Histone Acetylation Induced by Ionizing Radiation Causes Chromatin Decondensation

Eukaryotic DNA molecule is highly compressed and exist in the form of chromatin in the nucleus. The dynamic structure of chromatin plays an important role in the process of DNA replication, gene transcription and DNA repair. In situ high-resolution analysis of chromatin structure and quantitative characterization of its structural changes have been limited by the optical resolution of microscopic imaging. The super-resolution chromatin structure image in the nucleus was obtained by click-reaction labeled EdU and the STORM single-molecule-localization microscopy. Based on the proposed single molecule cluster analysis and nearest neighbor distance algorithm, we found that the number of nuclear nucleosome clusters increased significantly after X-ray irradiation and TSA treatment, the area ratio of nucleosome clusters in the cell nucleus increased compared with the control group, and the average number of EdU molecules in the cluster decreased. At the same time, the rate constant of XRCC1 recruitment kinetics obtained from the on-line imaging experiment of heavy ion irradiated living cells showed that acetylation reduced the density of DNA damage. These results showed that both ionizing radiation and acetylation led to the decondensation of chromatin structure. The imaging method, analysis algorithm and the distribution of nucleosome clusters provide direct quantitative characterization data support for the decondensation of chromatin structure in cell nucleus.