Ultrastructure of the lamprey head mesoderm reveals evolution of the vertebrate head

• Published in: iScience Vol. 26; no. 12; p. 108338
• Main Authors: Onai, Takayuki, Adachi, Noritaka, Urakubo, Hidetoshi, Sugahara, Fumiaki, Aramaki, Toshihiro, Matsumoto, Mami, Ohno, Nobuhiko
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-12-2023; Elsevier
• Subjects: Evolutionary biology; Evolutionary developmental biology; Life Sciences; Zoology; Evolutionary biology; Zoology; Evolutionary developmental biology
• ISSN: 2589-0042; 2589-0042
• DOI: 10.1016/j.isci.2023.108338

The cranial muscle is a critical component in the vertebrate head for a predatory lifestyle. However, its evolutionary origin and possible segmental nature during embryogenesis have been controversial. In jawed vertebrates, the presence of pre-otic segments similar to trunk somites has been claimed based on developmental observations. However, evaluating such arguments has been hampered by the paucity of research on jawless vertebrates. Here, we discovered different cellular arrangements in the head mesoderm in lamprey embryos (Lethenteron camtschaticum) using serial block-face scanning electron and laser scanning microscopies. These cell populations were morphologically and molecularly different from somites. Furthermore, genetic comparison among deuterostomes revealed that mesodermal gene expression domains were segregated antero-posteriorly in vertebrates, whereas such segregation was not recognized in invertebrate deuterostome embryos. These findings indicate that the vertebrate head mesoderm evolved from the anteroposterior repatterning of an ancient mesoderm and developmentally diversified before the split of jawless and jawed vertebrates.
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•Rosette pattern seen in somites is not a primal identity of segmentation•The vertebrate head mesoderm diverged during the early phase of evolution•Rostro-caudal segregation of mesodermal genes enabled to evolve the head mesoderm•Somites arose from an ancient deuterostome endomesoderm during gastrulation
Zoology; Evolutionary biology; Evolutionary developmental biology