Histone Acetylation Induced By Ionizing Radiation Causes Chromatin Decondensation

Ionizing radiation is increasingly closely related to human society,it may endanger human life while benefiting human beings.DNA is the principal target for the biological effects of radiation,including DNA mutations and even carcinogenesis.In eukaryotes,DNA molecules are often coiled with histones to form nucleosomes,which are highly helical and compressed to form chromatin in the nucleus.Chromatin is often transformable between euchromatin and heterochromatin depending on the cell cycle or physiological state,and the transformation process is accompanied by acetylation of lysine residues of histones H3 and H4.The dynamic structure of chromatin affects the accessibility of DNA and plays an important regulatory role in many processes such as DNA replication,gene transcription and DNA repair etc.However,in situ highresolution of chromatin structure in the nucleus and quantitative characterization of its structural dynamic have been limited by the resolution of microscopic imaging.In this paper,we investigate the quantitative characterization of chromatin structural decondensation based on STORM super-resolution microscopic images of chromatin,which helps us dive deep into the chromatin structural dynamics and provides a new perspective for the study of DNA repair mechanism.By using Ed U incubation and ‘click chemistry’ reaction,DNA molecules were labelled with fluorescence in high density,and we have obtained super-resolution images of chromatin structure in the nucleus with single-molecule localization microscopic imaging(STORM).Using single-molecule localization-based chromatin cluster structure analysis and nearest neighbour distance algorithm to quantitatively characterize the decondensation of chromatin structures,we found that the number of chromatin clusters in the nucleus was significantly increased after histone acetylation treatment and X-ray irradiation,with an increase in the area ratio of chromatin clusters compared to the control group,and a decrease in the total average number of fluorescent molecules in the clusters.Meanwhile,the XRCC1 recruitment rate constant obtained from heavy ion irradiated live cell imaging experiments indicated that acetylation treatment resulted in a decrease in DNA damage density.These results suggest that both acetylation treatment and ionizing radiation lead to the decondensation of chromatin structure,and the imaging method and analysis algorithm and the distribution pattern of chromatin cluster structures obtained by which provide quantitative characterization data to support the decondensation of chromatin structure and provide a new perspective for the study of chromatin structure dynamics.