In bilaterians, animal/vegetal axial (A/V) patterning is a fundamental early developmental event for establishment of animal/vegetal polarity and following specification of the germ layers (ectoderm, mesoderm, endoderm), of which the evolutionary origin is enigmatic. Understanding A/V axial patterning in a basal animal from each phylum would help to reconstruct the ancestral state of germ layer specification in bilaterians and thus, the evolution of mesoderm, the third intermediate cell layer. Herein, data show that the canonical Wnt/β‐catenin (cWnt) and Notch signaling pathways control mesoderm specification from the early endomesoderm in the basal chordate amphioxus. Amphioxus belongs to the deuterostome, one of the main superphyla in Bilateria. In the present study, genes (tcf, dsh, axin, gsk3β) encoding cWnt components were expressed in the endomesoderm during the gastrula stages. Excess cWnt signaling by BIO, a GSK3 inhibitor, expanded the expression domains of outer endomesodermal genes that include future mesodermal ones and suppressed inner endomesodermal and ectodermal genes. Interfering Notch signaling by DAPT, a γ‐secretase inhibitor, resulted in decreased expression of ectodermal and endomesodermal markers. These results suggest that cWnt and Notch have important roles in mesoderm specification in amphioxus embryos. The evolution of the mesoderm is also discussed.

中文翻译：

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典型的Wnt /β-catenin和Notch信号调节头孢类两栖动物中的动物/植物轴向模式。

在双边生物中，动物/植物的轴向（A / V）模式是建立动物/植物极性并遵循胚层（外胚层，中胚层，内胚层）规格的基本早期发育事件，其进化起源是神秘的。了解每个门的基础动物中的A / V轴向模式将有助于在Bilaterians中重建胚层规格的祖先状态，从而有助于中胚层（第三中间细胞层）的进化。本文中的数据表明，典型的Wnt /β-catenin（cWnt）和Notch信号通路控制着来自基础绒毛膜的早期内膜中膜的中膜规格。Amphioxus属于deuterostome，在Bilateria中是主要的上叶植物之一。在本研究中，基因（tcf，dsh，轴蛋白，GSK3β）编码cWnt组分在原肠胚阶段在endomesoderm表达。GSK3抑制剂BIO过量的cWnt信号传导扩展了包括未来中胚层基因在内的内胚层基因的表达域，并抑制了内胚层和外胚层基因。γ-分泌酶抑制剂DAPT干扰Notch信号转导导致外胚层和内胚层标记物的表达降低。这些结果表明cWnt和Notch在两栖类胚胎的中胚层规格中具有重要作用。还讨论了中胚层的演变。