Chromatin mechanics dictates subdiffusion and coarsening dynamics of embedded condensates

DNA is organized into chromatin, a complex polymeric material that stores information and controls gene expression. An emerging mechanism for biological organization, particularly within the crowded nucleus, biomolecular phase separation condensed droplets of protein nucleic acids. However, way in which chromatin impacts dynamics condensate formation poorly understood. Here we utilize powerful optogenetic strategy to examine interplay droplet coarsening with surrounding viscoelastic network. We demonstrate growth are directly inhibited by chromatin-dense environment, gives rise an anomalously slow exponent, ? ? 0.12, contrasting classical prediction = 1/3. Using scaling arguments simulations, show how this arrested can arise due subdiffusion individual condensates, predicting ?/3, where ? diffusive exponent. Tracking fluctuating motion condensates reveals subdiffusive 0.5, explains anomalous behaviour also consistent Rouse-like arising from entangled chromatin. Our findings have implications biophysical regulation size shape suggest emulsions be used probe mechanical environment living cells. Biomolecules cell nucleus form at rate slower than predicted theory growth. Experiments on cells attribute nucleus.