Modelling interactions between somites and neural tube with human Trunk-like Structures (hTLS)

Human stem cell-based embryo-like models have opened new avenues of research into the principles of embryonic development using experimentally amenable in vitro systems. One of the benefits of embryo-like models over organoids is their multilineage differentiation, which allows the co-development of different populations and interaction between tissues. Here, we develop a method of generating somite- and neural tube-containing models, called human Trunk-like Structures (hTLS). These hTLS contain SOX2+ TBXT+ neuromesodermal progenitors, presomitic mesoderm, and somitic epithelial tissues, alongside a neural tube structure. As well as the expression of Wnt/FGF ligands posteriorly and Retinoic Acid (RA) pathway components anteriorly, we observe oscillatory HES7 expression, and show that increasing exposure to a Sonic Hedgehog signalling agonist (SAG) increasingly ventralises tissue identity. Additionally, we show that RA and noncanonical Wnt interactions likely occur between the somites and neural tube. In particular, we observe medially-localised ALDH1A2 expression in the somites - at the interface with the neural tube – which we validated in mouse embryos, whereas in somite-only structures, ALDH1A2 is anteroposteriorly polarised. This suggests that interactions between the neural tube and the somites might be responsible for mediolateral somitic organisation, both in vitro and in vivo, and highlights the value of embryo models to reveal insights into mammalian tissue co-development. Human trunk-like structures were sampled at 3 timepoints (72, 96, 120h), dissociated to single cells, and sequenced using the 10x transcriptomic platform.

基于人类干细胞的胚胎样模型 (human stem cell-based embryo-like models) 为利用实验可操控的体外系统研究胚胎发育原理开辟了全新的研究路径。相较于类器官，胚胎样模型的核心优势之一在于其具备多谱系分化能力，可实现不同细胞群的协同发育以及组织间的相互作用。本研究开发了一种构建包含体节 (somite) 与神经管 (neural tube) 的模型的方法，该模型被命名为人类类躯干结构 (human Trunk-like Structures, hTLS)。此类人类类躯干结构包含表达SOX2与TBXT的神经中胚层祖细胞 (neuromesodermal progenitors)、体节中胚层 (presomitic mesoderm) 以及体节上皮组织 (somitic epithelial tissues)，同时伴随神经管结构。其后部表达Wnt/FGF配体 (Wnt/FGF ligands)，前部则表达视黄酸 (Retinoic Acid, RA) 通路相关组分；研究团队观察到振荡式HES7表达，并证实提高音猬因子信号通路激动剂 (Sonic Hedgehog signalling agonist, SAG) 的暴露剂量可使组织身份愈发偏向腹侧化。此外，本研究发现视黄酸与非经典Wnt信号通路 (noncanonical Wnt) 的相互作用可能发生在体节与神经管之间。尤为关键的是，研究人员在体节与神经管交界的内侧区域观察到ALDH1A2的表达，并在小鼠胚胎中验证了这一现象；而在仅含体节的结构中，ALDH1A2呈现前后极性分布。这一结果提示，无论在体外还是体内环境中，神经管与体节之间的相互作用可能介导体节的内外侧组织模式构建，同时也凸显了胚胎模型在揭示哺乳动物组织协同发育机制方面的重要价值。本研究对人类类躯干结构在3个时间节点（72h、96h、120h）进行取样，将其解离为单细胞后利用10x转录组平台 (10x transcriptomic platform) 进行了转录组测序。