National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
BMC Biol. 2018 Oct 3;16(1):110. doi: 10.1186/s12915-018-0573-9.
H3.3 is an ancient and conserved H3 variant and plays essential roles in transcriptional regulation. HIRA complex, which is composed of HIRA, UBN1 or UBN2, and Cabin1, is a H3.3 specific chaperone complex. However, it still remains largely uncharacterized how HIRA complex specifically recognizes and deposits H3.3 to the chromatin, such as promoters and enhancers.
In this study, we demonstrate that the UBN1 or UBN2 subunit is mainly responsible for specific recognition and direct binding of H3.3 by the HIRA complex. While the HIRA subunit can enhance the binding affinity of UBN1 toward H3.3, Cabin1 subunit cannot. We also demonstrate that both Ala87 and Gly90 residues of H3.3 are required and sufficient for the specific recognition and binding by UBN1. ChIP-seq studies reveal that two independent HIRA complexes (UBN1-HIRA and UBN2-HIRA) can cooperatively deposit H3.3 to cis-regulatory regions, including active promoters and active enhancers in mouse embryonic stem (mES) cells. Importantly, disruption of histone chaperone activities of UBN1 and UBN2 by FID/AAA mutation results in the defect of H3.3 deposition at promoters of developmental genes involved in neural differentiation, and subsequently causes the failure of activation of these genes during neural differentiation of mES cells.
Together, our results provide novel insights into the mechanism by which the HIRA complex specifically recognizes and deposits H3.3 at promoters and enhancers of developmental genes, which plays a critical role in neural differentiation of mES cells.
H3.3 是一种古老且保守的 H3 变体，在转录调控中发挥着重要作用。HIRA 复合物由 HIRA、UBN1 或 UBN2 和 Cabin1 组成，是一种 H3.3 特异性伴侣复合物。然而，HIRA 复合物如何特异性识别和将 H3.3 沉积到染色质（如启动子和增强子）中，在很大程度上仍未被阐明。
在这项研究中，我们证明 UBN1 或 UBN2 亚基主要负责 HIRA 复合物对 H3.3 的特异性识别和直接结合。虽然 HIRA 亚基可以增强 UBN1 与 H3.3 的结合亲和力，但 Cabin1 亚基不能。我们还证明 H3.3 的 Ala87 和 Gly90 残基对于 UBN1 的特异性识别和结合是必需且充分的。ChIP-seq 研究表明，两个独立的 HIRA 复合物（UBN1-HIRA 和 UBN2-HIRA）可以协同地将 H3.3 沉积到顺式调控区域，包括在小鼠胚胎干细胞（mES）中活性启动子和活性增强子。重要的是，通过 FID/AAA 突变破坏 UBN1 和 UBN2 的组蛋白伴侣活性，导致发育基因启动子处 H3.3 沉积缺陷，这些基因参与神经分化，随后导致 mES 细胞神经分化过程中这些基因的激活失败。
总之，我们的研究结果为 HIRA 复合物如何特异性识别和沉积 H3.3 提供了新的见解，在 mES 细胞的神经分化中发挥着关键作用。
