Decoding chromatin nanoscale plasticity in situ: Insights from native AFM imaging

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Chromatin's nanoscale structure and dynamics are crucial for gene regulation but remain poorly understood.
• Existing models do not fully capture the plasticity and heterogeneity of chromatin organization.

Purpose of the Study:

• To develop a novel in situ method for visualizing native chromatin structure at the nanoscale.
• To investigate the dynamic assembly and plasticity of chromatin fibers.
• To explore the influence of histone acetylation and ATP on chromatin structure.

Main Methods:

• Developed an in situ approach combining hypotonic treatment and high-drop spreading.
• Utilized atomic force microscopy (AFM) to visualize native, naked chromosomes.
• Observed chromatin under near-physiological conditions.

Main Results:

• Identified ~10 nm DNA-histone particles as fundamental chromatin units.
• Demonstrated remarkable structural plasticity of these particles, forming heterogeneous beaded chains via stacking and melting.
• Challenged the static "beads-on-a-string" model, revealing chromatin's nanoscale versatility.
• Showed that histone acetylation and ATP modulate chromatin plasticity.

Conclusions:

• Chromatin exhibits dynamic structural plasticity at the nanoscale, challenging classical models.
• A revised molecular framework highlights the interplay between core particle stability and dynamic variability.
• Chromatin's structural diversity is key to its complex regulatory functions.