Poopalasundaram Subathra, Richardson Jo, Scott Annabelle, Donovan Alex, Liu Karen, Graham Anthony
1Centre for Developmental Neurobiology, King's College London, London, UK.
2Centre for Craniofacial and Regenerative Biology, King's College London, London, SE1 1UL UK.
Zoological Lett. 2019 Feb 11;5:6. doi: 10.1186/s40851-019-0123-5. eCollection 2019.
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.
咽弓是在脊椎动物胚胎头部侧面发现的一系列隆起，后来解剖结构的组成部分正是在这些节段中奠定的。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，这些节段被认为会发育成喉部。目前尚不清楚随着羊膜动物的出现，这些节段的发育是如何发生改变的。
在本研究中，我们研究了羊膜动物咽弓的发育情况，结果表明该类群中耳后咽弓大大减少。我们发现耳后节段不经历肌发生或骨骼发生，而是在这些过程发生之前进行重塑。我们还发现嵌套的DLX表达（这是无羊膜动物所有咽弓的一个特征）与羊膜动物的前段相关，但与后段的相关性较小。我们进一步表明，小鼠胚胎的后弓未能正确界定，这表明这些后段在后期发育中缺乏功能。
在羊膜动物中，有颌类动物普遍具有的祖传“鳃”发育程序已经丧失；肌发生和骨骼发生。这可能促进了喉部作为一种不受咽后部节段组织限制的新结构的出现。
