Gao Jia, Li Hongyun, Tan Song, Zhou Ruobo, Lee Tae-Hee
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802.
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802.
bioRxiv. 2025 May 15:2025.05.09.653121. doi: 10.1101/2025.05.09.653121.
Chromatin condensation is dynamically regulated throughout the cell cycle and plays key roles in modulating gene accessibility at the highest physical level in a cell. The DNA-histone dynamics in short- and long-range inter-nucleosomal interactions are central to the regulation mechanisms of chromatin condensation which remain under active investigation. We employed 12-mer nucleosome arrays to investigate the roles of histone chaperone Nap1, and histone H3 and H4 N-terminal tails and their acetylation in regulating the formation and the properties of phase-separated chromatin condensates. These arrays form liquid-like condensate droplets under a physiological salt condition of 150 mM NaCl. According to our results from bright-field microscopy, fluorescence recovery after photobleaching, optical super-resolution imaging, and microrheology with optical tweezers, histone H4 tail lysine residues are the main drivers of liquid-liquid phase separation of chromatin arrays. We also found that the condensed liquid-like droplets contain both a mobile fraction and a relatively immobile structural scaffold and that histone chaperone Nap1 and histone H3 tail acetylation facilitate DNA-histone dynamics within the structural scaffold to lower the overall viscosity of the droplets. These results suggest that histone chaperone and histone H3/H4 tails play critical roles in regulating chromatin condensation and gene accessibility in condensed chromatin.
染色质凝聚在整个细胞周期中受到动态调控，并在细胞内最高物理水平上调节基因可及性方面发挥关键作用。短程和长程核小体间相互作用中的DNA-组蛋白动态是染色质凝聚调控机制的核心，目前仍在积极研究中。我们采用12聚体核小体阵列来研究组蛋白伴侣Nap1、组蛋白H3和H4的N端尾巴及其乙酰化在调节相分离染色质凝聚物的形成和性质方面的作用。这些阵列在150 mM NaCl的生理盐条件下形成液状凝聚液滴。根据我们通过明场显微镜、光漂白后荧光恢复、光学超分辨率成像以及光镊微流变学得到的结果，组蛋白H4尾巴赖氨酸残基是染色质阵列液-液相分离的主要驱动因素。我们还发现，凝聚的液状液滴既包含可移动部分，也包含相对不可移动的结构支架，并且组蛋白伴侣Nap1和组蛋白H3尾巴乙酰化促进了结构支架内的DNA-组蛋白动态，从而降低了液滴的整体粘度。这些结果表明，组蛋白伴侣和组蛋白H3/H4尾巴在调节染色质凝聚和凝聚染色质中的基因可及性方面发挥着关键作用。
