Deciphering the mechanisms underlying multicolumnar neuron pathfinding and specification in the Drosophila melanogaster optic lobe

项目摘要/摘要： 大脑中的电路是如何组装的，这是发育神经生物学中的一个关键问题。这个 果蝇的视觉系统为研究这个问题提供了一个优雅的模型；视叶由大约60,000个 允许动物执行复杂的视觉任务的神经元。这些单元格被组织成800个 代表在视网膜中感知视觉信息的800个单位眼(小眼)的列。 这个 延髓 是视觉系统中最复杂的神经纤维层。尽管十层髓质层中的每一层都高度专业化， 在一种被称为视网膜复制的现象中，从一层到另一层保持一致的神经元拓扑结构。这个 主办实验室已经确定了三个过程，它们产生了延髓中80多种神经类型的多样性。 -首先，~800个神经母细胞(NBS)中的每一个都顺序表达一系列六种时间转录因子 (TTF)，它们的组合指定了不同类型的神经元后代。该系统的综合输出 允许每个NB以1：1的比例指定大约20种类型的单柱(UC)神经元。 -第二，OPC内的空间线索与tTF相结合，指定第二组 神经元--多柱神经元(MC神经元)--具有更大的感受野，以低于1：1的比例存在 至柱，根据细胞类型的不同，分布于两列至半髓质的神经。 这些MC神经元只在神经上皮亚区产生。 -最后，Notch信号(Non或Noff)进一步使两个神经元的神经元身份多样化 神经节母细胞的分裂，是每个神经节的单一传递放大后代。 虽然MC神经元来自OPC的受限区域，但它们找到了它们的目标并连接到整个 延髓。虽然已经有关于MC神经元组织的描述，但其背后的机制是 他们发现他们的目标大多是未知的。此外，先前关于MC神经元规范的研究 专注于表达TTF同胸的神经母细胞的后代；其他TTF的后代- 表达NBS还有待探索。我的工作是试图理解MC神经元是如何被指定的，以及 这种命运规范如何在轴突引导中通知细胞的决定，从而建立 这个系统中的视网膜复制术。具体目标1将观察延髓内MC神经元靶向的动力学。 我们将使用实时成像和免疫荧光技术来确定MC神经元的谱系，识别 转录因子在这些细胞中表达，并观察这些细胞使用的机制，以找到它们的 目标。具体目标2将建立在具体目标1中发现的知识的基础上，并将使用候选人 一种结合转录组分析的方法以确定MC细胞所需的基因 MC神经元的识别和寻路。我们的研究将提供对身体和基因的新洞察力 复杂神经元是如何产生的，并在视网膜定位图上找到多个目标的机制， 让我们更好地理解神经系统组装的基本原理。

Project Summary/Abstract: How circuits in the brain are assembled is a crucial question in developmental neurobiology. The Drosophila visual system presents an elegant model to study this question; the optic lobes comprise ~60,000 neurons that allow the animal to perform sophisticated visual tasks. These cells are organized into 800 columns representing the 800 unit eyes (ommatidia) that perceive visual information in the retina. The medulla is the most complex neuropil of the visual system. Though each of the ten medulla layers is highly specialized, a consistent neuronal topology is maintained from layer to layer, in a phenomenon known as retinotopy. The host lab has identified three processes that generate the diversity of the over 80 neural types in the medulla. - First, each of the ~800 neuroblasts (NBs) sequentially expresses a series of six temporal transcription factors (tTFs), whose combination specifies different types of neuronal progeny. The integrated output of this system allows each NB to specify about 20 types of uni-columnar (UC) neurons at a 1:1 ratio to medulla columns. - Second, spatial cues within the OPC act in combination with tTFs to specify the fate of a second set of neurons—multicolumnar neurons (MC neurons)—that have a larger receptive field, exist at less than a 1:1 ratio to columns, and that innervate anywhere from two columns to half of the medulla, depending on the cell type. These MC neurons are only produced in subregions of the neuroepithelium. - Finally, Notch signaling (Non or Noff) further diversifies neuronal identity of the two neurons emerging from the division of the ganglion mother cell, the single transit-amplifying descendant of each NB. While MC neurons derive from restricted regions of the OPC, they find their targets and connect to the entire medulla. Although descriptions of MC neuron organization have been reported, the mechanisms behind how they find their targets are mostly unknown. Furthermore, previous research regarding MC neuron specification has focused on descendants of neuroblasts expressing the tTF Homothorax; the descendants of other tTF- expressing NBs have yet to be explored. My work seeks to understand how MC neurons are specified, and how this fate specification informs the cell's decisions in axon guidance, and thus, the establishment of retinotopy in this system. Specific aim 1 will look at the dynamics of MC neuron targeting within the medulla. We will use live imaging and immunofluorescence techniques to determine the lineage of MC neurons, identify the transcription factors expressed in these cells, and observe the mechanisms used by these cells to find their targets. Specific aim 2 will build upon the knowledge unearthed in Specific aim 1, and will use a candidate approach combined with transcriptome analysis of sorted MC cells in order to identify the genes required for MC neuron identity and pathfinding. Our research will provide novel insight into the physical and genetic mechanisms underlying how complex neurons are generated and find multiple targets on the retinotopic map, allowing us to better comprehend basic principles of nervous system assembly.