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PubMed1988

Chitin synthetase activity is bound to chitosomes and to the plasma membrane in protoplasts of Saccharomyces cerevisiae.

The sub-cellular distribution of chitin synthetase was studied in homogenates of Saccharomyces cerevisiae protoplasts. Use of a mild disruption method minimized rupture of vacuoles and ensuing contamination of subcellular fractions by vacuolar proteinases. After fractionation of whole or partially purified homogenates through an isopycnic sucrose gradient chitin synthetase activity was found to be distributed between two distinct particulate fractions with different buoyant density and particle diameter. When whole homogenates were used, about 52% of the chitin synthetase loaded was localized in a microvesicular population identified as chitosomes (diameter 40-110 nm; buoyant density (d) = 1.146 g/cm3). Another vesicular population containing 26% of the activity was identified as plasma membrane vesicles because of its large mean diameter (260 nm), its high buoyant density (d = 1.203 g/cm3) and by the presence of the vanadate-sensitive ATPase activity. Moreover, after surface labeling of protoplasts with 3H-concanavalin A, the label cosedimented with the presumed plasma membrane vesicles. There was a negligible cross-contamination of the chitosome fraction by yeast plasma membrane markers. In both the plasma membrane and the chitosome fractions, the chitin synthetase was stable and essentially zymogenic. Activation of the chitosome fraction produces microfibrils 100-250 nm in length. Our results support the idea that chitosomes do not originate by plasma membrane vesiculation but are defined sub-cellular organelles containing most of the chitin synthetase in protoplasts of Saccharomyces cerevisiae.

Ca(2+) Mg(2+)-ATPase↗
PubMed1985

The retention and ultrastructural appearances of various extracellular matrix molecules incorporated into three-dimensional hydrated collagen lattices.

Artificial extracellular matrices composed of collagen, glycosaminoglycans (GAG), proteoglycans (PG), plasma fibronectin (FN), and a hyaluronate-binding protein (HABP) have been prepared that morphologically resemble embryonic extracellular matrices in vivo at the light and electron microscope level. The effect of each of the above matrix molecules on the structure and "self-assembly" of these artificial matrices was delineated. (1) Matrix components assembled in vitro morphologically resemble their counterparts in vivo, for the most part. Scanning and transmission electron microscopy indicate that under our assembly and fixation conditions, collagen forms striated fibrils that are 125 nm in diameter, FN forms 30- to 60-nm granules, chondroitin sulfate proteoglycan (CSPG) forms 27- to 37-nm granules, chondroitin sulfate (CS) assembles into 100- to 250-nm spheres, and hyaluronate (HA) appears either as granular mats when fixed with cetylpyridinium chloride (CPC) or as 1.5- to 3-nm microfibrils when preserved with ruthenium red plus tannic acid. These molecules are known to assume the same configurations in embryonic matrices when the same preservation techniques are used with the exception of FN, which generally forms fibrillar arrays. (2) Addition of various matrix molecules can radically change the appearance of the collage gels. HA greatly expands the volume of the gel and increases the space between collagen fibrils. CSPG at low concentrations (less than 1 mg/ml) and CS at high concentrations (greater than 20 mg/ml) bundle the collagen fibrils into twisted ropes. (3) A variety of assays were used to examine binding between various matrix components and retention of these components in the hydrated collagen lattices. These assays included solid-phase binding assays, negative staining of spread mixtures of matrix components, cryostat sections of unfixed mixtures of matrix components, and retention of radiolabeled matrix molecules in fixed and washed gels. A number of these binding interactions may play a role in the assembly and stabilization of the matrix. (a) HA, CSPG, and FN bind to collagen. CS appears to only weakly bind to collagen, if at all. (b) FN promotes the increased retention of HA, CSPG, and to a very small degrees, CS, in collagen gels. Conversely, the GAG increase the retention of 3H-FN in the gels. Furthermore, FN binds to HA, CS, and CSPG as demonstrated by solid surface binding assays and morphological criteria. The increased retention of GAG and CSPG by the addition of FN may be due to both stabilization of binding to the collagen and trapping of matrix complexes within the gel. (c) HA binds to both CS and CSPG.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Pigment cell pattern formation in Taricha torosa: the role of the extracellular matrix in controlling pigment cell migration and differentiation.

The neural crest is a population of highly migratory mesenchymal cells that ultimately localize in specific sites and differentiate into a variety of cell types. This report describes studies on the factors governing the migratory pathways, differentiation, and ultimate localization of the neural crest-derived pigment cells (black melanophores and yellow xanthophores) in the California newt, Taricha torosa. Melanophores first appear scattered in the dorsal portion of the lateral neural crest migratory pathway (between the somites and the ectoderm). These cells are eventually found in two stripes: a dorsal stripe that runs along the apex of the somites, and a midbody stripe near the somite-lateral plate mesoderm border. Melanophores are not seen in the dorsal fin of prehatching embryos. Xanthophores can be identified with the light microscope using NH4OH-induced autofluorescence of pteridines and in the transmission electron microscope (TEM) by the presence of pterinosomes. Xanthophores first appear scattered among the melanophores over the surface of the somites; these cells eventually are found between the two melanophore stripes and in the dorsal fin. We were interested in determining the roles of the extracellular matrix (ECM) in controlling the formation of pigment cell patterns in T. torosa. Immunocytochemistry, Alcian blue staining of paraffin sections and ruthenium red staining of thin sections (accompanied by Streptomyces hyaluronidase and chondroitinase ABC digestion) were used to identify the composition and distribution of the ECM surrounding the pigment cells at various stages during development. The adhesive glycoprotein fibronectin is found in the dorsal portion of the lateral neural crest migratory pathway as well as in the dorsal fin matrix. Glycosaminoglycans (GAG) are found primarily in the dorsal fin and in the ECM surrounding the notochord. The dorsal fin ECM contains hyaluronate (HA), which was identified in the TEM as Streptomyces hyaluronidase-sensitive 3-5 nm microfibrils, as well as sulfated proteoglycan aggregates. We then confronted T. torosa neural crest cells in vitro with known ECM molecules. When neural folds are explanted onto tissue culture plastic in half-strength L-15 medium containing 10% fetal calf serum (FCS), cells migrate from the explant and differentiate into melanophores after 6 to 9 days. Xanthophores appear in the cultures 2 to 4 days after the appearance of melanophores. When cultured on three-dimensional collagen gels, xanthophores migrate significantly farther (P less than 0.01) onto and into the collagen than melanophores (336 +/- 183 vs 196 +/- 160 microns from the edge of the explant).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Biophysical mechanisms for morphogenetic progressions at the shoot apex.

Leaf primordia, first visible as small bumps, are produced in a cyclical pattern at the edges of the shoot apex, a smooth region at the top of the stem. Their formation is a biomechanical process. This review first considers hypothetical construction mechanisms and then summarizes research that provides information about how and where the primordia are made. Studies of growth at the primordium site indicate the importance of growth parallel to the surface in generating the forces for primordium emergence. The symmetry of the pattern of reinforcement by cellulose microfibrils correlates with the subsequent pattern of primordium production. Finite element models of the apex reveal that lateral bulging of the apex results in a gradient of shear stress, with high shear at the future primordium site. In contrast, tension parallel to the surface is lowest at the primordium site. Response of apical surface tissue to punctures indicates that an existing primordium can exert a pulling force tangential to its base and a compressive force perpendicular to its base. These observations lead to identification of a continuous biophysical cycle for apex morphogenesis, in which most of the steps are direct physical consequences of the previous step. Biophysical processes, subject to input from genetic, hormonal, and environmental sources, are thus involved in the construction and patterning of leaf primordia.

Computer Simulation↗
PubMed1983

Elastic and precursor fibres in the normal human eye.

Completely formed elastic fibres consist of a core of amorphous elastin within a mantle of microfibrils. The fibrillar component may occur as isolated bundles (oxytalan) or may be randomly intermingled with variable amounts of elastin (elaunin). The distribution of both mature elastic and incomplete oxytalan and elaunin fibres in the different parts of 53 human eyes from foetal life to old age is described, as evaluated by light microscopy of histochemical preparations. In general elastic tissue was most evident in the collagenous structures save the adult cornea in which incomplete elastic fibres occur rarely and then late in life. Precursor forms predominate in early childhood and show a limited and slow capacity for maturation. The suspensory zonular fibres of the lens appear to be composed largely of oxytalan throughout life. There is also evidence that corneal epithelium and endothelium, irideal smooth muscle and, less certainly, retinal pigment epithelium can synthesise the fibrillar component, although not elastin, of elastic tissue.

Adolescent↗
PubMed1984

Pseudoexfoliative material and oxytalan fibers.

Pseudoexfoliative material (PSX) was found to show oxytalan staining like the ocular zonular fibers. These two fibrous proteins also shared positive reactions for disulfide and sulhydryl groups and for acidic mucosubstances, both of which have been suggested as reactive groups in the oxytalan staining reaction. The deep striated zone in the pre-equatorial lens capsule and the lens capsular inclusions shared most of these reactions, indicating that they contain some similar components. PSX material showed histochemical differences from the zonule, including evidence of less PAS-positive glycoprotein and more acidic mucosubstance. Variations in staining within the PSX excrescences indicated that they are a composite of more than one substance. PSX material appears to be a product of local basement membrane-secreting cells, representing an abnormal polymerization of glycoconjugates similar to those in elastic microfibrils.

Connective Tissue↗
PubMed1996

Cell adhesion and integrin binding to recombinant human fibrillin-1.

Fibrillin-1 is a major constituent of tissue microfibrils that occur in most connective tissues, either in close association with or independent of elastin. To test possible cell-adhesive functions of this protein, we used recombinant human fibrillin-1 polypeptides produced in a mammalian expression system in cell attachment and solid-phase integrin binding assays. Fibrillin-1 polypeptides containing the single RGD sequence located in the fourth 8-cysteine domain, mediated distinct cell adhesion of a variety of cell lines and bound to purified integrin alphaVbeta3. Integrins alphaIIbbeta3, alpha5beta1, alpha2beta1 and alpha1beta1 did not interact with any of the recombinant fibrillin-1 peptides. Our results indicate a novel role for fibrillin-1 in cellular interactions mediated via an RGD motif that is appropriately exposed for recognition by integrin alphaVbeta3.

Amino Acid Sequence↗
PubMed1977

Myogenic foam cells in explants of fatty dots and streaks from rabbit aorta. Morphological studies.

Present studies indicate that in explants of early atherosclerotic lesions removed from aortae of young rabbits on a 1% hypercholesterolemic diet for four and seven weeks respectively, myogenic foam cells (MCF's) were capable of emigrating into the culture medium and maintained their ability to produce microfibrils, elastic tissue elements, and collagen fibrils. In explants of the smallest lesions (fatty dots and small streaks) the MFC's divided prior to, or while emigrating. At the interphase between the primary tissue and the culture medium they contained in intracytoplasmic vacuoles fragments of elastic tissue and extraneous substances which were reminiscent of cellular debris. It is possible that this phenomenon represents a true phagocytic property of the MFC's. All formed extracellular connective tissue components were also produced by the emigrated MFC's in the tissue surrounding the cellular outgrowth. In the large fatty streaks cell division was observed at the interphase between the tissue and culture medium, but not within the substance of the explant; here cellular necrosis was prominent. The fat inclusions in the MFC's of explants and the outgrowth had the appearance of conglomerateds of unorganized, and only at times concentric, membranous profiles rather than that of homogeneous droplets observed by electron microscopy in these cells in tissue sections. In the outgrowth from explants of normal aortic areas adjacent to the lesions a moderate number of smoot muscle cells contained fat inclusions; these were almost totally absent in cells of the primary aortic cultures from normal aortae. It is conceivable that the migratory and phagocytic properties of the MFC's observed in the present study relate to some aspects of regression of atherosclerotic lesions; this, however, remains highly speculative at present.

Animals↗
PubMed1979

Intimal thickening of human femoral arteries with special regard to elastin, Part 1. Diffuse intimal thickening due to growth and age.

In infants, human femoral arteries display seam-like internal elastic lamina (IEL) covered with endothelium on the luminal side and with smooth muscle cells (SMC) on the medial side. At birth the growth of IEL is finished, correlated with a loss of microfibrils (MF) at the periphery. With the onset of the postnatal vessel growth the joints of IEL seem to be mechanically widened until they have the appearance of gaps with progressing age. After the age of 40 years there are often rod-like crystallites in the IEL, probably composed of cholesterol esters. A small first consecutive lamina (CL) can be seen already in childhood; it enlarges until the 3rd decade of life and is interpreted as a substitute to the "fragmented" IEL. After the 5th decade of life the first CL is arranged within the intima at a certain distance from the IEL and consisting of loosely arranged elastic fibrils. In very old arteries (beyond the 8th decade of life) gaps are rarely seen in the first CL. In individuals over the age of 30 years, the space between IEL and the first CL is occupied by smooth muscle cells (SMC) which are tightly packed. Additional CLs above the first CL can be found in elderly individuals, there CL obviously contribute to the intimal thickening. The ultrastructure of the elastic elements of the vessel wall and their possible function are discussed.

Adolescent↗
PubMed1995

Intimal thickenings of human aorta contain modified reassembled lipoproteins.

The aim of this study was to determine whether in human aortas early minute changes such as minimal intimal thickenings (MIT), developed in areas known to have a predilection to atherosclerosis, contain modified reassembled lipoproteins (MRLp) such as extracellular liposomes (EL) and lipid droplets (LD). These features have been previously detected in the aortic lesion-prone areas of rabbits and hamsters fed a fat-rich diet. Tissue samples of the aortic arch and thoracic aorta from 12 young subjects who died in accidents were selectively collected from grossly normal regions. By light microscopy, some of these regions were found to contain MIT. The normal areas and the MIT were separately examined by electron microscopy or subjected to fractionation and partial biochemical characterization. The MIT (approximately 25-100 microns thick) were constituted by a pronounced proliferation of extracellular matrix, especially elastin and microfibrils, with interspersed lipid deposits appearing as EL and LD. Commonly, MIT did not contain smooth muscle cells, macrophages, foam cells or cytolytic debris. Such components were only occasionally found in specimens excised from the vicinity of fatty streaks. Saline extracts of MIT or grossly normal aortic regions were subjected to a four-step purification procedure consisting of gel filtration, affinity chromatography on anti-apo B and anti-albumin Sepharose, followed by density gradient ultracentrifugation. The entire procedure was monitored by negative staining, lipid assays, SDS PAGE and immunoblotting. From the initial MRLp mixture, two fractions were obtained: fraction 1 containing multilamellar EL and LD, and fraction 2 composed mostly of unilamellar EL. As compared with serum LDL, the cholesteryl ester/unesterified cholesterol ratio was 4-6-fold lower in fraction 1 and 15-19-fold lower in fraction 2. On SDS-PAGE the fraction 2 displayed a single protein band of 66 kDa, immunochemically identified as albumin. The MRLp isolated from human aortas with minimal intimal thickenings appeared to be similar to those purified from the prelesional stage aorta of hyperlipidemic rabbits and hamsters.

Adolescent↗
PubMed1984

Morphological study of the chorio-allantoic fetal membranes.

Morphological study of the chorio-allantoic fetal membranes has demonstrated the existence of foot processes extending from the main body of amniotic cells and containing microfibrils arranged in dense bundles as described in podocytes of renal glomerulae; on the surface fronds and between their bases many small pits and caveolae are seen; in the cytoplasm of amniotic cells large vacuoles are present; they frequently distort the nuclei into crescentic shapes. In the chorion underlying the amnios, fibroblasts and Hofbauer cells are found; their surface often has overlapping filopidal projections. The syncytium bounding the intervillous space shows a marked resemblance to that of the villi. These morphological features seem to indicate that chorio-allantoic fetal membranes might be an important route for the transporting of fluid from the maternal blood in the intervillous space into the amniotic compartment.

Allantois↗
PubMed1981

Aggressive fibromatosis involving the paramandibular soft tissues. A study with the aid of electron microscopy.

The distinction at the level of light microscopy between aggressive fibromatosis and low-grade malignancies with fibroblastic features may be difficult. An electron microscopic study of four cases of aggressive fibromatosis of the mandibular soft tissue was undertaken to determine whether any ultrastructural characteristics could be identified that would aid in a more uniform distinction between these lesions. The pertinent findings include the identification of cells of fibroblastic derivation showing a range of organelle-poor to organelle-rich features, cytoplasmic microfibrils, and dilated rough endoplasmic reticulum profiles. These features are discussed in the light of previously published findings of other forms of aggressive fibromatosis and closely related lesions. The study reaffirms that although electron microscopy may be useful in confirming the cell of origin in these lesions, the accurate diagnosis of fibrous tumors still rests with the proper correlation of clinical and light microscopic features. Clinical follow-up of the cases supports both the diagnosis of aggressive fibromatosis and the recommended treatment of adequate local excision.

Adolescent↗
PubMed1991

Organelle rearrangement and cell volume changes during squeezing invasion of peritoneal elastic lamina by targeted murine breast carcinoma cells.

Murine breast cancer cell lines were developed to selectively invade the peritoneum while they proliferated in ascites form in the abdominal cavity. In a dominant form of invasion, tumor cells showed special affinity for elastin fibers and squeezed through narrow gaps in the elastic fiber meshwork of the stroma. Even in fixed tissue, such cells could be recognized as being in the process of invasive migration because of their dumbbell shape. This appearance was similar to that of diapedetic blood cells traversing bone marrow sinus endothelium. Three-dimensional STERECON graphics reconstruction from serial thick sections of 44 such cells was carried out. The reconstructions showed that, in mid-penetration, the cells spread extensively over the exterior surface of the elastic fiber meshwork. The cell surface contact of these forward projections was mainly with the elastic fiber outer coat of microfibrils, but small areas of the cell surface also fused directly to inner-core elastin. The morphological rearrangement of the cytoskeleton was minimal in both types of attachment areas. The location of these forward facing attachments is consistent with mechanisms for pulling the invasive cell through the gap. Lamellopodia formation and clustering of cytoplasmic organelles occurred more commonly at the forward-facing part of the cell. Morphometry of the reconstructions showed that a contraction of the whole cell occurred during the squeezing/migration process suggestive of an additional pushing process. However, our invasive cell lines showed marked differences in the degree of cell shrinkage. The process of adhesion and squeezing of tumor cells through elastin meshworks in vivo is clearly a complex phenomenon. Changes in cell surface activity appear to play a significant role in establishing the necessary 'foothold' component of invasion and, possibly, in the generation of tractive force as well.

Animals↗
PubMed1989

Morphogenesis of abnormal elastic fibers in lungs of patients with panacinar and centriacinar emphysema.

Pulmonary elastic fibers in a patient with panacinar emphysema due to alpha-1-antitrypsin deficiency and three patients with centriacinar emphysema related to anthracosis were studied by electron microscopy and by light and electron microscopic immunohistochemistry for elastin. Four types of abnormal elastic fibers were found: (1) finely disrupted fibers, (2) fibers with vacuolar changes and deposits of electron-dense granular material, (3) accumulations of small, rounded amorphous components of elastic fibers near bundles of microfibrils, and (4) large, confluent masses consisting mainly of aggregates of irregularly and compactly arranged, small-sized amorphous components. The amorphous components in these four types of abnormal elastic fibers tended to stain evenly with antielastin antibody. This is attributed to greater penetration of antielastin antibody into fibers that were incompletely polymerized because of immaturity or hydrolytic damage. Finely disrupted fibers were frequently found in the patient with panacinar emphysema and were presumed to have been damaged by elastase. The other three types of elastic fibers were frequently found in the patients with centriacinar emphysema. The vacuoles and electron-dense deposits in elastic fibers probably represented the consequence of damage to elastic fibers. The small round amorphous components in elastic fibers might be formed from abnormal elastogenesis. The large, confluent elastic masses were thought to be formed by the aggregation of elastic fibers in areas of coalescence of alveolar walls undergoing structural remodeling.

Adult↗
PubMed1990

Age-related changes of the ciliary muscle in comparison with changes induced by treatment with prostaglandin F2 alpha. An ultrastructural study in rhesus and cynomolgus monkeys.

The relationship between individual ciliary muscle cells and the surrounding connective tissue was studied in the eyes of three normal, young (3-4 years) cynomolgus monkeys (Macaca fascicularis), three aged (34-36 years) rhesus monkeys (Macaca mulatta) and seven young (3-7 years) cynomolgus monkeys topically treated with prostaglandin F2 alpha (PGF2 alpha) for 4-8 days. In normal eyes, collagen fibrils and microfibrils are in places in continuity with the muscle cells' basal lamina, which is connected to the cell membrane by fine fibrillous material. In old eyes, the basal lamina is markedly thickened, masking the connection of fibrils with the muscle cells' membrane. A distinctive finding in several muscle cells of old eyes are electronlucent clefts, 60-80 nm wide, between basal lamina and cell membrane, which are not transversed by fibrils or fibrillous material. The cell membrane of these muscle cells shows large folds filled with disarranged myofilaments. Additionally, these cells contain inclusion bodies consisting of concentrically arranged double membranes. Following treatment with PGF2 alpha, similar changes are seen in young animals, too. Here, the muscle cells have lost their connection to the extracellular fibrils due to a PGF2 alpha-induced lysis of extracellular material. Lack of attachment between basal lamina and altered muscle cells in aged eyes might indicate an involvement of the extracellular matrix in age-related changes of the individual ciliary muscle cells.

Aging↗
PubMed1987

In vivo binding of immunoglobulin and complement to elastic structures in urinary bladder vascular walls in interstitial cystitis: demonstration by immunoelectron microscopy.

An ultrastructural immunoperoxidase staining technique was used to identify and localize immune deposits in the urinary bladder vessel walls of patients with interstitial cystitis. Deposition of immunoglobulin together with the C3 component of complement was found in the subendothelial space and in endothelial basement membranes. More peripherally, deposits were often found associated with elastic fibers between smooth muscle cells. In these fibers the staining was confined to the microfibrillar coat. The findings suggest that elastic microfibrils act as target sites for the immunologic reaction occurring in vivo. Following binding of autoantibodies to antigens in bladder mucosa, activation of complement could be involved in the production of tissue injury and in the chronic self-perpetuating inflammation typical of this disease.

Basement Membrane↗
PubMed1989

Differential growth in plants--a phenomenon that occurs at all levels of organization.

Differential growth is a feature of cells, the organs which they construct and the whole plant itself. The control of differential growth at each of these three levels of organization resides in the level lower than that in which it is expressed. Thus, differential growth of cells is regulated by the patterns of intracellular microtubules and cellulose microfibrils of the walls, that of organs by the pattern of growth of their cells, and that of the organism by the relative rates of organ growth. The latter is, in turn, determined an all-pervading system of correlative interactions. Plant hormones by may play a role in each of these regulatory systems.

Plant Cells↗
PubMed1990

Single crystals of chitosan.

Lamellar single crystals of chitosan were prepared at 125 degrees C by adding ammonia to a low DP fraction of chitosan dissolved in water. The crystals gave sharp electron diffraction diagrams which could be indexed in an orthorhombic P2(1)2(1)2(1) unit cell with a = 8.07 A, b = 8.44 A, c = 10.34 A. The unit cell contained two anti-parallel chitosan chains and no water molecules. It was found that cellulose microfibrils from Valonia ventricosa could act as nuclei for inducing the crystallization of chitosan on cellulose. This produced a shish-kebab morphology.

Chitin↗