Laboratory of the Neurogenetics of Language, The Rockefeller University, New York, New York, USA.
Vertebrate Genome Laboratory, The Rockefeller University, New York, New York, USA.
J Comp Neurol. 2021 Aug;529(12):3222-3246. doi: 10.1002/cne.25159. Epub 2021 May 7.
Over the last two decades, beginning with the Avian Brain Nomenclature Forum in 2000, major revisions have been made to our understanding of the organization and nomenclature of the avian brain. However, there are still unresolved questions on avian pallial organization, particularly whether the cells above the vestigial ventricle represent distinct populations to those below it or similar populations. To test these two hypotheses, we profiled the transcriptomes of the major avian pallial subdivisions dorsal and ventral to the vestigial ventricle boundary using RNA sequencing and a new zebra finch genome assembly containing about 22,000 annotated, complete genes. We found that the transcriptomes of neural populations above and below the ventricle were remarkably similar. Each subdivision in dorsal pallium (Wulst) had a corresponding molecular counterpart in the ventral pallium (dorsal ventricular ridge). In turn, each corresponding subdivision exhibited shared gene co-expression modules that contained gene sets enriched in functional specializations, such as anatomical structure development, synaptic transmission, signaling, and neurogenesis. These findings are more in line with the continuum hypothesis of avian brain subdivision organization above and below the vestigial ventricle space, with the pallium as a whole consisting of four major cell populations (intercalated pallium, mesopallium, hyper-nidopallium, and arcopallium) instead of seven (hyperpallium apicale, interstitial hyperpallium apicale, intercalated hyperpallium, hyperpallium densocellare, mesopallium, nidopallium, and arcopallium). We suggest adopting a more streamlined hierarchical naming system that reflects the robust similarities in gene expression, neural connectivity motifs, and function. These findings have important implications for our understanding of overall vertebrate brain evolution.
在过去的二十年中，从 2000 年的鸟类大脑命名学论坛开始，我们对鸟类大脑的组织和命名法的理解已经发生了重大修订。然而，关于鸟类大脑皮层的组织，特别是关于位于退化的脑室上方的细胞是否代表与下方不同的或相似的群体，仍存在未解决的问题。为了检验这两个假设，我们使用 RNA 测序和一个包含大约 22000 个注释完整基因的新斑胸草雀基因组组装，对位于退化的脑室边界上方和下方的主要鸟类大脑皮层亚区的转录组进行了分析。我们发现，脑室上方和下方的神经群体的转录组非常相似。背侧大脑皮层（Wulst）的每个亚区都有一个对应的腹侧大脑皮层（背侧脑室嵴）的分子对应物。反过来，每个对应的亚区都表现出共享的基因共表达模块，其中包含在功能特化中富集的基因集，如解剖结构发育、突触传递、信号转导和神经发生。这些发现更符合退化的脑室空间上方和下方鸟类大脑皮层亚区组织的连续体假说，整个大脑皮层由四个主要的细胞群体（插入大脑皮层、中脑皮层、超神经顶盖和前脑顶）组成，而不是七个（高级顶叶、间质高级顶叶、插入高级顶叶、高级顶叶密细胞、中脑皮层、神经顶叶和前脑顶）。我们建议采用更精简的层次命名系统，反映基因表达、神经连接模式和功能的稳健相似性。这些发现对我们理解整个脊椎动物大脑进化具有重要意义。
