Polymer Physics Predicts Conformational Diversity of Individual Chromatin Molecules

Recent advances in single-cell and super-resolution imaging have revealed that chromatin adopts highly heterogeneous and dynamic three-dimensional conformations across individual cells. However, the extent of this variability, its underlying mechanisms, and its functional consequences remain difficult to quantify experimentally. Here, we review recent progress in combining polymer physics, molecular dynamics simulations, and data-driven approaches to reconstruct and predict ensembles of three-dimensional chromatin conformations at the single-molecule level. We discuss how polymer phase-separation and loop-extrusion models can reproduce both population-averaged contact data and independent single-cell imaging measurements. These approaches help disentangle different sources of conformational diversity, including the intrinsic thermodynamic degeneracy of polymer folding and cell-to-cell heterogeneity. We further discuss how perturbation of key architectural factors, particularly cohesin, affects chromatin conformation and single-cell structural variability. Overall, polymer-physics models provide a quantitative framework to connect molecular mechanisms underlying chromatin folding with the heterogeneous conformational ensembles observed experimentally in individual molecules.