambiguity in nuclear elasticity mechanisms.

Purpose of the Study:

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

Main Methods:

• Utilized polymer physics simulations of a nucleus model.
• Validated the model using micromechanical measurements and chromosome conformation capture data.

Main Results:

• Peripheral heterochromatin attachment to the lamina is crucial 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's liquid-liquid phase separation interactions do not contribute to nuclear rigidity.
• Gel-like peripheral heterochromatin bears stress during stretching, while fluid-like euchromatin is less affected.

Conclusions:

• Heterochromatin's internal structure and stiffness regulate nuclear mechanics through peripheral lamina attachment.
• This mechanism enables nuclear mechanosensing of external forces and provides insights into the nucleus's internal architecture.