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 1,531 records · Page 85Linked to original sources
PubMed1998

Electron microscopic investigation of sulcus vocalis.

This investigation was carried out to determine the histopathologic findings of sulcus vocalis in two human adult larynges. Observations were made by light and transmission electron microscopy. The results are summarized as follows. Sulcus was confined to the squamous epithelium area. The basement membrane thickness increased at the sulcus. The sulcus was situated in the superficial layer of the lamina propria, which was thin around the bottom of the sulcus. Collagenous fibers were dense, and fibrous long-spacing collagen was seen around the bottom of the sulcus. Elastic fibers decreased in number and were composed predominantly of microfibrils and reticular amorphous substances. In the maculae flavae, the fibroblasts were decreased in number and degenerated. Collagenous and elastic fibers, synthesized by fibroblasts in the maculae flavae, were decreased. There were many abnormal elastic fibers in the maculae flavae. The quality and quantity of the fibrous components were changed in the mucosa of sulcus vocalis, owing in part to dysfunction of the fibroblasts and abnormal fibrogenesis in the maculae flavae.

Basement Membrane↗
PubMed1985

Ultrastructural morphology of leukemic cells in the cat.

Transmission and scanning electron microscopic characteristics of leukemic cells from eight cats with spontaneous leukemia are described. Nuclear blebs, myelin figures, cytoplasmic microfibrils and C-type virus were seen more frequently in leukemic cells. Surface ridges and ruffles seen with the scanning electron microscopy were helpful in distinguishing myelogenous from lymphogenous leukemia.

Animals↗
PubMed1994

Cardiovascular lesions in bovine Marfan syndrome.

Bovine Marfan syndrome is a genetic disease with many of the clinical and pathologic manifestations of human Marfan syndrome. Major manifestations include ectopia lentis and aortic dilatation, aneurysm, and rupture. Affected cattle have a defect in fibrillin metabolism similar to that in human patients. Ten cattle were followed and their disease progression and lesions documented. Ages ranged from a term fetus (No. 9) to a 4-year-old cow (No. 4); three animals were male (Nos. 1-3) and seven were female (Nos. 4-10). Of eight animals (80%) that died or were euthanatized (Nos. 1-3, 5-9), six (75%) had severe cardiovascular lesions identified at necropsy. Gross cardiovascular lesions of bovine Marfan syndrome included cardiac tamponade secondary to aortic rupture (animal Nos. 3, 6, 8), dissecting aneurysms of the aorta and pulmonary artery (animal No. 5), and intrauterine cardiac tamponade secondary to rupture of the pulmonary artery (animal No. 9). Microscopically, Verhoeff Van Gieson-stained sections of aorta contained severe fragmentation of the elastic laminae in the aortic media, but the cystic medial necrosis seen in human Marfan aortae was not identified, even in the chronic aortic dissection. Ultrastructurally, affected aortic tissue was characterized by thin, dark elastic fibers with abundant, tangled microfibrils on the periphery. Swirls of collagen fibers and bundles of hypertrophic smooth muscle cells replaced damaged elastic laminae. Gross and microscopic cardiovascular lesions in bovine Marfan syndrome are similar to those in human Marfan syndrome. Bovine Marfan syndrome is a valuable model for investigation of molecular pathogenesis and treatment of human Marfan syndrome.

Aortic Dissection↗
PubMed1997

Analysis of a general principle of crystal nucleation, formation in the different hard tissues.

We have found, at high EM magnification, on ultrathin sections of shock-frozen, freeze-dried, embedded pieces of the developing hard tissues, that the primary crystallites consist of strands composed of nanometer-sized apatitic islands, which rapidly coalesce to needles and afterward to platelets. By small-area electron diffraction, with energy-filtered electrons, it was clarified that these strands are already crystallographically oriented along the bipolar c-axis so that the center-to-center distances between the islands would reflect the distances between crystal-nucleating sites along the matrix. The EM analysis of the cross-cut stained unmineralized and of the unstained mineralized collagen fibers of turkey tibia tendon shows that the staining "nuclei" and the early crystallites, appearing as dark dots, surround "light" round structures, which we interpret as the collagen microfibrils, surrounded by the apatitic crystallites.

Animals↗
PubMed1983

Immunocytochemical localization of fibronectin in human fibroblast cultures using a cell surface replica technique.

The pericellular fibronectin-containing matrices of human foreskin fibroblasts cultured in ascorbate-supplemented medium were examined using surface replicas. An extensive filamentous network is present over and between adjacent cells, with a considerable amount at points of cell-to-cell contact. Indirect immunocytochemical localization of the distribution of fibronectin and procollagen type III within the matrix was done using the peroxidase-antiperoxidase (PAP) sandwich technique. The PAP molecule with the surrounding diaminobenzidine reaction product appears as a globular particle of approximately 39 nm in surface replicas. The apparent size of the marker was larger (60-80 nm) when bound to pericellular fibronectin, due presumably to the binding of more than one PAP complex to each fibronectin molecule. The immunocytochemical data suggest that fibronectin is a component of most, if not all, matrix fibrils. Some of the smallest filaments of the matrix (5-10 nm) exhibit a periodic, beaded appearance, with a repeat distance of approximately 70-100 nm. After either anti-fibronectin or anti-procollagen type III labeling, the filaments were decorated at regular 70-100 nm intervals with the globular marker. We suggest that the periodicity may be due to fibronectin molecules bound to collagen microfibrils at regular intervals. Our results demonstrate the usefulness of combined surface replica and immunocytochemical techniques for analysis of matrix components of cultured cells.

Cells, Cultured↗
PubMed1987

A new interpretation of the direct Schiff reaction of elastic connective tissue.

A direct Schiff reaction of elastic tissues has been known for many years, but the nature of the native aldehyde-rich components has not been clear. In this study, chicken, quail, and rat embryos and adult rat lung, aorta, and kidney were fixed in methacarn or in a formalin solution, embedded in paraffin, and sections of 8-10 micron obtained. Rehydrated sections were incubated for various periods in solutions of the enzymes chondroitinase ABC, clostripain, collagenase, elastase, heparatinase, hyaluronidase, subtilisin Carlsberg ("protease"), or trypsin, and in solutions of phosphomolybdic acid or sodium borohydride. After incubation, sections were placed, without prior oxidation, in Schiff's reagent, and were ultimately observed and photographed in transmitted light or with blue or green epifluorescence. A Schiff-positive substance was found, always and exclusively, in elastic tissues of the vasculature and lungs, which was hydrolyzed by the proteolytic enzymes to an extent that ranged from complete loss of Schiff reaction in minutes (trypsin) to no loss of Schiff reaction in 22 hr (clostripain). The Schiff-reactive protein preceded the time of appearance of elastin in the early embryos. We conclude that the aldehyde-rich protein responsible for this reaction is a harbinger of elastogenesis in vivo and speculate that it may represent the elastic microfibril or a component thereof.

Aldehydes↗
PubMed1991

Immunoelectron microscopic localization of collagens type I, V, VI and of procollagen type III in human periodontal ligament and cementum.

We examined the ultrastructural localization of collagens Type I, V, VI and of procollagen Type III in decalcified and prefixed specimens of the periodontal ligament and cementum, by immunoelectron microscopy using ultra-thin cryostat sections. Immunostaining for collagen Type I was pronounced on the major cross-striated fibrils entering cementum and in cementum proper, whereas staining for procollagen Type III was almost exclusively observed on the major fibrils in the periodontal ligament situated more remote from cementum. Reactivity for collagen Type V was limited to aggregated, unbanded filamentous material of about 12 nm diameter that was found mainly in larger spaces between bundles of cross-striated collagen fibrils and occasionally on single microfibrils that apparently originated from the ends of the major collagen fibrils, which may support the concept of this collagen as a component of core fibrils. Collagen Type VI was present as microfilaments appearing to interconnect single cross-striated fibrils. In the densely packed fibril bundles of the periodontal ligament, no collagen type VI was detected. Neither Type V or Type VI collagen was observed in cementum.

Adolescent↗
PubMed1991

Rotary shadowing of collagen monomers, oligomers, and fibrils during tendon fibrillogenesis.

Collagen monomers, oligomers, and fibrillar structures were isolated from chick tendons at various stages of development and studied by rotary shadowing. Monomers of Type I collagen, solubilized in 0.15 M NaCl solutions, were mostly present as collagen, pN-collagen, and pC-collagen with few procollagen molecules. They did not form polymers, nor were they associated with a carrier. Dimers of fibrillar collagen molecules were arranged in a 4-D stagger, suggesting that this was the preferred molecular interaction for the initiation of collagen fibrillogenesis. Type XII collagen molecules were mostly free, but some were attached by their central globular domain to one end of free fibrillar collagen molecules. Tenascin and Type VI collagen were also identified. The fibril populations consisted of collagen and beaded structures. These fibrils consisted of beads (globular domains) about 23 nm in diameter, separated by a period about 27 nm in length. Beads were linked by filamentous structures. These beaded fibrils probably represent the microfibrils of elastin.

Animals↗
PubMed1993

Distribution of undulin, tenascin, and fibronectin in the human periodontal ligament and cementum: comparative immunoelectron microscopy with ultra-thin cryosections.

We studied the ultrastructural localization of three distantly related glycoproteins of the extracellular matrix, undulin, tenascin and fibronectin, in decalcified sections of human periodontal ligament (PL) and cementum. Undulin was associated with tightly packed major collagen fibrils and not with microfibrils, indicating that this protein may be involved in the supramolecular and functional organization of collagen fibrils into flexible bundles. Tenascin was found on globular masses between less densely packed collagen fibrils, thus displaying a pattern quite distinct from that of undulin. Fibronectin was noted in bulky material between the cross-striated fibrils, often surrounding individual fibrils like garlands, and in the microfibrillar meshwork extending from cross-striated fibrils. The three glycoproteins displayed a distinct and unique pattern of distribution in PL that can be correlated with their molecular structure and potential functions.

Adolescent↗
PubMed1995

The association of human fibulin-1 with elastic fibers: an immunohistological, ultrastructural, and RNA study.

We examined the pattern of fibulin-1 mRNA and protein expression in human tissues and cell lines. Fibulin-1 transcripts were found in RNA isolated from most tissues and a variety of cultured cells, including fibroblasts, smooth muscle cells, and several epithelial cell lines, but not endothelial cells, lymphomyloid cells, or a number of carcinoma and melanoma lines. Immunohistochemical analysis showed that fibulin-1 is an intercellular component of connective tissues, predominantly associated with matrix fibers in tissues such as the cervix, dermis, intimal and medial layers of blood vessels, heart valves, meningeal tissue of the brain, Wharton's jelly of the umbilical cord, testis, and lung. Most of the fibers that were immunoreactive with fibulin-1 antibodies also stained with antibodies to the elastic fiber proteins elastin and fibrillin, as well as with Verhoeff's elastin stain. Immunoelectron microscopic analysis of elastin fibers of skin and saphenous vein revealed that fibulin-1 was located within the amorphous core of the fibers, similar to elastin, but it was not in the fibrillin-containing, elastin-associated microfibrils. Our finding that fibulin-1 is an elastic fiber component suggests several possible new functions for fibulin-1, e.g., that it is a structural protein that contributes to the elastic properties of connective tissue fibers or that is involved with the process of fibrogenesis.

Calcium-Binding Proteins↗
PubMed2001

Multi-exon deletions of the FBN1 gene in Marfan syndrome.

BACKGROUND: Mutations in the fibrillin -1 gene (FBN1) cause Marfan syndrome (MFS), an autosomal dominant multi-system connective tissue disorder. The 200 different mutations reported in the 235 kb, 65 exon-containing gene include only one family with a genomic multi-exon deletion. METHODS: We used long-range RT-PCR for mutation detection and long-range genomic PCR and DNA sequencing for identification of deletion breakpoints, allele-specific transcript analyses to determine stability of the mutant RNA, and pulse-chase studies to quantitate fibrillin synthesis and extracellular matrix deposition in cultured fibroblasts. Southern blots of genomic DNA were probed with three overlapping fragments covering the FBN1 coding exons RESULTS: Two novel multi-exon FBN1 deletions were discovered. Identical nucleotide pentamers were found at or near the intronic breakpoints. In a Case with classic MFS, an in-frame deletion of exons 42 and 43 removed the C-terminal 24 amino acids of the 5th LTBP (8-cysteine) domain and the adjacent 25th calcium-binding EGF-like (6-cysteine) domain. The mutant mRNA was stable, but fibrillin synthesis and matrix deposition were significantly reduced. A Case with severe childhood-onset MFS has a de novo deletion of exons 44-46 that removed three EGF-like domains. Fibrillin protein synthesis was normal, but matrix deposition was strikingly reduced. No genomic rearrangements were detected by Southern analysis of 18 unrelated MFS samples negative for FBN1 mutation screening. CONCLUSIONS: Two novel deletion cases expand knowledge of mutational mechanisms and genotype/phenotype correlations of fibrillinopathies. Deletions or mutations affecting an LTBP domain may result in unstable mutant protein cleavage products that interfere with microfibril assembly.

Journal Article↗
PubMed2005

The expansin superfamily.

The expansin superfamily of plant proteins is made up of four families, designated alpha-expansin, beta-expansin, expansin-like A and expansin-like B. alpha-Expansin and beta-expansin proteins are known to have cell-wall loosening activity and to be involved in cell expansion and other developmental events during which cell-wall modification occurs. Proteins in these two families bind tightly to the cell wall and their activity is typically assayed by their stimulation of cell-wall extension and stress relaxation; no bona fide enzymatic activity has been detected for these proteins. Alpha-expansin proteins and some, but not all, beta-expansin proteins are implicated as catalysts of 'acid growth', the enlargement of plant cells stimulated by low extracellular pH. A divergent group of beta-expansin genes are expressed at high levels in the pollen of grasses but not of other plant groups. They probably function to loosen maternal cell walls during growth of the pollen tube towards the ovary. All expansins consist of two domains; domain 1 is homologous to the catalytic domain of proteins in the glycoside hydrolase family 45 (GH45); expansin domain 2 is homologous to group-2 grass pollen allergens, which are of unknown biological function. Experimental evidence suggests that expansins loosen cell walls via a nonenzymatic mechanism that induces slippage of cellulose microfibrils in the plant cell wall.

Biological Evolution↗
PubMed2006

Features and genomic origins of matrix cell adhesion molecules-1 and -2 expressed by fibroblasts of human aortic adventitial origin.

Precursor mRNAs for proteins that we have called matrix cell adhesion molecules-1 and -2 (Mat-CAM-1 and Mat-CAM-2) were cloned from fibroblasts cultured from a specimen of human abdominal aorta. Both protein sequences have the unusual feature that there is an immunoglobulin kappa (Igkappa)-like domain at the N terminus and they are glycine/proline rich in the C-terminal domain. Antibodies were raised in rabbit against peptides synthesized for a specific unique sequence of Mat-CAM-1 and Mat-CAM-2, respectively (not detected in any other proteins referenced in GenBank). Both antibodies were immunoreactive with adventitial microfibrils of the aorta and some additional arteries. Mat-CAM-1 was detected in the common/internal iliac arteries, but it was not detected in the external iliac artery. Conversely, Mat-CAM-2 was conspicuous in the external iliac artery, but not the common/internal iliac arteries. Thus, these proteins show features of site-specific expression within the arterial tree. Computerized searches show that the genomic origins of Mat-CAM-1 and -2 are in the so-called nasopharnygocarcinoma (NPC) gene on chromosome 2, which is a putative oncogene. Expression of the two different gene products from the same genomic sequence requires shifts of reading frame. Further studies will be required to determine whether these proteins are prototypes for a larger family of tissue-specific matrix proteins arising from alternative transcriptions of the same genomic sequence.

Amino Acid Sequence↗
PubMed2002

Ullrich disease: collagen VI deficiency: EM suggests a new basis for muscular weakness.

Ullrich disease is a form of congenital muscular dystrophy characterized clinically by generalized muscle weakness, contractures of the proximal joints, and hyperflexibility of the distal joints from birth or early infancy. Recently, mutations of the collagen VI gene have been associated with Ullrich disease. The authors report on a boy with Ullrich disease who has complete deficiency of collagen VI and harbors compound heterozygous mutations in the collagen VI alpha 2 gene. Absence of microfibrils on EM, together with normal collagen fibrils and basal lamina, suggests that loss of a link between interstitium and basal lamina may be a new molecular pathomechanism of muscular dystrophy.

Child, Preschool↗
PubMed1988

The role of interstitial collagens in cleft formation of mouse embryonic submandibular gland during initial branching.

An interstitial collagenase was purified from the explant medium of bovine dental pulp and was shown to degrade collagens I and III but not IV and V. The enzyme halted cleft initiation in the epithelium of 12-day mouse embryonic submandibular glands in vitro, indicating the active involvement of interstitial collagens in the branching morphogenesis. Transmission electron microscopic observation of the intact 12-day gland without any clefts showed the scattered localization of a few collagen fibrils at the epithelial-mesenchymal interface of the bulb and also revealed the presence of numerous microfibrils around the stalk. Collagen bundles were regularly seen close to the wavy basal lamina at the bottom of clefts of the intact 13-day gland and 12-day gland cultured for 17 h under normal conditions. Mesenchymal cells were found in the clefts together with the frequent localization of peripheral nerve fibres and capillary endothelial cells. The collagen bundles were more often observed in the 12-day gland cultured in the presence of bovine dental pulp collagenase inhibitor, which had been shown to enhance cleft formation. In contrast, collagen fibrils were rarely found at the epithelial-mesenchymal interface of the 12-day gland cultured in the presence of Clostridial or bovine dental pulp collagenase. The findings indicated that the formation of interstitial collagen bundles is essential to form clefts in the epithelium both in vivo and in vitro.

Animals↗
PubMed1993

Synthesis and assembly of fibrillin by fibroblasts and smooth muscle cells.

The expression and assembly of the microfibrillar glycoprotein fibrillin has been investigated in cultures of nuchal ligament fibroblasts, skin fibroblasts and vascular smooth muscle cells. The level of fibrillin expression varied with the cell type and growth conditions. Higher levels of synthesis were recorded in quiescent post-confluent cells than in actively dividing subconfluent cultures. Nuchal ligament fibroblasts consistently synthesized the highest levels of fibrillin. Growth of cells in the presence of ascorbate resulted in an increased proportion of newly synthesized fibrillin retained within cell layers. Fibrillin was immunoprecipitated from medium and cell layer extracts in the form of monomers and high-M(r) disulphide-bonded aggregates. Rotary shadowing electron microscopy of cell layer extracts and collagen gels provided direct evidence for the assembly of extensive intact microfibrils by smooth muscle cells and fibroblast cultures. Gel filtration chromatography of medium and cell layer extracts, in combination with immunoprecipitation of column fractions, provided a means of analysing the size distribution and assembly of newly synthesized fibrillin. This cell culture approach provides an opportunity to evaluate normal and aberrant synthesis and assembly of fibrillin in a wide range of cell types.

Actin Cytoskeleton↗
PubMed1999

Fibrillin assembly: dimer formation mediated by amino-terminal sequences.

We have investigated recombinant fibrillin-1 (profib-1) and fibrillin-2 (glyfib-2) molecules encoding the proline- or glycine-rich regions with flanking domains (exons 9-11), in order to establish whether these sequences might mediate specific molecular recognition events important in fibrillin assembly. Our data demonstrate that both recombinant molecules can form extracellular dimers, but highlight subtle differences in the stability of these dimers. Following expression in COS-1 cells, SDS-PAGE analysis showed that glyfib-2 was present intracellularly as monomers, and extracellularly as monomers and disulphide-bonded dimers. Size fractionation in native non-reducing conditions prior to SDS-PAGE analysis highlighted that glyfib-2 also formed non-covalent associations. In contrast, profib-1 appeared monomeric in cells and medium. Using an in vitro translation system supplemented with semipermeabilised HT1080 cells together with chemical crosslinking, dimers of the fibrillin-1 and fibrillin-2 molecules were detected. Dimerisation was not cell-dependent since molecules translated in the absence of cells dimerised, and was not an intracellular event as judged by proteinase K digestions. A crosslinking and coimmunoprecipitation strategy provided a means of investigating whether molecular chaperones might be involved in preventing dimerisation of translocated molecules. Proteinase K-resistant recombinant molecules associated rapidly with BiP, and thereafter with protein disulphide isomerase and calreticulin. Differences between the two fibrillin isoforms in ability to form stable dimers prompted investigation of the proline- and glycine-rich sequences. Differences in solubility and pI were apparent that may contribute to reduced stability of proline-rich region interactions. These studies suggest that extracellular dimer formation mediated by interactions of the proline- and glycine-rich regions may be a crucial early step in the extracellular assembly of fibrillin into microfibrils.

Amino Acid Sequence↗
PubMed1999

Regulation of fibrillin carboxy-terminal furin processing by N-glycosylation, and association of amino- and carboxy-terminal sequences.

The molecular mechanisms of fibrillin assembly into microfibrils are poorly understood. In this study, we investigated human fibrillin-1 carboxy-terminal processing and assembly using a recombinant approach. Processing of carboxy-terminal fibrillin-1 was strongly influenced by N-glycosylation at the site immediately downstream of the furin site, and by association with calreticulin. The carboxy terminus of fibrillin-2 underwent less efficient processing than carboxy-terminal fibrillin-1 under identical conditions. Size fractionation of the amino-terminal region of fibrillin-1, and of unprocessed and furin-processed carboxy-terminal region of fibrillin-1, revealed that the amino terminus formed abundant disulphide-bonded aggregates. Some association of unprocessed carboxy-terminal fibrillin-1 was also apparent, but processed carboxy-terminal sequences remained monomeric unless amino-terminal sequences encoded by exons 12-15 were present. These data indicate the presence of fibrillin-1 molecular recognition sequences within the amino terminus and the extreme carboxy-terminal sequence downstream of the furin site, and a specific amino- and carboxy-terminal association which could drive overlapping linear accretion of furin-processed fibrillin molecules in the extracellular space. Differences in processing of the two fibrillin isoforms may reflect differential abilities to assemble in the extracellular space.

Endoplasmic Reticulum↗