Nat. Methods http://dx.doi.org/10.1038/nmeth.4031 (2016)

Before DNA transcription, replication and repair can occur in eukaryotes, chromatin must transition from a tightly packed, condensed state to a more 'open' state. Chen et al. modified a previously published method that can identify and sequence these 'accessible' regions of DNA so that they are labeled with a fluorescent tag. The new approach—termed 'ATAC-see'—can be used to visualize the locations of all open chromatin in a fixed or living cell. The authors first used DAPI, which stains tightly packed DNA, and ATAC-see to show that the spatial organization and accessibility of genomic DNA varies across different human cell types. They then obtained ATAC-see images of neutrophils, which can sacrifice themselves to kill bacteria via an unusual type of programmed cell death called NETosis. ATAC-see revealed that the chromatin in cells undergoing NETosis associates with lamina-associated domains at the nuclear periphery, where it disassembles into mononucleosomes and eventually disassociates into free histones and DNA. The authors also showed that ATAC-see could be combined with flow cytometry to sort cells that appeared to be at the same step in the cell cycle into distinct subpopulations, suggesting that this method could be used to uncover the molecular basis of cellular heterogeneity.