Structure of the dermal scales in gymnophiona (Amphibia)
01 Jul 1980-Journal of Morphology (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 165, Iss: 1, pp 41-54
TL;DR: Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization.
Abstract: Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization. Dermal scales are small flat disks set in pockets in the transverse ridges of the skin. Each pocket contains several scales of various sizes. A ring of "hypomineralization" of varying diameter may occur on scales of a particular dermal pocket but bears no relation to the diameter of these scales. Three different layers form the scales and are seen on sections perpendicular to the surface. The cells of the basal layer lie deepest. Each of the two or three more superficial fibrous layers is composed of bundles of fibres that are oriented in parallel. The orientation varies among layers. The striation of the fiber scales has a periodicity comparable to that of the surrounding dermal fibers. Squamulae form a discontinuous layer on the scale surface and are the only mineralized part of the scale. The minerals are deposited both on the collagen fibers passing from the fibrous layers into the squamulae, and in the interfibrillar spaces. Spherical concretions, either isolated or coalescent, reaching up to 1 μm, are found on the surface of the squamulae. The dermal scales of Gymnophiona present some analogies with those of evolved bony fishes. Their characteristics could make them an original model for the study of mineralization.
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TL;DR: This review deals with the following seven aspects of vertebrate skeletogenic and odontogenic tissues: innervation, chemoreception, histology, histopathology, “soft” and “hard” tissues.
Abstract: This review deals with the following seven aspects of vertebrate skeletogenic and odontogenic tissues. 1. The evolutionary sequence in which the tissues appeared amongst the lower craniate taxa. 2. The topographic association between skeletal (cartilage, bone) and dental (dentine, cement, enamel) tissues in the oldest vertebrates of each major taxon. 3. The separate developmental origin of the exo- and endoskeletons. 4. The neural-crest origin of cranial skeletogenic and odontogenic tissues in extant vertebrates. 5. The neural-crest origin of trunk dermal skeletogenic and odontogenic tissues in extant vertebrates. 6. The developmental processes that control differentiation of skeletogenic and odontogenic tissues in extant vertebrates. 7. Maintenance of developmental interactions regulating skeletogenic/odontogenic differentiation across vertebrate taxa. We derive twelve postulates, eight relating to the earliest vertebrate skeletogenic and odontogenic tissues and four relating to the development of these tissues in extant vertebrates and extrapolate the developmental data back to the evolutionary origin of vertebrate skeletogenic and odontogenic tissues. The conclusions that we draw from this analysis are as follows. 8. The dermal exoskeleton of thelodonts, heterostracans and osteostracans consisted of dentine, attachment tissue (cement or bone), and bone. 9. Cartilage (unmineralized) can be inferred to have been present in heterostracans and osteostracans, and globular mineralized cartilage was present in Eriptychius, an early Middle Ordovician vertebrate unassigned to any established group, but assumed to be a stem agnathan. 10. Enamel and possibly also enameloid was present in some early agnathans of uncertain affinities. The majority of dentine tubercles were bare. 11. The contemporaneous appearance of cellular and acellular bone in heterostracans and osteostracans during the Ordovician provides no clue as to whether one is more primitive than the other. 12. We interpret aspidin as being developmentally related to the odontogenic attachment tissues, either closer to dentine or a form of cement, rather than as derived from bone. 13. Dentine is present in the stratigraphically oldest (Cambrian) assumed vertebrate fossils, at present some only included as Problematica, and is cladistically primitive, relative to bone. 14. The first vertebrate exoskeletal skeletogenic ability was expressed as denticles of dentine. 15. Dentine, the bone of attachment associated with dentine, the basal bone to which dermal denticles are fused and cartilage of the Ordovician agnathan dermal exoskeleton were all derived from the neural crest and not from mesoderm. Therefore the earliest vertebrate skeletogenic/odontogenic tissues were of neural-crest origin.(ABSTRACT TRUNCATED AT 400 WORDS)
326 citations
TL;DR: Data support the notion that all osteoderms are derivatives of a neural crest‐derived osteogenic cell population and share a deep homology associated with the skeletogenic competence of the dermis, and that skeletogenesis is comparable with the formation of elasmoid scales.
Abstract: Although often overlooked, the integument of many tetrapods is reinforced by a morphologically and structurally diverse assemblage of skeletal elements. These elements are widely understood to be derivatives of the once all-encompassing dermal skeleton of stem-gnathostomes but most details of their evolution and development remain confused and uncertain. Herein we re-evaluate the tetrapod integumentary skeleton by integrating comparative developmental and tissue structure data. Three types of tetrapod integumentary elements are recognized: (1) osteoderms, common to representatives of most major taxonomic lineages; (2) dermal scales, unique to gymnophionans; and (3) the lamina calcarea, an enigmatic tissue found only in some anurans. As presently understood, all are derivatives of the ancestral cosmoid scale and all originate from scleroblastic neural crest cells. Osteoderms are plesiomorphic for tetrapods but demonstrate considerable lineage-specific variability in size, shape, and tissue structure and composition. While metaplastic ossification often plays a role in osteoderm development, it is not the exclusive mode of skeletogenesis. All osteoderms share a common origin within the dermis (at or adjacent to the stratum superficiale) and are composed primarily (but not exclusively) of osseous tissue. These data support the notion that all osteoderms are derivatives of a neural crest-derived osteogenic cell population (with possible matrix contributions from the overlying epidermis) and share a deep homology associated with the skeletogenic competence of the dermis. Gymnophionan dermal scales are structurally similar to the elasmoid scales of most teleosts and are not comparable with osteoderms. Whereas details of development are lacking, it is hypothesized that dermal scales are derivatives of an odontogenic neural crest cell population and that skeletogenesis is comparable with the formation of elasmoid scales. Little is known about the lamina calcarea. It is proposed that this tissue layer is also odontogenic in origin, but clearly further study is necessary. Although not homologous as organs, all elements of the integumentary skeleton share a basic and essential relationship with the integument, connecting them with the ancestral rhombic scale.
174 citations
Cites background from "Structure of the dermal scales in g..."
...…basal plate of elasmodine capped by superficial hypermineralized granules (squamulae) uncertain: hypothesized to develop similar to elasmoid scales Zylberberg et al. 1980; Zylberberg & Wake, 1990 Synapsida osteoderm dorsal body surface: polygonal and rectangular elements often organized into…...
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...Instead the histological organization includes a basal plate composed of unmineralized collagen lamellae arranged into a plywood-like tissue, superimposed by a discontinuous layer of squamulae (Zylberberg et al. 1980; Zylberberg & Wake, 1990)....
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...The basal plate is largely acellular and appears to be deposited by a retreating front of scleroblasts lining the deep surface of the dermal scale (Zylberberg et al. 1980; Zylberberg & Wake, 1990)....
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TL;DR: The absence of cartilage precursors indicates that osteoderms are dermal elements, possibly related to the all‐encompassing vertebrate dermal skeleton (exoskeleton), and instead is comparable with intramembranously derived elements of the skull.
Abstract: Among modern mammals, armadillos (Xenarthra, Cingulata) are the only group that possesses osteoderms, bony inclusions within the integument. Along the body, osteoderms are organized into five discrete assemblages: the head, pectoral, banded, pelvic, and tail shields. The pectoral, banded, and pelvic shields articulate to form the carapace. We examined osteoderm skeletogenesis in the armadillo Dasypus novemcinctus using serial and whole-mount histochemistry. Compared with the rest of the skeleton, osteoderms have a delayed onset of development. Skeletogenesis begins as condensations of osteoblasts secreting osteoid, localized within the papillary layer of the dermis. Osteoderm formation is asynchronous both within each shield and across the body. The first osteoderms to mineralize are situated within the pectoral shield of the carapace, followed by elements within the banded, head, pelvic, and tail shields. In general, within each shield ossification begins craniomedially and proceeds caudally and laterally, except over the head, where the earliest elements form over the frontal and parietal bones. The absence of cartilage precursors indicates that osteoderms are dermal elements, possibly related to the all-encompassing vertebrate dermal skeleton (exoskeleton). The mode of development of D. novemcinctus osteoderms is unlike that described for squamate osteoderms, which arise via bone metaplasia, and instead is comparable with intramembranously derived elements of the skull.
108 citations
Cites background from "Structure of the dermal scales in g..."
...Alternatively, among gymnophiones, these elements are dermal scales, nonosseous flattened disks with alternating layers of unmineralized and mineralized collagen (Zylberberg et al., 1980; Zylberberg and Wake, 1990)....
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TL;DR: Overall, demineralization is a rapidly growing and challenging aspect of various scientific disciplines such as astrobiology, paleoclimatology, geomedicine, archaeology,Geobiology, dentistry, histology, biotechnology, and others to mention just a few.
105 citations
TL;DR: New data on the ultrastructural features of the elasmoid scales of Carassius auratus have been obtained by use of rapid freezing with subsequent freeze-substitution in anhydrous solvents, compared with the results obtained using conventional aqueous fixatives.
Abstract: New data on the ultrastructural features of the elasmoid scales ofCarassius auratus have been obtained by use of rapid freezing with subsequent freeze-substitution in anhydrous solvents. These are compared with the results obtained using conventional aqueous fixatives. The external layer of the scales is composed of randomly oriented collagen fibres. In the first stages of mineralization, mineral deposits are located in the interfibrillary substance where dense granules appear to be active sites of mineralization. Spheritic mineralization occurs in this layer. The fibrillary plate is composed of two kinds of collagen fibres. Most of them are organized in lamellae forming the “plywood-like structure”. They are thicker than the so-called “TC fibres”, which are oriented from the basal part towards the superficial layer. These TC fibres are involved in the first stages of mineral deposition in the fibrillary plate where inotropic mineralization occurs. The mineral phase is almost always located in the interfibrillary matrix in both layers of the elasmoid scale. In this respect, teleost scales differ from those described so far in other lower vertebrates.
83 citations
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TL;DR: The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present, and is less likely to contaminate sections.
Abstract: Aqueous solutions of lead salts (1, 2) and saturated solutions of lead hydroxide (1) have been used as stains to enhance the electron-scattering properties of components of biological materials examined in the electron microscope. Saturated solutions of lead hydroxide (1), while staining more intensely than either lead acetate or monobasic lead acetate (l , 2), form insoluble lead carbonate upon exposure to air. The avoidance of such precipitates which contaminate surfaces of sections during staining has been the stimulus for the development of elaborate procedures for exclusion of air or carbon dioxide (3, 4). Several modifications of Watson's lead hydroxide stain (1) have recently appeared (5-7). All utilize relatively high pH (approximately 12) and one contains small amounts of tartrate (6), a relatively weak complexing agent (8), in addition to lead. These modified lead stains are less liable to contaminate the surface of the section with precipitated stain products. The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present. Lead citrate, soluble in high concentrations in basic solutions, is a chelate compound with an apparent association constant (log Ka) between ligand and lead ion of 6.5 (9). Tissue binding sites, presumably organophosphates, and other anionic species present in biological components following fixation, dehydration, and plastic embedding apparently have a greater affinity for this cation than lead citrate inasmuch as cellular and extracellular structures in the section sequester lead from the staining solution. Alkaline lead citrate solutions are less likely to contaminate sections, as no precipitates form when droplets of fresh staining solution are exposed to air for periods of up to 30 minutes. The resultant staining of the sections is of high intensity in sections of Aralditeor Epon-embedded material. Cytoplasmic membranes, ribosomes, glycogen, and nuclear material are stained (Figs. 1 to 3). STAIN SOLUTION: Lead citrate is prepared by
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TL;DR: The collagens appear to be characteristic structural proteins of soft tissues of all animals, but are perhaps typically the dominant structural materials in vertebrates, in which they may constitute up to a quarter of all the body protein.
Abstract: All multicellular organisms contain a framework of solid material which in part maintains their shape. The commonest of the materials used to make such frameworks are long chain carbohydrate polymers, for example cellulose, found in plants. In animals, however, these simple materials are not used to any extent, though cellulose has been recorded in ascidians (Schmidt, 1845; Ranby, 1952; van der Wyk & Schmorak, I 953). Materials of primarily carbohydrate origin are certainly concerned and may sometimes form a large part of the structural material, for example chitin in invertebrates, but the dominant structural materials are proteins; and of these the collagens appear to be the most important and widely distributed. There are other proteins of structural importance, found, for example in the arthropod cuticle (' arthropodine', see Fraenkel & Rudall, 1947; Duchateau & Florkin, 1954); in the hard skeletons of insects (see Richards, 1951; Wigglesworth, 1957); keratin in vertebrate hair and epidermis (see Kendrew, 1954; Ward & Lundgren, 1954); but these, with the exception of keratin, are as yet poorly defined and are restricted in distribution. The collagens appear to be characteristic structural proteins of soft tissues of all animals, but are perhaps typically the dominant structural materials in vertebrates, in which they may constitute up to a quarter of all the body protein. Collagen is a fibrous protein; that is to say, the individual molecules are thread-like, and are arranged together in threads of higher orders of size to form a continuous framework throughout the body. This fibrous framework is closely associated with other materials filling spaces within it and cementing it together. Such materials include crystalline solids, as in bone, but generally they appear to be gels containing a high proportion of water, associated with acid mucopolysaccharides, that is,
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