MeCP2 deficiency leads to the γH2AX nano foci expansion after ionizing radiation

DNA double-strand breaks (DSBs) trigger the recruitment of repair protein and promote signal transduction through posttranslational modifications such as phosphorylation. After DSB induction, ataxia telangiectasia mutated (ATM) phosphorylates H2AX on chromatin surrounds the mega-base pairs proximal to the DSBs. Advanced super-resolution microscopic technology has demonstrated the formation of gamma H2AX nano foci as a unit of nano domain comprised of multiple nucleosomes. The formation of gamma H2AX nano foci could be potentially affected by pre-existing chromatin structure prior to DSB induction; however, it remains unclear whether chromatin status around DSBs influences the formation of gamma H2AX nano foci. In this study, to investigate gamma H2AX nano foci formation in the context of chromatin relaxation, gamma H2AX nano foci were examined following the depletion of MeCP2, which is a factor promoting chromatin condensation. Remarkably, by using super-resolution imaging analysis, we found that the volume of gamma H2AX nano foci cluster in MeCP2-depleted cells was significantly greater than that in control cells, both 5 and 30 min after ionizing radiation (IR). Corresponding to the increased volume size, the number of gamma H2AX nano foci per cluster was greater than that in control cells, while the distance of each nano focus within foci clusters remained unchanged. These findings suggest that relaxed chromatin condition by MeCP2 depletion facilitates faster and more extensive gamma H2AX nano foci formation after IR. Collectively, our super-resolution analysis suggests that the chromatin status surrounding DSBs influences the expansion of gamma H2AX nano foci formation, thus, potentially influencing the DSB repair and signaling.