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PubMed1996

The fate of scleral grafts in the cornea.

There have been reports of the clearing of sclera that has been grafted into the cornea. This clearing was studied in the rabbit by transplanting full-thickness scleral buttons or by implanting slivers of sclera, both autografts and allografts, into the cornea. Some clearing around the edges of the implanted scleral tissues was observed to take place slowly over the following months. Electron microscopic observation of the borders of either type of graft showed that the collagen fibrils of the sclera were breaking down either by unraveling into smaller fibrils similar in diameter to those of the cornea by fraying into microfibrils. Attracting blood vessels over the scleral slivers did not appear to accelerate the changes. Both active macrophages and fibroblasts could be found in the transitional area.

Animals↗
PubMed1984

The fine structure of psammoma bodies in meningocytic whorls.

Psammoma bodies within meningocytic whorls in five cases of meningioma were examined by electron microscopy. The cells comprising the meningocytic whorls showed the conventional ultrastructural features of meningothelial cells with interdigitations and interconnections by means of junctional complexes. In some whorls, collagen fibers, elastic fibers, microfibrils, as well as finely reticulated material were observed. Calcified foci of various sizes were seen within many of these whorls. Extracellular matrix vesicles, with or without hydroxyapatite crystals, were occasionally noted at the periphery of extracellular psammoma bodies in the whorl. Furthermore, many small aggregates of crystals were present adjacent and parallel to the collagen and elastic fibers in the meningocytic whorls. Substantial amounts of collagen fibers were also observed within the large psammoma bodies. These findings suggest that the matrix vesicles, presumably produced by the meningothelial cell, may serve as the initial nidi of calcification of psammoma bodies as originally suggested by Lipper et al. Collagen fibers as well as elastic fibers in the whorls may also play an important role in orienting apatite crystal deposition during the growth of extracellular psammoma bodies and serve as early sites of calcification.

Adult↗
PubMed1983

The myofibroblast anchoring strand--the fibronectin connection in wound healing and the possible loci of collagen fibril assembly.

Myofibroblast anchoring strands (MAS) are extracellular structures that connect the termini of actin bundles within myofibroblasts to collagen fascicles in the extracellular space of wound healing tissues. The strands appear to be primarily comprised of microfibrils of fibronectin 2-5 nm in diameter. They also embody parallel arrays of intermediary sized filaments (ISF) and an amorphous matrix of collagen. The MAS effectively translate the cellular contractile forces required for cell motility into the collagen filament/fiber deformations required for wound contraction. However, the primary function of the strands appears to be the assembly of ISF into collagen fibrils.

Collagen↗
PubMed1993

Renal amyloidosis and other fibrillar glomerular diseases.

Fibrillar glomerular diseases are defined by the ultrastructural accumulation of glomerular extracellular microfibrils or microtubules. The deposits have compositions particular to specific diseases, and it is important to distinguish among these clinical pathologic entities and their differing clinical implications. Amyloidosis and immunotactoid glomerulopathy are two examples of fibrillar glomerular diseases. Amyloidosis is a systemic disease in which the fibrils stain with Congo red and contain various biochemically distinct proteins that identify diseases with differing prognostic and therapeutic implications. Immunotactoid glomerulopathy is a primary glomerular disease, and the deposits contain immunoglobulins that do not stain with Congo red. In contrast to amyloidosis, division of immunotactoid glomerulopathy based on the immunoglobulin content or ultrastructural appearance of the deposits has no clinical relevance.

Amyloidosis↗
PubMedDate not supplied

Therapeutic management of patients with Marfan syndrome: focus on cardiovascular involvement.

Marfan syndrome is an autosomal dominant disorder of the connective tissues, with mutation on the fibrillin-1 gene encoding for fibrillin, a major component of the extracellular microfibrils. The prevalence of the syndrome is 7 to 17 in 100,000. The mean life expectancy for untreated patients with Marfan syndrome is 32 years, with aortic dissection, aortic rupture, or cardiac failure from mitral or aortic valve regurgitation as the predominant cause of death in >90% of patients. However, with optimal clinical management of patients with Marfan syndrome, life expectancy may be improved substantially to a nearly normal life span. Cornerstones of clinical management include modern noninvasive imaging modalities, molecular analysis at the complementary deoxyribonucleic acid/deoxyribonucleic acid level of the fibrillin-1 gene, genetic counseling, lifestyle changes, and cardiovascular surveillance, the latter including regular imaging of the aorta and endocarditis prophylaxis. Prophylactic use of beta-blocking agents, the timing of elective surgery, and the optimal surgical technique are difficult issues that need to be evaluated individually. Juvenile, postoperative, and pregnant patients with Marfan syndrome pose particular problems. The goal of this review is to facilitate differential decision-making based on referenced evidence and to provide guidelines for medical and surgical therapeutic strategies.

Cardiovascular Diseases↗
PubMed2006

Identification of oxytalan fibers in Salzmann's nodular degeneration.

PURPOSE: Diagnosis of Salzmann's nodular degeneration is based on clinical findings, as histopathologic findings in nodules are nonspecific on routine examination. This study demonstrates that presence of oxytalan fibers (ie, elastic system fibers) in lesions of Salzmann's nodular degeneration under light and electron microscopy allows definitive diagnosis. METHODS: A 55-year-old woman noticed white nodular lesions on both corneas. Excised lesion tissues were examined under light microscopy with special staining and transmission electron microscopy. RESULTS: Nodular lesions comprised hyalinized connective tissue showing nonspecific findings on routine histologic examination. However, oxidized aldehyde fuchsin staining yielded positive results in lesions, indicating the presence of oxytalan fibers. Transmission electron microscopy identified bundles of microfibrils in lesions, confirming the presence of oxytalan fibers. CONCLUSIONS: Light microscopic examination by oxidized aldehyde fuchsin staining should be performed when diagnosing Salzmann's nodular degeneration.

Corneal Dystrophies, Hereditary↗
PubMed1979

Ultrastructure of graniferous tracheary elements in the haustorium of Exocarpus bidwillii, a root hemi-parasite of the Santalaceae.

The xylem in the body of the haustorium of E. bidwillii has the shape of an inverted conical flask with the expanded portion being known as the vascular core. The tracheary elements of the vascular core are notable for the occurrence of numerous granules within their lumina and the presence of mostly imperforate walls. Elsewhere in the haustorium graniferous tracheary elements are absent and the cells are usually ordinary vessel elements. Thin sections for transmission electron microscopy, post-stained in potassium permanganate, show that the secondary wall thickenings of the graniferous tracheary elements consist of eccentric layers in which the microfibrils of each successive layer run alternately longitudinally and transversely. The granules of the tracheary elements average 2 micrometer in diameter and consist of a homogeneous matrix which shows a fine fibrillar structure on high resolution. The granules are naked and mostly remain as separate structures within the lumen of the cell, but occasionally they fuse into small groups or irregular masses. In some cells the granules become transformed into fibrillar material that disperses throughout the lumen. This dispersed material may accumulate in vessels of the interrupted zone proximal to the vascular core. Occasionally, the granules also change into compacted amorphous masses that adhere to the walls of the cell. Ultrastructural cytochemistry confirms that the granules are protein and not starch as was originally believed for the Santalaceae. The function of the vascular core and its graniferous tracheary elements is discussed and we suggest that it might help regulate the pressure and flow of xylem sap entering the parasite from the host. Graniferous tracheary elements in the Santalaceae and in root parasites of the Serophulariaceae are compared and it is concluded that they represent examples of convergent evolution.

Histocytochemistry↗
PubMed1984

Isolation and structure of glucan from regenerating spheroplasts of Candida albicans.

Regenerating spheroplasts of Candida albicans formed organized glucan nets in liquid culture. The nets consisted of interwoven microfibrils about 50 nm wide, but of an undetermined length. Partial acid hydrolysis of the polysaccharide showed the presence of chains of beta(1----3)- and beta(1----6)-linked glucose residues, but no intrachain beta(1----3) and beta(1----6) linkages. Periodate oxidation and GLC of the methylated glucan indicated a highly branched polymer (9.5% branch points). Sequential enzymic degradation of the isolated nets confirmed the presence of chains of beta(1----3)- and beta(1----6)-linked glucose residues. Degradation by (1----3)-beta- and (1----6)-beta-glucanase released 23% (w/w) and 30% (w/w) respectively of the carbohydrate as glucose equivalents. The residual material was degraded by chitinase. Equal amounts of N-acetylglucosamine and glucose equivalents were detected in the chitinase hydrolysate, suggesting a possible linkage between glucan and chitin. Our data indicate that the cell wall of C. albicans contains at least two highly branched glucans with predominantly beta(1----3) or beta(1----6) linkages.

Candida albicans↗
PubMed1984

The co-ordination of chitosan and chitin synthesis in Mucor rouxii.

Chitin synthetase preparations from cell walls and chitosomes of the fungus Mucor rouxii were tested for their ability to synthesize chitosan when incubated with uridine diphosphate N-acetyl-D-glucosamine in the presence of chitin deacetylase. The most effective chitin synthetase preparation was one dissociated from cell walls with digitonin. The rate of chitosan synthesis by the wall-dissociated chitin synthetase was about three times that of an equivalent amount of cell walls. The chitosan-synthesizing ability of chitosomes was relatively low, but was more than tripled by treatment with digitonin. Presumably, digitonin improves chitosan yields of dissociating chitin synthetase. The dissociated enzyme would produce dispersed chitin chains that could be attacked by chitin deacetylase before they have time to crystallize into microfibrils. The regulation of chitin and chitosan syntheses in vivo may be determined by the organization of chitin synthetase molecules at the cell surface. Those molecules that remain organized as a complex, similar if not identical to that found in chitosomes, would produce mainly chitin. Chitosan would be preferentially produced by chitin synthetase molecules which are dispersed upon reaching the cell surface.

Cell Wall↗
PubMed1991

Cell surface structures in osmotically fragile mutants of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae characterized by osmotic fragility showed a marked fibrillar structure on the inner wall surface when studied by two electron microscopic techniques, i.e. freeze-etching of whole native cells and metal shadowing of isolated cell walls. The walls of the mutant cells were more permeable to macromolecules than were those of the wild-type parental strain. The synthesis and assembly of (1----3)-beta-D-glucan wall microfibrils studied in protoplasts of mutant cells were not impaired. It is suggested that the osmotic fragility of the mutant cells is related to the deficiency of the wall structure as a consequence of the srb1 mutation affecting biogenesis of the amorphous (glucan) component.

Cell Membrane↗
PubMed1976

Wall structure of the Neurospora hyphal apex: immunofluorescent localization of wall surface antigens.

Antisera have been raised in rabbits against three wall fractions from Neurospora crassa. Fractions were separated according to Mahadevan & Tatum (1965), i.e. fraction I, glucan-peptide-galactosamine complex; fraction III, laminarin-like glucan; and fraction IV, chitin. Distinct patterns of immunofluorescent staining were obtained using an indirect staining method. Hyphae stained with antiserum to fraction I showed maximum fluorescence in the apical and/or subapical regions: in both cases, fluorescence showed a sharp decrease with distance behing the subapical region. Hyphae stained with antiserum to fraction III showed faintly fluorescent tips with fluorescence increasing with distance from the tip. Hyphae stained with antiserum to fraction IV showed faint fluorescence, equivalent to levels of autofluorescence, except at the sites of hyphal fractures. Antisera were also raised against whole walls from 24 and 120 h cultures. Hyphae stained with antisera against whole walls which had previously been absorbed to remove antibodies to fractions I, III, and IV showed preferential staining of apices. The uncharacterized tip antigen(s) thus revealed was also demonstrated on immunodiffusion plates. This pattern of immunofluorescence was compared to the fluorescence of apices after staining with an optical brightener. Enzymic dissection procedures did not generally give reliable results with apices from 24 h cultures. Untreated apices appeared amorphous, while a drastic chemical treatment revealed randomly oriented microfibrils which were shown to be alpha-chitin. The apical hyphal walls were significantly thinner than those from more mature hyphal regions.

Antigens, Fungal↗
PubMed1995

Disruption of the actin cytoskeleton in budding yeast results in formation of an aberrant cell wall.

A temperature-sensitive, conditionally lethal actin mutant of Saccharomyces cerevisiae, DBY 1693, was used to study, using light and electron microscopy, dysfunction of the actin cytoskeleton in the morphogenesis of the cell wall. Cells of this mutant strain survived at least 24 h at the restrictive temperature (37 degrees C). These cells showed isodiametric growth. Mutant cells accumulated vesicles, probably as a consequence of chaotic secretory transport caused by loss of polarity. A conspicuous morphological response to the dysfunction of actin was the formation of an aberrant wall over the whole surface of the isodiametrically-growing cell. This wall was of loose texture with protruding glucan microfibrils incompletely masked with amorphous matrix. It resembled the regenerating cell wall on the surfaces of yeast protoplasts. The localization of wall synthesis over the whole surface of temperature sensitive actin mutant cells was in accordance with an even distribution of submembranous actin in the form of patches (similarly to regenerating protoplasts). Delocalization of finger-like invaginations of the plasma membrane from the bud region to the whole surface of the growing cell was also found in mutant cells.

Actins↗
PubMed1995

Actin cortical cytoskeleton and cell wall synthesis in regenerating protoplasts of the Saccharomyces cerevisiae actin mutant DBY 1693.

The relationship between the actin cytoskeleton and cell wall synthesis was studied by light and electron microscopy in protoplasts of Saccharomyces cerevisiae DBY 1693 containing the act1-1 allele. Since protoplasting also disturbs the actin cytoskeleton, these mutant protoplasts had a double error in their actin cytoskeletons. In the period between the onset of wall synthesis and completion of the wall, protoplasts grown at the permissive temperature showed an even distribution of actin patches all over the surface on which a new cell wall was being synthesized. After wall completion, actin patches partially disappeared, but then re-appeared, accumulated in growth regions at the start of polarized growth. This was compared with the pattern of actin patches observed in intact temperature-sensitive actin mutant cells cultivated at the permissive temperature. Electron microscopy of freeze-etched replicas revealed finger-like invaginations of the plasma membrane in both the actin mutant cells and their protoplasts. These structures showed a very similar distribution to the actin patches detected by rhodamine phalloidin staining in the fluorescence microscope. A hypothesis is presented, explaining the role of actin patches/finger-like invaginations of the plasma membrane in the synthesis of beta-(1-->3)-D-glucan wall microfibrils in yeast cells.

Actins↗
PubMed2003

Formation of the outer layer of the Dictyostelium spore coat depends on the inner-layer protein SP85/PsB.

The Dictyostelium spore is surrounded by a 220 microm thick trilaminar coat that consists of inner and outer electron-dense layers surrounding a central region of cellulose microfibrils. In previous studies, a mutant strain (TL56) lacking three proteins associated with the outer layer exhibited increased permeability to macromolecular tracers, suggesting that this layer contributes to the coat permeability barrier. Electron microscopy now shows that the outer layer is incomplete in the coats of this mutant and consists of a residual regular array of punctate electron densities. The outer layer is also incomplete in a mutant lacking a cellulose-binding protein associated with the inner layer, and these coats are deficient in an outer-layer protein and another coat protein. To examine the mechanism by which this inner-layer protein, SP85, contributes to outer-layer formation, various domain fragments were overexpressed in forming spores. Most of these exert dominant negative effects similar to the deletion of outer-layer proteins, but one construct, consisting of a fusion of the N-terminal and Cys-rich C1 domain, induces a dense mat of novel filaments at the surface of the outer layer. Biochemical studies show that the C1 domain binds cellulose, and a combination of site-directed mutations that inhibits its cellulose-binding activity suppresses outer-layer filament induction. The results suggest that, in addition to a previously described early role in regulating cellulose synthesis, SP85 subsequently contributes a cross-bridging function between cellulose and other coat proteins to organize previously unrecognized structural elements in the outer layer of the coat.

Animals↗
PubMed2002

Disruption of the gene encoding the latent transforming growth factor-beta binding protein 4 (LTBP-4) causes abnormal lung development, cardiomyopathy, and colorectal cancer.

Transforming growth factor-betas (TGF-betas) are multifunctional growth factors that are secreted as inactive (latent) precursors in large protein complexes. These complexes include the latency-associated propeptide (LAP) and a latent transforming growth factor-beta binding protein (LTBP). Four isoforms of LTBPs (LTBP-1-LTBP-4) have been cloned and are believed to be structural components of connective tissue microfibrils and local regulators of TGF-beta tissue deposition and signaling. By using a gene trap strategy that selects for integrations into genes induced transiently during early mouse development, we have disrupted the mouse homolog of the human LTBP-4 gene. Mice homozygous for the disrupted allele develop severe pulmonary emphysema, cardiomyopathy, and colorectal cancer. These highly tissue-specific abnormalities are associated with profound defects in the elastic fiber structure and with a reduced deposition of TGF-beta in the extracellular space. As a consequence, epithelial cells have reduced levels of phosphorylated Smad2 proteins, overexpress c-myc, and undergo uncontrolled proliferation. This phenotype supports the predicted dual role of LTBP-4 as a structural component of the extracellular matrix and as a local regulator of TGF-beta tissue deposition and signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2001

COBRA encodes a putative GPI-anchored protein, which is polarly localized and necessary for oriented cell expansion in Arabidopsis.

To control organ shape, plant cells expand differentially. The organization of the cellulose microfibrils in the cell wall is a key determinant of differential expansion. Mutations in the COBRA (COB) gene of Arabidopsis, known to affect the orientation of cell expansion in the root, are reported here to reduce the amount of crystalline cellulose in cell walls in the root growth zone. The COB gene, identified by map-based cloning, contains a sequence motif found in proteins that are anchored to the extracellular surface of the plasma membrane through a glycosylphosphatidylinositol (GPI) linkage. In animal cells, this lipid linkage is known to confer polar localization to proteins. The COB protein was detected predominately on the longitudinal sides of root cells in the zone of rapid elongation. Moreover, COB RNA levels are dramatically upregulated in cells entering the zone of rapid elongation. Based on these results, models are proposed for the role of COB as a regulator of oriented cell expansion.

Amino Acid Sequence↗
PubMed1996

An accurate method for comparing transcript levels of two alleles or highly homologous genes: application to fibrillin transcripts in Marfan patients' fibroblasts.

We introduce here a novel and generally applicable, solid-phase minisequencing-based approach for rapid estimation of relative levels of transcripts with high sequence homology. This study was undertaken to screen for the consequences of different fibrillin-1 mutations on the transcript levels in patients with the Marfan syndrome (MFS). This dominantly inherited, connective tissue disorder is characterized by pleiotrophic symptoms in cardiovascular, skeletal, and ocular systems. A spectrum of disease mutations in the gene encoding fibrillin-1 (FBN1), a glycoprotein component of extracellular matrix microfibrils, has been identified in MFS patients, but the mechanisms by which mutations result in different phenotypic manifestations are still unknown to a large extent. Our data from the quantitation of FBN1 transcripts provide support for the hypothesis that mutations causing premature stop codons result in a milder phenotype than classical MFS by reducing the stability of the mutant transcript and, consequently, decreasing the interference of mutant polypeptide in the formation of fibrillin fibers. We also applied this mRNA quantitation method to determine the relative ratio between transcripts from the genes coding for two highly homologous microfibrillar components, FBN1 and FBN2, in control fibroblast cultures as well as in fibroblasts from MFS patients. Interestingly, these data show large variations between the levels of the two transcripts in fibroblast cultures, but these variations do not correlate either with the nature of the disease mutation or to the clinical MFS phenotype.

Alleles↗
PubMed1992

Effect of cellulose synthesis inhibition on growth and the integration of xyloglucan into pea internode cell walls.

2,6-Dichlorobenzonitrile (DCB, 100 mum) inhibited by 80 to 85% the incorporation of [(3)H]glucose into cellulose in stem segments of etiolated pea (Pisum sativum) seedlings. The inhibition lasted for at least 24 h. In the period 1 to 4 h after the excision of the segments, DCB did not influence elongation in the presence or absence of 2,4-dichlorophenoxyacetic acid (2,4-D). However, during the period 1 to 24 h after excision, DCB enhanced endogenous and 2,4-D-stimulated elongation by 65 and 34%, respectively. DCB did not affect the incorporation of (3)H from [(3)H]arabinose into xyloglucan, and did not change the ability of the [(3)H]xyloglucan formed in vivo to bind strongly to the cell wall. Therefore, at least 80 to 85% of newly synthesized cellulose was excess to the requirements for tight wall binding of newly synthesized xyloglucan. This conflicts with the hypothesis that xyloglucan is held in the cell wall solely by direct hydrogen bonding to the surfaces of cellulosic microfibrils.

Journal Article↗