Departments of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
Cell Transplant. 2009;18(10):1197-211. doi: 10.3727/096368909X12483162197204. Epub 2009 Aug 5.
Emerging information indicates that epigenetic modification (i.e., histone code and DNA methylation) may be integral to the maintenance and differentiation of neural stem cells (NSCs), but their actual involvement has not yet been illustrated. In this study, we demonstrated the dynamic nature of epigenetic marks during the differentiation of quiescent adult rat NSCs in neurospheres. A subpopulation of OCT4(+) NSCs in the neurosphere contained histone marks, trimethylated histone 3 on lysine 27 (3me-H3K27), 2me-H3K4, and acetylated H4 (Ac-H4). A major decrease of these marks was found prior to or during differentiation, and was further diminished or reprogrammed in diverse subpopulations of migrated NSCs expressing nestin or beta-III-tubulin. The DNA methylation mark 5-methyl-cytosine (5-MeC), and DNA methyltransferase (DNMT) 1 and 3a expression also correlated to the state of differentiation; they were highly present in undifferentiated NSCs but downregulated in migrated populations. In contrast, DNA methyl-CpG-binding protein (MBD1) was low in undifferentiated NSCs in neurospheres, but highly appeared in differentiating NSCs. Furthermore, we found an outward translocation of DNA methylation marker 5-MeC, DNMT1, DNMT3a, and MBD1 in NSCs as differentiation began and proceeded; 5-MeC from homogeneous nucleus to peripheral nucleus, and DMNT1a and 3a from nuclear to cytoplasm, indicating chromatin remodeling. Treatment with DNA methylation inhibitor, 5-aza-cytidine, altered DNA methylation and disrupted migration as indicated by a reduction of migrated neurons and differentiation. These results indicate that chromatin is dynamically remodeled when NSCs transform from the quiescent state to active growth, and that DNA methylation modification is essential for neural stem cell differentiation.
新兴信息表明，表观遗传修饰（即组蛋白密码和 DNA 甲基化）可能是神经干细胞（NSCs）维持和分化的重要组成部分，但它们的实际参与尚未得到说明。在这项研究中，我们展示了在神经球中静止成年大鼠 NSCs 分化过程中表观遗传标记的动态性质。神经球中的 OCT4(+) NSCs 亚群包含组蛋白标记物，赖氨酸 27 上的三甲基化组蛋白 3（3me-H3K27）、2me-H3K4 和乙酰化 H4（Ac-H4）。这些标记物在分化前或分化过程中大量减少，并在表达巢蛋白或β-III-微管蛋白的不同迁移 NSCs 亚群中进一步减少或重新编程。DNA 甲基化标记 5-甲基胞嘧啶（5-MeC）和 DNA 甲基转移酶（DNMT）1 和 3a 的表达也与分化状态相关；它们在未分化的 NSCs 中高度存在，但在迁移的群体中下调。相比之下，在神经球中的未分化 NSCs 中，DNA 甲基-CpG 结合蛋白（MBD1）含量较低，但在分化的 NSCs 中含量较高。此外，我们发现随着分化的开始和进行，DNA 甲基化标记物 5-MeC、DNMT1、DNMT3a 和 MBD1 在 NSCs 中发生向外易位；5-MeC 从均匀核到周边核，DNMT1a 和 3a 从核到细胞质，表明染色质重塑。用 DNA 甲基化抑制剂 5-氮杂胞苷处理后，DNA 甲基化改变，并通过减少迁移神经元和分化来破坏迁移。这些结果表明，当 NSCs 从静止状态转变为活跃生长状态时，染色质会动态重塑，DNA 甲基化修饰对于神经干细胞分化至关重要。
