Near-critical chromatin fluctuations facilitate long-range contacts in Drosophila chromosomes

Recent live imaging in Drosophila embryonic nuclei revealed anomalous dynamics of synthetic enhancer promoter locus pairs, challenging classical polymer models. To identify the physical mechanisms underlying this behavior, we performed coarse-grained polymer simulations exploring three chromatin organization modes: an ideal polymer, loop extrusion, and compartmental segregation. We found that genome compartments, when tuned near the coil globule phase transition, best captured both structural and dynamical observables. Importantly, we demonstrate that the agreement with experimental data is maximized in a narrow regime characterized by near critical polymer behavior. Incorporating loop extrusion does not markedly improve the overall fit, suggesting that the mechanism plays a limited role in shaping chromatin organization and dynamics in the Drosophila embryo. These results support a picture in which chromatin operates in a near-critical physical regime, enabling efficient exploration of nuclear space and frequent long-range interactions.