Transgenic tools targeting striatal and pallidal subpopulations reveal both evolutionary conservation and specialization of cortico-basal ganglia circuits in zebrafish. Transgenic tools targeting striatal and pallidal subpopulations reveal both evolutionary conservation and specialization of cortico-basal ganglia circuits in zebrafish

The cortico-basal ganglia circuit mediates decision-making. Here, we generated transgenic tools for adult zebrafish targeting specific subpopulations of the components of this circuit and utilized them to identify evolutionary homologs of the mammalian direct- and indirect-pathway striatal neurons which respectively project to the homologs of the internal and external segment of the globus pallidus (dEN and Vl) as in mammals. Unlike in mammals, the Vl mainly projected to the dEN directly, not by way of the subthalamic nucleus. Further single-cell RNA sequencing analysis revealed two pallidal output pathways: a major shortcut pathway directly connecting the dEN with the pallium and the evolutionarily conserved closed loop by way of the thalamus. Our resources and circuit map provide the common basis for the functional study of the basal ganglia in a small and optically tractable zebrafish brain for the comprehensive mechanistic understanding of the cortico-basal ganglia circuit. Overall design: To identify genetic markers of the npy-negative thalamus-projecting neurons in the dEN, we conducted single-cell RNA sequencing analysis. We dissected the dEN and its surrounding regions from six adult individuals of TgBAC(npy:GAL4VP16);Tg(UAS:GFP). We then dissociated the dissected tissue and used the droplet-based 3’end scRNAseq system Chromium (10x Genomics). We obtained transcriptomic data from 3,381 cells and performed unbiased clustering by Seurat.

皮层-基底神经节环路（cortico-basal ganglia circuit）介导决策过程。本研究开发了靶向该环路组分特定亚群的成年斑马鱼转基因工具，并利用这些工具鉴定出哺乳动物直接通路与间接通路纹状体神经元的进化同源物：两类神经元分别向哺乳动物苍白球内段（dEN）和外段（Vl）的同源结构投射，与哺乳动物的投射模式一致。与哺乳动物不同的是，Vl主要直接投射至dEN，而非经由丘脑底核（subthalamic nucleus）。进一步的单细胞RNA测序（single-cell RNA sequencing）分析揭示了两条苍白球输出通路：一条是连接dEN与端脑的主要捷径通路，另一条是经由丘脑的进化保守闭合环路。本研究的相关资源与环路图谱，为在小型且光学可操控的斑马鱼脑中开展基底神经节功能研究提供了通用基础，为全面解析皮层-基底神经节环路的机制提供支撑。
实验设计概述：为鉴定dEN内神经肽Y（neuropeptide Y, NPY）阴性的丘脑投射神经元的遗传标记，我们开展了单细胞RNA测序分析。我们从6只TgBAC(npy:GAL4VP16);Tg(UAS:GFP)转基因成年个体体内分离了dEN及其周边区域，随后解离获取的组织，并使用基于液滴的3'端单细胞RNA测序系统Chromium（10x Genomics公司）完成测序。最终获得3381个细胞的转录组数据，并通过Seurat软件完成无偏聚类分析。