Genetic and Molecular Studies of Neurogenesis

摘要 巨大的人类大脑皮层被认为起源于一个专门的人群 外室下区(OSVZ)内的外径向神经胶质(Org)神经干细胞。这些 干细胞分裂产生中间神经前体细胞(INPs)，这些细胞本身 分裂产生8-12个神经元。相比之下，大多数非灵长类神经干细胞会产生 每个区有1到2个神经元，导致大脑变小。因此，老鼠和鱼 为灵长类的脑扩张和灵长类的直接研究提供了一个相对较差的模型 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实验室开发了一种果蝇模型 以了解组织样干细胞谱系。我们发现了一群果蝇 脑神经干细胞(称为II型神经母细胞；T2NBs)产生INP，从而 每个细胞产生8-12个神经元，类似于灵长类组织干细胞。现在我们可以使用 果蝇遗传学研究T2NBs在脑中作用的能力和速度 发展，并为人脑有机体研究提出了可检验的假说。 我们之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T2NBs中顺序表达的蛋白质；这些 是确定谱系中神经元的“时间同一性”的极佳候选者。 我们还发现了一系列在每个INP中顺序表达的TTF 产生了它的血统，并显示其中一个(盲眼，Ey；Pax6)是经过验证的 指定晚出生神经元身份的功能性时间因素。但许多人都打开了 问题仍然存在：从T2NB的每个时间窗出生的神经元是什么 血统？T2NBs中的候选时间因素实际上指定了神经元的身份吗？ 大多数TTF在祖细胞(神经母细胞和INP)中瞬时表达，但缺乏成体 表达；TTF指定的神经元身份是如何在 成虫苍蝇？是否有TTF靶基因起到维持神经元特性的作用？和 最后，T2NB时态身份和INP时态身份如何整合以指定 独特的神经元亚型？这些问题将分别在目标1-4中阐述。 我们的发现将提供对INP在扩大脑容量中的作用的洞察 并提出了有针对性的假说来测试 灵长类组织。此外，我们的结果可能会对未来的发展有所启示。 中央复合体，一个保守的昆虫大脑区域，用于苍蝇的天文导航， 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.