Genetic and Molecular Studies of Neurogenesis

摘要 大的人类大脑皮层被认为起源于一个特殊的群体， 外室管膜下区（OSVZ）中的外放射状胶质（oRG）神经干细胞。这些 干细胞分裂产生中间神经祖细胞（INPs）， 分裂产生8-12个神经元。相反，大多数非灵长类神经干细胞产生 每次分裂1或2个神经元，导致大脑变小。因此，老鼠和鱼 为灵长类动物的大脑扩展提供了一个相对较差的模型，并直接研究灵长类动物的大脑。 胎儿脑组织是有问题的 在过去的几年里，我们的实验室和其他人开发了一个果蝇模型， 来理解org样干细胞谱系。我们发现了一群果蝇 脑神经干细胞（称为II型神经母细胞; T2 NBs）产生INPs， 每个细胞产生8-12个神经元，类似于灵长类动物oRG干细胞。现在我们可以使用 果蝇遗传学表征T2 NBs在大脑中作用的能力和速度 发展，并提出可验证的假设，为人类大脑类器官的研究。 我们以前发现了一系列转录因子（TF）和RNA结合 在幼虫生命的五天内在T2 NB中顺序表达的蛋白质;这些 是用于指定谱系中神经元的“时间身份”的优秀候选者。 我们还发现了一系列TTF，它们在每个INP中顺序表达， 他们的后裔，并显示其中之一（Eyeless，Ey; Pax 6）是一个有效的 功能性时间因素，指定晚出生的神经元身份。但许多开放 问题仍然存在：T2 NB中每个时间窗产生的神经元是什么？ 血统？T2 NBs中的候选时间因子实际上指定了神经元身份吗？ 大多数TTF在祖细胞（成神经细胞和INPs）中瞬时表达，但缺乏成熟的TTF。 TTF特异性的神经元身份是如何在神经元中巩固和维持的？ 成年苍蝇？是否存在TTF靶基因来维持神经元的身份？和 最后，如何将T2 NB时间标识和INP时间标识集成以指定 独特的神经元亚型这些问题将分别在目标1-4中讨论。 我们的研究结果将提供深入了解INPs在扩大大脑大小中的作用， 果蝇，并提出重点假设，以测试保守的机制， 灵长类动物组织此外，我们的研究结果可能有助于了解 中央复合体，一个保守的昆虫大脑区域，用于苍蝇的天体导航， 蜜蜂和蝴蝶

Abstract The large human cerebral cortex is thought to arise from a specialized population of outer radial glia (oRG) neural stem cells in the outer subventricular zone (OSVZ). These stem cells divide to produce intermediate neural progenitors (INPs) that themselves divide to produce 8-12 neurons. In contrast, most non-primate neural stem cells produce 1 or 2 neurons with each division, resulting in a smaller brain. Thus, mouse and fish provide a relatively poor model for primate brain expansion, and direct study of primate fetal brain tissue is problematic. Over the past few years, our lab and others have developed a Drosophila model for understanding oRG-like stem cell lineages. We discovered a population of Drosophila brain neural stem cells (called type II neuroblasts; T2NBs) that generate INPs which each generate 8-12 neurons, similar to primate oRG stem cells. Now we can use the power and rapidity of Drosophila genetics to characterize the role of T2NBs in brain development, and suggest testable hypotheses for human brain organoid research. We previously discovered a series of transcription factors (TFs) and RNA-binding proteins that are sequentially expressed in T2NBs over the five days of larval life; these are excellent candidates for specifying the “temporal identity” of neurons in the lineage. We also discovered a series of TTFs that were sequentially expressed in each INP as it produced its lineage, and showed one of them (Eyeless, Ey; Pax6) was a validated functional temporal factor that specified late-born neuron identity. But many open questions remained: What are the neurons born from each temporal window in the T2NB lineage? Do the candidate temporal factors in T2NBs actually specify neuronal identity? Most TTFs are transiently expressed in progenitors (neuroblasts and INPs) but lack adult expression; how are TTF-specified neuronal identities consolidated and maintained in the adult fly? Are there TTF target genes that act to maintain neuronal identity? And lastly, how is T2NB temporal identity and INP temporal identity integrated to specify unique neuronal subtypes? These questions will be addressed in Aims 1-4, respectively. Our findings will provide insight into the role of INPs in expanding brain size in Drosophila, and suggest focused hypotheses to test for conserved mechanisms in primate tissue. Furthermore, our results may shed light on the development of the central complex, a conserved insect brain region used for celestial navigation of flies, bees, and butterflies.