Résumé
Recent advancements in experimental fluorescence microscopy have revolutionized our ability to accurately determine the three-dimensional physical location of multiple chromosomal regions with a resolution down to 50 nm. In this study, we leverage publicly available microscopy data focusing on loci from human Chr21 obtained through multiplexed fluorescence in situ hybridization (mFISH) techniques across various cell lines and treatments. Inspired by models from polymer physics, our analysis delves into the distance distributions between different tagged regions, aiming to elucidate the chromatin's conformational arrangements. Our findings reveal the presence of at least two distinct conformational arrangements, which we term phase α and phase β, coexisting at any given genomic site. These phases exhibit contrasting scaling behaviors: phase α aligns with a crumpled globule model, while phase β suggests a confined yet more extended conformation resembling a looped domain. The identification of these distinct phases not only sheds light on the multifaceted nature of chromatin topology but also offers insights into the impact of cellular context and/or treatments on chromatin structure.