What it is
Combining single-nucleosome imaging and tracking with super-resolution 3D structured illumination microscopy and euchromatin-specific labeling of histone H3.3, the authors imaged how the cohesin complex organizes active chromatin in living human cells. They found that euchromatin forms condensed domains constrained by cohesin-mediated loops, with transcription machinery located near the domain surfaces or borders. Removing cohesin increased nucleosome fluidity within the domains without changing their overall compaction, causing local mixing of neighboring domains and compromising transcriptional insulation.
Why it matters
How cohesin organizes chromatin domains in living cells, especially in active euchromatin, had remained unclear. By showing euchromatin as condensed domains held apart by cohesin loops rather than largely open, the work refines the classical textbook picture and assigns cohesin an unexpected physical role in keeping domains distinct and preserving transcriptional insulation.
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Filed underSingle-cell and spatial transcriptomics, Diffusion and Search Dynamics, melanin and skin pigmentation