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Lacalli T. The Cambrian fossil Pikaia, and the origin of chordate somites. EvoDevo 2024; 15:1. [PMID: 38302988 PMCID: PMC10832150 DOI: 10.1186/s13227-024-00222-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 01/17/2024] [Indexed: 02/03/2024] Open
Abstract
The Middle Cambrian fossil Pikaia has a regular series of vertical bands that, assuming chordate affinities, can be interpreted as septa positioned between serial myotomes. Whether Pikaia has a notochord and nerve cord is less certain, as the dorsal organ, which has no obvious counterpart in living chordates, is the only clearly defined axial structure extending the length of the body. Without a notochord to serve as a reference point, the location of the nerve cord is then conjectural, which begs the question of how a dorsal neural center devoted to somite innervation would first have arisen from a more diffuse ancestral plexus of intraepithelial nerves. This question is examined using hemichordates as a reference point, first for the information they provide on the organization of the ancestral deuterostome nervous system, and second, extending the analysis of E. E. Ruppert, to explain why neural infoldings like the enteropneust collar cord would first have evolved. Both implicate the medial surface of the anterior-most part of the metacoel as the likely site for the evolution of the first somites. The analysis highlights the importance of the somatobranchial condition in chordates, meaning the linkage between the anterior trunk, hox1 expression, and the beginning of the gill series and somites. This feature is arguably a valid criterion by which to assess extinct taxa from the Cambrian that resemble chordates (e.g., vetulicolians and yunnanozoans), but may be unrelated to them. In a more speculative vein, the nature of the dorsal organ is discussed, including the possibility that it is an expanded neural tube combining neural and support functions in one structure.
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Affiliation(s)
- Thurston Lacalli
- Biology Department, University of Victoria, Victoria, V8W-3N5, Canada.
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Onai T, Adachi N, Urakubo H, Sugahara F, Aramaki T, Matsumoto M, Ohno N. Ultrastructure of the lamprey head mesoderm reveals evolution of the vertebrate head. iScience 2023; 26:108338. [PMID: 38187188 PMCID: PMC10767164 DOI: 10.1016/j.isci.2023.108338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 09/20/2023] [Accepted: 10/23/2023] [Indexed: 01/09/2024] Open
Abstract
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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Affiliation(s)
- Takayuki Onai
- Department of Anatomy, University of Fukui, School of Medical Sciences, 23-3, Matsuokashimoaizuki, Eiheiji, Yoshida, Fukui, Japan
- Life Science Innovation Center, University of Fukui, 23-3, Matsuokashimoaizuki, Eiheiji, Yoshida, Fukui, Japan
| | - Noritaka Adachi
- Aix-Marseille Université, IBDM, CNRS UMR 7288, Campus De Luminy Case 907, 13288 Marseille Cedex 9, France
| | - Hidetoshi Urakubo
- Section of Electron Microscopy, National Institute for Physiological Sciences, 38, Nishigonaka, Myodaiji, Okazaki, Aichi, Japan
| | - Fumiaki Sugahara
- Division of Biology, Hyogo Medical University, 1-1, Mukogawa, Nishinomiya, Hyogo, Japan
| | - Toshihiro Aramaki
- Graduate School of Frontier Biosciences, Osaka University, 1-1, Yamadaoka, Suita, Osaka, Japan
| | - Mami Matsumoto
- Section of Electron Microscopy, Supportive Center for Brain Research, National Institute for Physiological Sciences, 38, Nishigonaka, Myodaiji, Okazaki, Aichi, Japan
- Department of Developmental and Regenerative Biology, Nagoya City University Graduate School of Medical Sciences, 1, Kawasumi, Mizuho, Nagoya, Aichi, Japan
| | - Nobuhiko Ohno
- Department of Anatomy, Division of Histology and Cell Biology, School of Medicine, Jichi Medical University, 3311-1, Yakushiji, Shimotsuke, Tochigi, Japan
- Division of Ultrastructural Research, National Institute for Physiological Sciences, 38, Nishigonaka, Myodaiji, Okazaki, Aichi, Japan
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Tominaga H, Nishitsuji K, Satoh N. A single-cell RNA-seq analysis of early larval cell-types of the starfish, Patiria pectinifera: Insights into evolution of the chordate body plan. Dev Biol 2023; 496:52-62. [PMID: 36717049 DOI: 10.1016/j.ydbio.2023.01.009] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Revised: 01/10/2023] [Accepted: 01/23/2023] [Indexed: 01/29/2023]
Abstract
Ambulacrarians (echinoderms and hemichordates) are a sister group to chordates; thus, their larval cell-types may provide clues about evolution of chordate body plans. Although most genic information accumulated to date pertains to sea urchin embryogenesis, starfish embryogenesis represents a more ancestral mode than that of sea urchins. We performed single-cell RNA-seq analysis of cell-types from gastrulae and bipinnarial larvae of the starfish, Patiria pectinifera, and categorized them into 22 clusters, each of which is composed of cells with specific, shared profiles of development-relevant gene expression. Oral and aboral ectoderm, apical plate, hindgut or archenteron, midgut or intestine, pharynx, endomesoderm, stomodeum, and mesenchyme of the gastrulae, and neurons, ciliary bands, enterocoel and muscle of larvae were characterized by expression profiles of at least two relevant transcription factor genes and signaling molecular genes. Expression of Hox2, Hox7, Hox9/10, and Hox11/13b was detected in cells of clusters that form the larval enterocoel. By comparing homologous gene expression profiles in chordate embryos, we discuss and propose how the chordate body plan evolved from a deuterostome ancestor, from which the echinoderm body plan also evolved.
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Affiliation(s)
- Hitoshi Tominaga
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan.
| | - Koki Nishitsuji
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Noriyuki Satoh
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan.
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Della Gaspera B, Weill L, Chanoine C. Evolution of Somite Compartmentalization: A View From Xenopus. Front Cell Dev Biol 2022; 9:790847. [PMID: 35111756 PMCID: PMC8802780 DOI: 10.3389/fcell.2021.790847] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Accepted: 11/26/2021] [Indexed: 11/13/2022] Open
Abstract
Somites are transitory metameric structures at the basis of the axial organization of vertebrate musculoskeletal system. During evolution, somites appear in the chordate phylum and compartmentalize mainly into the dermomyotome, the myotome, and the sclerotome in vertebrates. In this review, we summarized the existing literature about somite compartmentalization in Xenopus and compared it with other anamniote and amniote vertebrates. We also present and discuss a model that describes the evolutionary history of somite compartmentalization from ancestral chordates to amniote vertebrates. We propose that the ancestral organization of chordate somite, subdivided into a lateral compartment of multipotent somitic cells (MSCs) and a medial primitive myotome, evolves through two major transitions. From ancestral chordates to vertebrates, the cell potency of MSCs may have evolved and gave rise to all new vertebrate compartments, i.e., the dermomyome, its hypaxial region, and the sclerotome. From anamniote to amniote vertebrates, the lateral MSC territory may expand to the whole somite at the expense of primitive myotome and may probably facilitate sclerotome formation. We propose that successive modifications of the cell potency of some type of embryonic progenitors could be one of major processes of the vertebrate evolution.
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Yasuoka Y. Enhancer evolution in chordates: Lessons from functional analyses of cephalochordate cis‐regulatory modules. Dev Growth Differ 2020; 62:279-300. [DOI: 10.1111/dgd.12684] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/25/2020] [Accepted: 05/27/2020] [Indexed: 12/20/2022]
Affiliation(s)
- Yuuri Yasuoka
- Laboratory for Comprehensive Genomic Analysis RIKEN Center for Integrative Medical Sciences Tsurumi‐ku Japan
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Yasuoka Y. Morphogenetic mechanisms forming the notochord rod: The turgor pressure-sheath strength model. Dev Growth Differ 2020; 62:379-390. [PMID: 32275068 DOI: 10.1111/dgd.12665] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 03/30/2020] [Accepted: 03/31/2020] [Indexed: 12/14/2022]
Abstract
The notochord is a defining feature of chordates. During notochord formation in vertebrates and tunicates, notochord cells display dynamic morphogenetic movement, called convergent extension, in which cells intercalate and align at the dorsal midline. However, in cephalochordates, the most basal group of chordates, the notochord is formed without convergent extension. It is simply developed from mesodermal cells at the dorsal midline. This suggests that convergent extension movement of notochord cells is a secondarily acquired developmental attribute in the common ancestor of olfactores (vertebrates + tunicates), and that the chordate ancestor innovated the notochord upon a foundation of morphogenetic mechanisms independent of cell movement. Therefore, this review focuses on biological features specific to notochord cells, which have been well studied using clawed frogs, zebrafish, and tunicates. Attributes of notochord cells, such as vacuolation, membrane trafficking, extracellular matrix formation, and apoptosis, can be understood in terms of two properties: turgor pressure of vacuoles and strength of the notochord sheath. To maintain the straight rod-like structure of the notochord, these parameters must be counterbalanced. In the future, the turgor pressure-sheath strength model, proposed in this review, will be examined in light of quantitative molecular data and mathematical simulations, illuminating the evolutionary origin of the notochord.
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Affiliation(s)
- Yuuri Yasuoka
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan.,Laboratory for Comprehensive Genomic Analysis, RIKEN Center for Integrative Medical Sciences, Yokohama, Japan
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