Louise Zylberberg

Cytoskeletal organization and collagen orientation in the fish scales

SummaryImmunofluorescence 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.

Non-Apatitic Environments in Bone Mineral: FT-IR Detection, Biological Properties and Changes in Several Disease States

Resolution enhanced FT-IR spectroscopy shows that non-apatitic environments of phosphate and carbonate ions occur in bone mineral. The spectroscopic characteristics of these environments and their chemical and biological properties are reviewed. The potential effectiveness of FT-IR for the detailed study of bone mineral changes in bone disease is shown by analysis of several samples.

New data on the structure and the growth of the osteoderms in the reptile Anguis fragilis L. (Anguidae, Squamata)

Light and electron microscopy shows the osteoderms of Anguis fragilis to be small, flat disks located in the dermis along the adult trunk: microradiography established the extent of the mineralization.

Fine structural aspects of silk secretion in a spider (Araneus diadematus). I. Elaboration in the pyriform glands

Pyriform glands of Araneus diadematus which produce the silky material used for the attachment discs of the web, consist of two kinds of secretory cells. One, located in the distal half of the glands, elaborates finely fibrillar proteinic granules through an extensive rough endoplasmic reticulum; another, in the proximal half of the glands, secretes complex-structured granules in areas of the cell where Golgi and ergastoplasmic cisternae are equally developed. The opaque nascent granules of secretion appear in swollen Golgi saccules. These aggregate is superposed circular interconnected layers leaving an electron-lucent space between them; in the course of maturation the space is progressively filled with a fibrillar material. Histochemical tests suggest that the secretory product of the proximal half is mainly a protein rich in acidic groups and associated with a carbohydrate component. The two products, extruded by a merocrine process, form respectively the core and the envelope of the silk fibre. The dual composition of the pyriform gland silk, which did not appear from the results of chemical analyses, is compared to the association of fibroin and sericin in Lepidoptera silk and to certain double-layered Trichoptera silks.

EXT 1 gene mutation induces chondrocyte cytoskeletal abnormalities and defective collagen expression in the exostoses

Hereditary multiple exostoses (HME), an autosomal skeletal disorder characterized by cartilage‐capped excrescences, has been ascribed to mutations in EXT 1 and EXT 2, two tumor suppressor‐related genes encoding glycosyltransferases involved in the heparan sulfate proteoglycan (HSPG) biosynthesis. Taking advantage of the availability of three different exostoses from a patient with HME harboring a premature termination codon in the EXT 1 gene, morphological, immunologic, and biochemical analyses of the samples were carried out. The cartilaginous exostosis, when compared with control cartilage, exhibited alterations in the distribution and morphology of chondrocytes with abundant bundles of actin filaments indicative of cytoskeletal defects. Chondrocytes in the exostosis were surrounded by an extracellular matrix containing abnormally high amounts of collagen type X. The unexpected presence of collagen type I unevenly distributed in the cartilage matrix further suggested that some of the hypertrophic chondrocytes detected in the cartilaginous caps of the exostoses underwent accelerated differentiation. The two mineralized exostoses presented lamellar bone arrangement undergoing intense remodeling as evidenced by the presence of numerous reversal lines. The increased electrophoretic mobility of chondroitin sulfate and dermatan sulfate proteoglycans (PGs) extracted from the two bony exostoses was ascribed to an absence of the decorin core protein. Altogether, these data indicate that EXT mutations might induce a defective endochondral ossification process in exostoses by altering actin distribution and chondrocyte differentiation and by promoting primary calcification through decorin removal.

Structure of the dermal scales in gymnophiona (Amphibia)

Histology and cytology of dermal scales of the gymnophionans Ichthyophis kohtaoensis and Hypogeophis rostratus reveal their structure and the nature of their mineralization.

Histochemistry and ultrastructure of amphibian lingual glands and phylogenetic relations.

SynopsisThe lingual glands of amphibians are confined to the dorsal face of the tongue and are formed by invaginations of the lingual epithelium. The secretory products have a heterogeneous composition. Mucosubstances are usually associated with proteins. The secretory product of the outer glandular cells is rich in mucosubstances of an acidity varying with species. In Anourans and Urodeles, the secretory product of the tubes contains abundant proteins and, where present, mucosubstances are less abundant and less acid than those produced at the surface of the tongue. Proteins and mucosubstances coexist in the same secretory granules, which exhibit a more or less homogeneous appearence in Gymnophiona and in Anourans while having a complex structure in Urodeles.In spite of their primitive anatomical features, the amphibian lingual glands present histochemical signs of a complete cellular evolution.

Phylogenetic Analysis of Vertebrate Fibrillar Collagen Locates the Position of Zebrafish α3(I) and Suggests an Evolutionary Link Between Collagen α Chains and Hox Clusters

Type I collagen in tetrapods is usually a heterotrimeric molecule composed of two α1 and one α2 chains. In some teleosts, a third α chain has been identified by chromatography, suggesting that type I collagen should also exist as an α1(I)α2(I)α3(I) heterotrimer. We prepared, from zebrafish, three distinct cDNAs identified to be those of the collagen α1(I), α2(I), and α3(I) chains. In this study on the evolution of fibrillar collagen α chains and their relationships, an exhaustive phylogenetic analysis, using vertebrate fibrillar collagen sequences, showed that each α chain constitutes a monophyletic cluster. Results obtained with the newly isolated sequences of the zebrafish showed that the α3(I) chain is phylogenetically close to the α1(I) chain and support the hypothesis that the α3(I) chain arose from a duplication of the α1(I) gene. The duplication might occur during the duplication of the actinopterygian genome, soon after the divergence of actinopterygians and sarcopterygians, a hypothesis supported by the demonstration of a syntenic evolution between a set of fibrillar collagen genes and Hox clusters in mammals. An evolutionary scenario is proposed in which phylogenetic relationships of the α chains of fibrillar collagens of vertebrates could be related to Hox cluster history.

Fine structural aspects of silk secretion in a spider. II. Conduction in the pyriform glands

The excretory duct of pyriform glands in Araneus diadematus is connected to the secretory sac through an intermediary cell ring. Apices of these cells bear thick, long microvilli and cytoplasmic extensions containing microtubules in bundles, some of which are derived from normal basal bodies. These finger-like extensions lie between the cuticular intima and the secretory product; they are thought to protect the intima and to initiate moulding of the silk thread. Structural features of the duct cells suggest that the latter play a role in the control of the water content of the silk glue which is restricted to the last portion of the duct where numerous nerve endings are inserted between cells. It is evident that duct structure and chemical and physical characteristics of silk are correlated in all spider silk glands.

Structural and mechanical characteristics of the hyperdense bone of the rostrum of Mesoplodon densirostris (Cetacea, Ziphiidae): Summary of recent observations

This note provides a brief account of several recent studies of the basic physical properties, histology and ultrastructure, and biomechanical behaviour of the bone that forms the rostrum of the beaked whale Mesoplodon densirostris. The density (2.612 to 2.686 g cm−3), mineral content (86% to 87%) and compactness (99%) of this bone reach the highest values hitherto observed for mammalian bone. Histologically, the rostrum is composed of dense Haversian tissue, the secondary osteons of which are oriented longitudinally, themselves consisting of hypermineralized parallel‐fibered osseous tissue. The ultrastructure of the walls of the secondary osteons is characterized by a strong volumetric reduction of the collagenous network, which is composed of very thin fibrils (0.017 μm in diameter) that are oriented longitudinally. The biomechanical behaviour of the rostrum is that of an exceptionally rigid (Youngs modulus up to 46.9 GPa), hard (hardness > 200 VHN) but also very brittle (bending strength > 59 MPa) material. These data are discussed in reference to the possible functional role(s) of the hyperdense rostrum.