小鼠胚胎干细胞定向分化中异染色质域与核纤层的相互作用

Epigenetic modifications are critical for stem cell differentiation. High-order chromatin is currently a hot field in epigenetics, but the mechanisms underling its formation and the roles of higher-order chromatin in stem cell differentiation still await further studies. We previously indicated that large H3K9me2 heterochromatin domains, i.e. LOCKs, are tightly linked to higher-order chromatin, and genome-wide distribution of LOCKs are highly overlapping that of lamina-associated domains (LADs). However, the functional relationship between LOCKs and lamina remain unclear. Based on an in-vitro differentiation system from embryonic stem cells to definitive endoderm cells, this project aims to 1) analyze genome-wide distribution of LOCKs and LADs and their correlation; 2) define protein complexes interacting with LOCKs and LADs and their differential components in differentiation, and identify key factors mediating LOCKs-lamina interactions; 3) investigate the function and mechanisms of these key factors in differentiation. This project bears substantial significance to reveal the mechanisms of nuclear member-dependent high-order chromatin formation. Moreover, it is helpful to uncover how higher-order chromatin influence stem cell differentiation, and thus shorten the distance between basic researches and clinical uses of stem cells.

表观遗传调控在干细胞分化中具有关键作用。高级结构染色质是最近颇受关注的表观遗传调控方式，但其形成机制以及对干细胞分化的影响还有待研究。我们的前期工作发现由大片段组蛋白修饰H3K9me2（LOCKs）所标记的异染色质域与高级结构染色质密切相关，其基因组分布与核纤层关联域（LADs）高度吻合，但二者之间功能上的联系仍不明确。本项目拟基于已建立的小鼠胚胎干细胞-定型性内胚层细胞体外分化模型，1）分析定向分化中LOCKs与LADs的基因组分布及相关性；2）鉴定LOCKs与核纤层的相互作用复合物及分化中的差别性成分，并确定介导LOCKs-核纤层相互作用的关键因子；3）研究关键互作因子在胚胎干细胞定向分化中的作用及机制。本项的研究对于揭示依赖于核膜的高级结构染色质的形成机制具有重要意义，并且有助于阐明高级结构染色质在干细胞定向分化中的作用及机制，以进一步缩短干细胞基础研究与临床应用之间的距离。

本项目旨在以核纤层为切入点，探析染色质高级结构形成及维持的分子机制。通过本项目的研究，主要取得了如下成果。1）鉴定出300多个与核纤层相互作用的蛋白质；2）发现组蛋白变体MacroH2A与组蛋白修饰H3K9me2共定位并集中分布于核膜，扰动其表达会降低染色质的整体浓缩程度；3）发现核基质蛋白hnRNPU对不同层级的染色质高级结构均有全局性调控作用。相关成果发表于《Genome Research》等杂志。这些研究有助于阐释染色质高级结构建立及维持的分子机理，并为相关领域的研究提供了新的视角及依据。