Unraveling Chromatin Multi-scale Subdiffusion in Live Cells Using Scattering-based Interference Microscopy

Yi-Teng Hsiao^1*, Wong-Ka Lok¹, Chia-Lung Hsieh¹

¹Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan

* Presenter:Yi-Teng Hsiao, email:tonyhsian@gmail.com

Chromatin organization and dynamics in live cell nuclei span a wide range of spatial and temporal scales, playing a critical role in regulating nuclear processes. At the nanoscale, nucleosomes fluctuate within microseconds, promoting chromatin accessibility, while chromatin domains translocate at larger scales over minutes to hours. Investigating these multi-scale chromatin structures and dynamics presents significant challenges. Although fluorescence microscopy provides high sensitivity, its application for studying chromatin structures and dynamics is limited by photobleaching and phototoxicity. Thus, the investigation of nanoscale chromatin largely relies on sequencing-based techniques and numerical studies. Recent advances in scattering-based microscopy offer a powerful alternative for measuring nanoscopic biological entities without any labels. In this study, we employ coherent brightfield microscopy (COBRI), a scattering-based interference microscopy technique developed in our group, to investigate chromatin dynamics in live cell nuclei across different timescales. By performing temporal correlation analysis at multiple acquisition rates, we measure the mean square displacement (MSD) of chromatin in microsecond timescales, corresponding to length scales below 100 nm. Our findings reveal subdiffusive chromatin behavior in this previously unexplored regime, providing new insights into the chromatin remodeling process. We further examine how chromatin dynamics are influenced by histone post-translational modifications and DNA methylation. This label-free approach opens new avenues for understanding chromatin dynamics across multiple timescales, offering critical insights into the fundamental mechanisms of nuclear organization.

Keywords: chromatin dynamics, subdiffusion, scattering-based interference microscopy, temporal correlation analysis, label-free imaging