Varied Ensembles of Long-range ChROmatin interactions drive chromatin compartmentalization.

In viable Caenorhabditis elegans mutants, HPL-2 and LIN-61 define VELCROs—30–50 kb H3K9me2-bound interfaces—that drive A/B chromatin compartmentalization.

• Why it matters: It remains unclear which chromatin components and interaction patterns organize eukaryotic genomes into active and inactive compartments.
• What they did: The authors analyzed mutants lacking chromatin-regulatory proteins, mapping HPL-2 and LIN-61 binding with H3K9me2 to define VELCROs, then tested compartment defects and used polymer simulations.
• The result: VELCROs are marked by high site density (not peak intensity), and defective compartmentalization mutants show impaired VELCROs; simulations indicate these ensembles can phase-separate B from A compartments based on peak densities.

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