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Castillo H, Hanna P, Sachs LM, Buisine N, Godoy F, Gilbert C, Aguilera F, Muñoz D, Boisvert C, Debiais-Thibaud M, Wan J, Spicuglia S, Marcellini S. Xenopus tropicalis osteoblast-specific open chromatin regions reveal promoters and enhancers involved in human skeletal phenotypes and shed light on early vertebrate evolution. Cells Dev 2024:203924. [PMID: 38692409 DOI: 10.1016/j.cdev.2024.203924] [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: 03/09/2024] [Revised: 04/18/2024] [Accepted: 04/26/2024] [Indexed: 05/03/2024]
Abstract
While understanding the genetic underpinnings of osteogenesis has far-reaching implications for skeletal diseases and evolution, a comprehensive characterization of the osteoblastic regulatory landscape in non-mammalian vertebrates is still lacking. Here, we compared the ATAC-Seq profile of Xenopus tropicalis (Xt) osteoblasts to a variety of non mineralizing control tissues, and identified osteoblast-specific nucleosome free regions (NFRs) at 527 promoters and 6747 distal regions. Sequence analyses, Gene Ontology, RNA-Seq and ChIP-Seq against four key histone marks confirmed that the distal regions correspond to bona fide osteogenic transcriptional enhancers exhibiting a shared regulatory logic with mammals. We report 425 regulatory regions conserved with human and globally associated to skeletogenic genes. Of these, 35 regions have been shown to impact human skeletal phenotypes by GWAS, including one trps1 enhancer and the runx2 promoter, two genes which are respectively involved in trichorhinophalangeal syndrome type I and cleidocranial dysplasia. Intriguingly, 60 osteoblastic NFRs also align to the genome of the elephant shark, a species lacking osteoblasts and bone tissue. To tackle this paradox, we chose to focus on dlx5 because its conserved promoter, known to integrate regulatory inputs during mammalian osteogenesis, harbours an osteoblast-specific NFR in both frog and human. Hence, we show that dlx5 is expressed in Xt and elephant shark odontoblasts, supporting a common cellular and genetic origin of bone and dentine. Taken together, our work (i) unravels the Xt osteogenic regulatory landscape, (ii) illustrates how cross-species comparisons harvest data relevant to human biology and (iii) reveals that a set of genes including bnc2, dlx5, ebf3, mir199a, nfia, runx2 and zfhx4 drove the development of a primitive form of mineralized skeletal tissue deep in the vertebrate lineage.
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Affiliation(s)
- Héctor Castillo
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile.
| | - Patricia Hanna
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Laurent M Sachs
- UMR7221, Physiologie Moléculaire et Adaptation, CNRS, MNHN, Paris Cedex 05, France
| | - Nicolas Buisine
- UMR7221, Physiologie Moléculaire et Adaptation, CNRS, MNHN, Paris Cedex 05, France
| | - Francisco Godoy
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Clément Gilbert
- Université Paris-Saclay, CNRS, IRD, UMR Évolution, Génomes, Comportement et Écologie, 12 route 128, 91190 Gif-sur-Yvette, France
| | - Felipe Aguilera
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - David Muñoz
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile
| | - Catherine Boisvert
- School of Molecular and Life Sciences, Curtin University, Perth, WA, Australia
| | - Mélanie Debiais-Thibaud
- Institut des Sciences de l'Evolution de Montpellier, ISEM, Univ Montpellier, CNRS, IRD, Montpellier, France
| | - Jing Wan
- Aix-Marseille University, INSERM, TAGC, UMR 1090, Marseille, France; Equipe Labelisée LIGUE contre le Cancer, Marseille, France
| | - Salvatore Spicuglia
- Aix-Marseille University, INSERM, TAGC, UMR 1090, Marseille, France; Equipe Labelisée LIGUE contre le Cancer, Marseille, France
| | - Sylvain Marcellini
- Group for the Study of Developmental Processes (GDeP), School of Biological Sciences, University of Concepción, Chile.
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2
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Milgram J, Rehav K, Ibrahim J, Shahar R, Weiner S. The 3D organization of the mineralized scales of the sturgeon has structures reminiscent of dentin and bone: A FIB-SEM study. J Struct Biol 2023; 215:108045. [PMID: 37977509 DOI: 10.1016/j.jsb.2023.108045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 11/14/2023] [Accepted: 11/14/2023] [Indexed: 11/19/2023]
Abstract
Scales are structures composed of mineralized collagen fibrils embedded in the skin of fish. Here we investigate structures contributing to the bulk of the scale material of the sturgeon (Acipencer guldenstatii) at the millimeter, micrometer and nanometer length scales. Polished and fracture surfaces were prepared in each of the three anatomic planes for imaging with light and electron microscopy, as well as focused ion beam - scanning electron microscopy (FIB-SEM). The scale is composed of three layers, upper and lower layers forming the bulk of the scale, as well as a thin surface layer. FTIR shows that the scale is composed mainly of collagen and carbonated hydroxyapatite. Lacunae are present throughout the structure. Fracture surfaces of all three layers are characterized by large diameter collagen fibril bundles (CFBs) emanating from a plane comprising smaller diameter CFBs orientated in different directions. Fine lineations seen in polished surfaces of both major layers are used to define planes called here the striation planes. FIB-SEM image stacks of the upper and lower layers acquired in planes aligned with the striation planes, show that CFBs are oriented in various directions within the striation plane, with larger CFBs emanating from the striation plane. Fibril bundles oriented in different directions in the same plane is reminiscent of a similar organization in orthodentin. The large collagen fibril bundles emanating out of this plane are analogous to von Korff fibrils found in developing dentin with respect to size and orientation. Scales of the sturgeon are unusual in that their mineralized collagen fibril organization contains structural elements of both dentin and bone. The sturgeon scale may be an example of an early evolved mineralized material which is neither bone nor dentin but contains characteristics of both materials, however, the fossil data required to confirm this is missing.
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Affiliation(s)
- Joshua Milgram
- Hebrew University Jerusalem, Faculty of Agriculture Food & Environment, Koret School of Veterinary Medicine, P.O.B. 12, Rehovot 7610001, Israel.
| | - Katya Rehav
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 7610001, Israel.
| | - Jamal Ibrahim
- Archaeological Science Unit, Weizmann Institute of Science, Rehovot 7610001, Israel.
| | - Ron Shahar
- Hebrew University Jerusalem, Faculty of Agriculture Food & Environment, Koret School of Veterinary Medicine, P.O.B. 12, Rehovot 7610001, Israel.
| | - Stephen Weiner
- Archaeological Science Unit, Weizmann Institute of Science, Rehovot 7610001, Israel; Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot, 7610001, Israel.
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3
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Gillis JA. Scales, scutes, and embryonic origins of the vertebrate dermal skeleton. Proc Natl Acad Sci U S A 2023; 120:e2310552120. [PMID: 37531377 PMCID: PMC10433271 DOI: 10.1073/pnas.2310552120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/04/2023] Open
Affiliation(s)
- J. Andrew Gillis
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA02543
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4
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Stundl J, Martik ML, Chen D, Raja DA, Franěk R, Pospisilova A, Pšenička M, Metscher BD, Braasch I, Haitina T, Cerny R, Ahlberg PE, Bronner ME. Ancient vertebrate dermal armor evolved from trunk neural crest. Proc Natl Acad Sci U S A 2023; 120:e2221120120. [PMID: 37459514 PMCID: PMC10372632 DOI: 10.1073/pnas.2221120120] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 04/26/2023] [Indexed: 07/20/2023] Open
Abstract
Bone is an evolutionary novelty of vertebrates, likely to have first emerged as part of ancestral dermal armor that consisted of osteogenic and odontogenic components. Whether these early vertebrate structures arose from mesoderm or neural crest cells has been a matter of considerable debate. To examine the developmental origin of the bony part of the dermal armor, we have performed in vivo lineage tracing in the sterlet sturgeon, a representative of nonteleost ray-finned fish that has retained an extensive postcranial dermal skeleton. The results definitively show that sterlet trunk neural crest cells give rise to osteoblasts of the scutes. Transcriptional profiling further reveals neural crest gene signature in sterlet scutes as well as bichir scales. Finally, histological and microCT analyses of ray-finned fish dermal armor show that their scales and scutes are formed by bone, dentin, and hypermineralized covering tissues, in various combinations, that resemble those of the first armored vertebrates. Taken together, our results support a primitive skeletogenic role for the neural crest along the entire body axis, that was later progressively restricted to the cranial region during vertebrate evolution. Thus, the neural crest was a crucial evolutionary innovation driving the origin and diversification of dermal armor along the entire body axis.
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Affiliation(s)
- Jan Stundl
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA91125
- Faculty of Fisheries and Protection of Waters, University of South Bohemia in Ceske Budejovice, 38925Vodnany, Czech Republic
| | - Megan L. Martik
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA91125
| | - Donglei Chen
- Department of Organismal Biology, Uppsala University, SE-75236Uppsala, Sweden
| | - Desingu Ayyappa Raja
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA91125
| | - Roman Franěk
- Faculty of Fisheries and Protection of Waters, University of South Bohemia in Ceske Budejovice, 38925Vodnany, Czech Republic
| | - Anna Pospisilova
- Department of Zoology, Faculty of Science, Charles University in Prague, 128 00Prague, Czech Republic
| | - Martin Pšenička
- Faculty of Fisheries and Protection of Waters, University of South Bohemia in Ceske Budejovice, 38925Vodnany, Czech Republic
| | - Brian D. Metscher
- Department of Evolutionary Biology, Theoretical Biology Unit, University of Vienna, 1010Vienna, Austria
| | - Ingo Braasch
- Department of Integrative Biology, Michigan State University, East Lansing, MI48824
- Ecology, Evolution and Behavior Program, Michigan State University, East Lansing, MI48824
| | - Tatjana Haitina
- Department of Organismal Biology, Uppsala University, SE-75236Uppsala, Sweden
| | - Robert Cerny
- Department of Zoology, Faculty of Science, Charles University in Prague, 128 00Prague, Czech Republic
| | - Per E. Ahlberg
- Department of Organismal Biology, Uppsala University, SE-75236Uppsala, Sweden
| | - Marianne E. Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA91125
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Charest F, Mondéjar Fernández J, Grünbaum T, Cloutier R. Evolution of median fin patterning and modularity in living and fossil osteichthyans. PLoS One 2023; 18:e0272246. [PMID: 36921006 PMCID: PMC10016723 DOI: 10.1371/journal.pone.0272246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 02/24/2023] [Indexed: 03/16/2023] Open
Abstract
Morphological and developmental similarities, and interactions among developing structures are interpreted as evidences of modularity. Such similarities exist between the dorsal and anal fins of living actinopterygians, on the anteroposterior axis: (1) both fins differentiate in the same direction [dorsal and anal fin patterning module (DAFPM)], and (2) radials and lepidotrichia differentiate in the same direction [endoskeleton and exoskeleton module (EEM)]. To infer the evolution of these common developmental patternings among osteichthyans, we address (1) the complete description and quantification of the DAFPM and EEM in a living actinopterygian (the rainbow trout Oncorhynchus mykiss) and (2) the presence of these modules in fossil osteichthyans (coelacanths, lungfishes, porolepiforms and 'osteolepiforms'). In Oncorhynchus, sequences of skeletal elements are determined based on (1) apparition (radials and lepidotrichia), (2) chondrification (radials), (3) ossification (radials and lepidotrichia), and (4) segmentation plus bifurcation (lepidotrichia). Correlations are then explored between sequences. In fossil osteichthyans, sequences are determined based on (1) ossification (radials and lepidotrichia), (2) segmentation, and (3) bifurcation of lepidotrichia. Segmentation and bifurcation patterns were found crucial for comparisons between extant and extinct osteichthyan taxa. Our data suggest that the EEM is plesiomorphic at least for actinopterygians, and the DAFPM is plesiomorphic for osteichthyans, with homoplastic dissociation. Finally, recurrent patterns suggest the presence of a Lepidotrichia Patterning Module (LPM).
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Affiliation(s)
- France Charest
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, Rimouski, Québec, Canada
- Parc National de Miguasha, Nouvelle, Québec, Canada
| | - Jorge Mondéjar Fernández
- Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Frankfurt am Main, Germany
- Centre de Recherche en Paléontologie–Paris, Département Origines & Évolution, Muséum National d’Histoire Naturelle, UMR 7207 (MNHN–Sorbonne Université–CNRS), Paris, France
| | - Thomas Grünbaum
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, Rimouski, Québec, Canada
| | - Richard Cloutier
- Département de Biologie, Chimie et Géographie, Université du Québec à Rimouski, Rimouski, Québec, Canada
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6
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Johanson Z. Vertebrate cranial evolution: Contributions and conflict from the fossil record. Evol Dev 2023; 25:119-133. [PMID: 36308394 DOI: 10.1111/ede.12422] [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: 02/03/2022] [Revised: 08/12/2022] [Accepted: 10/05/2022] [Indexed: 01/14/2023]
Abstract
In modern vertebrates, the craniofacial skeleton is complex, comprising cartilage and bone of the neurocranium, dermatocranium and splanchnocranium (and their derivatives), housing a range of sensory structures such as eyes, nasal and vestibulo-acoustic capsules, with the splanchnocranium including branchial arches, used in respiration and feeding. It is well understood that the skeleton derives from neural crest and mesoderm, while the sensory elements derive from ectodermal thickenings known as placodes. Recent research demonstrates that neural crest and placodes have an evolutionary history outside of vertebrates, while the vertebrate fossil record allows the sequence of the evolution of these various features to be understood. Stem-group vertebrates such as Metaspriggina walcotti (Burgess Shale, Middle Cambrian) possess eyes, paired nasal capsules and well-developed branchial arches, the latter derived from cranial neural crest in extant vertebrates, indicating that placodes and neural crest evolved over 500 million years ago. Since that time the vertebrate craniofacial skeleton has evolved, including different types of bone, of potential neural crest or mesodermal origin. One problematic part of the craniofacial skeleton concerns the evolution of the nasal organs, with evidence for both paired and unpaired nasal sacs being the primitive state for vertebrates.
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7
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Andreev PS, Sansom IJ, Li Q, Zhao W, Wang J, Wang CC, Peng L, Jia L, Qiao T, Zhu M. The oldest gnathostome teeth. Nature 2022; 609:964-968. [PMID: 36171375 DOI: 10.1038/s41586-022-05166-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Accepted: 07/29/2022] [Indexed: 11/09/2022]
Abstract
Mandibular teeth and dentitions are features of jawed vertebrates that were first acquired by the Palaeozoic ancestors1-3 of living chondrichthyans and osteichthyans. The fossil record currently points to the latter part of the Silurian period4-7 (around 425 million years ago) as a minimum date for the appearance of gnathostome teeth and to the evolution of growth and replacement mechanisms of mandibular dentitions in the subsequent Devonian period2,8-10. Here we provide, to our knowledge, the earliest direct evidence for jawed vertebrates by describing Qianodus duplicis, a new genus and species of an early Silurian gnathostome based on isolated tooth whorls from Guizhou province, China. The whorls possess non-shedding teeth arranged in a pair of rows that demonstrate a number of features found in modern gnathostome groups. These include lingual addition of teeth in offset rows and maintenance of this patterning throughout whorl development. Our data extend the record of toothed gnathostomes by 14 million years from the late Silurian into the early Silurian (around 439 million years ago) and are important for documenting the initial diversification of vertebrates. Our analyses add to mounting fossil evidence that supports an earlier emergence of jawed vertebrates as part of the Great Ordovician Biodiversification Event (approximately 485-445 million years ago).
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Affiliation(s)
- Plamen S Andreev
- Research Center of Natural History and Culture, Qujing Normal University, Qujing, China.,Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China
| | - Ivan J Sansom
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - Qiang Li
- Research Center of Natural History and Culture, Qujing Normal University, Qujing, China.,Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China
| | - Wenjin Zhao
- Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing, China.,College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Jianhua Wang
- Research Center of Natural History and Culture, Qujing Normal University, Qujing, China
| | - Chun-Chieh Wang
- National Synchrotron Radiation Research Center, Hsinchu, Taiwan
| | - Lijian Peng
- Research Center of Natural History and Culture, Qujing Normal University, Qujing, China
| | - Liantao Jia
- Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China
| | - Tuo Qiao
- Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing, China
| | - Min Zhu
- Key CAS Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (CAS), Beijing, China. .,CAS Center for Excellence in Life and Paleoenvironment, Beijing, China. .,College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China.
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8
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Wang Y, Zhu M. Squamation and scale morphology at the root of jawed vertebrates. eLife 2022; 11:76661. [PMID: 35674421 PMCID: PMC9177148 DOI: 10.7554/elife.76661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Accepted: 05/11/2022] [Indexed: 11/13/2022] Open
Abstract
Placoderms, as the earliest branching jawed vertebrates, are crucial to understanding how the characters of crown gnathostomes comprising Chondrichthyes and Osteichthyes evolved from their stem relatives. Despite the growing knowledge of the anatomy and diversity of placoderms over the past decade, the dermal scales of placoderms are predominantly known from isolated material, either morphologically or histologically, resulting in their squamation being poorly understood. Here we provide a comprehensive description of the squamation and scale morphology of a primitive taxon of Antiarcha (a clade at the root of jawed vertebrates), Parayunnanolepis xitunensis, based on the virtual restoration of an articulated specimen by using X-ray computed tomography. Thirteen morphotypes of scales are classified to exhibit how the morphology changes with their position on the body in primitive antiarchs, based on which nine areas of the post-thoracic body are distinguished to show their scale variations in the dorsal, flank, ventral, and caudal lobe regions. In this study, the histological structure of yunnanolepidoid scales is described for the first time based on disarticulated scales from the type locality and horizon of P. xitunensis. The results demonstrate that yunnanolepidoid scales are remarkably different from their dermal plates as well as euantiarch scales in lack of a well-developed middle layer. Together, our study reveals that the high regionalization of squamation and the bipartite histological structure of scales might be plesiomorphic for antiarchs, and jawed vertebrates in general.
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Affiliation(s)
- Yajing Wang
- School of Earth Sciences and Engineering, Nanjing University
| | - Min Zhu
- School of Earth Sciences and Engineering, Nanjing University
- Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
- CAS Center for Excellence in Life and Paleoenvironment
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9
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Redeployment of odontode gene regulatory network underlies dermal denticle formation and evolution in suckermouth armored catfish. Sci Rep 2022; 12:6172. [PMID: 35418659 PMCID: PMC9007992 DOI: 10.1038/s41598-022-10222-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 04/05/2022] [Indexed: 11/21/2022] Open
Abstract
Odontodes, i.e., teeth and tooth-like structures, consist of a pulp cavity and dentin covered by a mineralized cap. These structures first appeared on the outer surface of vertebrate ancestors and were repeatedly lost and gained across vertebrate clades; yet, the underlying genetic mechanisms and trajectories of this recurrent evolution remain long-standing mysteries. Here, we established suckermouth armored catfish (Ancistrus sp.; Loricariidae), which have reacquired dermal odontodes (dermal denticles) all over most of their body surface, as an experimental model animal amenable to genetic manipulation for studying odontode development. Our histological analysis showed that suckermouth armored catfish develop dermal denticles through the previously defined odontode developmental stages. De novo transcriptomic profiling identified the conserved odontode genetic regulatory network (oGRN) as well as expression of paired like homeodomain 2 (pitx2), previously known as an early regulator of oGRN in teeth but not in other dermal odontodes, in developing dermal denticles. The early onset of pitx2 expression in cranial dermal denticle placodes implies its function as one of the inducing factors of the cranial dermal denticles. By comprehensively identifying the genetic program for dermal odontode development in suckermouth armored catfish, this work illuminates how dermal odontodes might have evolved and diverged in distinct teleost lineages via redeployment of oGRN.
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10
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Atake OJ, Eames BF. Mineralized Cartilage and Bone-Like Tissues in Chondrichthyans Offer Potential Insights Into the Evolution and Development of Mineralized Tissues in the Vertebrate Endoskeleton. Front Genet 2022; 12:762042. [PMID: 35003210 PMCID: PMC8727550 DOI: 10.3389/fgene.2021.762042] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 11/30/2021] [Indexed: 11/25/2022] Open
Abstract
The impregnation of biominerals into the extracellular matrix of living organisms, a process termed biomineralization, gives rise to diverse mineralized (or calcified) tissues in vertebrates. Preservation of mineralized tissues in the fossil record has provided insights into the evolutionary history of vertebrates and their skeletons. However, current understanding of the vertebrate skeleton and of the processes underlying its formation is biased towards biomedical models such as the tetrapods mouse and chick. Chondrichthyans (sharks, skates, rays, and chimaeras) and osteichthyans are the only vertebrate groups with extant (living) representatives that have a mineralized skeleton, but the basal phylogenetic position of chondrichthyans could potentially offer unique insights into skeletal evolution. For example, bone is a vertebrate novelty, but the internal supporting skeleton (endoskeleton) of extant chondrichthyans is commonly described as lacking bone. The molecular and developmental basis for this assertion is yet to be tested. Subperichondral tissues in the endoskeleton of some chondrichthyans display mineralization patterns and histological and molecular features of bone, thereby challenging the notion that extant chondrichthyans lack endoskeletal bone. Additionally, the chondrichthyan endoskeleton demonstrates some unique features and others that are potentially homologous with other vertebrates, including a polygonal mineralization pattern, a trabecular mineralization pattern, and an unconstricted perichordal sheath. Because of the basal phylogenetic position of chondrichthyans among all other extant vertebrates with a mineralized skeleton, developmental and molecular studies of chondrichthyans are critical to flesh out the evolution of vertebrate skeletal tissues, but only a handful of such studies have been carried out to date. This review discusses morphological and molecular features of chondrichthyan endoskeletal tissues and cell types, ultimately emphasizing how comparative embryology and transcriptomics can reveal homology of mineralized skeletal tissues (and their cell types) between chondrichthyans and other vertebrates.
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Affiliation(s)
- Oghenevwogaga J Atake
- Department of Anatomy, Physiology, and Pharmacology, University of Saskatchewan, Saskatoon, SK, Canada
| | - B Frank Eames
- Department of Anatomy, Physiology, and Pharmacology, University of Saskatchewan, Saskatoon, SK, Canada
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11
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The Dorsal Integument of the Southern Long-Nosed Armadillo Dasypus hybridus (Cingulata, Xenarthra), and a Possible Neural Crest Origin of the Osteoderms. Discussing Evolutive Consequences for Amniota. J MAMM EVOL 2021. [DOI: 10.1007/s10914-021-09538-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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12
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Dzik J. Protaspis larva of an aglaspidid-like arthropod from the Ordovician of Siberia and its habitat. ARTHROPOD STRUCTURE & DEVELOPMENT 2021; 61:101026. [PMID: 33508709 DOI: 10.1016/j.asd.2020.101026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 12/30/2020] [Accepted: 12/30/2020] [Indexed: 06/12/2023]
Abstract
A fossil larva lacking segmentation of the calcified carapace, closely resembling the trilobite protaspis, has been found associated with other skeletal elements of an angarocaridid Girardevia species in the mid Darriwilian of central Siberia. The presence of protaspis larvae in the angarocaridids, generally believed to represent a branch of the Aglaspidida, supports their proximity to trilobites and proves a low position on the arthropod phylogenetic tree but does not necessarily contradict the chelicerate affinity. The cephalic appendages of angarocaridids bore massive gnathobases with detachable spines, closely similar to those known in extant xiphosurans and in their probable Cambrian relatives. The stratigraphic succession of the angarocaridids, their phosphatized cuticle pieces being abundant in the Ordovician strata of Siberia, shows a gradual improvement of mechanical resistance of their carapaces, eventually resulting in a honeycomb structure. The associated benthic mollusc assemblage is dominated with the bellerophontids showing high mortality at metamorphosis and only the limpet-like Pterotheca, infaunal bivalves, and scaphopods being able to survive this in a substantial number. This suggests a strong selective pressure from predators equipped with well-skeletonised oral apparatuses able to crush mineralized body covers of their prey. Possibly, these were some of the associated conodonts of appropriate size and co-evolving towards their ability to crush more and more resistant cuticle. Less likely candidates for durophagy are endoceratid or orthoceratid cephalopods. Also the angarocaridids themselves, equipped with robust gnathobases of cephalic appendages, apparently predated on benthic shelly animals.
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Affiliation(s)
- Jerzy Dzik
- Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland; Institute of Evolutionary Biology, Faculty of Biology, Biological and Chemical Research Centre (CNBCh UW), University of Warsaw, Warszawa, 02-089 Żwirki i Wigury 101, Poland.
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13
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Haridy Y, Osenberg M, Hilger A, Manke I, Davesne D, Witzmann F. Bone metabolism and evolutionary origin of osteocytes: Novel application of FIB-SEM tomography. SCIENCE ADVANCES 2021; 7:eabb9113. [PMID: 33789889 PMCID: PMC8011976 DOI: 10.1126/sciadv.abb9113] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Accepted: 02/11/2021] [Indexed: 06/10/2023]
Abstract
Lacunae and canaliculi spaces of osteocytes are remarkably well preserved in fossilized bone and serve as an established proxy for bone cells. The earliest bone in the fossil record is acellular (anosteocytic), followed by cellular (osteocytic) bone in the jawless relatives of jawed vertebrates, the osteostracans, about 400 million years ago. Virtually nothing is known about the physiological pressures that would have initially favored osteocytic over anosteocytic bone. We apply focused ion beam-scanning electron microscopy tomography combined with machine learning for cell detection and segmentation to image fossil cell spaces. Novel three-dimensional high-resolution images reveal areas of low density around osteocyte lacunae and their canaliculi in osteostracan bone. This provides evidence for demineralization that would have occurred in vivo as part of osteocytic osteolysis, a mechanism of mineral homeostasis, supporting the hypothesis that a physiological demand for phosphorus was the principal driver in the initial evolution of osteocytic bone.
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Affiliation(s)
- Yara Haridy
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany.
| | - Markus Osenberg
- Helmholtz Centre for Materials and Energy (HZB), Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - André Hilger
- Helmholtz Centre for Materials and Energy (HZB), Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Ingo Manke
- Helmholtz Centre for Materials and Energy (HZB), Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Donald Davesne
- Department of Earth Sciences, University of Oxford, OX1 3AN Oxford, UK
- Institut de Systématique, Évolution, Biodiversité (UMR 7205), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, 75005 Paris, France
| | - Florian Witzmann
- Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
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14
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Stundl J, Bertucci PY, Lauri A, Arendt D, Bronner ME. Evolution of new cell types at the lateral neural border. Curr Top Dev Biol 2021; 141:173-205. [PMID: 33602488 DOI: 10.1016/bs.ctdb.2020.11.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
During the course of evolution, animals have become increasingly complex by the addition of novel cell types and regulatory mechanisms. A prime example is represented by the lateral neural border, known as the neural plate border in vertebrates, a region of the developing ectoderm where presumptive neural and non-neural tissue meet. This region has been intensively studied as the source of two important embryonic cell types unique to vertebrates-the neural crest and the ectodermal placodes-which contribute to diverse differentiated cell types including the peripheral nervous system, pigment cells, bone, and cartilage. How did these multipotent progenitors originate in animal evolution? What triggered the elaboration of the border during the course of chordate evolution? How is the lateral neural border patterned in various bilaterians and what is its fate? Here, we review and compare the development and fate of the lateral neural border in vertebrates and invertebrates and we speculate about its evolutionary origin. Taken together, the data suggest that the lateral neural border existed in bilaterian ancestors prior to the origin of vertebrates and became a developmental source of exquisite evolutionary change that frequently enabled the acquisition of new cell types.
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Affiliation(s)
- Jan Stundl
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States
| | | | | | - Detlev Arendt
- European Molecular Biology Laboratory, Heidelberg, Germany.
| | - Marianne E Bronner
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.
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15
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Kawasaki K, Keating JN, Nakatomi M, Welten M, Mikami M, Sasagawa I, Puttick MN, Donoghue PC, Ishiyama M. Coevolution of enamel, ganoin, enameloid, and their matrix SCPP genes in osteichthyans. iScience 2021; 24:102023. [PMID: 33506188 PMCID: PMC7814152 DOI: 10.1016/j.isci.2020.102023] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 11/14/2020] [Accepted: 12/29/2020] [Indexed: 12/19/2022] Open
Abstract
We resolve debate over the evolution of vertebrate hypermineralized tissues through analyses of matrix protein-encoding secretory calcium-binding phosphoprotein (SCPP) genes and phylogenetic inference of hypermineralized tissues. Among these genes, AMBN and ENAM are found in both sarcopterygians and actinopterygians, whereas AMEL and SCPP5 are found only in sarcopterygians and actinopterygians, respectively. Actinopterygian AMBN, ENAM, and SCPP5 are expressed during the formation of hypermineralized tissues on scales and teeth: ganoin, acrodin, and collar enamel in gar, and acrodin and collar enameloid in zebrafish. Our phylogenetic analyses indicate the emergence of an ancestral enamel in stem-osteichthyans, whereas ganoin emerged in stem-actinopterygians and true enamel in stem-sarcopterygians. Thus, AMBN and ENAM originated in concert with ancestral enamel, SCPP5 evolved in association with ganoin, and AMEL evolved with true enamel. Shifts in gene expression domain and timing explain the evolution of different hypermineralized tissues. We propose that hypermineralized tissues in osteichthyans coevolved with matrix SCPP genes. Ganoin emerged in actinopterygians; true enamel arose in sarcopterygians Dental enamel, acrodin, and enameloid in actinopterygians are related to ganoin SCPP5 evolved in association with ganoin, whereas AMEL evolved with true enamel Shifts in SCPP gene expression explain the evolution of hypermineralized tissues
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Affiliation(s)
- Kazuhiko Kawasaki
- Department of Anthropology, Pennsylvania State University, University Park, PA 16802, USA
- Corresponding author
| | - Joseph N. Keating
- School of Earth Sciences, University of Bristol, Bristol BS8 1TQ, UK
| | - Mitsushiro Nakatomi
- Division of Anatomy, Kyushu Dental University, Kitakyushu, Fukuoka 803-8580, Japan
| | - Monique Welten
- School of Earth Sciences, University of Bristol, Bristol BS8 1TQ, UK
| | - Masato Mikami
- Department of Microbiology, School of Life Dentistry at Niigata, the Nippon Dental University, Niigata, Niigata 951-8580, Japan
| | - Ichiro Sasagawa
- Advanced Research Center, School of Life Dentistry at Niigata, the Nippon Dental University, Niigata, Niigata 951-8580, Japan
| | - Mark N. Puttick
- School of Earth Sciences, University of Bristol, Bristol BS8 1TQ, UK
- Milner Centre for Evolution, Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK
| | | | - Mikio Ishiyama
- Department of Histology, School of Life Dentistry at Niigata, the Nippon Dental University, Niigata, Niigata 951-8580, Japan
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16
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Shirley B, Bestmann M, Jarochowska E. The cono-dos and cono-dont's of phosphatic microfossil preparation and microanalysis. Micron 2020; 138:102924. [PMID: 32854079 DOI: 10.1016/j.micron.2020.102924] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 07/27/2020] [Accepted: 08/07/2020] [Indexed: 11/29/2022]
Abstract
Scanning electron microscope (SEM) imaging of fossils allows unlocking ultrastructural information about their skeletal tissues, but sample preparation of biominerals forming their skeletons requires time, patience, and knowledge. SEM and associated analytical methods allow the observation of internal microstructure, shedding light on function, growth and chemistry. Sample preparation is the process by which material is fixed within a medium (e.g. epoxy resin), a transect created and surface defects removed. This step is arguably the most important in any SEM-based analysis, allowing for the acquisition of reliable, high quality data sets. When conducting any SEM-based technique, the presence of a flat surface is needed to collect consistent and reliable data. Surfaces with topography will both induce charging effects but will also compromise the reliability of data acquired. Techniques from material science are continuously adapted to palaeontological applications, in particular with respect to calcareous microfossils. However, similar studies have not been extensively conducted on bioapatite, owing in part to the difficulties faced in sample preparation alongside its susceptibility to electron beam damage. This case study focuses on conodonts, a marine vertebrate group ranging from the late Cambrian to the Late Triassic. They have been chosen as a model due to the abundance of material, complexity of internal tissues and previous work focused on histological features. With these phosphatic microfossils, we attempt to outline the process of sample preparation and provide information on how to avoid and overcome common pitfalls.
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Affiliation(s)
- Bryan Shirley
- Fachgruppe Paläoumwelt, GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg, Loewenichstr. 28, 91054 Erlangen, Germany.
| | - Michel Bestmann
- Fachgruppe Strukturgeologie, GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg, Schlossgarten 5, 91054 Erlangen, Germany.
| | - Emilia Jarochowska
- Fachgruppe Paläoumwelt, GeoZentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg, Loewenichstr. 28, 91054 Erlangen, Germany.
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17
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Murdock DJE. The ‘biomineralization toolkit’ and the origin of animal skeletons. Biol Rev Camb Philos Soc 2020; 95:1372-1392. [DOI: 10.1111/brv.12614] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 04/28/2020] [Accepted: 04/30/2020] [Indexed: 12/29/2022]
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18
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Lemierre A, Germain D. A new mineralized tissue in the early vertebrate Astraspis. J Anat 2019; 235:1105-1113. [PMID: 31355451 DOI: 10.1111/joa.13070] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/09/2019] [Indexed: 11/27/2022] Open
Abstract
The dermoskeleton of the earliest vertebrates is well known but their endoskeleton is thought to have been largely cartilaginous until the Late Silurian. We confirm that the dermal plates of Astraspis are three-layered, with a superficial layer of enameloid and orthodentine, a middle layer of aspidin and a basal layer of lamellar acellular bone. This dermoskeleton is found in association with globular calcified cartilage, indicating the presence of a partially mineralized endoskeleton. In addition to the classical three-layered organization, some dermal plates exhibit alignments of chondrocyte-like lacunae, very similar to a pattern typical of chondroid metaplastic bone, previously unknown in early vertebrates. This discovery implies the presence of a proliferative cartilage, hitherto only known in Osteichthyans. This discovery indicates that a pattern similar to the first step of endochondral ossification was already present in the earliest vertebrates.
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Affiliation(s)
- Alfred Lemierre
- CR2P, MNHN-CNRS-Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France
| | - Damien Germain
- CR2P, MNHN-CNRS-Sorbonne Université, Muséum National d'Histoire Naturelle, Paris, France
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19
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O'Shea J, Keating JN, Donoghue PCJ. The dermal skeleton of the jawless vertebrate
Tremataspis mammillata
(Osteostraci, stem‐Gnathostomata). J Morphol 2019; 280:999-1025. [DOI: 10.1002/jmor.20997] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 04/02/2019] [Accepted: 04/23/2019] [Indexed: 01/18/2023]
Affiliation(s)
- James O'Shea
- School of Earth SciencesUniversity of Bristol, Life Sciences Building Bristol UK
| | - Joseph N. Keating
- School of Earth SciencesUniversity of Bristol, Life Sciences Building Bristol UK
- School of Earth and Environmental SciencesUniversity of Manchester Manchester UK
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20
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The nature of aspidin and the evolutionary origin of bone. Nat Ecol Evol 2018; 2:1501-1506. [PMID: 30065354 PMCID: PMC6109381 DOI: 10.1038/s41559-018-0624-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 06/27/2018] [Indexed: 11/16/2022]
Abstract
Bone is the key innovation underpinning the evolution of the vertebrate skeleton, yet its origin is mired by debate over interpretation of the most primitive bone-like tissue, aspidin. This has variously been interpreted as cellular bone, acellular bone, dentine or as an intermediate of dentine and bone. The crux of the controversy is the nature of unmineralised spaces pervading the aspidin matrix, which have alternatively been interpreted as having housed cells, cell processes, or Sharpey’s Fibres. Discriminating between these hypotheses has been hindered by the limits of traditional histological methods. Here we use Synchrotron X-ray Tomographic Microscopy (srXTM) to reveal the nature of aspidin. We show the spaces exhibit a linear morphology, incompatible with interpretations that they represent voids left by cells or cell processes. Instead, these spaces represent intrinsic collagen fibre bundles that form a scaffold, about which mineral was deposited. Aspidin is thus acellular dermal bone. We reject hypotheses that it is a type of dentine, cellular bone, or transitional tissue. Our study suggests the full repertoire of skeletal tissue types was established prior to the divergence of the earliest known skeletonising vertebrates, indicating that the corresponding cell types evolved rapidly following the divergence of cyclostomes and gnathostomes.
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21
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Petermann H, Gauthier JA. Fingerprinting snakes: paleontological and paleoecological implications of zygantral growth rings in Serpentes. PeerJ 2018; 6:e4819. [PMID: 29844972 PMCID: PMC5971835 DOI: 10.7717/peerj.4819] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 05/01/2018] [Indexed: 11/23/2022] Open
Abstract
We introduce a new non-destructive source of skeletochronological data with applications to species identification, associating disarticulated remains, assessing minimum number of individuals (MNI), and collection management of fossil snakes, but with potential implications for all bony vertebrates, extinct or extant. Study of a diverse sample of Recent henophidian snakes confirms that annual growth cycles (AGCs) visible on the surface of the vertebral zygantrum correspond to lines of arrested growth in osteohistological thin sections and accordingly reflect chronological age. None of the specimens considered here showed signs of remodelling of the zygantrum, suggesting that a complete, unaltered age record is preserved. We tested potential influences on AGCs with a single experimental organism, a male Bogertophis subocularis, that was raised at a controlled temperature and with constant access to mice and water. The conditions in which this individual was maintained, including that it had yet to live through a full reproductive cycle, enabled us to determine that its AGCs reflect only the annual solar cycle, and neither temperature, nor resource availability, nor energy diversion to gametogenesis could explain that it still exhibited lines of arrested growth. Moreover, growth lines in this specimen are deposited toward the end of the growth season in the fall, and not in the winter, during which this individual continued to feed and grow, even though this mid-latitude species would normally be hibernating and not growing. This suggests that growth lines are not caused by hibernation, but reflect the onset of a physiological cycle preparing Bogertophis subocularis for winter rest. That being said, hibernation and reproductive cycle could still influence the amount of time represented by an individual growth line. Growth-line number and AGC spacing-pattern, plus centrum length, are used to estimate MNI of the Early Eocene fossil snake Boavus occidentalis collected from the Willwood Formation over two field seasons during the late 19th century. We identified eight or nine individuals among specimens previously parcelled among two specimen lots collected during those expeditions.
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Affiliation(s)
- Holger Petermann
- Department of Geology and Geophysics, Yale University, New Haven, CT, United States of America
| | - Jacques A Gauthier
- Department of Geology and Geophysics, Yale University, New Haven, CT, United States of America.,Yale Peabody Museum of Natural History, Yale University, New Haven, CT, United States of America
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22
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Trunk neural crest origin of dermal denticles in a cartilaginous fish. Proc Natl Acad Sci U S A 2017; 114:13200-13205. [PMID: 29158384 DOI: 10.1073/pnas.1713827114] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Cartilaginous fishes (e.g., sharks and skates) possess a postcranial dermal skeleton consisting of tooth-like "denticles" embedded within their skin. As with teeth, the principal skeletal tissue of dermal denticles is dentine. In the head, cranial neural crest cells give rise to the dentine-producing cells (odontoblasts) of teeth. However, trunk neural crest cells are generally regarded as nonskeletogenic, and so the embryonic origin of trunk denticle odontoblasts remains unresolved. Here, we use expression of FoxD3 to pinpoint the specification and emigration of trunk neural crest cells in embryos of a cartilaginous fish, the little skate (Leucoraja erinacea). Using cell lineage tracing, we further demonstrate that trunk neural crest cells do, in fact, give rise to odontoblasts of trunk dermal denticles. These findings expand the repertoire of vertebrate trunk neural crest cell fates during normal development, highlight the likely primitive skeletogenic potential of this cell population, and point to a neural crest origin of dentine throughout the ancestral vertebrate dermal skeleton.
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23
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Keating JN, Donoghue PCJ. Histology and affinity of anaspids, and the early evolution of the vertebrate dermal skeleton. Proc Biol Sci 2016; 283:20152917. [PMID: 26962140 PMCID: PMC4810860 DOI: 10.1098/rspb.2015.2917] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2015] [Accepted: 02/15/2016] [Indexed: 12/03/2022] Open
Abstract
The assembly of the gnathostome bodyplan constitutes a formative episode in vertebrate evolutionary history, an interval in which the mineralized skeleton and its canonical suite of cell and tissue types originated. Fossil jawless fishes, assigned to the gnathostome stem-lineage, provide an unparalleled insight into the origin and evolution of the skeleton, hindered only by uncertainty over the phylogenetic position and evolutionary significance of key clades. Chief among these are the jawless anaspids, whose skeletal composition, a rich source of phylogenetic information, is poorly characterized. Here we survey the histology of representatives spanning anaspid diversity and infer their generalized skeletal architecture. The anaspid dermal skeleton is composed of odontodes comprising spheritic dentine and enameloid, overlying a basal layer of acellular parallel fibre bone containing an extensive shallow canal network. A recoded and revised phylogenetic analysis using equal and implied weights parsimony resolves anaspids as monophyletic, nested among stem-gnathostomes. Our results suggest the anaspid dermal skeleton is a degenerate derivative of a histologically more complex ancestral vertebrate skeleton, rather than reflecting primitive simplicity. Hypotheses that anaspids are ancestral skeletonizing lampreys, or a derived lineage of jawless vertebrates with paired fins, are rejected.
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Affiliation(s)
- Joseph N Keating
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK Department of Earth Sciences, Natural History Museum, Cromwell Road, South Kensington, London SW7 5BD, UK
| | - Philip C J Donoghue
- School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK
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