The formation of the vertebrate body involves the coordinated production of trunk tissues from progenitors located in the posterior of the embryo. Although in vitro models using pluripotent stem cells replicate aspects of this process^{1,2,3,4,5,6,7,8,9,10}, they lack crucial components, most notably the notochord—a defining feature of chordates that patterns surrounding tissues¹¹. Consequently, cell types dependent on notochord signals are absent from current models of human trunk formation. Here we performed single-cell transcriptomic analysis of chick embryos to map molecularly distinct progenitor populations and their spatial organization. Guided by this map, we investigated how differentiating human pluripotent stem cells develop a stereotypical spatial organization of trunk cell types. We found that YAP inactivation in conjunction with FGF-mediated MAPK signalling facilitated WNT pathway activation and induced expression of TBXT (also known as BRA). In addition, timely inhibition of WNT-induced NODAL and BMP signalling regulated the proportions of different tissue types, including notochordal cells. This enabled us to create a three-dimensional model of human trunk development that undergoes morphogenetic movements, producing elongated structures with a notochord and ventral neural and mesodermal tissues. Our findings provide insights into the mechanisms underlying vertebrate notochord formation and establish a more comprehensive in vitro model of human trunk development. This paves the way for future studies of tissue patterning in a physiologically relevant environment.

脊椎动物体的形成涉及位于胚胎后部的祖细胞协调产生躯干组织。尽管使用多能干细胞的体外模型复制了这个过程的各个方面^{1,2,3,4,5,6,7,8,9,10}，但它们缺乏关键组成部分，最明显的是脊索——脊索的一个定义特征，它塑造了周围的组织¹¹。因此，当前人类躯干形成模型中不存在依赖于脊索信号的细胞类型。在这里，我们对雏鸡胚胎进行了单细胞转录组学分析，以绘制分子上不同的祖细胞群及其空间组织。在此图的指导下，我们研究了分化的人类多能干细胞如何形成树干细胞类型的刻板印象空间组织。我们发现 YAP 失活与 FGF 介导的 MAPK 信号传导相结合促进了 WNT 通路激活并诱导了 TBXT （也称为 BRA） 的表达。此外，及时抑制 WNT 诱导的 NODAL 和 BMP 信号传导调节了不同组织类型的比例，包括脊索细胞。这使我们能够创建一个人体躯干发育的三维模型，该模型经历形态发生运动，产生具有脊索和腹侧神经和中胚层组织的细长结构。我们的研究结果为脊椎动物脊索形成的机制提供了见解，并建立了更全面的人类躯干发育体外模型。这为未来在生理相关环境中研究组织模式铺平了道路。