Epigenetic Regulation of Mode of cortical Interneuron Migration

了解控制大脑发育过程中及时有序的发育过程的细胞和分子机制，如神经元分化和迁移，是神经科学的基本目标。神经元成熟的不同步骤依赖于特定阶段的基因表达程序，这些程序受局部环境刺激的调节。这对于抑制性GABA能皮质中间神经元从它们在基底端脑内的起始点到它们最终的皮质靶区的迁移变得明显。在切向扩展到不同的皮质区域后，中间神经元切换到径向迁移模式，以侵入皮质层。这些不同的步骤是由分泌的或膜结合的蛋白调节的，这些蛋白触发特定阶段的基因表达程序，指导细胞骨架重塑等生理反应。在迁移模式下，破译环境信号和转录程序之间的相互作用是至关重要的，因为它的时间决定了给定皮质区域的最终中间神经元数量。了解这些过程和信号网络是探讨精神分裂症和癫痫等神经精神疾病病因学的先决条件，因为此类疾病至少部分依赖于抑制性GABA能中间神经元的缺陷发育和分布。表观遗传基因调控机制，如DNA甲基化、组蛋白修饰和非编码RNA，似乎在将来自局部微环境的刺激整合到基因组中，从而影响阶段特异性转录网络方面发挥关键作用。然而，到目前为止，关于在皮质中间神经元中建立阶段特异性转录程序的离散表观遗传学特征，以及它们如何受到外部信号的影响，人们还知之甚少。在初步研究中，我们提供了DNA甲基转移酶1(DNMT1)调控迁移中皮质中间神经元阶段特异性基因表达的证据。此外，我们发现DNMT1与特定的基因位点和特定的lncRNAs的结合可以在外部刺激下通过一个重要的调节膜蛋白来改变。这与所提出的lncRNAs靶向DNA甲基化的功能相吻合。基于这些数据，我们将在这里讨论阶段特定的DNMT1依赖的DNA甲基化在指导转录网络引导皮质神经元间迁移的切向到径向开关方面的作用。我们进一步询问，DNMT1靶向是否依赖于微环境和lncRNA功能的变化。为此，我们将应用一系列创新方法，包括小鼠遗传学、大脑皮层中间神经元的高通量测序，以及复杂的体内和体外功能验证方法。除了有助于了解神经精神疾病的病因学，该项目还将为长期开发基于表观遗传的治疗策略奠定基础。

Understanding the cellular and molecular mechanisms that govern the timely ordered developmental processes during brain unfolding like neuronal differentiation and migration, is a fundamental goal in neuroscience. The different steps of neuronal maturation rely on stage-specific gene expression programs, which are modulated by local environmental stimuli. This becomes clearly evident for the migration of inhibitory GABAergic cortical interneurons from their sites of origin within the basal telencephalon to their final cortical target regions. After tangentially spreading over the different cortical areas, interneurons switch to a radial mode of migration to invade the cortical layers. These different steps are modulated by secreted or membrane-bound proteins, which trigger stage-specific gene expression programs that direct the physiological responses such as cytoskeletal remodeling. To decipher the interplay of environmental signals and transcriptional programs underlying this switch in migration mode is critical, as its timing defines the final interneuron number in a given cortical area. Understanding these processes and signaling networks is prerequisite to approach the etiology of neuropsychiatric diseases like schizophrenia and epilepsy, as such disorders at least in part rely on defective development and distribution of inhibitory GABAergic interneurons. Epigenetic gene regulatory mechanisms, such as DNA methylation, histone modification and non-coding RNAs, seem to play a key role in integrating stimuli from the local microenvironment into the genome, thereby influencing stage-specific transcriptional networks. However, so far little is known about discrete epigenetic profiles in setting up stage-specific transcriptional programs in cortical interneurons, and how they can be shaped by external signals.In preliminary studies we provided evidence that the DNA methyltransferase 1 (DNMT1) regulates stage-specific gene expression in migrating cortical interneurons. Further, we found that DNMT1 binding to specific gene loci and to particular lncRNAs can be altered upon external stimulation with an important regulatory membrane protein. This fits to the proposed function of lncRNAs in targeting DNA methylation. Based on these data, we here will address the role of stage-specific DNMT1-dependent DNA methylation for instructing transcriptional networks that direct the tangential to radial switch of cortical interneuron migration. We further ask, whether DNMT1 targeting depends on changing microenvironment and lncRNA function. To this end, we will apply a battery of innovative methods including mouse genetics, high-throughput sequencing of cortical interneurons, and sophisticated in vivo and in vitro functional validation approaches. Besides contributing to the understanding of neuropsychiatric disease etiology, this project will set the basis to develop epigenetic-based therapy strategies on the long run.