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PubMed1979

Matrical ordering in the morphogenesis of tunica media.

The cells which will form the smooth muscle tunica media are derived embryologically from the cardiac mesenchyme referred to as endocardial cushion tissue. These progenitor smooth muscle cells, however, are derived primarily from aortic arch mesenchyme as opposed to the endocardium in the prevalvular areas. The matrical microenvironments of these cells begin to change at approximately 5 days of development when the progenitor smooth muscle cells acquire a more fibrillar matrix. The prospective adventitia and valvular areas still maintain an environment rich in hyaluronate and proteoglycans. By Day 6, the 110Ao microfibril, characteristic of smooth muscle cells, appears in the matrix well in advance of the amorphous elastin component seen at Days 8 and 9. The orientation of the collagenous microfibrils and elastic microfibrils is non-random with respect to the layers of cells, and this precludes a simple substrate alignment model in establishing the characteristic laminarity of this tissue.

Animals↗
PubMed1984

Platelet adhesion.

Platelets do not adhere to surfaces to which flowing blood is normally exposed in vivo. When the lining of a blood vessel is altered or damaged, however, platelets do adhere to the injured site. Platelet adhesion is one of the first events in the formation of hemostatic plugs and thrombi, and plays a part in the development of atherosclerotic lesions. Other surfaces to which platelets adhere include particulate matter in the blood stream, bacteria and other microorganisms, the artificial surfaces of prosthetic devices, and some altered cells in the blood, particularly macrophages. The majority of investigators have studied the interaction of platelets with the subendothelium of normal vessels of young animals, or with isolated vessel wall constituents such as collagen. There are very few studies of platelet adhesion to repeatedly damaged or diseased blood vessels, although it is generally assumed that platelets interact with the connective tissue, fibrin, and cholesterol crystals in atherosclerotic lesions. Underlying the endothelium of blood vessel is the basement membrane, which has been shown to contain type IV collagen, elastin with its associated microfibrils, von Willebrand Factor, fibronectin, thrombospondin, laminin, and heparan sulfate. If only the endothelium is removed, the main structure exposed is the basement membrane with its associated proteins, but deeper injuries expose fibrillar type III collagen and microfibrils. In most studies in which large arteries have been injured by passage of a balloon catheter, basement membrane, type III collagen and the microfibrils around elastin have been exposed. Platelets do not react strongly with basement membrane and the type IV collagen in it is relatively inert. In contrast, platelets adhere firmly to type III (and type I) collagen and spread on it. Although in vitro studies have shown that platelets can interact with collagen in artificial media without plasma proteins, investigations of platelet adhesion at high shear rates indicate that von Willebrand Factor is necessary for firm platelet adhesion under these conditions. Fibronectin and thrombospondin may also have a role in platelet adhesion. However, platelets do not bind von Willebrand Factor or fibronectin until the platelets have been stimulated to release their granule contents, so these binding sites probably do not become available until the platelets have interacted with collagen or another release-inducing agent such as thrombin.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Elastic fibres of the human ductus deferens.

The distribution of elastic fibres in the human ductus deferens from birth to senility was studied by light and electron microscopy. Elastic fibres are lacking in the ductus deferens in infants and children. In the adult ductus deferens, they form two layers in the lamina propria: (1) an inner layer of circumferentially oriented elastic fibres, and (2) an outer meshwork of elastic fibres. Elastic fibres are also present in the narrow intercellular spaces between the smooth muscle cells of the muscular coat, mainly in the inner muscular layer. A layer of elastic fibres surrounds the muscular coat. The ductus deferens of ageing subjects shows fragmentation and disorganisation of the elastic fibre layers of the lamina propria. Elastic fibres in the muscular coat are more abundant than in younger adults, forming larger bundles. Electron microscopy demonstrated the presence of immature elastic fibres at puberty as collections of microfibrils, some of them containing loci of amorphous substance (elastin). In the adult ductus most elastic fibres have a mature appearance. The amount of amorphous substance has increased and the number of microfibrils has decreased. Electron-dense inclusions are present within the amorphous substance. With advancing age the amorphous substance forms large, structureless masses showing abundant electron-dense inclusions and areas of rarefaction. A thin layer of microfibrils is present only at the periphery of the elastic fibres. Whether or not androgenic hormones are in any way involved in the formation of elastic fibres in the ductus deferens and testis is something which requires further study.

Adolescent↗
PubMed1982

Cyclophosphamide-induced glomerular injury in newborn mice.

The glomeruli of newborn mice from mothers given a single intraperitoneal injection of cyclophosphamide (50 or 110 mg. per kg.) showed varying degrees of mesangiolysis and subsequent diffuse mesangial and segmental sclerosis. The sclerosis was preceded by the formation of a considerable amount of mesangial microfibrils. This change was accompanied by a marked subendothelial widening of the glomerular capillary and an increase in the number of microfibrils in this space. These results support our previous notion that glomerular microfibrils play an important role in the process of glomerular repair. The results also show that cyclophosphamide can induce injury in the developing glomeruli of newborn mice.

Animals↗
PubMed1981

An electron microscopic study of the development of the ependyma of the central canal of the mouse spinal cord.

The central canal of the adult mouse spinal cord is lined for most of its extent by ependymal cells which are rich in microfilaments and whose apical surface is covered with matted, broad microvilli. The canal itself is filled with amorphous material containing glycogen granules. Two forms of this material are present, a dark form rich in glycogen, and a light form containing a few glycogen granules. Each type appears to be surrounded by a membrane. The upper cervical region, however, has a large empty lumen and the ependymal cells in this region have only scattered, narrow microvilli. During development, the floor and roof plates are at first composed largely of ependymoglial cells, unlike the lateral walls, where undifferentiated neuroepithelial cells predominate. By E15 few undifferentiated neuroepithelial cells remain. At E17 the morphology of the ependymal cells changes. Their apical surface becomes covered with matted, club-shaped microvilli and the central canal is filled with glycogen-containing material. By P5 microfibrils are present in large bundles in the ependymal cells. The piaglial surface opposite the roof and floor plates has finger-like projections unique to these regions and these persist at the surface of the dorsal median septum until myelination is well advanced after P5. The fibres forming the dorsal median septum are at first pale processes containing scattered glycogen granules and microtubules. By P5 microfibrils are present and at P150 the processes are packed with masses of microfibrils.

Animals↗
PubMed1981

[Contribution to hair medulla study (author's transl)].

In this study, the authors aim to bring to light the anatomical characteristics of the medullary cells of hairs and to examine the evolution of these characteristics according to the mammals genuses. Previous studies of the morphogenesis of the medullary cells have shown that the cytoplasm of the medulla would turn amorphous while microfibrils are formed in the cytoplasm of the inner root sheath. The medulla and the inner root sheath are sulfur-poor but are rich in citrulline and the proteins are bound by epsilon(gammaglutamyl)lysine dipeptides. Our observations, both anatomical and ultrastructural, with the SEM and the TEM, have showed that the medullary cell is also evolved and complex that the others hairs cells. Furthermore, we have observed that the medullary cell content of some mammal's hairs is amorphous, as was shoôn in previous works; but it seems to evolve towards a biphasic phase (or granular) in superior mammals while the medullary cells of the hairs of human and closely related anthropoids contain macrofibrils and microfibrils. Medullary microfibrils are similar to those of the inner root sheath of the hair and therefore, we now understand why citrulline and epsilon(gammaglutamyl)lysine bonds are also found in the medullary cells.

Animals↗
PubMed1993

Structure, chromosomal localization, and expression pattern of the murine Magp gene.

The microfibril-associated glycoprotein (MAGP) was recently established as a discrete constituent of 10-nm microfibrils. We have characterized the primary structure of the mouse transcript, the structure and chromosomal localization of the murine gene, and the developmental pattern of gene expression. The transcript consists of 1,037 base pairs as determined by cDNA cloning, Northern blot analysis, S1 nuclease mapping, and primer extension mapping. Using a cDNA fragment as a probe, we isolated a single genomic clone that contained the entire mouse gene. Analysis of this clone indicated that Magp is fragmented into 9 exons, with the initiator Met codon located in exon 2. As determined by analysis of somatic cell hybrid lines and by fluorescence in situ hybridization, the mouse gene was mapped to chromosome 4 at a location corresponding to region D3-E1. Genomic sequence immediately upstream of the transcription start site was found to be GC-rich but lacked TATA or CCAAT boxes as well as other cis-acting motifs known to regulate transcription. Promoters of this type are usually found in genes that exhibit broad temporal and spatial patterns of expression. Consistent with this idea, the Magp transcript appeared to be the widespread product of mesenchymal/connective tissue cells throughout mouse development. This study presents the first comprehensive evaluation of microfibril gene expression during mammalian development.

Amino Acid Sequence↗
PubMed1993

Co-localization of von Willebrand factor and type VI collagen in human vascular subendothelium.

The binding of von Willebrand factor (vWF) to subendothelium constitutes an important initial step in the process of platelet adhesion to exposed subendothelium following blood vessel injury. We previously demonstrated that vWF is present in human vascular subendothelium and recently found that a 150 kd vWF-binding protein, which we extracted from subendothelium, is type VI collagen. Although we have established that vWF and type VI collagen bind in vitro, it is not known whether these two proteins are associated in the vascular subendothelium in situ. We, therefore, 1) investigated the morphological effects of our biochemical extraction procedure on human umbilical veins by scanning and transmission electron microscopy, 2) analyzed the subendothelial extract by immunofluorescence for the presence of vWF and collagens and by electron microscopy for morphological characteristics, and 3) localized vWF and type VI collagen in subendothelium by immunofluorescence and by single- and double-label immunoelectron microscopic studies with protein A-conjugated gold particles. We found that the surface exposed following de-endothelialization is composed of microfibrils and contains very little fibrillar collagen. The subendothelium is stripped after sodium dodecyl sulfate-urea extraction, and the extract itself contains immunoreactive vWF and type VI collagen but no immunoreactive type I or III fibrillar collagens. Immunofluorescence and immunoelectron microscopic studies showed that vWF and type VI collagen are both present in subendothelium, where both co-localized to microfibrils. In conclusion, vWF that binds to type VI collagen in vitro, also co-localizes with type VI collagen in subendothelium, where both are associated with microfibrils. Type VI collagen, therefore appears to serve as a biologically significant binding site for vWF in vivo and may thereby play a role in mediating platelet adhesion to exposed subendothelium following vascular injury.

Collagen↗
PubMed1993

Confocal laser scanning microscopic and immunoelectron microscopic studies of the anatomical distribution of fibrillar IgA deposits in dermatitis herpetiformis.

BACKGROUND AND DESIGN: The fibrillar immunofluorescent pattern of IgA deposition in dermatitis herpetiformis is considered by most authorities to be a variant of the granular IgA pattern. It has been hypothesized that the fibrillar vs the granular pattern is related to longitudinal vs transverse sectioning of affected dermal microfibril bundles. However, direct evidence for this possibility has yet to be presented. Confocal laser scanning microscopy and immunoelectron microscopy were performed to determine the anatomical distribution of fibrillar IgA deposits, using skin specimens from a patient with typical fibrillar IgA deposition. OBSERVATIONS: Confocal laser scanning microscopy showed numerous fibrils stained with anti-IgA extending from the dermoepidermal junction to a depth of 50 to 110 microns in the dermis. They crossed each other at various angles to form a three-dimensional network. Immunoelectron microscopy demonstrated a diffuse dispersion of immune deposits on the surface of microfibrils of dermal microfibril bundles, with sporadic distribution of small aggregates, 0.1 to 0.3 micron in diameter. CONCLUSIONS: To our knowledge, this is the first article to present evidence for the actual distribution of fibrillar IgA. Insofar as the present case is concerned, the distribution of fibrillar IgA is greatly at variance with that indicated in previous reports on granular IgA. However, studies on more cases should be conducted to determine whether this is a distinctive feature of the fibrillar type of IgA deposition.

Dermatitis Herpetiformis↗
PubMed1996

A high resolution ultrastructural study of experimental murine AA amyloid.

An essential and distinguishing feature of all amyloids is the presence of fibrillar structures of approximately 10-nm width. The precise nature of the fibril is not yet clearly understood, particularly in situ, and the ultrastructure of isolated fibrils differs significantly from that of fibrils observed in situ. The fibrils are generally believed to be composed of a protein specific to each type of amyloid, but increasing evidence suggests additional associations with other components such as heparan sulfate proteoglycan (HSPG) and amyloid P component (AP). Experimental AA amyloidosis was induced in mice by amyloid enhancing factor and an inflammatory stimulus (subcutaneous AgNO3); fibrils were thereafter examined in detail. Particular attention was paid to ultrastructural characteristics known to represent particular molecular components of basement membranes such as HSPG and AP. Additionally, rabbit anti-mouse AA antisera was used with 5-nm and 1-nm gold particles to establish the location of the AA protein in-situ. Amyloid fibrils could be identified in their mature form as well as at apparent intermediate stages of formation. The fibril contained an apparent core which is composed of an assembly of 3.5-nm wide pentosomal particles having the characteristics of AP. Wound around the AP assembly in a helical fashion is a "double tracked" ribbon-like entity, 3 nm wide, having the morphologic characteristics of chondroitin sulfate proteoglycan (CSPG). Covering the surface of this structure is a second ribbon-like double track structure, but this one is wider (4.6 nm vs 3.0 nm) than the CSPG. These have the ultrastructural characteristics of HSPG. Routine fixation and tissue preparation techniques that usually remove HSPG from microfibrils did not do so with amyloid fibrils, suggesting an alteration in affinity between these components. The AA protein could be identified as a 1 - to 2-nm filament network on the most exterior surface of the fibril. The ultrastructure of AA amyloid fibrils in situ resembles that of connective tissue microfibrils, and, in addition to AA protein, is likely composed of HSPG, CSPG, and AP. Amyloid fibrils can be distinguished from microfibrils by the apparently stronger binding of HSPG to the surface of the amyloid fibril and the presence of the AA filaments. A model of the in situ organization of AA amyloid fibrils is proposed.

Amyloidosis↗
PubMed1996

Cell-type specific recognition of RGD- and non-RGD-containing cell binding domains in fibrillin-1.

The fibrillins are large glycoprotein components of 10-nm microfibrils found in the extracellular matrix of most tissues. Microfibrils play a role in elastic fiber assembly and serve to link cells to elastic fibers in the extracellular matrix. To determine whether fibrillin-1 specifically interacts with receptors on cells from fibrillin-rich tissues, we evaluated whether two cell types that produce different types of fibrillin can adhere to purified fibrillin-1 in cell adhesion assays. Our results indicate that both cell types attach and spread on fibrillin-1 and that the RGD sequence in the fourth 8-cysteine motif mediates this interaction. Fibroblast attachment to fibrillin-1 was sensitive to inhibition by antibodies to the alphavbeta3 receptor and by peptides encoding the RGD sequence in fibrillin-1 and the second RGD sequence in fibrillin-2. In contrast, adhesion of auricular chondroblasts to fibrillin-1 was only partially inhibited by these reagents, suggesting that some cell types recognize a second, non-RGD binding site within the fibrillin molecule. These findings confirm and extend ultrastructural studies that suggest a direct interaction between microfibrils and the cell surface and provide a functional explanation for how this association occurs.

Amino Acid Sequence↗
PubMed1997

The significance of subendothelial von Willebrand factor.

von Willebrand factor (vWf) serves to bridge between receptors on the platelet cytoplasmic membrane and the extracellular matrix. In addition to circulating in plasma, vWf is deposited into the extracellular matrix of the subendothelium where it is associated with type VI collagen microfibrils, but not with the elastin-associated microfibrils which are present in the deepest portion of the subendothelium at the zone of the internal elastic lamina. The reaction of platelets to type VI collagen in flow systems is qualitatively different from the shear rate dependent adhesion and aggregation response which is observed with fibrillar type I collagen, exhibiting a response only at low shear rates. The adhesion response to type VI collagen is dependent upon vWf, GP Ib and the GP IIb-IIIa complex. Platelets exposed to purified fibrillin-containing elastin-associated microfibrils adhere and aggregate at low shear rates; this response appears to involve GP IIb-IIIa but not GP Ib. The data are consistent with the hypothesis that type VI collagen is a physiologically relevant binding site for vWf in subendothelium.

Animals↗
PubMed1997

An immunological correlation between the anchoring filaments of initial lymph vessels and the neighboring elastic fibers: a unified morphofunctional concept.

Little has been published on the histochemical and cytochemical properties of anchoring filaments of initial lymph vessels. Previous research suggests that the microfibrils of the anchoring filaments have ultrastructural, histochemical and cytochemical characteristics similar to those of the microfibrils associated with elastic fibers. With the aim of further investigating the histological identity of anchoring filaments, we performed an immunohistochemical study with human skin lymphatics, using antibody HB8, specific for elastic fiber microfibrils. The findings suggested strong molecular similarities between elastic fibers and the fibrils of anchoring filaments of the initial lymph vessels. A comparison of these fibrils showed both constitutional homogeneity and structural continuity from the abluminal surface of the initial lymph vessel to the perivascular elastic fibers and to the adjacent elastic network of connective tissue. In conjunction with previous findings, we propose a unified hypothesis that the elastic fiber system composed of anchoring filaments, perilymphatic sheath and adjacent connective tissue acts by alternating stretching and relaxation to propel lymph towards lymph collectors and draining lymph nodes.

Actin Cytoskeleton↗
PubMed2001

Structural variation of tracheids in Norway spruce (Picea abies [L.] Karst.).

The orientation of cellulose microfibrils in the cell wall and the shape and the dimensions of the cells of earlywood of four Norway spruce (Picea abies [L.] Karst.) stems grown in Finland were studied by X-ray diffraction and optical microscopy. The average microfibril angle (MFA) decreased and the diameter of the cell increased rapidly up to rings 5-10 from the pith and remained at the same level after that. The average MFA close to the pith was over 20 degrees and decreased to about 8 degrees after ring 10 from the pith. The average diameter of the cells was 35 microm in the outer rings. The shape of the cross section of the lumen changed from circular to rectangular from the pith to the bark. The tracheid length increased also as a function of the distance from the pith. The thickness of the cell wall varied between 2.8 and 3.5 microm. Automatic cell lumen and cell wall recognition procedures were developed for the analysis of the images of the cross sections of the cells.

Cell Wall↗
PubMed1998

Expansins.

Biochemical dissection of the "acid-growth" process of plant cell walls led to the isolation of a new class of wall loosening proteins, called expansins. These proteins affect the rheology of growing walls by permitting the microfibril matrix network to slide, thereby enabling the wall to expand. Molecular sequence analysis suggests that expansins might have a cryptic glycosyl transferase activity, but biochemical results suggest that expansins disrupt noncovalent bonding between microfibrils and the matrix. Recent discoveries of a new expansin family and gene expression in fruit meristems and cotton fibers have enlarged our view of the developmental functions of this group of wall loosening proteins.

Cell Fractionation↗
PubMed2001

Cellulose in the house of the appendicularian Oikopleura rufescens.

By electron diffraction analysis, highly crystalline cellulose I beta was found in the house (a special structure in which the tunicate lives) of the appendicularian Oikopleura rufescens. Cellulose microfibrils 20 nm in width were observed in a random array or highly organized with rectangular spacing of 2 to 10 microns in the house. The bundled cellulose microfibrils formed in the inlet filters, which are highly ordered meshwork structures. This paper provides the first account of the existence of cellulose in the house of an appendicularian. Our findings showed that the house and tunic are homologous tissues among the tunicates, and that the common ancestor of the tunicates (ascidians, thaliaceans, and appendicularians) already possessed cellulose-biosynthetic ability.

Animals↗
PubMed2003

Mechanical, chemical and X-ray analysis of wood in the two tropical lianas Bauhinia guianensis and Condylocarpon guianense: variations during ontogeny.

Mechanical and chemical properties as well as microfibril angles of wood tissues from different ontogenetic stages are determined for the neotropical lianas Bauhinia guianensis and Condylocarpon guianense. The mechanical properties include the elastic moduli under bending and under dynamic torsion. The chemical analyses cover (i) the content of cellulose, lignin and hemicelluloses fractions, (ii) the monomeric composition of the uncondensed lignin, and (iii) the composition of the hemicelluloses with respect to neutral monosaccharides. By comparing the wood properties of these lianas with the corresponding properties of wood from self-supporting deciduous trees, common characteristics and differences are revealed. Additionally, the changes in the lignin and polysaccharides fractions as well as the variations in microfibril orientation that occur during ontogeny of the two liana species are discussed with regard to their implications for the mechanical properties of wood.

Apocynaceae↗
PubMed2005

Secondary cell-wall assembly in flax phloem fibres: role of galactans.

Non-lignified fibre cells (named gelatinous fibres) are present in tension wood and the stems of fibre crops (such as flax and hemp). These cells develop a very thick S2 layer within the secondary cell wall, which is characterised by (1) cellulose microfibrils largely parallel to the longitudinal axis of the cell, and (2) a high proportion of galactose-containing polymers among the non-cellulosic polysaccharides. In this review, we focus on the role of these polymers in the assembly of gelatinous fibres of flax. At the different stages of fibre development, we analyse in detail data based on sugar composition, linkages of pectic polymers, and immunolocalisation of the beta-(1-->4)-galactans. These data indicate that high molecular-mass gelatinous galactans accumulate in specialised Golgi-derived vesicles during fibre cell-wall thickening. They consist of RG-I-like polymers with side chains of beta-(1-->4)-linked galactose. Most of them are short, but there are also long chains containing up to 28 galactosyl residues. At fibre maturity, two types of cross-linked galactans are identified, a C-L structure that resembles the part of soluble galactan with long side chains and a C-S structure with short chains. Different possibilities for soluble galactan to give rise to C-L and C-S are analysed. In addition, we discuss the prospect for the soluble galactan in preventing the newly formed cellulose chains from completing immediate crystallisation. This leads to a hypothesis that firstly the secretion of soluble galactans plays a role in the axial orientation of cellulose microfibrils, and secondly the remodelling and cross-linking of pectic galactans are linked to the dehydration and the assembly of S2 layer.

Cell Wall↗