Chromatin as a biomolecular condensate
Cells package their genomic DNA into a complex with proteins called chromatin. Chromatin is partitioned into subcompartments that differ from each other with respect to their compaction, molecular composition and biological function. One example are the micron-sized spherical heterochromatin foci that are present in several differentiated cell types and that are readily visible under the microscope. It is a key question how such compartments can form even though diffusion constantly mixes the nuclear interior. One biophysical mechanism that can explain this phenomenon is liquid-liquid phase separation, which creates biomolecular condensates via multivalent interactions. Another one is adsorption to the polymeric chromatin scaffold, which can occur without multivalent interactions or phase separation. I will describe the differences between different demixing mechanisms and will present strategies to distinguish them in living cells.