Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Microfibrils”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed1990

A miniature voltmeter for monitoring small amplitude electrical activity in the hypothermic arrested myocardium.

A measurement system which is capable of detecting microfibrillation in the hypothermic, arrested heart has been developed. It is shown that this system can reliably measure microfibrillation signals as low as 10 microV in amplitude. Using this system, it has been shown that even after the heart has been rendered visibly arrested using cold potassium, it may still be producing a low level of electrical activity. It has also been shown that the presence of this microfibrillation during the period of the cold potassium administration and visible arrest, is very highly correlated with the decrease in high energy phosphates (ATP), mitochondrial injury, and a decreased cardiac function post-operatively. Using the information obtained from this first measurement system, a miniature, battery powered voltmeter has been designed and fabricated. This voltmeter has been tested using the initial measurement system as reference and produces the same information concerning the small signal electrical activity (i.e.: same waveform and RMS value). Because this voltmeter is battery powered and is, therefore, completely isolated from all electrical equipment in the operating theatre, it can be used to monitor the presence, or absence, of microfibrillation in the human heart. Of greatest importance, however, is the fact that the voltmeter can serve as a monitoring device which will indicate when the potassium should be administered in order to render the heart both mechanically and electrically arrested.

Animals↗
PubMed1988

[Amyloid P components in normal human skin and skin with lesions].

Amyloid P component (AP) is a glycoprotein which is found in tissue deposits of all types of amyloid and is identical to and derived from serum amyloid P component (SAP). SAP binds in a calcium-dependent fashion to various ligands, such as agarose, desoxyribonucleic acid, fibronectin, C4-binding protein, glycosaminoglycans and isolated amyloid fibrils. Tissue AP (TAP) is also a constituent of the normal human renal glomerular basement membrane and is, in adult humans, invariably associated with elastic fiber microfibrils in connective tissue throughout the body, including that of blood vessels. In normal human skin anti-AP antibody binding was localized to the microfibrils of oxytalan fibers in the papillary dermis and to the peripheral microfibrillar mantle of elaunin and mature elastic fibers in the reticular dermis. Since SAP binds to fibronectin and glycosaminoglycans, which in turn bind to collagen fibers, TAP on elastic fiber microfibrils may play an important role in the maintenance of the normal dermal architecture and in dermo-epidermal adhesion. Under pathological conditions, AP is found in all forms of cutaneous amyloidosis, including primary localized cutaneous amyloid (PLCA); it is also detectable on keratin bodies, which represent precursor structures for PLCA. The association of AP with elastic fiber microfibrils and amyloid fibrils and their close anatomical relationship in vivo may reflect the significance of AP in the deposition of cutaneous amyloid.

Amyloidosis↗
PubMed1985

Immunolocalization of type IV collagen and laminin in nonbasement membrane structures of murine corneal stroma. A light and electron microscopic study.

The extracellular matrix of adult vertebrate corneal stroma is composed primarily of the interstitial collagen type I and smaller amounts of types III and V collagen. These collagens are organized into overlapping lamellae of striated filaments. In addition to these lamellar structures, the corneal stroma also contains 100- to 250-nm bundles of nonstriated 8- to 11-nm microfibrils. By immunofluorescent localization and electron microscopic immunolocalization, these microfibril bundles in the mouse are associated with type III collagen, type IV collagen, and laminin. By immunologic and histochemical criteria, these bundles do not contain either type I collagen, type V collagen, elastin, or oxytalan microfibrils. The cellular source, composition, and possible functions of these microfibril bundles are discussed.

Animals↗
PubMed1983

The molecular interaction between platelet and vascular wall.

Two different subendothelial macromolecules have been identified as being thrombogenic: collagen and the microfibrils associated with elastin. The interaction between platelets and collagen involves the binding of platelet membrane receptors by numerous sites repeatedly staggered along a collagen fiber: this explains why the preservation of ordered structures (quaternary and tertiary structures) is so important in the reactivity of collagen towards platelets. In the case of Type III collagen, a nonapeptide has been identified as possibly being part of these repetitive sites. The microfibrils have not yet been characterized, although the biochemical data presently available show that they are acidic glycoproteins resistant to collagenase. Microfibrils extracted from human placenta or bovine aorta induce the aggregation of platelets in a reaction which involves platelet glycoprotein Ib and FVIII/vWF. A general model proposed for explaining platelet adhesion to subendothelium suggests that two different mechanisms should be envisaged depending on the thrombogenic macromolecules (collagen, microfibrils) involved.

Binding Sites↗
PubMed2001

Role of Ca(2+) for the mechanical properties of fibrillin.

Fibrillin-rich microfibrils are important structural elements widespread throughout connective tissues. Genetic defects identified in the Ca(2+) binding sites of fibrillin have severe effects and in addition Ca(2+) has a marked effect on the microfibrillar structure. We have studied the role of Ca(2+) on the mechanical behavior of fibrillin-rich microfibrils using the micro-needle technique. We find that Ca(2+)-depletion results in a 50% decrease in rest length and reduces the stiffness of fibrillin-rich microfibrils. At high strain, irreversible damage occurs. This behavior is consistent with Ca(2+) stabilization of interactions between consecutive EGF-like domains and breakdown in the quaternary structure upon over-extension.

Animals↗
PubMed2002

Mechanical implications of the domain structure of fiber-forming collagens: comparison of the molecular and fibrillar flexibilities of the alpha1-chains found in types I-III collagen.

Fibrillar collagens store, transmit and dissipate elastic energy during tensile deformation. Results of previous studies suggest that the collagen molecule is made up of alternating rigid and flexible domains, and extension of the flexible domains is associated with elastic energy storage. In this study, we model the flexibility of the alpha1-chains found in types I-III collagen molecules and microfibrils in order to understand the molecular basis of elastic energy storage in collagen fibers by analysing the areas under conformational plots for dipeptide sequences. Results of stereochemical modeling suggest that the collagen triple helix is made up of rigid and flexible domains that alternate with periods that are multiples of three amino acid residues. The relative flexibility of dipeptide sequences found in the flexible regions is about a factor of five higher than that found for the flexibility of the rigid regions, and the flexibility of types II and III collagen molecules appears to be higher than that found for the type I collagen molecule. The different collagen alpha1-chains were compared by correlating the flexibilities. The results suggest that the flexibilities of the alpha1-chains of types I and III collagen are more closely related than the flexibilities of the alpha1-chains in types I and II and II and III collagen. The flexible domains found in the alpha1-chains of types I-III collagen were found to be conserved in the microfibril and had periods of about 15 amino acid residues and multiples thereof. The flexibility profiles of types I and II collagen microfibrils were found to be more highly correlated than those for types I and III and II and III. These results suggest that the domain structure of the alpha1-chains found in types I-III collagen is an efficient means for storage of elastic energy during stretching while preserving the triple helical structure of the overall molecule. It is proposed that all collagens that form fibers are designed to act as storage elements for elastic energy. The function of fibers rich in type I collagen is to store and then transmit this energy while fibers rich in types II and III collagen may store and then reflect elastic energy for dissipation through viscous fibrillar slippage. Impaired elastic energy storage by extracellular matrices may lead to cellular damage and changes in signaling by mechanochemical transduction at the extracellular matrix-cell interface.

Animals↗
PubMed2002

Diurnal difference in the amount of immunogold-labeled glucomannans detected with field emission scanning electron microscopy at the innermost surface of developing secondary walls of differentiating conifer tracheids.

The differences between cell wall formation at night, when the tangential strain used as an index of the volumetric changes in differentiating cells is high, and in the day, when the tangential strain is low, were investigated in Cryptomeria japonica D. Don. Samples containing differentiating xylem were collected at 0500 hours and 1400 hours. The innermost surface of developing secondary walls in differentiating tracheids was observed by field emission scanning electron microscopy. In the specimens collected at 0500 hours, an amorphous material was observed covering the cellulose microfibrils. The cell wall surface was immunogold-labeled with an anti-glucomannan antiserum. After chlorite treatment, the amorphous material disappeared, and immunogold labeling was rarely observed. In the specimens collected at 1400 hours, cellulose microfibrils were clearly evident, and amorphous material and immunogold labeling were rarely observed. We thus confirmed that much amorphous material containing glucomannans is observed at night, when differentiating tracheids are turgid due to the increase in their volume, while the amorphous material was rarely observed during the day when cellulose microfibrils are clearly observed.

Cell Wall↗
PubMed2006

Cell-wall structure and anisotropy in procuste, a cellulose synthase mutant of Arabidopsis thaliana.

In dark-grown hypocotyls of the Arabidopsis procuste mutant, a mutation in the CesA6 gene encoding a cellulose synthase reduces cellulose synthesis and severely inhibits elongation growth. Previous studies had left it uncertain why growth was inhibited, because cellulose synthesis was affected before, not during, the main phase of elongation. We characterised the quantity, structure and orientation of the cellulose remaining in the walls of affected cells. Solid-state NMR spectroscopy and infrared microscopy showed that the residual cellulose did not differ in structure from that of the wild type, but the cellulose content of the prc-1 cell walls was reduced by 28%. The total mass of cell-wall polymers per hypocotyl was reduced in prc-1 by about 20%. Therefore, the fourfold inhibition of elongation growth in prc-1 does not result from aberrant cellulose structure, nor from uniform reduction in the dimensions of the cell-wall network due to reduced cellulose or cell-wall mass. Cellulose orientation was quantified by two quantitative methods. First, the orientation of newly synthesised microfibrils was measured in field-emission scanning electron micrographs of the cytoplasmic face of the inner epidermal cell wall. The ordered transverse orientation of microfibrils at the inner face of the cell wall was severely disrupted in prc-1 hypocotyls, particularly in the early growth phase. Second, cellulose orientation distributions across the whole cell-wall thickness, measured by polarised infrared microscopy, were much broader. Analysis of the microfibril orientations according to the theory of composite materials showed that during the initial growth phase, their anisotropy at the plasma membrane was sufficient to explain the anisotropy of subsequent growth.

Anisotropy↗
PubMed2005

Establishing and maintaining axial growth: wall mechanical properties and the cytoskeleton.

Organ morphology depends on cell placement and directional cell expansion. Microtubules are involved in both of these processes so genetic approaches to understand the role microtubules play in organ expansion are not straightforward. Our use of the temperature-sensitive mor1-1 mutants led to the surprising discovery that Arabidopsis thaliana (L.) Heynh. root cells can establish and maintain transverse cellulose texture without well organized microtubule arrays. This work also demonstrated that cells can lose the ability to expand anisotropically without losing transversely oriented cellulose microfibrils. We suggest that microtubule disruption affects the cell's ability to generate long cellulose microfibrils, which may be essential for achieving growth anisotropy. Thus organ shape may depend not only on the orientation but also on the relative length of cellulose microfibrils during axis establishment and growth. More recent work has shown an important correlation between microtubule organization and the deposition patterns of the glycosylphosphatidylinositol (GPI)-anchored wall protein COBRA. Loss of microtubule organization is associated with the dissipation of transverse banding patterns of COBRA, suggesting that COBRA's function in maintaining anisotropic expansion may be microtubule-dependent.

Anisotropy↗
PubMed2005

Fibrillins 1 and 2 perform partially overlapping functions during aortic development.

Fibrillin-rich microfibrils are extracellular assemblies that impart structural properties to the connective tissue. To elucidate the contribution of fibrillin-rich microfibrils to organogenesis, we have examined the vascular phenotype of a newly created strain of mice that completely lacks fibrillin-1 and the consequences of combined deficiency of fibrillins 1 and 2 on tissue formation. The results demonstrated that fibrillins 1 and 2 perform partially overlapping functions during aortic development. Fbn1-/- mice died soon after birth from ruptured aortic aneurysm, impaired pulmonary function, and/or diaphragmatic collapse. Analysis of the neonatal Fbn1-/- aorta documented a disorganized and poorly developed medial layer but normal levels of elastin cross-links. Transcriptional profiling revealed that aneurysm progression in Fbn1 null mice is accompanied by unproductive up-regulation of gene products normally involved in tissue repair and vascular integrity, such as plasminogen activator inhibitor-1, activin A, and cysteine-rich angiogenic protein 61. In contrast to Fbn1-/- mice, Fbn2 null mice had a well developed and morphologically normal aortic wall. However, virtually all Fbn1-/-;Fbn2-/- embryos and about half of the Fbn1+/-;Fbn2-/- embryos died in utero and displayed a significantly more severe vascular phenotype than Fbn1-/- mice. Consistent with a specialized function of fibrillin-2, electron microscopy visualized ultrastructurally different microfibrils in Fbn1 null compared with control cell cultures. Collectively, these data demonstrate that involvement of fibrillin-2 in the initial assembly of the aortic matrix overlaps in part with fibrillin-1 and that continued fibrillin-1 deposition is absolutely required for the maturation and function of the vessel during neonatal life.

Activins↗
PubMed2005

Cellulose biosynthesis: current views and evolving concepts.

AIMS: To outline the current state of knowledge and discuss the evolution of various viewpoints put forth to explain the mechanism of cellulose biosynthesis. * SCOPE: Understanding the mechanism of cellulose biosynthesis is one of the major challenges in plant biology. The simplicity in the chemical structure of cellulose belies the complexities that are associated with the synthesis and assembly of this polysaccharide. Assembly of cellulose microfibrils in most organisms is visualized as a multi-step process involving a number of proteins with the key protein being the cellulose synthase catalytic sub-unit. Although genes encoding this protein have been identified in almost all cellulose synthesizing organisms, it has been a challenge in general, and more specifically in vascular plants, to demonstrate cellulose synthase activity in vitro. The assembly of glucan chains into cellulose microfibrils of specific dimensions, viewed as a spontaneous process, necessitates the assembly of synthesizing sites unique to most groups of organisms. The steps of polymerization (requiring the specific arrangement and activity of the cellulose synthase catalytic sub-units) and crystallization (directed self-assembly of glucan chains) are certainly interlinked in the formation of cellulose microfibrils. Mutants affected in cellulose biosynthesis have been identified in vascular plants. Studies on these mutants and herbicide-treated plants suggest an interesting link between the steps of polymerization and crystallization during cellulose biosynthesis. * CONCLUSIONS: With the identification of a large number of genes encoding cellulose synthases and cellulose synthase-like proteins in vascular plants and the supposed role of a number of other proteins in cellulose biosynthesis, a complete understanding of this process will necessitate a wider variety of research tools and approaches than was thought to be required a few years back.

Cellulose↗
PubMed2006

Cellulose orientation determines mechanical anisotropy in onion epidermis cell walls.

The role of cellulose microfibril orientation in determining cell wall mechanical anisotropy and in the control of the wall plastic versus elastic properties was studied in the adaxial epidermis of onion bulb scales using the constant-load (creep) test. The mean or net cellulose orientation in the outer periclinal wall of the epidermis was parallel to the long axis of the cells. In vitro cell wall extensibility was 30-90% higher in the direction perpendicular to the net microfibril orientation than parallel to it. This was the case for the size of the initial deformation occurring just after the load application and for the rate of time-dependent creep. Loading/unloading experiments confirmed the presence of a real irreversible component in cell wall extension. The plastic component of the time-dependent deformation was higher perpendicular to the net cellulose orientation than parallel to it. An acid buffer (pH 4.5) increased the creep rate by 25-30% but this response was not related to cellulose orientation. The present data provide direct evidence that the net orientation of cellulose microfibrils confers mechanical anisotropy to the walls of seed plants, a characteristic that may be relevant to understanding anisotropic cell growth.

Anisotropy↗
PubMed2006

Fibrillin in Marfan syndrome and tight skin mice provides new insights into transforming growth factor-beta regulation and systemic sclerosis.

PURPOSE OF REVIEW: Important recent understandings of fibrillins and fibrillin-associated microfibril proteins suggest new ways these proteins might contribute to tissue fibrosis seen in systemic sclerosis by regulating latent transforming growth factor-beta. This review discusses mutant-fibrillin mouse models of Marfan syndrome and SSc (Tsk mice), and studies suggesting that alterations in microfibrils might contribute to human SSc. RECENT FINDINGS: Fibrillin-1 mutations associated with Marfan syndrome have recently been shown to induce genes activated by TGF-beta. The inhibition of TGF-beta in these mouse models largely reverses phenotypic and pathologic disease manifestations. Recent studies suggest that alterations in the fibrillin-1 structure from mutant Tsk fibrillin cause hypodermal fibrosis and associated changes in dermal gene expression, suggesting stimulation of cytokine-mediating signals. Genetic mutations in fibrillin-1, in a higher frequency in SSc patient populations, and autoantibodies to fibrillin provide potential links to human SSc. SUMMARY: Fibrillin is placed centrally not only as the primary structural component of microfibrils, but also a key regulator of cytokines in the TGF-beta superfamily. Fibrillin may thus communicate alterations in matrix to fibroblast gene expression. These observations complement emerging understandings of the effects of Tsk fibrillin, and genetic and autoimmune studies of human fibrillin on dermal fibrosis.

Animals↗
PubMed2004

Interaction between wall deposition and cell elongation in dark-grown hypocotyl cells in Arabidopsis.

A central problem in plant biology is how cell expansion is coordinated with wall synthesis. We have studied growth and wall deposition in epidermal cells of dark-grown Arabidopsis hypocotyls. Cells elongated in a biphasic pattern, slowly first and rapidly thereafter. The growth acceleration was initiated at the hypocotyl base and propagated acropetally. Using transmission and scanning electron microscopy, we analyzed walls in slowly and rapidly growing cells in 4-d-old dark-grown seedlings. We observed thick walls in slowly growing cells and thin walls in rapidly growing cells, which indicates that the rate of cell wall synthesis was not coupled to the cell elongation rate. The thick walls showed a polylamellated architecture, whereas polysaccharides in thin walls were axially oriented. Interestingly, innermost cellulose microfibrils were transversely oriented in both slowly and rapidly growing cells. This suggested that transversely deposited microfibrils reoriented in deeper layers of the expanding wall. No growth acceleration, only slow growth, was observed in the cellulose synthase mutant cesA6(prc1-1) or in seedlings, which had been treated with the cellulose synthesis inhibitor isoxaben. In these seedlings, innermost microfibrils were transversely oriented and not randomized as has been reported for other cellulose-deficient mutants or following treatment with dichlorobenzonitrile. Interestingly, isoxaben treatment after the initiation of the growth acceleration in the hypocotyl did not affect subsequent cell elongation. Together, these results show that rapid cell elongation, which involves extensive remodeling of the cell wall polymer network, depends on normal cellulose deposition during the slow growth phase.

Arabidopsis↗
PubMed2005

Anisotropic expansion of the plant cell wall.

Plants shape their organs with a precision demanded by optimal function; organ shaping requires control over cell wall expansion anisotropy. Focusing on multicellular organs, I survey the occurrence of expansion anisotropy and discuss its causes and proposed controls. Expansion anisotropy of a unit area of cell wall is characterized by the direction and degree of anisotropy. The direction of maximal expansion rate is usually regulated by the direction of net alignment among cellulose microfibrils, which overcomes the prevailing stress anisotropy. In some stems, the directionality of expansion of epidermal cells is controlled by that of the inner tissue. The degree of anisotropy can vary widely as a function of position and of treatment. The degree of anisotropy is probably controlled by factors in addition to the direction of microfibril alignment. I hypothesize that rates of expansion in maximal and minimal directions are regulated by distinct molecular mechanisms that regulate interactions between matrix and microfibrils.

Anisotropy↗
PubMed1995

Initial lymph vessels of the skin and elastic fibres form an integral morphofunctional structure.

Little has been published on the histochemical and cytochemical properties of anchoring filaments of the 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 the elastic fibres. With the aim of further investigating the histological identity of anchoring filaments, we performed an immunohistochemical study in human skin lymphatics, using the antibody HB8, specific for elastic fibre microfibrils. There is now a body of evidence suggesting a new concept in the framework of the lymphatic system. It unifies the initial lymph vessels, the anchoring filaments and the satellite elastic fibres in a single and integral entity.

Adolescent↗
PubMed2001

Fibrillary glomerulonephritis.

The occurrence of fibrillary glomerulonephritis is unusual in Taiwan, whereas it occurs in approximately 1% of renal biopsy specimens taken in the United States of American. This disease is characterized by extracellular randomly arranged non-branching Congo red-negative microfibrils within glomeruli. The microfibrils are less than 30 nm in diameter, and electron microscopy is essential for diagnosis. Differential diagnosis of the deposition of extracellular non-branching microfibrils within glomeruli is important because discrete diseases have different therapeutic and prognostic implications. The report will discuss two cases of biopsy-proved fibrillary glomerulonephritis who presented with proteinuria, hematuria, renal insufficiency, and hypertension. It is noteworthy that the renal function persistently went downhill, even though the physician treated the patients with corticosteroids, pulse treatment and immunosuppressive agents.

Aged↗
PubMed2001

Cell wall architecture of the elongating maize coleoptile.

The primary walls of grasses are composed of cellulose microfibrils, glucuronoarabinoxylans (GAXs), and mixed-linkage beta-glucans, together with smaller amounts of xyloglucans, glucomannans, pectins, and a network of polyphenolic substances. Chemical imaging by Fourier transform infrared microspectroscopy revealed large differences in the distributions of many chemical species between different tissues of the maize (Zea mays) coleoptile. This was confirmed by chemical analyses of isolated outer epidermal tissues compared with mesophyll-enriched preparations. Glucomannans and esterified uronic acids were more abundant in the epidermis, whereas beta-glucans were more abundant in the mesophyll cells. The localization of beta-glucan was confirmed by immunocytochemistry in the electron microscope and quantitative biochemical assays. We used field emission scanning electron microscopy, infrared microspectroscopy, and biochemical characterization of sequentially extracted polymers to further characterize the cell wall architecture of the epidermis. Oxidation of the phenolic network followed by dilute NaOH extraction widened the pores of the wall substantially and permitted observation by scanning electron microscopy of up to six distinct microfibrillar lamellae. Sequential chemical extraction of specific polysaccharides together with enzymic digestion of beta-glucans allowed us to distinguish two distinct domains in the grass primary wall. First, a beta-glucan-enriched domain, coextensive with GAXs of low degrees of arabinosyl substitution and glucomannans, is tightly associated around microfibrils. Second, a GAX that is more highly substituted with arabinosyl residues and additional glucomannan provides an interstitial domain that interconnects the beta-glucan-coated microfibrils. Implications for current models that attempt to explain the biochemical and biophysical mechanism of wall loosening during cell growth are discussed.

Cell Division↗