The Structural Basis of Genome Silencing: The Inactive X Chromosome Resolved by Electron Spectroscopic Imaging

Electron Spectroscopic Imaging resolves chromatin, RNA, and protein features within the inactive X (Xi) chromosome territory, revealing a 3D spatial organization and a large, previously uncharacterized mesoscale non-chromatin structure.

• Why it matters: Chromosome-scale gene silencing needs mesoscale structural explanations, but conventional EM and cryo-EM cannot directly separate chromatin from RNA and protein components.
• What they did: The Xi was analyzed with Electron Spectroscopic Imaging using elemental signatures without contrast-enhancing stains, and ESI was coupled to electron tomography for 3D mapping of chromatin fibres relative to RNA and proteins.
• The result: Correlative light microscopy with ESI in physical serial sections enabled computational assembly of a model of the entire Xi, showing distinct chromatin domains, distributed RNA-protein clusters, and a large non-chromatin structure.

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