Spatial Organization and Mineralization of the Basal Plate of Elasmoid Scales in Osteichthyans

In Sarcopterygii (Latimeria, Neoceratodus, Protopterus, Leptdosiren)and Amiidae (Amia) collagen fibrils of the basal plate are packedin bundles whereas they remain isolated in Teleostei. The basalplate looks like plywood, a system of superimposed layers ofparallel fibers or fibrils the directions of which rotate witha regular angle in two successive layers. The double twistedplywood is constituted of two imbricate systems, the odd andthe even, where the rotation of the fibrillar directions isright-handed in Sarcopterygii and lefthanded in Amiidae andnumerous primitive Teleostei. The orthogonal plywood, with itstwo main orthogonal fibrillar directions, characterizes theevolved Teleostei and some more primitive ones. In most teleosteanspecies, as in Amia and Protopterus, mineralization of the basalplate in elasmoid scales involves Mandl's corpuscles that mineralizewithout contact with a pre-existing calcified tissue; they growand coalesce with the neighbouring ones and fuse to the mineralizingfront. Their shape is directly influenced by the local arrangementof the collagenous fibrils. In two teleostean families (Osteoglossidaeand Mormyridae) Mandl's corpuscles are completely lacking butspreading of mineralization in the basal plate has a peculiaraspect. Whatever that may be, the various characteristic organizationsof the skeletal tissues or isopedine that constitute the basalplate of osteichthyan elasmoid scales, all are varieties ofbone tissue that have undergone more or less important specializationlinked to the general regression of dermal ossifications andto functional adaptations.     

‘Twisted plywood’ structure and mineralization in the scales of a primitive living fish Amia calva

The basal plate of the scales of Amia calva is composed of regular double twisted plywood, as in Latimeria and Dipnoan scales. However, the progressive rotation of the fibrils direction is left-handed in Amia and right-handed in the ‘Sarcopterygians’. So, the similarity between these peculiar plywoods is probably the result of convergence. The basal plate of Amia scales is incompletely mineralized. There are numerous calcified ovoid corpuscles which look very like the Mandl's corpuscles of Teleost scales. The mineralization probably progresses essentially by the fusion of these corpuscles, as in Teleost scales, and would be inotropic rather than spheritic.     

Les relations isopedine - tissu osseux dans le post-temporal et les ecailJes de la ligne laterale de Latimeria chalumnae (Smith)

The scaly part of the posttemporal bone and the lateral-line scales have the same structure as other scales. However, the lateral line with its bony canal induces some local transformations in both structures. The posttemporal bone can be interpreted as a lateral-line scale whose "dermo"-component is extensively developed. With its composite structure, both osseous and scaly, the posttemporal bone affords an instance peculiarly well suited for studying the relationships between isopedine and bone. The observations demonstrate that isopedine whose superposed collagen layers make a double-twisted plywood, is a specialized structure which evolved from a bony tissue. The fibrous basal plate of a Latimeria scale is homologous to the osseous basal plate of a cosmoid scale.     

Scales in young Polypterus senegalus are elasmoid: new phylogenetic implications

A component of the basal plate which has a plywood-like organization similar to that of the elasmoid scales of teleosts is described in the scales of Polypterus senegalus for the first time. The origin and development of this structure is studied in young (50-117 mm, standard length) and adult (225 and 240 mm) specimens using light and electron microscopy. In 50 mm fish, the scales are imbricated and composed mainly of a succession of orthogonal collagen layers forming a plywood-like structure, the isopedin. The outer surface of the scale is ornamented locally by irregular patches of collagenous material. The layers are not mineralized, whereas the superficial patches are well calcified. The isopedin thickens until it has 12-15 layers and then stops growing (88 mm fish). It mineralizes irregularly from its upper part, and two vascular regions, surrounded by woven-fibered osseous material, form on the outer and deeper surfaces of the isopedin. These regions thicken while the vascular canals close by centripetal deposition of parallel-fibered osseous tissue. The outer region is the superficial part of the mature scale (called here osteodentin), which is covered by the ganoine deposited by the epidermal cells. The deeper part constitutes the definitive basal plate, composed of parallel-fibered osseous tissue. The results show 1) that the young ganoid scales of Polypterus senegalus have a structure similar to that of typical elasmoid scales; and 2) that the isopedin structure does not change during ontogeny and so represents a permanent record of the first ontogenetic stages. The phylogenetic implication of these results is that the elasmoid scales of teleosts arose by a process of paedomorphosis.     

Microstructure,mechanical, and biomimetic properties of fish scales from Pagrus major

The fish scale of Pagrus major has an orthogonal plywood structure of stratified lamellae, 1-2 microm in thickness, consisting of closely packed 70- to 80-nm-diameter collagen fibers. X-ray diffraction, energy-dispersive X-ray analysis, and infrared spectroscopy indicate that the mineral phase in the scale is calcium-deficient hydroxyapatite containing a small amount of sodium and magnesium ions, as well as carbonate anions in phosphate sites of the apatite lattice. The tensile strength of the scale is high (approximately 90 MPa) because of the hierarchically ordered structure of mineralized collagen fibers. Mechanical failure occurs by sliding of the lamellae and associated pulling out and fracture of the collagen fibers. In contrast, demineralized scales have significantly lower tensile strength (36 MPa), indicating that interactions between the apatite crystals and collagen fibers are of fundamental importance in determining the mechanical properties. Thermal treatment of fish scales to remove the organic components produces remarkable inorganic replicas of the native orthogonal plywood structure of the fibrillary plate. The biomimetic replica produced by heating to 873 K consists of stratified porous lamellae of c-axis-aligned apatite crystals that are long, narrow plates, 0.5-0.6 microm in length and 0.1-0.2 microm in width. The textured inorganic material remains intact when heated to 1473 K, although the size of the constituent crystals increases as a result of thermal sintering.     

Ultrastructural data on the scales of the dipnoan Protoptems annectens (Sarcopterygii, Osteichthyes)

The structure and the mineralization of the scales of the living dipnoan (lungfish) Protoptems annectens have been investigated by transmission electron microscopy (TEM). The thin and imbricated scales are composed of two layers: the squamulae and the basal plate. At the outer surface, the squamulae form isolated plates superficially ornamented with spines and concretions and made up of acellular bone. After demineralization, the squamulae show a heterogeneous organic matrix composed of thin randomly oriented collagen fibrils forming a loose network within which the concretions appear as electronlucent circular areas. Abundant and aggregated concretions are located within the spines. The crystallites are oriented by the collagen fibrils except in the concretions. Anchoring bundles composed of parallel collagen fibrils arise from the squamulae and connect the scales to the overlying dermis.
The basal plate, the most developed part of the scale, is made up of isopedine. Its main component consists of thick, closely packed collagen fibrils organized in a 'double twisted plywood-like structure'. Fibroblasts are present in the basal plate. Mineralization occurs only in few plies located beneath the squamulae. Mandl's corpuscles are found in front of the mineralization front. The mineral deposit is oriented by the collagen fibrils.
The scales of Protoptems annectens differ from the typical elasmoid scales of the teleosts by the peculiar structure of the squamulae, nevertheless they show enough structural characteristics to support the hypothesis that they can be considered as scales of the elasmoid grade, which have retained some plesiomorphic characteristics.     

The fibrous structure of coelacanth scales: A twisted ‘Plywood’

Isopedin is a network of collagen bundles present in the scales of most fishes. The scales of coelacanths show a remarkable three-dimensional arrangement of this network which is similar to a regularly twisted plywood. The successive fibrous layers cross at an angle which differs slightly from a right angle. It results that the whole system is twisted. The progressive rotation of the fibril direction is right-handed. Certain preferential orientations of fibrils have been observed, namely parallel to the growth rings. Such arrangements also exist in the embryonic cornea of birds and in the cuticle of certain insects, but do not present such an extensive and regular development.     

Structure and composition of teleost scales from snakehead Channa argus (Cantor) (Perciformes: Channidae)

The structure of teleost scales from snakehead Channa argus was investigated using thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive analysis of X-rays (EDAX), Fourier transform infra-red spectroscopy (FTIR) and X-ray diffraction (XRD). Thermal treatment of fish scales indicates that the fibrillary plate is partially calcified. SEM shows two kinds of scale denticles, arranged along the circuli in the anterior field and the lateral fields, respectively. TEM indicates the stratum laxum with abundant fibrils, chromatophores and capillary blood vessels within the scale covering, and shows the fibrillary plate as an 'orthogonal plywood structure' of stratified lamellae, consisting of 80–100 nm diameter collagen fibres co-aligned in individual lamellae and alternated by c. 90° of the fibre alignment between adjacent lamellae. EDAX, FTIR and XRD show that the mineral phase of the scales is a carbonated hydroxyapatite with a Ca:P molar ratio of 1·85.     

The twisted collagen network of the box-fish scutes

The present article describes the three-dimensional arrangement of collagen fibrils in dermal plates of different species of Ostraciidae. These dermal plates or 'scutes' are transformed scales, which have a polygonal shape and form a rigid tiling. They are natural composites, associating a fibrous network with a mineral deposit lying at two different levels of the scute, the 'ceiling' and the 'floor', plus a set of similarly mineralized walls joining the two levels. The three-dimensional structure of the collagen network can be compared to that of 'plywood': fibrils align parallel within superposed layers of uniform thickness, and their direction changes from layer to layer. In the dermal plate, two types of plywood have been evidenced: (1) one lying between the two mineralized plates, where the orientation of fibrils rotates continuously, and (2) one under the lower plate, with thick layers of fibrils, each showing a constant orientation, but abrupt angular changes are observed at the transition from one layer to the following one. In oblique sections, both types of plywood reveal large series of arced patterns, testifying to a twisted arrangement of collagen fibrils, analogous to the arrangement of molecules or polymers in cholesteric liquid crystals. The network is reinforced by some collagen fibrils running unidirectionally and almost normally to the lamellate structure. Moreover in the overall organization of the scute, these plywood systems form a set of nested boxes. This original architecture is compared to the arrangement of the collagenous network previously described in most fish scales and in other extracellular matrices.     

Contribution Biochimique à la Systématique de l''Ordre des centrospermales

A chemosystematic survey of flavonoids have been made in 55 centrospermous species. On the basis of both the experimental results and published data, the evolutionary significance of distribution patterns of proanthocyanidins, anthocyanidins, C-glycoflavones, flavonols and flavones is discussed. The Nyctaginaceae and Didiereaceae appear to be particularly primitive families, while Caryophyllaceae, Aizoaceae, Cactaceae, Amaranthaceae and Chenopodiaceae are the most advanced of the order.     

Heteropteran ovaries: variations on the theme

Ovaries of heteropterans consist of telotrophic meroistic ovarioles that are composed of apically located tropharium and basal vitellarium, containing developing oocytes. The tropharium (trophic chamber) houses trophocytes (nurse cells) that are connected with the centrally located trophic core. The organization of the heteropteran tropharia is highly variable and differs in representatives of primitive versus advanced families. The differences concern the mitotic activity of the apical nurse cells, organization of the trophocytes (individual cells or "syncytial lobes"), their connection with the trophic core and the development of F-actin meshwork around the trophic core. In members of primitive taxa of the Heteroptera, tropharia are composed of individual, usually mononucleate trophocytes. On the contrary, tropharia in advanced heteropterans are built of large "cytoplasmic lobes" that contain several trophocyte nuclei. Mitotic divisions of the trophocytes in the apical part of the trophic chamber are observed in most bugs (except Dipsocoridae, Miridae and Cimicidae). Tropharia of Miridae represent an entirely different organization (they are built of one type of highly polyploid trophocytes). Anagenesis of heteropteran trophic chamber is discussed in the context of presented data.     

Elastic anisotropy of bone lamellae as a function of fibril orientation pattern

In this study, the homogenized anisotropic elastic properties of single bone lamellae are computed using a finite element unit cell method. The resulting stiffness tensor is utilized to calculate indentation moduli for multiple indentation directions in the lamella plane which are then related to nanoindentation experiments. The model accounts for different fibril orientation patterns in the lamellae—the twisted and orthogonal plywood pattern, a 5-sublayer pattern and an X-ray diffraction-based pattern. Three-dimensional sectional views of each pattern facilitate the comparison to transmission electron (TEM) images of real lamella cuts. The model results indicate, that the 5-sublayer- and the X-ray diffraction-based patterns cause the lamellae to have a stiffness maximum between 0° and 45° to the osteon axis. Their in-plane stiffness characteristics are qualitatively matching the experimental findings that report a higher stiffness in the osteon axis than in the circumferential direction. In contrast, lamellae owning the orthogonal or twisted plywood fibril orientation patterns have no preferred stiffness alignment. This work shows that the variety of fibril orientation patterns leads to qualitative and quantitative differences in the lamella elastic mechanical behavior. The study is a step toward a deeper understanding of the structure—mechanical function relationship of bone lamellae.     

A histologic survey of diencephalic circumventricular organs in teleosts with special reference to osteoglossomorphs

Diencephalic circumventricular organs of various teleosts were studied histologically. Special attention was paid to osteoglossomorphs. The neurohypophysis of osteoglossomorphs (Arapaima, Notopterus, Xenomystus, andGymnarchus) is well differentiated into the median eminence and the neural lobe. The pituitary organization of these species is an intermediate between that of holosteans and of more advanced teleosts. The saccus vasculosus is absent inPantodon andGymnarchus, but it is well developed inNotopterus andXenomystus. The light microscopically discernible pineal is absent inGymnarchus: this may be the only species that lacks the pineal among teleosts. The paraphysis is found in various species including most osteoglossomorphs and some perciforms. In advanced teleosts such as gobiids and tetraodontids, the saccus dorsalis and velum transversum are absent, but the diencephalic choroid plexus is well developed instead. Some evolutionary trends are apparent in the occurrence and organization of these circumventricular organs among teleosts.     

The metabolic organization of a primitive air-breathing fish, the Florida gar (Lepisosteus platyrhincus)

The metabolic organization of the air-breathing Florida gar, Lepisosteus platyrhincus, was assessed by measuring the maximal activities of key enzymes in several metabolic pathways in selected tissues, concentrations of plasma metabolites including nonesterified fatty acids (NEFA), free amino acids (FAA) and glucose as well as tissue FAA levels. In general, L. platyrhincus has an enhanced capacity for carbohydrate metabolism as indicated by elevated plasma glucose levels and high activities of gluconeogenic and glycolytic enzymes. Based upon these properties, glucose appears to function as the major fuel source in the Florida gar. The capacity for lipid metabolism in L. platyrhincus appears limited as plasma NEFA levels and the activities of enzymes involved in lipid oxidation are low relative to many other fish species. L. platyrhincus is capable of oxidizing both D- and L-beta-hydroxybutyrate, with tissue-specific preferences for each stereoisomer, yet the capacity for ketone body metabolism is low compared with other primitive fishes. Based on enzyme activities, the metabolism of the air-breathing organ more closely resembles that of the mammalian lung than a fish swim bladder. The Florida gar sits phylogenetically and metabolically in an intermediate position between the "primitive" elasmobranchs and the "advanced" teleosts. The apparently unique metabolic organization of the gar may have evolved in the context of a bimodal air-breathing environmental adaptation.     

Morphogenesis and histology of large scales of batoids (Elasmobranchii)

Large scales occur only in three families of batoids. Though they have a wide spectrum of different shapes they all serve protective functions in bottom-dwelling species. The crown consists of enameloid, orthodentine and osteodentine. Three different types of basal plates occur: (a) thin basal plate consisting of acellular bone; (b) basal plate which is secondarily thickened; it consists of massive acellular bone and thin denteons which surround the vascular canals; (c) basal plate which is secondarily thickened, consisting of a peculiar type of microspongy bone which has never been found in other elasmobranchs. The scales have either one or several crown elements. None of the scales, however, belongs to a growing type. All large scales were probably replaced regularly. It is the first time that dentine was found within the basal plate of an elasmobranch scale.     

Cytoskeletal organization and collagen orientation in the fish scales

Summary Immunofluorescence and electron microscopy were used to analyze the relationships between the organization of collagen fibrils in elasmoid scales, and the orientation of microtubules and actin microfilaments in the scleroblasts producing this collagenous stroma. Attention was focused on the basal plate of the scales because of the highly ordered three-dimensional arrangement of the collagen fibrils in superimposed plies forming an acellular plywood-like structure. The collagen fibrils are synthesized by the scleroblasts forming a monolayered pseudo-epithelium, the hyposquama, at the lowest surface of the scale. Fully developed scales with a low collagen deposition rate were compared with regenerating scales active in fibrillogenesis. When an ordered array of the collagen fibrils is found, the innermost collagen fibrils are coaligned with microtubules and actin microfilaments. Thus, because of this coalignment, microtubules and actin microfilaments of the hyposquamal scleroblasts are subjected to consecutive alterations during the formation of the plies of the basal plate. The sequence of events when the collagen fibrils change their direction from one ply to the other in the basal plate is deduced from immunofluorescence and phase-contrast-microscopic observations. During the formation of the orthogonal plywood-like structure in the regenerating scales, first microtubules may change their curse with a rotating angle of about 90°; then, actin microfilaments are disorganized and reorganized by interacting mechanically with the microtubules with which they are coaligned. Collagen fibrils are synthesized in a direction that is roughly perpendicular to that of the preceding ply. The unknown signals inducing the change in direction of the cytoskeleton may be transmitted throughout the hyposquama via gap junctions.This work is dedicated to the memory of Jacques Escaig     

Evidences for shared features in the organization of the basal ganglia in tetrapods: studies in amphibians.

In a series of recent studies, the organization of the basal ganglia of amphibians, more in particular their connectivity and chemoarchitecture, has been thoroughly analyzed. The pattern of organization found for the amphibian basal ganglia includes dorsal and ventral striatopallidal systems, reciprocal connections between the striatopallidal complex and structures derived from the diencephalic and mesencephalic parts of the basal plate (striatonigral and nigrostriatal projections), and descending pathways from the striatopallidal system to the midbrain tectum and the reticular formation of the brain stem. A comparative analysis of the organization of the basal ganglia in tetrapods strongly supports the notion that a primitive pattern was most likely present in ancestral tetrapods, and that many features can still be recognized in extant amphibians and amniotes.     

The distribution of Tyr- and Glu-microtubules during fish scale regeneration

Cyclic rearrangements of the microtubules (Mts) occur in the hyposquamal scleroblasts which synthesize the highly ordered three-dimensional collagen network forming the basal plate of the fish scale. The distribution of Mts containing tyrosinated and detyrosinated alpha-tubulin (Tyr-Mts and Glu-Mts, respectively) was analyzed in relation to the frequency of Mt reorganization in the teleostean elasmoid scale during collagen deposition using two specific monoclonal antibodies. In the very flat hyposquamal scleroblasts of fully developed scales (with a very low synthetic activity) two microtubule populations were identified. Most contain Tyr-tubulin while Glu-tubulin is found in some "stable" Mts. In the tall prismatic scleroblasts of regenerating scales (active in collagen synthesis) only Tyr-Mts have been revealed. In late stage of regeneration, when the synthetic activity decreases and the scleroblasts flatten, an increasing centriole and Mt labeling with Glu-tubulin antibody was observed. The intimate relationship of intracellular microtubule arrangement and extracellular collagen fibril pattern reported earlier (Zylberberg et al., Cell Tissue Res. 253, 597-603 (1988], together with the results presented here, support the hypothesis that a changing Mt pattern is involved in the generation of the collagen plywood.     

Vegetative anatomy and morphology of Amentiferae

Some of the important vegetative characters of amentiferous families described in research papers concerned with interfamilial relationships and published since 1947–1948 are briefly summarized. Important conclusions by the writers are also reviewed. Thus, Bataceae are considered derivatives of the Centrospermae ; Betulaceae, Casuarinaceae, and Ulmaceae are hamamelidaceous derivatives; Garryaceae and Cornaceae are closely related; and Julianiaceae and Anacardiaceae are plausible relatives. A more extensive tabulation of vegetative characters of essentially all amentiferous and ranalean families and Dilleniaceae is also presented, and the data are utilized to compare the percentages of advanced and primitive characters in these same taxa. The logic for considering trends whose evolutionary directions were initiated previous or incidental to angiospermous origin as more valid than other evolutionary trends is offered. The following principal conclusions are based upon the analysis of the tabulation: (1) the Amentiferae have sufficient advanced vegetative characters to preclude consideration of them as earliest angiosperms or their direct derivatives unless a large number of primitive features of other sorts offers strong counter evidence; (2) they also have sufficient primitive characters to discount the concept that they are highly evolved; (3) most Amentiferae clearly possess many more advanced vegetative characters than do most Magnoliales, Laurales, Trochodendrales, or Dilleniaceae ; and (4) relationships of several Amentiferae to various, unrelated angiospermous families have been demonstrated.     

Aluminium accumulation in leaves of 127 species in Melastomataceae,with comments on the order Myrtales

The distribution and systematic significance of aluminium accumulation is surveyed based on semi-quantitative tests of 166 species, representing all tribes and subfamilies of the Melastomataceae as well as a few members of related families within the Myrtales. The character is strongly present in nearly all members of the Memecylaceae and in most primitive taxa of the Melastomataceae, while non-accumulating taxa are widespread in the more derived tribes of the Melastomataceae. The variable distribution of Al accumulation in advanced clades of the latter family is probably associated with the tendency to herbaceousness, although it is unclear whether the more herbaceous representatives have developed more specialized Al-response mechanisms that may exclude high Al levels from the shoot. It is hypothesized that Al accumulation is symplesiomorphic for Melastomataceae and Memecylaceae, and that the feature characterizes the most primitive families in the Myrtales. Indeed, Al accumulation is also characteristic of Crypteroniaceae, Rhynchocalycaceae and Vochysiaceae. Crypteroniaceae and Rhynchocalycaceae probably take a basal position in a sister clade of the Memecylaceae and Melastomataceae, while Al accumulation suggests a basal position for Vochysiaceae in the Myrtaceae clade.