Novel developmental bases for the evolution of hypobranchial muscles in vertebrates
Novel developmental bases for the evolution of hypobranchial muscles in vertebrates
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DOI：
10.1186/s12915-020-00851-y
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发表时间：
2020-09-09
期刊：
影响因子：
5.4
通讯作者：
Kuratani, Shigeru
中科院分区：
文献类型：
--
作者：
Kusakabe, Rie;Higuchi, Shinnosuke;Kuratani, Shigeru
背景脊椎动物的特点是拥有下鳃肌（HBM）。圆口动物，或现代无颌脊椎动物，具有一个基本的和浅表的HBM侧咽，而在有颌脊椎动物的HBM是内化和前后指定。前体细胞的HBM，标志着Lbx 1的表达，起源于体节，并进行广泛的迁移，然后成为受支配的舌下神经。HBM的复杂形式如何在进化中出现与脊椎动物身体计划的建立有关，但尽管长期以来一直被认为与肢体肌肉相似，但HBM发育机制的修改仍然是个谜。结果在这里，我们描述了Lbx基因在七鳃鳗和盲鳗（圆口目）和猫鲨（有颌类;有颌类脊椎动物）中的表达。我们发现，表达模式的单一圆口藻Lbx同源物，Lbx-A，不类似于体细胞表达的EscherialianLbx 1。Lbx-A的破坏揭示了LjLbx-A是HBM和体壁肌肉形成所必需的，可能是由于前体细胞延伸不足而不是阻碍肌肉分化。这两个同系物的Lbxin的猫鲨的体节肌肉原基中的表达，不像在。在猫鲨胚胎发育过程中，Lbx 2在尾侧HBM和腹直肌中表达，类似于七鳃鳗Lbx-A，而Lbx 1标记吻侧HBM和胸鳍肌。结论我们的结论是，脊椎动物HBM最初出现作为一个专门的躯体肌肉覆盖咽，和前内化的HBM的颚口可能是一个新奇的添加到圆口类HBM的吻，复制和功能化的Lbx基因将是一个先决条件。
Background Vertebrates are characterized by possession of hypobranchial muscles (HBMs). Cyclostomes, or modern jawless vertebrates, possess a rudimentary and superficial HBM lateral to the pharynx, whereas the HBM in jawed vertebrates is internalized and anteroposteriorly specified. Precursor cells of the HBM, marked by expression ofLbx1, originate from somites and undergo extensive migration before becoming innervated by the hypoglossal nerve. How the complex form of HBM arose in evolution is relevant to the establishment of the vertebrate body plan, but despite having long been assumed to be similar to that of limb muscles, modification of developmental mechanisms of HBM remains enigmatic. Results Here we characterize the expression ofLbxgenes in lamprey and hagfish (cyclostomes) and catshark (gnathostome; jawed vertebrates). We show that the expression patterns of the single cyclostomeLbxhomologue,Lbx-A, do not resemble the somitic expression of mammalianLbx1. Disruption ofLbx-Arevealed thatLjLbx-Ais required for the formation of both HBM and body wall muscles, likely due to the insufficient extension of precursor cells rather than to hindered muscle differentiation. Both homologues ofLbxin the catshark were expressed in the somitic muscle primordia, unlike in amniotes. During catshark embryogenesis,Lbx2is expressed in the caudal HBM as well as in the abdominal rectus muscle, similar to lampreyLbx-A, whereasLbx1marks the rostral HBM and pectoral fin muscle. Conclusions We conclude that the vertebrate HBM primarily emerged as a specialized somatic muscle to cover the pharynx, and the anterior internalized HBM of the gnathostomes is likely a novelty added rostral to the cyclostome-like HBM, for which duplication and functionalization ofLbxgenes would have been a prerequisite.