Department of Zoology, University of Oxford, Oxford, UK.
Dev Dyn. 2019 Nov;248(11):1028-1043. doi: 10.1002/dvdy.77. Epub 2019 Jul 10.
The vertebrate spinal cord is organized across three developmental axes, anterior-posterior (AP), dorsal-ventral (DV), and medial-lateral (ML). Patterning of these axes is regulated by canonical intercellular signaling pathways: the AP axis by Wnt, fibroblast growth factor, and retinoic acid (RA), the DV axis by Hedgehog, Tgfβ, and Wnt, and the ML axis where proliferation is controlled by Notch. Developmental time plays an important role in which signal does what and when. Patterning across the three axes is not independent, but linked by interactions between signaling pathway components and their transcriptional targets. Combined this builds a sophisticated organ with many different types of cell in specific AP, DV, and ML positions. Two living lineages share phylum Chordata with vertebrates, amphioxus, and tunicates, while the jawless fish such as lampreys, survive as the most basally divergent vertebrate lineage. Genes and mechanisms shared between lampreys and other vertebrates tell us what predated vertebrates, while those also shared with other chordates tell us what evolved early in chordate evolution. Between these lie vertebrate innovations: genetic and developmental changes linked to evolution of new morphology. These include gene duplications, differences in how signals are received, and new regulatory connections between signaling pathways and their target genes.
脊椎动物的脊髓沿着三个发育轴组织，从前到后（AP）、从背到腹（DV）和从内到外（ML）。这些轴的模式由经典的细胞间信号通路调节：AP 轴由 Wnt、成纤维细胞生长因子和视黄酸（RA）调节，DV 轴由 Hedgehog、Tgfβ和 Wnt 调节，ML 轴的增殖由 Notch 控制。发育时间在哪个信号做什么和什么时候起作用方面起着重要作用。三个轴的模式不是独立的，而是通过信号通路成分及其转录靶标之间的相互作用联系在一起的。综合起来，这就构建了一个具有许多不同类型细胞的复杂器官，它们位于特定的 AP、DV 和 ML 位置。与脊椎动物共享脊索动物门的两种活谱系是文昌鱼和被囊动物，而无颌鱼如七鳃鳗则作为最基础的脊椎动物谱系存活下来。七鳃鳗和其他脊椎动物之间共享的基因和机制告诉我们什么是脊椎动物之前的，而那些也与其他脊索动物共享的则告诉我们什么是在脊索动物进化早期进化的。在这些之间是脊椎动物的创新：与新形态进化相关的遗传和发育变化。这些变化包括基因复制、信号接收方式的差异，以及信号通路及其靶基因之间新的调控联系。
