Compartmentalization with nuclear landmarks yields random, yet precise, genome organization.

Area of Science:

• Genomics
• Computational Biology
• Cell Biology

Background:

• Eukaryotic genome 3D organization is crucial for function.
• Understanding large-scale chromosome arrangement in the nucleus remains challenging.
• Previous studies focused on individual chromosome folding, not whole-genome spatial dynamics.

Purpose of the Study:

• To model the diploid human genome's spatial organization relative to nuclear bodies.
• To investigate the principles governing the dynamic arrangement of all chromosomes within the nucleus.
• To explore self-organization mechanisms driving genome architecture.

Main Methods:

• Utilized polymer simulations to model the human genome.
• Incorporated nuclear bodies like nuclear lamina, nucleoli, and speckles into the model.
• Analyzed simulated 3D structures against experimental genomic mapping and imaging data.

Main Results:

• Demonstrated that cophase separation between chromosomes and nuclear bodies self-organizes genome structure.
• The model successfully reproduced chromosome territories, A/B compartment phase separation, and nuclear body properties.
• Simulated structures accurately reflected experimental data on chromatin interactions with nuclear bodies.
• Captured heterogeneous chromosome positioning across cells while maintaining precise chromatin-speckle distances.

Conclusions:

• Cophase separation is a robust mechanism for achieving functional 3D genome organization.
• This process explains genome compartmentalization and chromosome positioning without requiring difficult thermodynamic equilibration.
• The model reconciles heterogeneous genome distribution with precise functional contacts, highlighting the role of nonspecific phase separation and slow chromosome dynamics.