Functional characterization of neurotransmitter-mediated signaling in human neocortical development

从进化论的角度来看，新皮质是哺乳动物大脑的最新部分，也是哺乳动物复杂认知技能的来源。虽然基因组相对稳定，但新皮质在灵长类血统中显著扩大。在人类大脑的进化过程中，新皮质中的细胞数量和不同类型的细胞数量都有所增加。因此，问题是如何在新皮质发育过程中实现细胞产量的增加和不同类型细胞的分化。先前的研究表明，神经前体细胞类型的扩大是构成成熟新皮质的大量神经元和神经胶质细胞生成的基础。然而，这些神经前体细胞如何在人类延长的神经发生期保持其增殖能力，以及如何产生如此多的细胞类型尚不清楚。在啮齿动物身上的研究表明，发育中的大脑中的神经递质介导的信号既调节神经前体细胞的增殖，也调节新生神经元的分化。我们假设，神经递质介导的细胞间信号在复杂的人脑发育中发挥着更重要的作用。因此，我们的目标是研究人类大脑中不同类型的神经前体细胞如何受到神经递质的调节。我们将使用细胞内钙浓度的变化来读出细胞对不同神经递质的反应，因为钙是将细胞间信号与转录变化联系起来的重要第二信使，从而可以改变细胞的命运。在目标1中，我们将描述人类神经前体细胞和新生神经元对一系列不同神经递质的生理反应。在目标2中，我们将使用一种新的高通量方法，通过分析单细胞转录本，将生理反应与细胞类型和状态联系起来。在目标3中，我们将通过分析神经递质应用后单个细胞的转录本和通过研究组织切片增殖的变化来研究神经递质信号对不同类型细胞增殖和分化的长期影响。这种系统生物学方法将使我们第一次阐明发育中的人类新皮质中不同类型的细胞如何通过神经递质介导的信号相互调节。由于许多神经发育障碍，如自闭症谱系障碍，是由编码突触蛋白的基因突变引起的，这项研究有助于了解这些突变是如何在突触形成之前影响大脑发育的。

In evolutionary terms, the neocortex is the newest part of the mammalian brain and is the source of the complex cognitive skills of mammals. While the genome has been relatively stable, the neocortex has expanded significantly in the primate lineage. Both the number of cells and the number of different cell types in the neocortex has increased during the evolution of the human brain. The question therefore arises how the increased production of cells and the differentiation of different cell types is achieved during neocortical development. Previous research has shown that an enlarged repertoire of neural progenitor types underlies the generation of the larger number of neurons and glia that constitute the mature neocortex. However, how these neural progenitor cells maintain their proliferative potential throughout the extended neurogenic period in humans and how the large diversity of cell types is generated remains unknown. Studies in rodents have shown that neurotransmitter-mediated signaling in the developing brain regulates both the proliferation of neural progenitor cells and the differentiation of newborn neurons. We hypothesize that neurotransmitter-mediated intercellular signaling plays an even more important role in the development of the complex human brain. We therefore aim to study how the different neural progenitor cell types in the human brain are regulated by neurotransmitters. We will use changes in the concentration of intracellular calcium as a readout of the responsiveness of a cell to different neurotransmitters, since calcium is an important second messenger that links intercellular signaling to changes in transcription and thereby can alter cell fates. In Objective 1 we will characterize the physiological response profiles of human neural progenitor cells and newborn neurons to a range of different neurotransmitters. In Objective 2, we will use a novel high-throughput approach to link the physiological response profiles to cell types and states by analyzing single-cell transcriptomes. In Objective 3, we will study the long-term effects of neurotransmitter signaling on the proliferation and differentiation of different cell types by analyzing transcriptomes of single cells after neurotransmitter application and by studying changes in proliferation in tissue slices. This systems biology approach will allow us for the first time to elucidate how different cell types in the developing human neocortex regulate each other through neurotransmitter-mediated signaling. Since many neurodevelopmental disorders, such as autism spectrum disorders, are caused by mutations in genes that encode synaptic proteins, this research is instrumental for understanding how these mutations affect brain development even prior to the formation of synapses.