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1.
Elife ; 112022 06 08.
Artigo em Inglês | MEDLINE | ID: mdl-35674421

RESUMO

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.


Many vertebrates have an outer skeleton covering their body. Some, like crocodiles, have large bony plates of armor, while others, like fish, have small slippery scales. The type, shape, and arrangement of these structures can tell scientists a lot about how different species evolved. Most modern fish are completely covered in scales, but this has not always been the case. Over 400 millions of years ago in the Earth's oceans lived a major group of armored fish called antiarch placoderms which had a combination of bony plates, scales and naked skin. These ancient fish are particularly interesting to scientists because they were one of the first jawed vertebrates to evolve. However, much of what is known about this group has come from isolated materials, which has made it difficult to study the organization and shape of their scales. To overcome this, Wang and Zhu used a specialized x-ray imaging procedure to create a three-dimensional model of one of the best-preserved antiarch placoderm species, Parayunnanolepis xitunensis. The model showed that the fish had thirteen types of scales, found in nine distinct regions on its body. To better understand the structure of these scales, Wang and Zhu looked at the fossils of other extinct jawed fish which where were found in the region where P. xitunensis once lived. The scales of these ancient fish were very different from their bony plates, and from the scales of modern fish. Understanding the skin armor of ancient fish could help to explain how the scales of modern vertebrates evolved. The next step is to look in more detail at the scales of other placoderms to see how they changed over time.


Assuntos
Evolução Biológica , Fósseis , Animais , Peixes/anatomia & histologia , Arcada Osseodentária/anatomia & histologia , Filogenia , Vertebrados/anatomia & histologia
2.
Nature ; 606(7912): 109-112, 2022 06.
Artigo em Inglês | MEDLINE | ID: mdl-35614222

RESUMO

Palaeospondylus gunni, from the Middle Devonian period, is one of the most enigmatic fossil vertebrates, and its phylogenetic position has remained unclear since its discovery in Scotland in 1890 (ref. 1). The fossil's strange set of morphological features has made comparisons with known vertebrate morphotype diversity difficult. Here we use synchrotron radiation X-ray micro-computed tomography to show that Palaeospondylus was a sarcopterygian, and most probably a stem-tetrapod. The skeleton of Palaeospondylus consisted solely of endoskeletal elements in which hypertrophied chondrocyte cell lacunae, osteoids and a small fraction of perichondral bones developed. Despite the complete lack of teeth and dermal bones, the neurocranium of Palaeospondylus resembles those of stem-tetrapod Eusthenopteron2 and Panderichthys3, and phylogenetic analyses place Palaeospondylus in between them. Because the unique features of Palaeospondylus, such as the cartilaginous skeleton and the absence of paired appendages, are present in the larva of crown tetrapods, our study highlights an unanticipated heterochronic evolution at the root of tetrapods.


Assuntos
Fósseis , Filogenia , Vertebrados , Animais , Peixes/anatomia & histologia , Peixes/classificação , Crânio/anatomia & histologia , Vertebrados/anatomia & histologia , Vertebrados/classificação , Microtomografia por Raio-X
3.
Nat Ecol Evol ; 6(5): 604-613, 2022 May.
Artigo em Inglês | MEDLINE | ID: mdl-35314784

RESUMO

Limb muscles are remarkably complex and evolutionarily labile. Although their anatomy is of great interest for studies of the evolution of form and function, their homologies among major amniote clades have remained obscure. Studies of adult musculature are inconclusive owing to the highly derived morphology of modern amniote limbs but correspondences become increasingly evident earlier in ontogeny. We followed the embryonic development of forelimb musculature in representatives of six major amniote clades and found, contrary to current consensus, that these early splitting patterns are highly conserved across Amniota. Muscle mass cleavage patterns and topology are highly conserved in reptiles including birds, irrespective of their skeletal modifications: the avian flight apparatus results from slight early topological modifications that are exaggerated during ontogeny. Therian mammals, while conservative in their cleavage patterns, depart drastically from the ancestral amniote musculoskeletal organization in terms of topology. These topological changes occur through extension, translocation and displacement of muscle groups later in development. Overall, the simplicity underlying the apparent complexity of forelimb muscle development allows us to resolve conflicting hypotheses about homology and to trace the history of each individual forelimb muscle throughout the amniote radiations.


Assuntos
Evolução Biológica , Vertebrados , Animais , Aves , Membro Anterior/anatomia & histologia , Membro Anterior/fisiologia , Mamíferos , Músculo Esquelético , Répteis/anatomia & histologia , Vertebrados/anatomia & histologia
4.
J Anat ; 240(2): 253-267, 2022 02.
Artigo em Inglês | MEDLINE | ID: mdl-34542171

RESUMO

Regionalization of the vertebral column occurred early during vertebrate evolution and has been extensively investigated in mammals. However, less data are available on vertebral regions of crown gnathostomes. This is particularly true for batoids (skates, sawfishes, guitarfishes, and rays) whose vertebral column has long been considered to be composed of the same two regions as in teleost fishes despite the presence of a synarcual. However, the numerous vertebral units in chondrichthyans may display a more complex regionalization pattern than previously assumed and the intraspecific variation of such pattern deserves a thorough investigation. In this study, we use micro-computed tomography (µCT) scans of vertebral columns of a growth series of thorny skates Amblyraja radiata to provide the first fine-scale morphological description of vertebral units in a batoids species. We further investigate axial regionalization using a replicable clustering analysis on presence/absence of vertebral elements to decipher the regionalization of the vertebral column of A. radiata. We identify four vertebral regions in this species. The two anteriormost regions, named synarcual and thoracic, may undergo strong developmental or functional constraints because they display stable patterns of shapes and numbers of vertebral units across all growth stages. The third region, named hemal transitional, is characterized by high inter-individual morphological variation and displays a transition between the monospondylous (one centrum per somite) to diplospondylous (two centra per somite) conditions. The posteriormost region, named caudal, is subdivided into three sub-regions with shapes changing gradually along the anteroposterior axis. These regionalized patterns are discussed in light of ecological habits of skates.


Assuntos
Rajidae , Animais , Rajidae/anatomia & histologia , Somitos , Coluna Vertebral/anatomia & histologia , Vertebrados/anatomia & histologia , Microtomografia por Raio-X
5.
Science ; 374(6575): eabf5787, 2021 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-34941418

RESUMO

Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this diversity are largely unknown. High primary production of modern oceans is considered a prerequisite for the emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We describe the new giant ichthyosaur Cymbospondylus youngorum sp. nov. with a 2-meter-long skull from the Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.


Assuntos
Evolução Biológica , Tamanho Corporal , Cetáceos/anatomia & histologia , Fósseis , Répteis/anatomia & histologia , Animais , Organismos Aquáticos , Cetáceos/fisiologia , Simulação por Computador , Dieta , Ecossistema , Cadeia Alimentar , Filogenia , Répteis/classificação , Répteis/fisiologia , Crânio/anatomia & histologia , Vertebrados/anatomia & histologia , Vertebrados/fisiologia
6.
Naturwissenschaften ; 108(4): 26, 2021 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-34115204

RESUMO

The non-mammalian therapsids comprise a paraphyletic assemblage of Permian-Jurassic synapsids closely related to mammals that includes six major clades of largely unresolved phylogenetic affinity. Understanding the early evolutionary radiation of therapsids is complicated by a gap in the fossil record during the Roadian (middle Permian) known as Olson's gap. Because of its early stratigraphic occurrence and its primitive features, Raranimus dashankouensis, from the Dashankou fauna (Rodian), Qingtoushan Formation (China), is currently considered the best candidate to fill this gap. However, it is known from only a single specimen, an isolated snout, which limits the amount of usable phylogenetic characters to reconstruct its affinities. In addition, understanding of the stratigraphy of the Qingtoushan Formation is poor. Here, we used CT scanning techniques to digitally reconstruct the bones and trigeminal canals of the snout of Raranimus in 3D. We confirm that Raranimus shares a high number of synapomorphies with more derived therapsids and is the only therapsid known so far to display a "pelycosaur"-like maxillary canal bearing a long caudal alveolar canal that gives off branches at regular intervals. This plesiomorphic feature supports the idea that Raranimus is basal to other therapsids.


Assuntos
Fósseis , Filogenia , Vertebrados/classificação , Animais , China , Tomografia Computadorizada por Raios X , Vertebrados/anatomia & histologia
7.
Proc Natl Acad Sci U S A ; 118(20)2021 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-33990463

RESUMO

To investigate the origins and stages of vertebrate adaptive radiation, we reconstructed the spatial and temporal histories of adaptive alleles underlying major phenotypic axes of diversification from the genomes of 202 Caribbean pupfishes. On a single Bahamian island, ancient standing variation from disjunct geographic sources was reassembled into new combinations under strong directional selection for adaptation to the novel trophic niches of scale-eating and molluscivory. We found evidence for two longstanding hypotheses of adaptive radiation: hybrid swarm origins and temporal stages of adaptation. Using a combination of population genomics, transcriptomics, and genome-wide association mapping, we demonstrate that this microendemic adaptive radiation of novel trophic specialists on San Salvador Island, Bahamas experienced twice as much adaptive introgression as generalist populations on neighboring islands and that adaptive divergence occurred in stages. First, standing regulatory variation in genes associated with feeding behavior (prlh, cfap20, and rmi1) were swept to fixation by selection, then standing regulatory variation in genes associated with craniofacial and muscular development (itga5, ext1, cyp26b1, and galr2) and finally the only de novo nonsynonymous substitution in an osteogenic transcription factor and oncogene (twist1) swept to fixation most recently. Our results demonstrate how ancient alleles maintained in distinct environmental refugia can be assembled into new adaptive combinations and provide a framework for reconstructing the spatiotemporal landscape of adaptation and speciation.


Assuntos
Adaptação Fisiológica/genética , Especiação Genética , Peixes Listrados/genética , Filogenia , Análise Espaço-Temporal , Vertebrados/genética , Animais , Bahamas , Região do Caribe , Proteínas de Peixes/genética , Perfilação da Expressão Gênica/métodos , Estudo de Associação Genômica Ampla/métodos , Genômica/métodos , Genótipo , Geografia , Peixes Listrados/anatomia & histologia , Peixes Listrados/classificação , Polimorfismo de Nucleotídeo Único , Vertebrados/anatomia & histologia , Vertebrados/classificação
9.
J Vis Exp ; (168)2021 02 28.
Artigo em Inglês | MEDLINE | ID: mdl-33720141

RESUMO

Somitogenesis is a hallmark of vertebrate embryonic development. For years, researchers have been studying this process in a variety of organisms using a wide range of techniques encompassing ex vivo and in vitro approaches. However, most studies still rely on the analysis of two-dimensional (2D) imaging data, which limits proper evaluation of a developmental process like axial extension and somitogenesis involving highly dynamic interactions in a complex 3D space. Here we describe techniques that allow mouse live imaging acquisition, dataset processing, visualization and analysis in 3D and 4D to study the cells (e.g., neuromesodermal progenitors) involved in these developmental processes. We also provide a step-by-step protocol for optical projection tomography and whole-mount immunofluorescence microscopy in mouse embryos (from sample preparation to image acquisition) and show a pipeline that we developed to process and visualize 3D image data. We extend the use of some of these techniques and highlight specific features of different available software (e.g., Fiji/ImageJ, Drishti, Amira and Imaris) that can be used to improve our current understanding of axial extension and somite formation (e.g., 3D reconstructions). Altogether, the techniques here described emphasize the importance of 3D data visualization and analysis in developmental biology, and might help other researchers to better address 3D and 4D image data in the context of vertebrate axial extension and segmentation. Finally, the work also employs novel tools to facilitate teaching vertebrate embryonic development.


Assuntos
Padronização Corporal , Imageamento Tridimensional/métodos , Vertebrados/anatomia & histologia , Vertebrados/embriologia , Animais , Embrião de Mamíferos/anatomia & histologia , Embrião de Mamíferos/diagnóstico por imagem , Desenvolvimento Embrionário , Imunofluorescência , Camundongos Knockout , Fatores de Transcrição da Família Snail/deficiência , Fatores de Transcrição da Família Snail/metabolismo , Software , Fatores de Tempo , Fixação de Tecidos , Tomografia Óptica
10.
Dokl Biol Sci ; 496(1): 9-12, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33635482

RESUMO

A study of the diversity of sculpture and histological structure of the exoskeleton in various osteostracan taxa (Osteostraci, Agnatha) enabled the first characterization of the main elements (geometric modules) of the planar organization of the complex relief on their armor surface. The armor relief was analyzed using a circular model of the formation of exoskeletal hard structures. The model was applied to unique material, fragments of a shield of the osteostracan Oeselaspis pustulata (Patten, 1931) from the Silurian of the Severnaya Zemlya Archipelago (Russia).


Assuntos
Exoesqueleto/ultraestrutura , Fósseis/ultraestrutura , Filogenia , Animais , Evolução Biológica , Peixes/anatomia & histologia , Federação Russa , Vertebrados/anatomia & histologia
11.
Curr Top Dev Biol ; 141: 1-38, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33602485

RESUMO

The development and evolution of multicellular body plans is complex. Many distinct organs and body parts must be reproduced at each generation, and those that are traceable over long time scales are considered homologous. Among the most pressing and least understood phenomena in evolutionary biology is the mode by which new homologs, or "novelties" are introduced to the body plan and whether the developmental changes associated with such evolution deserve special treatment. In this chapter, we address the concepts of homology and evolutionary novelty through the lens of development. We present a series of case studies, within insects and vertebrates, from which we propose a developmental model of multicellular organ identity. With this model in hand, we make predictions regarding the developmental evolution of body plans and highlight the need for more integrative analysis of developing systems.


Assuntos
Evolução Biológica , Redes Reguladoras de Genes , Vertebrados/anatomia & histologia , Asas de Animais , Animais , Crustáceos/anatomia & histologia , Biologia do Desenvolvimento , Genes Homeobox , Genitália Masculina/fisiologia , Proteínas de Homeodomínio/genética , Insetos , Masculino , Pelve , Filogenia , Fatores de Transcrição/genética , Asas de Animais/anatomia & histologia
12.
Curr Top Dev Biol ; 141: 207-239, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33602489

RESUMO

Modern vertebrates consist of two sister groups: cyclostomes and gnathostomes. Cyclostomes are a monophyletic jawless group that can be further divided into hagfishes and lampreys, which show conspicuously different developmental and morphological patterns. However, during early pharyngula development, there appears to be a stage when the embryos of hagfishes and lampreys resemble each other by showing an "ancestral" craniofacial pattern; this pattern enables morphological comparison of hagfish and lamprey craniofacial development at late stages. This cyclostome developmental pattern, or more accurately, this developmental pattern of the jawless grade of vertebrates in early pharyngula was very likely shared by the gnathostome stem before the division of the nasohypophyseal placode led to the jaw and paired nostrils. The craniofacial pattern of the modern jawed vertebrates seems to have begun in fossil ostracoderms (including galeaspids), and was completed by the early placoderm lineages. The transition from jawless to jawed vertebrates was thus driven by heterotopy of development, mainly caused by separation and shift of ectodermal placodes and resultant ectomesenchymal distribution, and shifts of the epithelial-mesenchymal interactions that underlie craniofacial differentiation. Thus, the evolution of the jaw was not a simple modification of the mandibular arch, but a heterotopic shift of the developmental interactions involving not only the mandibular arch, but also the premandibular region rostral to the mandibular arch.


Assuntos
Evolução Biológica , Feiticeiras (Peixe)/anatomia & histologia , Lampreias/anatomia & histologia , Vertebrados , Animais , Embrião não Mamífero , Fósseis , Regulação da Expressão Gênica no Desenvolvimento , Genes Homeobox , Feiticeiras (Peixe)/embriologia , Lampreias/embriologia , Adeno-Hipófise/embriologia , Crânio/anatomia & histologia , Vertebrados/anatomia & histologia , Vertebrados/embriologia
13.
Curr Top Dev Biol ; 141: 241-277, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33602490

RESUMO

Amniotes, a clade of terrestrial vertebrates, which includes all of the descendants of the last common ancestor of the reptiles (including dinosaurs and birds) and mammals, is one of the most successful group of animals on our planet. In addition to having an egg equipped with an amnion, an adaptation to lay eggs on land, amniotes possess a number of other major morphological characteristics. Chief among them is the amniote skull, which can be classified into several major types distinguished by the presence and number of temporal fenestrae (windows) in the posterior part. Amniotes evolved from ancestors who possessed a skull composed of a complex mosaic of small bones separated by sutures. Changes in skull composition underlie much of the large-scale evolution of amniotes with many lineages showing a trend in reduction of cranial elements known as the "Williston's Law." The skull of amniotes is also arranged into a set of modules of closely co-evolving bones as revealed by modularity and integration tests. One of the most consistently recovered and at the same time most versatile modules is the "face," anatomically defined as the anterior portion of the head. The faces of amniotes display extraordinary amount of variation, with many adaptive radiations showing parallel tendencies in facial scaling, e.g., changes in length or width. This review explores the natural history of the amniote face and discusses how a better understanding of its anatomy and developmental biology helps to explain the outstanding scale of adaptive facial diversity. We propose a model for facial evolution in the amniotes, based on the differential rate of cranial neural crest cell proliferation and the timing of their skeletal differentiation.


Assuntos
Evolução Biológica , Face/anatomia & histologia , Crânio/anatomia & histologia , Vertebrados , Animais , Padronização Corporal , Face/embriologia , Regulação da Expressão Gênica no Desenvolvimento , Crista Neural/citologia , Crânio/embriologia , Vertebrados/anatomia & histologia
15.
Elife ; 92020 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-33274719

RESUMO

Phylogenetic analysis of morphological data proceeds from a fixed set of primary homology statements, the character-by-taxon matrix. However, there are cases where multiple conflicting homology statements can be justified from comparative anatomy. The upper jaw bones of placoderms have traditionally been considered homologous to the palatal vomer-dermopalatine series of osteichthyans. The discovery of 'maxillate' placoderms led to the alternative hypothesis that 'core' placoderm jaw bones are premaxillae and maxillae lacking external (facial) laminae. We introduce a BEAST2 package for simultaneous inference of homology and phylogeny, and find strong evidence for the latter hypothesis. Phenetic analysis of reconstructed ancestors suggests that maxillate placoderms are the most plesiomorphic known gnathostomes, and the shared cranial architecture of arthrodire placoderms, maxillate placoderms and osteichthyans is inherited. We suggest that the gnathostome ancestor possessed maxillae and premaxillae with facial and palatal laminae, and that these bones underwent divergent evolutionary trajectories in placoderms and osteichthyans.


Assuntos
Anatomia Comparada/métodos , Evolução Biológica , Arcada Osseodentária/anatomia & histologia , Filogenia , Vertebrados/anatomia & histologia , Animais , Teorema de Bayes , Humanos
16.
J Morphol ; 281(12): 1617-1627, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-33068309

RESUMO

This analysis was inspired by the recent paper by Siomava et al. (2020) who attempted to deconstruct the serial homology concept, but retain the special homology. The criticism against this attempt is presented based on reconsideration of the original Owen's trinitarian concept of the general, serial, and special homology, and on a number of evidence on the vertebrate limbs serial homologies and on the vertebrate occiput special homologies which are currently missed by the morphologist community. The research of Belogolowy (1911) proved that the concept of special homology can be deconstructed with the same reasoning as suggested by Siomava et al. (2020) against the serial homology concept. It is argued that the deconstruction attempts come from wrong expectations in respect of homology. It is argued, that, due to developmental singularities, such as the zygote, or spore, or bud (in vegetative reproduction), the true homogeny is possible for genes only. The organs do not arise from organs, and therefore their genetic basis, and hence homology, can be changed in the developmental singularities. Thus, the morphological homology is not static. It can be acquired and it can evolve. Genetically, the evolution of morphological homologies can be thought of as a succession of co-options. The evidence for a succession of serial homologies in vertebrate limbs is suggested. It is argued that homology and analogy have a sense only in relation to each other. When two correspondences between two organs exist simultaneously, the older (deeper in time) is homology, and the newer (more superficial) is analogy. In this conceptual framework of evolvable homology, neither of the three Owen's types of homology can be abandoned. Three respective types of analogy should be added-the general analogy, the serial analogy, and the special analogy.


Assuntos
Extremidades/anatomia & histologia , Vertebrados/anatomia & histologia , Animais , Evolução Biológica , Membro Anterior/anatomia & histologia
17.
Micron ; 138: 102924, 2020 11.
Artigo em Inglês | MEDLINE | ID: mdl-32854079

RESUMO

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.


Assuntos
Fósseis/ultraestrutura , Microscopia Eletrônica de Varredura/métodos , Manejo de Espécimes/métodos , Manejo de Espécimes/normas , Animais , Resinas Epóxi/química , Fósseis/anatomia & histologia , Imageamento Tridimensional/métodos , Fosfatos , Reprodutibilidade dos Testes , Vertebrados/anatomia & histologia
18.
Proc Jpn Acad Ser B Phys Biol Sci ; 96(7): 273-296, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32788551

RESUMO

Although the human body appears superficially symmetrical with regard to the left-right (L-R) axis, most visceral organs are asymmetric in terms of their size, shape, or position. Such morphological asymmetries of visceral organs, which are essential for their proper function, are under the control of a genetic pathway that operates in the developing embryo. In many vertebrates including mammals, the breaking of L-R symmetry occurs at a structure known as the L-R organizer (LRO) located at the midline of the developing embryo. This symmetry breaking is followed by transfer of an active form of the signaling molecule Nodal from the LRO to the lateral plate mesoderm (LPM) on the left side, which results in asymmetric expression of Nodal (a left-side determinant) in the left LPM. Finally, L-R asymmetric morphogenesis of visceral organs is induced by Nodal-Pitx2 signaling. This review will describe our current understanding of the mechanisms that underlie the generation of L-R asymmetry in vertebrates, with a focus on mice.


Assuntos
Vertebrados/anatomia & histologia , Animais , Padronização Corporal , Humanos , Vertebrados/embriologia
19.
Science ; 369(6500): 211-216, 2020 07 10.
Artigo em Inglês | MEDLINE | ID: mdl-32647004

RESUMO

The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.


Assuntos
Evolução Biológica , Dentição , Arcada Osseodentária/anatomia & histologia , Vertebrados/anatomia & histologia , Vertebrados/classificação , Animais , República Tcheca , Tomografia com Microscopia Eletrônica , Fósseis , Filogenia , Síncrotrons , Dente/anatomia & histologia
20.
Sci Rep ; 10(1): 8970, 2020 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-32488139

RESUMO

Fossil melanosomes, micron-sized granules rich in melanin in vivo, provide key information for investigations of the original coloration, taxonomy and internal anatomy of fossil vertebrates. Such studies rely, in part, on analysis of the inorganic chemistry of preserved melanosomes and an understanding of melanosome chemical taphonomy. The extent to which the preserved chemistry of fossil melanosomes is biased by biotic and abiotic factors is, however, unknown. Here we report the discovery of hierarchical controls on the inorganic chemistry of melanosomes from fossil vertebrates from nine biotas. The chemical data are dominated by a strong biota-level signal, indicating that the primary taphonomic control is the diagenetic history of the host sediment. This extrinsic control is superimposed by a biological, tissue-level control; tissue-specific chemical variation is most likely to survive in fossils where the inorganic chemistry of preserved melanosomes is distinct from that of the host sediment. Comparative analysis of our data for fossil and modern amphibians reveals that most fossil specimens show tissue-specific melanosome chemistries that differ from those of extant analogues, strongly suggesting alteration of original melanosome chemistry. Collectively, these findings form a predictive tool for the identification of fossil deposits with well-preserved melanosomes amenable to studies of fossil colour and anatomy.


Assuntos
Biota , Fósseis , Melanossomas , Espectrometria por Raios X/métodos , Síncrotrons , Vertebrados/classificação , Anfíbios , Animais , Classificação , Cor , Extinção Biológica , Melanossomas/química , Vertebrados/anatomia & histologia
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