How chromatin is spatially organized in the nucleus has long been studied through the lens of large-scale A/B compartments, but whether these sizes reflect true biological units or analytical artifacts has remained unclear. We find that limits imposed by the conventional eigenvector-based compartment calling have required extreme sequencing depth and coarse resolution, obscuring regulatory-scale organization. We developed CRUSH to iteratively refine compartments to 1 kb resolution without the need for extreme sequencing depth, we show that kilobase-scale A/B segregation (micro-compartments) is evident across cell types. Across these maps, we demonstrate that RNA polymerase II pausing contributes to a sub-genic compartment signature at the transcription start site and that active enhancers almost universally occupy the A compartment. We then show that fine-scale compartment maps can resolve cancer subtype-specific regulatory programs, single-cell tissue identity, and cold-adaptation regulomes in a 52,000-year-old woolly mammoth. These findings establish chromatin compartmentalization as a gene-scale regulatory feature with broad implications for development, disease, and genome evolution.
CRUSH uses iterative resolution walking to identify and correct A/B compartment measurements. This allows identification of A/B compartments at kilobase resolution with low sequencing depth and consistency across methodologies. Kilobase-scale compartments reveal sub-genic compartment organization, compartment identities in single-cells, and a distinct cold-adapted regulome in mammoths.
