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At least 667 records · Page 37Linked to original sources
PubMed2000

Abnormal elastic system fibers in fibrotic human liver.

The network of elastic system fibers in human fibrotic liver was investigated by histological methods, immunohistochemical staining, and electron microscopy. Type III collagen was seen not only in regions of portal fibrosis but also in the sinusoidal wall. However, elastic system fibers were not found in the Disse space of the sinusoidal wall. Elastic system fibers including oxytalan, elaunin, and elastic fibers were found successively in the course of elastogenesis. A few normal oxytalan fibers and abnormal oxytalan fibers were observed in the periportal tracts. Few normal elaunin and abnormal elaunin fibers were observed in regions of portal fibrosis but not in the surrounding margin. Elastic fibers, only in scarce amounts, were observed around the portal veins in the case of chronic active hepatitis but not in acute hepatitis. Abnormal oxytalan fibers were seen as a bundle of wavelike microfibrils and had an irregular arrangement. Abnormal elaunin fibers were not associated with bundles of microfibrils. Abnormal elaunin fibers in large amounts were found interspersed with spiraled collagen, which most likely indicates that the oxytalan fibers degenerated in the course of elastogenesis. Thus, in a fibrotic liver it is possible that synthesis of normal elaunin and elastic fibers does not occur or that the quantity of such fibers synthesized may be small because of the effect of the degenerated oxytalan fibers. As a characteristic of liver fibrosis, the composition of abnormal elastic system fibers and spiraled collagen differs from that in other fibrotic organs.

Adult↗
PubMed2002

Recent progress in cellulose biosynthesis.

Cellulose comprises the major polymer of the plant cell wall. It consists of a set of parallel chains composed of glucans and these chains are highly oriented to form a structure known as a microfibril. The orientation of the microfibrils controls the extension of the direction of the plant cell. Extensive studies on the cellulose biosynthesis have been carried out for over three decades, and recently (1996) genes for cellulose biosynthesis in plants ( CesA) were isolated. In the year 2002, a specific primer for cellulose biosynthesis reaction has been discovered and cellulose synthetic activity has been also confirmed by recombinant protein derived from the plant CesA gene. Furthermore, other proteins involved in cellulose biosynthesis besides CesA proteins were also proposed at the same time. One of these proteins, Korrigan cellulase, was suggested to act by removing sitosterol from the primer for biosynthesis reaction of cellulose. A membrane-bound sucrose synthase was also suggested to provide UDP-glucose as a substrate for cellulose biosynthesis. On the basis of these results, a new pathway for cellulose biosynthesis was proposed. Now, the research field of cellulose biosynthesis is facing a major turning point.

Journal Article↗
PubMed2006

A principal role for AtXTH18 in Arabidopsis thaliana root growth: a functional analysis using RNAi plants.

Rearrangement of cellulose microfibrils within cell-wall matrices is considered one of the most critical steps in the regulation of both the orientation and extent of cell expansion in plants. Xyloglucan endotransglucosylase/hydrolases (XTHs) are a family of enzymes that mediate the construction and restructuring of load-bearing cross links among cellulose microfibrils. The Arabidopsis thaliana XTH genes AtXTH17, 18, 19, and 20 are phylogenetically closely related to one another and are preferentially expressed in the roots. However, they exhibit different expression profiles within the root and respond to hormonal signals differently. To investigate their functions in root growth, we examined phenotypes of loss-of-function mutants for these genes using T-DNA insertion lines and RNAi plants. These functional analyses disclosed a principal role for the AtXTH18 gene in primary root elongation. Of the four XTH genes, AtXTH18 exhibits the highest level of mRNA expression. We also determined auxin-signaling pathways for these genes using a mutant with a defect in the AXR2/IAA7 gene and found that the expression of AtXTH19 in the elongation/maturation region of the root is under the control of the AXR2/IAA7 signaling pathway.

Arabidopsis↗
PubMed1975

Structural aspects of human cervical mucus.

Two types of fibrous structures can be demonstrated in midcycle cervical mucus: (1) long, thick fibers that vary in diameter from 0.5 to 5 mum and run parallel to each other, and (2) microfibrils that vary in diameter from 500 to 1,500 A and form bundles or networks. The spaces in such networks usually measure from 800 to 4,0000 A. The fibers are made up of the microfibrils and most likely represent the micelles that give spermatozoa their directional transport through the cervix.

Cervix Mucus↗
PubMed1988

Ultrastructural duality of extracellular fibrillar components of the odontoblast layer in the mouse molar.

The application of detergent solutions to dissociated molar dental papillae of mice permitted precise observation of the extracellular fibrillar material in the odontoblast layer and the predentine. Two types of fibrils were identified: cross-banded fibrils of variable diameter (25-200 nm) and aperiodic microfibrils of regular diameter (12.5 nm) and undetermined length. If the collagenic nature of the cross-banded fibrils is evident, the composition of the aperiodic microfibrils is probably different.

Animals↗
PubMed1984

Aortic endothelial cells in culture secrete glycoproteins reacting with blood platelets.

The culture medium of bovine aortic endothelial cells contains proteins which inhibit the aggregation of platelets induced by aortic microfibrils but not by type III collagen. From this medium, fibronectin, thrombospondin and a glycoprotein with MW of 128 Kd (GP 128), similar to a glycoprotein described in a microfibrillar extract from bovine aorta were separated by affinity and ion exchange chromatography. GP 128 was further purified by molecular sieve chromatography on SW 3000 column. GP 128 inhibited the aggregation of platelets by microfibrils. This suggests a role of GP 128 in the platelet/subendothelium interaction.

Amino Acids↗
PubMed1991

Comparative histogenesis of Bruch's membrane (complexus basalis).

We documented the comparative histogenesis and timing of development of Bruch's membrane (complexus basalis) in five mammalian models with different lengths of gestation. Retinas with attached choroid from the central posterior pole of the eye were obtained from hamster, vole, rabbit, ferret and cat, from mid-gestation onward until the time at which all components of Bruch's membrane could be detected. The sequence of events in the development of Bruch's membrane was similar among species, however the time of appearance of the components varied. At mid-gestation, the basement membrane of the retinal pigment epithelium (RPE) was present to some degree in all species and microfibrils were developing in the connective tissue space external to the RPE basement membrane. The appearance of an initially scant endothelial basement membrane around the choriocapillaries occurred on post-natal (P) day 1 (P1) in hamster, pre-natal (E) day 20 (E20) in vole, E16 in rabbit, P2 in ferret, and E48 in cat. Among the microfibrils within the connective tissue space external to the RPE, electron-dense islands presumed to be elastin were detected on P7 in hamster, P9 in vole, E24 in rabbit, P19 in ferret, and P1 in cat. Relative to birth date and eye opening, the components of Bruch's membrane in the ferret were detected at a later date than that of the other species studied. However, relative to the interval from conception to the appearance of the components of Bruch's membrane, the ferret and cat are similar, paralleling their similar intervals from conception to eye opening.

Animals↗
PubMed1991

Molecular packing in type I collagen fibrils. A model with neighbouring collagen molecules aligned in axial register.

A detailed stereochemical analysis of intermolecular interactions of collagens made with molecular models and summarized experimental data resulted in a new three-dimensional structural model for collagen fibrils. In this model collagen molecules aligned in axial register form a bunch. The bunches are aligned head to tail and penetrate by 300 A into each other, forming microfibrils; these in turn assemble into fibrils. The new model differs from all the others in that its characteristic axial regularity, with a period of 670 A, results from staggering of the adjacent microfibrils formed by unstaggered molecules rather than from the axial staggering of neighbouring collagen molecules.

Animals↗
PubMed1979

Fine structure of the cuticle of the desert scorpion, Hadrurus arizonensis.

The structure of the sclerite and intersegmental cuticle of the opithosoma of the desert scorpion, Hadrurus arizonensis, has been examined by transmission electron microscopy. The sclerite cuticle contains a four-layered epicuticle, a hyaline exocuticle, an inner exocuticle and an endocuticle. The outer part of the hyaline exocuticle and the whole of the inner exocuticle are constructed of helicoidally arranged planes of microfibrils. Within the endocuticle, the overall architecture is not helicoidal as previously assumed, but consists of bundles of microfibrils oriented horizontally and vertically. Microbibrils of the inner exocuticle and the endocutile are seen as simple unstained rods, but those of the hyaline exocuticle are electron dense rods with an unstained central core. The intersegmental cuticle contains a four-layered epicuticle and a procuticle. In detail, its fine structure differs in most respects from that of the sclerite cuticle. Electron microscopy reveals that hyaline exocuticle, previously assumed to be continuous from sclerite to intersegmental membrane, is absent in the latter.

Animals↗
PubMed1991

Elastofibroma: disturbed elastic fibrillogenesis by periosteal-derived cells? An immunoelectron microscopic and in situ hybridization study.

Monospecific antibodies to elastic tissue components have been used for immunoelectron microscopy of two examples of elastofibroma. The elastic-staining fibers typically seen in these lesions exhibited a variety of morphologies with differing ratios of the amorphous and microfibrillar components usually seen in elastic fibers. The amorphous elastic material in these fibers had variable affinity for ionic stains and exhibited several substructural morphologies. Despite this, each form reacted specifically with anti-elastin antibodies. Most of the elastic fibers were associated with relatively large numbers of 12-nm diameter microfibrils that were typical of those associated with normal elastic fibers, and were specifically reactive with monospecific antibodies to microfibril-associated glycoprotein. In situ hybridization studies with a cRNA probe for human elastin confirmed that active elastin biosynthesis was occurring patchily within the lesions. The appearances and staining characteristics of the elastic tissue elements, the morphology of the cells, and the structure of the collagen fibers in these lesions were shown to have many features in common with those of normal periosteum. It is proposed that elastofibromas arise from the periosteum as a result of chronic irritation and that the different elastic fiber morphologies represent disturbances of elastic fibrillogenesis by periosteal-derived cells.

Aged↗
PubMed1994

Modification of crystallinity and crystalline structure of Acetobacter xylinum cellulose in the presence of water-soluble beta-1,4-linked polysaccharides: 13C-NMR evidence.

Cellulose produced by Acetobacter xylinum in medium containing 0.5% xyloglucan or glucomannan showed altered crystallinities and shifted I alpha/I beta ratios when analysed by solid-state 13C-NMR. By estimating the spectra of cellulose components in each composite, a decreased I alpha content was shown to be countered by increased I beta content in cellulose aggregated in the presence of xyloglucan, causing minimal loss of crystallinity. However, the I alpha decrease was linked primarily to increased disordered content in cellulose produced in medium containing glucomannan. These results are considered in the light of two models for the morphological disposition of the I alpha phase: (i) a series model, proposed on the basis of electron diffraction measurements for an algal cellulose, in which regions of I alpha and I beta alternate along the length of a microfibril, and (ii) a superlattice model, in which the I alpha and I beta domains co-exist throughout the cross-section of each microfibril and form as a result of hierarchical aggregation. The latter model offers clearer insight into the role of the polysaccharides in inhibiting the formation of I alpha crystalline regions. In this superlattice model, polysaccharides adsorbed on surfaces of the most elementary aggregates are displaced to varying degrees during subsequent aggregation, with the presence of these polysaccharides altering the extent of I alpha production at interfaces.

Cellulose↗
PubMed1996

Single crystals of V amylose complexed with glycerol.

Lamellar single crystals of amylose V glycerol were grown at 100 degrees C by evaporating water from solutions of amylose in aqueous glycerol. The crystals which were square, with lateral dimensions of several micrometers, gave sharp electron diffraction patterns presenting an orthorhombic symmetry with a probable space group P2(1)2(1)2(1) and unit cell parameters: a = 1.93 +/- 0.01 nm, b = 1.86 +/- 0.01 nm and c (fiber axis) = 0.83 +/- 0.03 nm. The amylose Vglycerol crystal structure which is isomorphous to that of VDMSO consists of an antiparallel pair of left-handed six-fold amylose helices centered on the two-fold screw axes of the cell and probably separated by glycerol molecules. This packing mode is confirmed by de-solvation experiments where the Vglycerol amylose crystals, annealed in ethanol, could be converted into VH amylose without losing their external appearance. The Vglycerol amylose crystals could be seeded by cellulose microfibrils to yield a shish-kebab structure where the amylose crystalline lamellae grew perpendicular to the microfibril directions.

Amylases↗
PubMed1995

Fibrillin immunofluorescence in pseudoxanthoma elasticum.

BACKGROUND: Pseudoxanthoma elasticum (PXE) is a rare heritable connective tissue disorder manifested by skin, ocular, and cardiovascular anomalies. The basic defect is unknown; however, the microscopic findings are indicative of defects in elastic fibers. Among the components of the elastic fibers are elastin and elastin-associated microfibrils. OBJECTIVE: We assessed the fidelity of this fibrillar system in PXE with the use of antibodies to fibrillin, a major component of elastin-associated microfibrils. METHODS: Using a well-established immunofluorescence assay, we studied fibrillin deposition in dermal fibroblast cultures from 16 patients with PXE. RESULTS: Six of the 16 patients (37%) showed some abnormality of fibrillin deposition in fibroblasts derived from lesional skin. Fibroblasts from nonlesional skin displayed normal fibrillin immunofluorescence. The only sibship studied, however, was discordant for fibrillin immunostaining. CONCLUSION: Unlike the findings in Marfan syndrome, these data are not suggestive of causal fibrillin defects in PXE.

Actin Cytoskeleton↗
PubMed1983

Macromolecular basis of globular protein exclusion and of swelling pressure in loose connective tissue (umbilical cord).

The macromolecular basis of tissue swelling pressure and of the ability of tissue to exclude globular proteins, according to size, have been investigated using human umbilical cord. Exclusion data of tissue, and tissue from which the polysaccharides had been removed by hyaluronidase were compared. Exclusion of globular proteins by the polysaccharides, obtained by difference from the two sets of data, was similar to that reported for isolated polysaccharides in solution. It can be described by a sphere/cylinder geometric exclusion model. The exclusion behavior of the polysaccharide-free tissue was accounted for in terms of the component collagen fibrils, glycoprotein microfibrils and cells. Average pore diameters of 18 and 110 nm, respectively, for the intact tissue and for the polysaccharide-free tissue were estimated. Swelling pressure measurements were performed on intact, on hyaluronidase-treated and on hyaluronidase and then Pronase-treated tissues to obtain the contributions of the polysaccharides, of collagen and of microfibrils. Close to the in vivo volume of tissue, the swelling pressure is given almost entirely by the polysaccharides and is consistent with the osmotic pressure expected from the relative amounts of hyaluronic acid and proteoglycan present and their distribution in the extrafibrillar, extracellular space. Upon swelling or deswelling a small net contribution of the fibrillar system to the swelling pressure is evident.

Collagen↗
PubMed1983

Tissue structure and macromolecular diffusion in umbilical cord. Immobilization of endogenous hyaluronic acid.

Diffusion of endogenous hyaluronic acid and 125I-labelled albumin, monitored by desorption from umbilical cord (Wharton's jelly) slices, was studied in relation to tissue structure. Diffusion of hyaluronic acid was Fickian and some two orders of magnitude slower than that in free solution. After treatment of tissue with trypsin which removes proteoglycan(s) and degrades glycoprotein microfibrils, hyaluronic acid mobility through the collagen fibril network that remains is increased by an order of magnitude. These findings indicate that the mobility of hyaluronic acid in tissue is reduced both by the collagen network and by the presence of proteoglycan(s) and/or microfibrils. Estimates of the reduction in mobility due to physical entanglements with the fibrillar networks show that these play a major role. The mobility of hyaluronic acid found for intact tissue is sufficient for it to permeate the extracellular space within its metabolic turnover time. Labelled albumin diffusion is intact tissue, on the other hand, is reduced by only some 30% relative to free solution. This is consistent with the approximate 10% reduction found for the polysaccharide-free tissue (given by the excluded volume fraction) and the approximate 20% reduction expected for the polysaccharides in the interstitial fluid. Similar effects appear to be involved in the mobility of endogenous diffusible proteins in tissue.

Connective Tissue↗
PubMed1991

Localization of the fibrillin (FBN) gene to chromosome 15, band q21.1.

Fibrillin (FBN), a large extracellular matrix glycoprotein, is an important component of structures called microfibrils. Because fibrillin microfibrils appear to be abnormal in patients with the Marfan syndrome, fibrillin is a candidate for the gene defect in the Marfan syndrome. Derived clones from fibrillin cDNA were used as probes in isotopic and nonisotopic in situ hybridization studies to map the chromosomal location of the fibrillin gene. Fluorescent signals were found on chromosome 15 band q21.1; an excess of silver grains was noted over a similar region of chromosome 15 following in situ hybridization with a tritium-labeled probe. These results are consistent with linkage studies that localize the Marfan gene to chromosome 15.

Amino Acid Sequence↗
PubMedDate not supplied

Plasma membrane "rosettes" in carrot and sycamore suspension culture cells.

Suspension culture cells of carrot, Daucus carota L., and sycamore, Acer pseudoplatanus L., were freeze-fractured after ultrarapid freezing without fixation or cryoprotection in a propane-jet freezer. Infrequently, rosettes (ca. 24 nm diameter) of six (occasionally five) subunits (ca. 8 nm diameter) were observed in P-face views of the plasma membrane of both taxa. When present, rosette density was approximately 1/micron 2. Generally, rosettes were less frequently seen on plasma membranes exhibiting numerous vesicle fusion figures. Due to the high quality of the freezing, cellulose microfibril impressions were rarely seen on either PF or EF views of the plasma membrane, thus precluding correlations between microfibrils on the one hand and rosettes (and terminal globules) on the other. The presence of rosettes in suspension culture cells of these two species supports the putative role of rosettes in cellulose biosynthesis in higher plants.

Cell Membrane↗
PubMedDate not supplied

Extracellular matrix-sarcolemmal surface interconnections: a quick-freeze deep-etch study.

Using ultrarapid freezing and deep-etch fracture techniques, the extracellular matrix in unfixed rabbit papillary muscles is seen to consist of an extensive network of collagen, microfibrils, and microthreads. The microfibril-microthread lattice appears to weave around collagen fibers connecting them to each other and to the external lamina of the sarcolemma. The external lamina appears to insert into the bilayer via trabeculae. With 10 min exposure to zero-Ca solution, the external lamina of the myocytes detaches from the membrane surface but is held from complete removal by some remaining trabecular attachments. This detachment of external lamina affords a view for the first time of the surface of the myocardial sarcolemma. Particles of varying sizes (6-13 nm) may represent the external portions of some integral proteins or protein molecules associated with the membrane surface. They can also represent attachment sites of the external lamina. The serious risks for the fibrous network structure representing an artifact caused by precipitation of matrix proteins during deep etching are discussed.

Animals↗