Aberrant chromatin landscape upon loss of the H3.3 chaperone Daxx leads to Pu.1-mediated neutrophilia and inflammation [CUT&Tag]. Aberrant chromatin landscape upon loss of the H3.3 chaperone Daxx leads to Pu.1-mediated neutrophilia and inflammation [CUT&Tag]

Defective silencing of retroviral elements has been linked to inflamm-aging, cancer and auto-immune diseases. However, the underlying mechanisms are only partially understood. Here, we implicate the histone H3.3 chaperone Daxx, a retrotransposable element (RTE) repressor inactivated in myeloid leukemia and other neoplasms, in protection from inflammatory disease. Loss of Daxx has profound effects on chromatin landscapes and histone marks of hematopoietic progenitors, leading to engagement of a Pu.1-dependent transcriptional program for myelopoiesis at the expense of B-cell differentiation. This causes neutrophilia and inflammation, predisposing mice to development of an autoinflammatory skin disease. These molecular and phenotypic perturbations are in part reverted in animals lacking both Pu.1 and Daxx. However, hematopoietic progenitors in these mice also show unique chromatin and transcriptome alterations, suggesting synergistic interaction between the two pathways. Overall, our findings implicate RTE silencing in hematopoiesis and reveal a potential functional relationship between the H3.3 loading machinery and the pioneer transcription factor Pu.1. Overall design: Examination of gene expression profiles, chromatin accessibility and epigenetic changes in hematopoietic stem/progenitor cells comparing wild-type and Daxx knock-out cells.

逆转录病毒元件的沉默缺陷与炎症衰老（inflamm-aging）、癌症及自身免疫疾病密切相关。然而，其背后的分子机制仅部分得到解析。本研究证实，组蛋白H3.3伴侣蛋白Daxx——一种在髓系白血病及其他肿瘤中失活的逆转录转座子（retrotransposable element, RTE）阻遏因子——可抵御炎症性疾病的发生。Daxx缺失会对造血祖细胞的染色质景观与组蛋白修饰产生显著影响，进而触发依赖Pu.1的髓系生成转录程序，以牺牲B细胞分化为代价。这一过程引发中性粒细胞增多与炎症反应，使小鼠易患自身炎症性皮肤病。在同时缺失Pu.1与Daxx的小鼠中，上述分子与表型紊乱可得到部分逆转。但此类小鼠的造血祖细胞仍表现出独特的染色质与转录组改变，提示两条通路间存在协同互作。综上，本研究将逆转录转座子沉默与造血过程建立了功能关联，并揭示了H3.3装载机制与先锋转录因子Pu.1之间潜在的功能联系。实验整体设计：对造血干/祖细胞的基因表达谱、染色质可及性及表观遗传变化进行检测，比较野生型与Daxx基因敲除细胞的差异。