Dynamic and decay kinetics of H3 variants in live cells reveal the pivotal role of HIRA/NSD2 in maintaining the distinct H3.3 specific chromatin landscape

The incorporation of variant histone H3.3 into the genome is tightly linked with transcriptional activity, yet its precise regulatory mechanisms remain elusive. Traditional methods like Chromatin Immunoprecipitation offer static views of H3.3 distribution, lacking dynamic insights. Here, using the SNAP tag system, we employed Fluorescence Recovery After Photobleaching (FRAP) and live-cell imaging to investigate H3.3 mobility and decay kinetics in live mouse embryonic fibroblast cells. Our focus on interferon-induced transcriptional activation revealed rapid H3.3 exchange, indicative of its transcriptional regulatory role. Transcription inhibition hindered H3.3 mobility, emphasizing its involvement in transcription. Additionally, we probed into turnover dynamics(decay) of H3.1-SNAP and H3.3-SNAP variants, uncovering differential decay rates influenced by transcriptional activity and histone modifiers such as NSD2 and HIRA. Live-cell imaging showed faster decay of H3.3 compared to H3.1, further exacerbated upon NSD2/HIRA loss. Notably, HIRA and NSD2, regulators of H3.3 dynamics, proved crucial for both H3.3 mobility and decay, underscoring their pivotal role. These findings deepen our understanding of epigenetic regulation, emphasizing the dynamic nature of histone turnover in cellular function and its implications for disease pathogenesis. Taken together, this study sheds light on the dynamic behavior of H3.3 and its regulatory mechanisms, providing valuable insights into epigenetic regulation in cellular processes and disease contexts.