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PubMed1998

Molecular genetics of Marfan syndrome and Ehlers-Danlos type IV.

Two inherited disorders of connective tissue have major cardiovascular complications, Marfan syndrome and Ehlers-Danlos syndrome type IV. Major progress has been made toward understanding both the genetic defect and the molecular pathogenesis of these two disorders. Marfan syndrome results from mutations in the FBN1 gene, which encodes fibrillin-1, an extracellular matrix component found in structures called microfibrils. Histologic characterization of the effect of FBN1 mutations on fibrillin-1 cellular processing and microfibril formation has provided insights into fibrillin-1 function. Ehlers-Danlos syndrome type IV results from mutations in the COL3A1 gene, which encodes the polypeptides in type III collagen. Despite advances in the molecular genetics of these two disorders, there is not a molecular diagnostic test for these syndromes based on the identification of gene mutations. Marfan syndrome remains primarily a clinical diagnosis. Biochemical analysis of the amount of type III collagen produced by dermal fibroblasts has proven to be a powerful diagnostic test for Ehlers-Danlos syndrome type IV.

DNA Mutational Analysis↗
PubMed1998

Elastic fiber abnormalities associated with a leaflet perforation in floppy mitral valve.

The alterations observed in the elastic fibers of the perforated floppy mitral valve of a 68-year-old man are described. The patient had not history of infective endocarditis and no stigmata of Marfan syndrome or Ehlers-Danlos syndrome. Ultrastructurally, the elastic fibers in the area of the perforation showed unique, round-shaped expansion of the amorphous components, which lacked associated microfibrils. These features resembled those of the elastic fibers in animals treated with beta-aminopropionitrile, an inhibitor of lysyl oxidase. Aggregations of microfibrils without amorphous components were also observed. These abnormalities are considered to be related to the pathogenesis of the perforation in this valve.

Aged↗
PubMed1976

Platelet adhesion, release and aggregation in flowing blood: effects of surface properties and platelet function.

Platelet adhesion to natural and artificial surfaces and adhesion-induced aggregation were investigated in vitro using an annular perfusion chamber. The surfaces were exposed to anticoagulated blood under identical flow conditions (approximately arterial shear rates). The initial attachment of platelets (contact) appeared less surface specific than spreading and release. Fibrillar collagen was the most powerful inducer of platelet degranulation whereas elastin, microfibrils and epon were virtually inactive. Fibrillar collagen caused release also in the absence of spreading. Surface coverage with platelets did not exceed 25% unless spreading occurred. Perfusion with platelet-free plasma or platelet-poor blood did not remove adhering platelets. However, platelets were translocated from mural thrombi to the surface by such perfusion. In addition, platelets which detached from mural thrombi adhered more readily to elastin or microfibrils than platelets from the circulating blood. The initial attachment of platelets to subendothelium was inhibited in von Willebrand's disease, the Bernard-Soulier syndrome and at high concentrations of dipyridamole; spreading was inhibited in storage pool disease of rats, at low temperature (20 degrees C), with EDTA (3 MM) and Prostaglandin E1 (1 muM); and adhesion-induced aggregation was inhibited in thrombasthenia, storage pool disease and after ingestion of sulfinpyrazone or Aspirin. It is concluded that the initial attachment (contact) of platelets, spreading and surface-induced release of platelet constituents are at least partially indendent phenomena, the latter two being highly surface specific. At flow conditions which cause the disappearance of platelet adhesion appears as an irreversible process.

Animals↗
PubMed2005

Recent progress towards a molecular understanding of Marfan syndrome.

Marfan syndrome (MFS) is a systemic disorder of the connective tissue that is inherited as an autosomal dominant trait and which displays variable manifestations in the ocular, skeletal, and cardiovascular systems. These pleiotropic manifestations are accounted for by mutations in fibrillin-1, the building block of extracellular microfibrils. During the past 10 years, we have witnessed significant progress in delineating the pathological events responsible for the manifestations of MFS. Much of this progress has been based on the creation and analysis of fibrillin-1 mutant mouse lines that faithfully recapitulate the spectrum of clinical severity of MFS. These studies have established the critical contribution of fibrillin-1 deficiency to disease progression through altered cell-matrix interactions and dysregulated TGF-beta signaling. As a result, our definition of MFS as the prototypical structural disorder of the connective tissue has changed to that of a developmental abnormality with broad and complex effects on the morphogenesis and function of multiple organ systems. Importantly, new biological targets have emerged that may yield exciting new opportunities for the development of productive treatment strategies in MFS.

Animals↗
PubMed2004

Subectodermal microfibrillar bundles are organized into a distinct parallel array in the developing chick limb bud.

In this study, a unique fiber system in the subectodermal mesenchyme of the chick limb bud was visualized immunohistochemically with the use of a novel monoclonal antibody termed "FB1." This antibody stained a subset of extracellular fibers in the embryonic mesenchyme. Among the fibers visualized, those running perpendicularly to the limb bud ectoderm became progressively prominent in their thickness and length, and organized into a parallel array in the subectodermal region. This fiber system was distinct from that of major collagens, fibronectin, or tenascin. A molecule immunoprecipitated with FB1 comigrated with JB3 antigen, or chicken fibrillin-2. The fibers visualized immunohistochemically by FB1 and JB3 were indistinguishable from each other, and ultrastructurally appeared to be bundles composed of tubular-like microfibrils that originated directly from the ectodermal basal lamina. They lacked the amorphous deposits that are characteristic of elastin. A similar array of subectodermal fibers was also found in the developing axilla and some truncal regions, again well before the development of a definitive dermis. These findings suggest that a parallel array of subectodermal FB1-positive fibers constitutes a precocious fiber system in the presumptive dermis prior to the substantial formation of collagenous fibers. These fibers could be developmentally linked to oxytalan fibers, which are known to be present in the papillary dermis in mature cutaneous tissue.

Animals↗
PubMed2000

From hormone signal, via the cytoskeleton, to cell growth in single cells of tobacco.

Cultured mesophyll protoplasts of Nicotiana tabacum L. can be hormonally induced into different developmental pathways. In a medium containing auxins (NAA) and cytokinins (BAP) cells divide and eventually give rise to calli. When only auxins are present cells elongate and finally differentiate into very long tubular cells. We focused on the sequence of events leading to elongation. When cultured in a high (1 mg/l) auxin concentration elongating cells seem to pass a certain threshold and increase their nuclear DNA up to about 16C. Cells cultured in a low (0.065 mg/l) auxin concentration only have C-values up to 4C, are unable to pass this threshold and finally fail to elongate. Besides the concentration dependence of the auxin signal, the efflux of auxin seems to be necessary for elongation since addition of TIBA drastically reduces the amount of elongating cells. Concomitant with the changes in nuclear physiology, auxin-induced axiality is seen as sequential rearrangements of microtubules and actin-filaments and of cell wall cellulose microfibrils from 'randomly' arranged in spherical cells to an orientation perpendicular to the long axis of elongating cells.

Adenine↗
PubMed2003

A mechanics model for the compression of plant and vegetative tissues.

The mechanics analysis of plant or vegetable tissue under a compressive stress has been developed based on large deformation elasticity theory. The tissue was treated as a lattice of regular perfect three-dimensional hexagonal cells. The cell walls were assumed to be impermeable under the time-scale of the loading. The cell walls of plants and vegetables are polymeric composite materials, consisting of a relatively amorphous matrix and a highly structured network of microfibrils embedded in the cell wall matrix. The micromechanical features of the individual cells have been related to the macroscopic properties of the whole tissue. The effects of microfibrillar stiffening factors k(1) and k(2), the cell wall matrix property alpha and the initial cell expansion ratio nu(i) on the compressive behaviour of a plant or vegetable tissue have been investigated. The predicted results have also been related to some experimental evidence.

Cell Wall↗
PubMed2001

The molecular pathogenesis of the Marfan syndrome.

The Marfan syndrome (MFS) is an autosomal dominant heritable disorder of connective tissue with highly variable clinical manifestations including aortic dilatation and dissection, ectopia lentis, and a range of skeletal anomalies. Mutations in the gene for fibrillin-1 (FBN1) cause MFS and other related disorders of connective tissue collectively termed type-1 fibrillinopathies. Fibrillin-1 is a main component of the 10- to 12-nm extracellular microfibrils that are important for elastogenesis, elasticity, and homeostasis of elastic fibers. Mutations in fibrillin-1 are hypothesized to exert their effects by dominant negative mechanisms, but recent work has also emphasized the potential role of proteases and disturbances in tissue homeostasis in the pathogenesis of the MFS. This article provides an overview of the clinical aspects of the MFS and current thinking on the pathogenesis of this disorder.

Animals↗
PubMed2001

A dynamical model for plant cell wall architecture formation.

We discuss a dynamical mathematical model to explain cell wall architecture in plant cells. The highly regular textures observed in cell walls reflect the spatial organisation of the cellulose microfibrils (CMFs), the most important structural component of cell walls. Based on a geometrical theory proposed earlier [A. M. C. Emons, Plant, Cell and Environment 17, 3-14 (1994)], the present model describes the space-time evolution of the density of the so-called rosettes, the CMF synthesizing complexes. The motion of these rosettes in the plasma membrane is assumed to be governed by an optimal packing constraint on the CMFs plus adherent matrix material, that couples the direction of motion, and hence the orientation of the CMF being deposited, to the local density of rosettes. The rosettes are created inside the cell in the endoplasmatic reticulum and reach the cell-membrane via vesicles derived from Golgi-bodies. After being inserted into the plasma membrane they are assumed to be operative for a fixed, finite lifetime. The plasma membrane domains within which rosettes are activated are themselves also supposed to be mobile. We propose a feedback mechanism that precludes the density of rosettes to rise beyond a maximum dictated by the geometry of the cell. The above ingredients lead to a quasi-linear first order PDE for the rosette-density. Using the method of characteristics this equation can be cast into a set of first order ODEs, one of which is retarded. We discuss the analytic solutions of the model that give rise to helicoidal, crossed polylamellate, helical, axial and random textures, since all cell walls are composed of (or combinations of) these textures.

Cell Wall↗
PubMed2005

Disulphide reaction staining for the identification of integumental elastic fibres.

Based on specific methods (Sippel-APM-chromotropic acid technique; IC3-PE-maleimide fluorescence reaction) and skin samples of four domesticated mammals (dog, cattle, horse, pig), disulphide groups were demonstrated in the elastic component of the basement membrane of the epidermis, the elastic fibre system of the dermis, the elastic components of the connective tissue sheath of hair follicles, apocrine tubular glands, and sebaceous glands, and of the connective tissue surrounding the cutaneous muscle. The results are discussed regarding the relation of this reaction staining to the presence of microfibrils (fibrillin) in the elastic fibres.

Animals↗
PubMed2003

Innervation and functional characteristics of connective tissues, especially elastic fibers, in human fetal thoracic intervertebral articular capsule and its surroundings.

The articular capsules between the thoracic vertebrae, which have physiologically different functions from those of other levels of the vertebrae, have yet to be subjected to neuro-anatomical and fine structural analysis. In the present study, we analyzed serial frozen sections of decalcified thoracic vertebrae in human fetuses, and identified the articular capsule tissue with its unique distribution of elastic fibers. The fine structure of the elastic fibers was studied by transmission electron microscopy. In the early-stage fetus, the fibrous membrane forming the lateral intervertebral articular capsule contained abundant thin elastic fibers consisting of microfibrils. In the late-stage fetus, the lateral capsule of fibrous membrane was occupied by thick elastic fibers. A medial articular capsule, namely the ligamenta flava, contained numerous thick elastic fibers in both early and late-stage fetuses. The distributional differences in nerve fibers between early and late-stage fetuses were determined by immunostaining, using antibodies raised against protein gene product 9.5 (PGP 9.5; ubiquitin carboxyl-terminal hydrolase). Innervation by PGP 9.5 immunoreactive fibers was limited to the areas of the articular capsules near the blood vessels, which may indicate their functional relation with blood flow. No PGP 9.5 immunoreactive fibers were found in the ligamenta flava of the late-stage fetus. Innervation might be directly involved in the development of the intervertebral articular capsules in normal human fetuses.

Antibodies↗
PubMed2000

Distribution of fibrillin I in extracellular matrix and epithelia during early development of avian embryos.

Fibrillin microfibrils are widely distributed components of extracellular matrices that function in the formation of elastin, serve structural roles and provide substrates for cell adhesion. To determine when and how fibrillin-1 (fib-1) may function in early development we have examined the temporal and spatial distribution of fib-1 in chicken embryos. Using homologous PCR we amplified and cloned a 407 nt fragment of chicken cDNA that appears to code for an orthologue of FBN-1. Bacterially expressed protein was used to prepare two monoclonal antibodies, both of which recognize a 350 kD band in immunoblots or immunoprecipitates in supernatants of chicken embryonic aorta cells or human MG-63 cells. Both antibodies recognize fibrillar material associated with the surfaces of cultured cells. The antibodies appear to be specific for fib- as there was only weak cross reactivity to a bacterially expressed fragment from the corresponding region of fib-2 and the pattern of immunofluorescence in embryonic tissue is distinctly different from that of JB-3, a fib-2 specific antibody (Rongish et al. 1998). In embryos, fib-1 is first detected at stage 6 in the epiblast during gastrulation. In subsequent stages fib-1 fibers appear in all tissues and are present throughout the first 6 days of development. Immunoreactive fibers are present in basal laminae and mesenchyme filled spaces, but they also form random arrays with an apical-basal polarity within epithelia. Using primers specific for FBN-1 and FBN-2 in RT-PCR reactions we confirm the presence of fib- 1 and fib-2 mRNA in early embryonic stages. This temporal and spatial distribution indicates fib-1 has functions in early development that are distinct from fib-2.

Amino Acid Sequence↗
PubMed2004

Transplantation of reconstructed human skin on nude mice: a model system to study expression of human tenascin-X and elastic fiber components.

Tenascin-X is a large extracellular matrix protein that is widely expressed in connective tissues during development and in the adult. Genetically determined deficiency of tenascin-X causes the connective tissue disease Ehlers-Danlos syndrome. These patients show reduced collagen density and fragmentation of elastic fibers in their skin. In vitro studies on the role of tenascin-X in elastic fiber biology are hampered because monolayers of fibroblasts do not deposit tenascin-X and elastic fibers into the extracellular matrix. Here, we applied an organotypic culture model of fibroblasts and keratinocytes to address this issue. We investigated the deposition of tenascin-X and elastin into skin-equivalent in vitro and also in vivo after transplantation onto immunodeficient mice. Whereas tenascin-C and fibrillin-1 were readily expressed in the skin-equivalents before transplantation, tenascin-X and elastin were not present. Three weeks post-grafting, a network of elastin was observed that coincided with the appearance of tenascin-X. At the ultrastructural level, microfibrils were observed, some of which were associated with elastin. Transplanted skin-equivalents containing tenascin-X-deficient fibroblasts showed deposition of immunoreactive elastin in similar quantities and distribution as those containing control fibroblasts. This suggests that tenascin-X is important for the stability and maintenance of established elastin fibers, rather than for the initial phase of elastogenesis. Thus, the transplantation of reconstructed skin on nude mice allows the study of tenascin-X and elastin expression and could be used as a model system to study the potential role of tenascin-X in matrix assembly and stability.

Animals↗
PubMed2004

Membrane-wall attachments in plasmolysed plant cells.

Field emission scanning electron microscopy of plasmolysed Tradescantia virginiana leaf epidermal cells gave novel insights into the three-dimensional architecture of Hechtian strands, Hechtian reticulum, and the inner surface of the cell wall without the need for extraction. At high magnification, we observed fibres that pin the plasma membrane to the cell wall after plasmolysis. Treatment with cellulase caused these connecting fibres to be lost and the pinned out plasma membrane of the Hechtian reticulum to disintegrate into vesicles with diameters of 100-250 nm. This suggests that the fibres may be cellulose. After 4 h of plasmolysis, a fibrous meshwork that labelled with anti-callose antibodies was observed within the space between the plasmolysed protoplast and the cell wall by field emission scanning electron microscopy. Interestingly, macerase-pectinase treatment resulted in the loss of this meshwork, suggesting that it was stabilised by pectins. We suggest that cellulose microfibrils extending from strands of the Hechtian reticulum and entwining into the cell wall matrix act as anchors for the plasma membrane as it moves away from the wall during plasmolysis.

Cell Membrane↗
PubMed2003

HSP47 as a collagen-specific molecular chaperone: function and expression in normal mouse development.

A large family of molecular chaperones can be divided into two major groups: general chaperone and substrate-specific chaperone. HSP47 is a collagen-specific molecular chaperone residing in the endoplasmic reticulum (ER). Recent studies revealed that HSP47 is essential molecular chaperone for mouse development and is essential for collagen molecular maturation in the ER. In the absence of HSP47, collagen microfibril formation and basement membrane formation are impaired in mouse embryos because the failure in the molecular maturation of types I and IV collagens, respectively. The tissue-specific expression of HSP47 is always correlated with that of various types of collagens and closely related with the collagen-related diseases including fibrosis in various organs. The importance of HSP47 in the therapeutic strategy for fibrotic diseases as well as for a marker of collagen-related autoimmune diseases will also be discussed.

Animals↗
PubMed2001

Cell-wall architecture and lignin composition of wheat developed in a microgravity environment.

The microgravity environment encountered during space-flight has long been considered to affect plant growth and developmental processes, including cell wall biopolymer composition and content. As a prelude to studying how microgravity is perceived - and acted upon - by plants, it was first instructive to investigate what gross effects on plant growth and development occurred in microgravity. Thus, wheat seedlings were exposed to microgravity on board the space shuttle Discovery (STS-51) for a 10 day duration, and these specimens were compared with their counterparts grown on Earth under the same conditions (e.g. controls). First, the primary roots of the wheat that developed under both microgravity and 1 g on Earth were examined to assess the role of gravity on cellulose microfibril (CMF) organization and secondary wall thickening patterns. Using a quick freeze/deep etch technique, this revealed that the cell wall CMFs of the space-grown wheat maintained the same organization as their 1 g-grown counterparts. That is, in all instances, CMFs were randomly interwoven with each other in the outermost layers (farthest removed from the plasma membrane), and parallel to each other within the individual strata immediately adjacent to the plasma membranes. The CMF angle in the innermost stratum relative to the immediately adjacent stratum was ca 80 degrees in both the space and Earth-grown plants. Second, all plants grown in microgravity had roots that grew downwards into the agar; they did not display "wandering" and upward growth as previously reported by others. Third, the space-grown wheat also developed normal protoxylem and metaxylem vessel elements with secondary thickening patterns ranging from spiral to regular pit to reticulate thickenings. Fourthly, both the space- and Earth-grown plants were essentially of the same size and height, and their lignin analyses revealed no substantial differences in their amounts and composition regardless of the gravitational field experienced, i.e. for the purposes of this study, all plants were essentially identical. These results suggest that the microgravity environment itself at best only slightly affected either cell wall biopolymer synthesis or the deposition of CMFs, in contrast to previous assertions.

Cell Membrane↗
PubMed2003

Tensile deformation of bacterial cellulose composites.

The polymeric basis for the mechanical properties of primary plant cell walls has been investigated by forming analogous composites based on fermentation of the bacterium Acetobacter xylinus, either alone or in the presence of xyloglucan or pectin. Simultaneous small-angle X-ray scattering and uniaxial deformation experiments has shown how the cellulose microfibrils reorient during deformation. Despite very different stress/strain curves, the reorientation behaviour is similar, regardless of the presence or absence of xyloglucan or pectin. A simple theory has been developed to predict the orientation behaviour. This is qualitatively similar to the measured behaviour, but differs quantitatively.

Bacterial Physiological Phenomena↗
PubMedDate not supplied

Three-dimensional reconstructions of extracellular matrix polymers using automated electron tomography.

The extracellular matrix is an intricate network of macromolecules which provides support for cells and a framework for tissues. The detailed structure and organisation of most matrix polymers is poorly understood. These polymers have a complex ultrastructure, and it has proved a major challenge both to define their structural organisation and to relate this to their biological function. However, new approaches using automated electron tomography are beginning to reveal important insights into the molecular assembly and structural organisation of two of the most abundant polymer systems in the extracellular matrix. We have generated three-dimensional reconstructions of collagen fibrils from bovine cornea and fibrillin microfibrils from ciliary zonules. Analysis of these data has provided new insights into the organisation and function of these large macromolecular assemblies.

Animals↗