The pharyngeal arches are a series of bulges found on the lateral surface of the head of vertebrate embryos, and it is within these segments that components of the later anatomy are laid down. In most vertebrates, the post-otic pharyngeal arches will form the branchial apparatus, while in amniotes these segments are believed to generate the larynx. It has been unclear how the development of these segments has been altered with the emergence of the amniotes. In this study, we examined the development of pharyngeal arches in amniotes and show that the post-otic pharyngeal arches in this clade are greatly diminished. We find that the post-otic segments do not undergo myogenesis or skeletogenesis, but are remodelled before these processes occur. We also find that nested DLX expression, which is a feature of all the pharyngeal arches in anamniotes, is associated with the anterior segments but less so with the posterior arches in amniotes. We further show that the posterior arches of the mouse embryo fail to properly delineate, which demonstrates the lack of function of these posterior segments in later development. In amniotes, there has been a loss of the ancestral “branchial” developmental programme that is a general feature of gnathostomes; myogenesis and skeletogenesis This is likely to have facilitated the emergence of the larynx as a new structure not constrained by the segmental organisation of the posterior pharyngeal region.

中文翻译：

---

咽部分割的减少和羊膜的进化

咽弓是在脊椎动物胚胎头部侧面发现的一系列隆起，后来的解剖结构的组成部分正是在这些节段内形成的。在大多数脊椎动物中，耳后咽弓将形成鳃器，而在羊膜动物中，这些节段被认为会产生喉部。目前尚不清楚这些部分的发育如何随着羊膜的出现而改变。在这项研究中，我们检查了羊膜动物咽弓的发育，并表明该进化枝中的耳后咽弓大大减少。我们发现耳后节段不会发生肌生成或骨骼生成，而是在这些过程发生之前被重塑。我们还发现嵌套的 DLX 表达，这是羊膜动物所有咽弓的一个特征，与前段有关，但与羊膜后弓的关系较小。我们进一步表明，小鼠胚胎的后弓未能正确描绘，这表明这些后段在以后的发育中缺乏功能。在羊膜动物中，祖先的“分支”发育程序已经丧失，这是有颚类动物的一般特征。肌生成和骨骼生成 这可能促进了喉部作为一种不受后咽区域节段组织限制的新结构的出现。这表明这些后段在以后的发育中缺乏功能。在羊膜动物中，祖先的“分支”发育程序已经丧失，这是有颚类动物的一般特征。肌生成和骨骼生成 这可能促进了喉部作为一种不受后咽区域节段组织限制的新结构的出现。这表明这些后段在以后的发育中缺乏功能。在羊膜动物中，祖先的“分支”发育程序已经丧失，这是有颚类动物的一般特征。肌生成和骨骼生成 这可能促进了喉部作为一种不受后咽区域节段组织限制的新结构的出现。