Thyroid hormone regulates DNA methylation in the developing brain through direct modulation of the DNA methyltransferase 3a gene

 描述(由申请人提供)：表观遗传修饰在人类大脑发育中发挥着核心作用，它导致基因功能的可遗传变化，而不涉及DNA序列的变化。从头DNA甲基转移酶(DNMT)对DNA甲基化的动态调节在神经元和神经胶质细胞分化的控制中起着重要作用。 我们最近发现，DNMT3A基因是小鼠脑内甲状腺激素受体(TH)的直接靶点。胚胎后大脑发育严重依赖甲状腺激素(TH)；在胎儿和新生儿发育期间，TH缺乏会导致严重的智力和生长迟缓，称为克汀病。我们假设DNMT3A的调节在正常的神经发育中起着关键作用，因为最近的证据支持DNMT3A的出生后动态调节可能是在发育中的大脑中建立DNA甲基化模式所必需的。在拟议的研究中，我们将：1)研究TH对小鼠脑内DNMT3A基因在整个出生后早期发育过程中的调控。我们将研究TH对DNMT3A基因座的TRR募集，以及TH诱导的组蛋白修饰。我们将直接测试我们确定的反应元件是否对DNMT3A基因的调节是必需的。2)研究DNMT3A在TH依赖的神经细胞周期停滞和分化中的作用。我们将研究细胞周期控制基因Cyclin D1的启动子的DNMT3A甲基化是否介导了细胞周期停滞，可能还有其他E2F靶基因。对于这些实验，我们将使用小鼠神经细胞模型来表达tr的1个亚型。适当地退出细胞周期、细胞分化和维持细胞周期停滞是正常发育所必需的。胚胎和胎儿这些过程的中断可能会导致异常发育；成年人的中断可能会导致癌症和其他疾病。甲状腺激素在中枢神经系统的细胞周期退出和细胞分化中起着中心作用。一些证据支持细胞周期蛋白D1受DNMT3A介导的DNA甲基化的直接调控。我们推测，细胞周期控制基因调节区DNA甲基化的调节在这一过程中起着关键作用。这项研究的成功完成将有助于我们理解DNA甲基化在发育过程中的调控机制，以及TH依赖的DNA甲基化在细胞增殖和分化中的作用。

 DESCRIPTION (provided by applicant): Epigenetic modifications, which result in heritable changes in gene function that do not involve changes to the DNA sequence, play central roles in human brain development. Dynamic regulation of DNA methylation by de novo DNA methyltransferases (Dnmts) is implicated in the control of neuronal and glial cell differentiation. We recently discovered that the Dnmt3a gene is a direct thyroid hormone (TH) receptor (TR) target in mouse brain. Postembryonic brain development is critically dependent on thyroid hormone (TH); TH deficiency during fetal and neonatal periods of human development leads to a condition of severe mental and growth retardation known as cretinism. We hypothesize that TH regulation of Dnmt3a plays a pivotal role in normal neurological development, since recent evidence supports that dynamic postnatal regulation of Dnmt3a may be essential for establishing DNA methylation patterns in the developing brain. In the proposed research we will: 1) Investigate the regulation of the Dnmt3a gene in mouse brain in vivo by TH throughout early postnatal development. We will investigate TR recruitment to the Dnmt3a locus, and histone modifications induced by TH. We will directly test whether TH response elements that we identified are required for TH regulation of the Dnmt3a gene. 2) Investigate a role for Dnmt3a in TH-dependent neural cell cycle arrest and differentiation. We will investigate whether cell cycle arrest is mediated by Dnmt3a methylation of the promoter of the cell cycle control gene Cyclin D1, and possibly other E2F target genes. For these experiments we will use mouse neuronal cell models that expresses the ß1 isoform of TR. Proper exit from the cell cycle, cell differentiation and the maintenance of cell cycle arrest is essential for normal development. Disruption of these processes in the embryo and fetus can lead to abnormal development; disruption in the adult can lead to cancer and other disease. Thyroid hormone plays a central role in cell cycle exit and cell differentiation in the central nervous system. Several lines of evidence support that Cyclin D1 is directly regulated by Dnmt3a-mediated DNA methylation. We hypothesize that TH regulation of DNA methylation of regulatory regions of cell cycle control genes plays a key role in this process. Successful completion of the proposed research will lead to advances in our understanding of the mechanisms by which DNA methylation is regulated during development, and the roles of TH-dependent DNA methylation in cell proliferation and differentiation.