Showing papers on "Ultrastructure published in 1991"

Extraction of extendable beaded structures and their identification as fibrillin-containing extracellular matrix microfibrils.

Abstract: High molecular weight aggregates were extracted from human amnion using buffers containing 6 M guanidine hydrochloride. Rotary shadowed preparations and negatively stained samples examined by electron microscopy showed that each aggregate appeared to be a string of globular structures joined by fine filaments, giving the appearance of beads on a string. The periodicity of the beads was variable. A mouse monoclonal antibody directed against a previously characterized pepsin fragment of fibrillin was used with gold-conjugated secondary antibody and immunoelectron microscopy to show that the aggregates contained fibrillin. Similar structures were found in non-denaturing homogenates of skin, tongue, ligament, ciliary zonule, cartilage, and vitreous humor. When immunogold-labeled beaded structures were prepared for electron microscopy in the same manner as tissue, the beaded structures could no longer be seen. Instead, gold-labeled microfibrils were found which appeared to be the same as the fibrillin-containing matrix microfibrils observed in connective tissues and often associated with elastin. Thus, standard TEM protocols including fixation, dehydration, and embedding alter the ultrastructural appearance of microfibrils as compared with negative stain or rotary shadowing techniques. When skin was stretched and prepared for electron microscopy while still under tension, beaded filaments were seen in the tissue sections, but were not visible in non-stretched controls. In addition, when stretched ligament was immunolabeled with antibody directed against fibrillin while still under tension, the periodicity of antibodies along the microfibrils increased compared with non-stretched controls. We propose that microfibrils contain globular structures connected by fine filaments composed at lease in part of highly ordered, periodically distributed fibrillin molecules, whose periodicity is subject to change dependent on the tensional forces applied to the tissue in which they are contained.

Retention of chloroplasts and bathymetric distribution in the Sublittoral Foraminiferan Nonionellina Labradorica

Abstract: The distribution of Nonionellina labradonca was studied with the help of bottom samples collected in the 1920§, 1930§ and 1980§ from soft bottoms at the Swedish west coast It was found only below the pycnocline where the water is relatively cold (4-14°C) and has a salinity of more than 30‰ It had roughly the same bathymetric distributional pattern in the 1980§ as in the 1920§ and 1930§ Microscopical and ultrastructural studies showed that its protoplasm contains symbiotic or sequestered chloroplasts down to 300 m depth Specimens with chloroplasts from 45 m depth were incubated with 14C in the laboratory and were able to photosynthesize During the winter, the foraminiferan has a low feeding activity, a reduced chloroplast content, and a slow growth

Three-dimensional ultrastructure of human tendons.

Abstract: The three-dimensional ultrastructure of human tendons has been studied. Epitenon and peritenon consis of a dense network of longitudinal, oblique and transversal collagen fibrils crossing the tendon f

Proteoglycan : collagen interactions and corneal ultrastructure

Abstract: Introduction Cornea presents a deceptively simple picture. It is a transparent structure that looks much the same in all sighted animals, and throughout life; a window that helps focus light on the back of the eye. It is a typical connective tissue (the dry weight consists mainly of collagen and proteoglycans) but it also contains much water ( 80% of wet weight e.g. [ 11). In essence it is a slice of water, stabilized in three dimensions by a meshwork of fibrils and soluble polymers. The subtleties lie in the way this is done. David Maurice [2] pointed out that the fibrils had to be arranged in a very orderly way for transparency, and that their separations were critical if ‘visible’ light was not to be totally refracted. Subsequent studies showed that interfibrillar distances were not only constant across the cornea, but also in the corneas of a large number of different species [3]. Furthermore, the fibrils themselves not only have the same diameter across the cornea but also in the corneas of a large number of species [4]. As a corollary, the volume between the fibrils should also be constant, and since this space contains mainly water, the water content should be constant in different species, and this is also the case [ 11. Hedbys [ S ] elegantly showed that ( a ) the interfibrillar glycosaminoglycan (GAG) had swelling pressure, and ( b ) this pressure was the sum of two contributions, one from chondroitin sulphate (CS) and the other from keratan sulphate (KS). It would also have been possible to conclude from his data that CS and KS were on different molecules, but this point was not appreciated until much later [6]. It was speculated [7] that the interfibrillar proteoglycan (PG) was organized to keep the fibrils apart. This paper will elucidate this relationship.

The proximal border of the human respiratory unit, as shown by scanning and transmission electron microscopy and light microscopical cytochemistry.

Abstract: The epithelial cell types present in respiratory (= distal alveolarized) and terminal (= distal nonalveolarized) bronchioles in adult human lung were characterized with scanning and transmission electron microscopy (SEM, TEM) and light microscopic cytochemistry, using specific antibodies against surfactant protein SP-A and mucins, and Alcian blue/periodic acid-Schiff (AB/PAS) staining. In the respiratory bronchiole, two epithelial cell populations share the same basal lamina: one pseudostratified columnar with ciliated, secretory, and basal cells and the other predominantly simple cuboid with some interspersed flat (type I) cells. The columnar secretory cells show the ultrastructure of mucous cells. Light microscopically, they react with mucin antibodies and contain primarily periodatereactive acid mucins. The mucous cells are the distal secretory cells described by Clara (1937). The cuboid cells are identified as type II (precursor) cells based on ultrastructural criteria for embryonic type II cells (Ten Have-Opbroek et al., 1988a, 1990a), including a cuboid cell shape, a large and roundish nucleus, rough and smooth endoplasmic reticulum (ER), osmiophilic multivesicular bodies, and dense bodies. These dense bodies in turn frequently exhibit—like those in embryonic type II cells—internal vesicles or lamellae, variability in size and shape, a specific relationship to ER and a widespread cytoplasmic distribution. Finally, the cuboid cells show a cytoplasmic staining pattern for SP-A. The terminal bronchiole is lined by the columnar cell population. In the respiratory bronchiole, the columnar (bronchial) and cuboid (alveolar) cell populations occupy distinctly different zones (pulmonary artery zone versus remaining wall). The alveolar part of the respiratory bronchiole (called alveolar tubule) defines the proximal border of a true respiratory unit.

Silica deposition and ultrastructure in the cell wall of Equisetum arvense: the importance of cell wall structures and flow control in biosilicification?

Abstract: Scanning and transmission electron microscopy have been used in the investigation of the surface micromorphology and ultrastructure of silicas extracted from different regions of the horsetail Equisetum arvense . The surface micromorphology was found to be very complex and varied with the anatomical region of the plant. Principally fibrillar, globular and sheet-like ultrastructural motifs of silica were observed, their proportions and detailed structure also varying with the anatomical region studied. The physiocochemical mechanisms by which these structural motifs arise are discussed in relation to the surface micromorphologies observed and to their anatomical function.

An ultrastructural study on the early development of Zea mays somatic embryos.

Abstract: Friable embryogenic callus, obtained from immature embryos of Zea mays L., was cultured on N6 medium supplemented with 1 mg/L 2,4-dichlorophenoxyacetic acid, 6 mM proline, and 2% sucrose. Cultured tissue fragments containing several globular embryoids were excised and examined by light and electron microscopy to follow the early development of maize embryoids. The somatic embryos consist of an apical region and a suspensor region. Cells of the apical region are small, cytoplasm rich, and mitotically active. They contain much starch and numerous bundles of microtubules. Suspensor cells are larger and more vacuolated. A high metabolic activity in both cell types is indicated by the presence of many organelles, coated vesicles, and multivesicular bodies. Transition units appear to form intermediate stages between the embryogenic callus cells and the somatic embryo. A transition unit consists of a group of embryogenic cells and shows an apical and a basal region. The unit has many intercellular spaces, and wi...

Diversity of ultrastructure in different phenotypes of cultured microvessel endothelial cells isolated from bovine corpus luteum

Abstract: Five different types of cultured microvessel endothelial cells defined by use of light microscopy and scanning electron microscopy in a preceding study were investigated by transmission electron microscopy. Type-1 cells displayed a deep invagination of the cell membrane or a single cilium. Granules of low electron density were abundant. A perinuclear ring of intermediate filaments occurred. Cultures of type-2 cells were subdivided into phenotype A, reminiscent of cell-type 1, and into phenotype B, assumed to be vascular smooth muscle cells. Many highly electron-dense granules appeared in late postconfluent cultures of both phenotypes. Cell-type 3 was conspicuous because of a large intracytoplasmic vacuole. Lysosomes with curvilinear bodies were found in cell-types 3 and 4. Both cell types developed a peripheral regular network of microfilaments. Cell-type 5 showed vesiculation of the rough endoplasmic reticulum, lipid droplets and a peripheral felt-like belt of microfilaments. Tubular forms seen in late postconfluent cultures of cell-types 1 to 3 displayed a core of extracellular matrix. Pseudotubular forms of cell-type 4 contained apoptotic bodies. Thus, as seen at the ultrastructural level, different features are maintained by cultured microvessel endothelial cells, suggesting that they have different inherent properties.

Aspects of molecular organization and ultrastructure in starch granules.

Abstract: Introduction: starch granule organization and biosynthetic implications The organization of starch polysaccharides into discrete granules is encountered throughout the plant kingdom and has a major impact on both biological and technological functionality. The insoluble granule form contains densely packed polysaccharide and is therefore an efficient means of storing reserve energy in plants. It may also be significant that amylolytic enzyme reactions are relatively slow and/or limited with granular starch substrates, thus potentially allowing control of glucose availability during mobilization of the energy reserve. In food and commercial uses of starch, the relatively non-functional granule is usually cooked in one way or another, resulting in loss of granule form and massive uptake of water. It has been recognized for a long time that starch granules contain ordered structures, traditionally identified by birefringence effects at the light microscope level, and through characteristic X-ray powder diffraction patterns [ 1 I. More recently it has been shown that observed diffraction patterns are due to packing of left-handed co-axial double helices [ 1, 21 into extended regular arrays. Several lines of evidence implicate the amylopectin component as being the predominant, if not sole, contributor to crystalline order within granules [ 11. Recent advances in electron microscopy coupled with scatteringldiffraction measurements have shown significant layering within granule fragments, with unit blocks spaced at regular intervals of cu. 10 nm [O], and have provided good evidence that crystalline ordered structures tend to radiate outwards from the centre of a granule [4]. Transmission electron micrographs of etched and stained granule thin sections show a layered ‘growth ring’ structure with ring spacings of the order of 1 p m [ 11. There is therefore good evidence that various levels of structural organization exist within granular starch. The generation of such hierarchical order is a major achievement for the biosynthetic apparatus, particularly as the granule form appears to be remote from thermodynamic equilibrium. This is

Using electron microscopy to study plant pathogenic fungi

Abstract: (1991). Using Electron Microscopy to Study Plant Pathogenic Fungi. Mycologia: Vol. 83, No. 1, pp. 1-19.

Morphological and physiological studies on the olfactory organ of the striped eel catfish,Plotosus lineatus

Abstract: The olfactory organ of the striped eel catfish,Plotosus lineatus (Thunberg), obtained off Kyushu Island, Japan, was examined both morphologically and electrophysiologically. The olfactory organ ofP. lineatus differs from that of most other catfishes, possessing a small olfactory rosette containing only relatively few lamellae, a well-developed olfactory ventilation sac used as the primary means of propelling water through the olfactory chamber, and olfactory sensory epithelia lying in discrete patches rather than continuously distributed across the lamellae. Although morphological differences in the olfactory organ betweenP. lineatus and other catfishes are significant, the physiological characteristics are remarkably similar. Response thresholds for amino acids (L-cysteine and L-glutamine) were ca. 10−9M, and the relative effectiveness of 16 amino-acid stimuli differed little from those reported for other catfishes.

The ultrastructure of human cumulus-corona cells at the time of fertilization and early embryogenesis. A scanning and transmission electron microscopic study in an in vitro fertilization program.

Abstract: We observed the ultrastructure of the cumuluscorona cells (CC cells) surrounding: 1) human preovulatory oocytes unfertilized after in vitro insemination and 2) in vitro-fertilized polypronuclear ova (PO) at the pronuclear stage (3 pronuclei) and during early cleavage, at the 3-8 cell stage (cleaving PO). All the samples were obtained from women who underwent pharmacological hormonal stimulation during in vitro-fertilization procedures. Both cell groups were composed of irregularly rounded CC cells, showing an oval nucleus with one or more reticular nucleoli. Spermatozoa in close contact with CC cells were also seen. Linear and annular gap junctions between neighbouring cells were present, particularly in Group 1. Lipid droplets were present in both groups, appearing slightly more numerous and electron-dense in Group 2. In Group 1, mitochondria were numerous, polymorphic, and provided with cristae varying from lamellar to tubular. In Group 2, mitochondria also showed polymorphism, with bacilliform organelles with tubular cristae being predominant. In both groups cisternae and associated vacuoles and vesicles belonging to the Golgi complex were scattered in the cytoplasm of CC cells. Similarly, tubular and vesicular profiles of smooth endoplasmic reticulum were abundant and uniformly distributed throughout the cytoplasm of CC cells of both groups. In contrast, the abundant rough endoplasmic reticulum in Group 1 was formed by parallel stacks of flattened cisternae, whereas it was less plentiful and not arranged in stacks in Group 2. The CC-cell surface appeared covered by numerous membrane expansions in both groups. The expansions in Group 1 were mainly composed of blebs of various sizes and a few short microvilli, whereas in Group 2 numerous microvilli covered the cell surface.These observations demonstrate that a gradual establishment and maintainance of a steroidosynthetic capability (luteinization) takes place in CC cells, particularly during and shortly after fertilization, as occurs contemporaneously in the granulosa cells of the postovulatory follicle. Our results may be considered as ultrastructural confirmation of the capability of the CC cells to produce small amounts of steroids (estrogens and mainly progesterone). These hormones, alone or together with other substances (proteins, nutrients, growth factors?), might—around the fertilization time—act positively upon the early embryo itself, as well as on the microenvironment in which the embryo develops, both in vivo and in vitro conditions.

Detection of B19 parvovirus in human fetal tissues by electron microscopy.

Abstract: We present the electron microscopy observations on samples from 38 pregnancies that were investigated for B19 parvovirus infection. Thirty-four had resulted in fetal loss thought to be due to a virus infection and 22 of the 38 were positive for B19 parvovirus in one or more of the tissues. Twenty-one placentas and 75 fetal tissue samples were examined. Fresh samples were investigated by immune electron microscopy while formalin-fixed tissues were examined as thin sections and by negative staining of tissue extracts with direct electron microscopy. Electron microscopy was more sensitive on fresh than on fixed samples. The ultrastructural observations on thin sections of fixed tissues yielded new information locating B19 parvovirus particles in both nucleus and cytoplasm of infected fetal cells. The diagnostic results of the range of electron microscopy assays were compared with those of two hybridization methods. The fresh samples yielded comparable results from electron microscopy and hybridisation assays but on formalin-fixed materials hybridisation was more sensitive.

Effects of High Pressure Treatment on the Ultrastructure and Solubilization of Isolated Myofibrils

Abstract: High hydrostatic pressures of 100 MPa to 300 MPa were applied to isolated myofibrils prepared from rabbit skeletal muscle to investigate the pressure-induced degradation of myofibrillar structure in the muscle.A marked loss of the regular structure was observed in the phase-contrast image of the isolated myofibrils pressurized at 150 MPa, with further progress of the rupture of structure with increasing pressure applied. When exposed to pressures of 200 MPa or higher, clumping of the crushed myofibrils was observed. Electron microscopic studies of the pressurized myofibrils showed that the loss of M-line materials, rupture of I-filament, and the loss of the structural continuity with the loss of Z-line progressed in the myofibrils with increasing pressure applied. A sigmoidal relationship was obtained between the degree of solubilization and the intensity of the pressure applied to the isolated myofibrils. The electrophoretic analysis indicated that the amount and the species of the protein released from ...

Ultrastructural study of asexual development of Cryptosporidium parvum in a human intestinal cell line.

Abstract: The lack of a well-defined in vitro model of Cryptosporidium infection has severely hampered research on the biology of parasitic invasion of the host cell and on intracellular development of the parasite. In vitro infection of the differentiated human enterocyte cell line HT29.74 was studied by electron microscopy to detect changes in parasite and host cell morphology. Cryptosporidium oocysts obtained from AIDS patients were applied to a monolayer of cloned differentiated HT29.74 cells. Parasites and infected cells were evaluated by transmission electron microscopy at 20 min, 1 h, 6 h, 24 h and 7 days. Sporozoite invagination within the epithelial cell microvilli and subsequent penetration was evident at 1 h. At 6 h, the development of a dense band and feeder layer was visible. Development of the trophozoite into a schizont occurred over 24 h. Micronemes and dense granules were clearly visible within sporozoites and merozoites. Organization of vacuoles within the cytoplasm of the host cell was evident below the dense band. A sexual Cryptosporidium development in vitro was morphologically no different from initial development in vivo. In vitro infection of HT29.74 cells provides an excellent model to study parasite-host cell interaction and asexual parasite development.

Structure and ultrastructure of the epididymis of the viviparous lizard during the annual hormonal cycle: Changes of the epithelium related to secretory activity.

Abstract: This study deals with the structure and ultrastructure of the epithelial cells of the lizard (Lacerta vivipara Jacquin) epididymis as related to secretory activity. The epithelium contains only two types of cells, secretory cells and basal cells. The secretory cells undergo an annual cycle which has been divided into 10 stages. In its most active secretory state, epithelium forms 65.3% of the organ volume. The secretory cell is a tall columnar cell (from 55 ± 3.4 μm to 74.3 ± 2.4 μm height) with a basal nucleus and a supranuclear cytoplasm almost entirely occupied by numerous large secretory granules (5 to 7 μm in diameter). At the ultrastructural level, secretory cells contain rough endoplasmic reticulum (RER), Golgi complex, and secretory granules at various stages of synthesis before being discharged into the lumen. Each granule is membrane-limited and contains a spherical electron dense central core and a peripheral vacuole which varies in density. The secretory cell originates from small cubic cells (13.8 ± 0.7 μm) with few organelles (stage 1). The height of the cell increases gradually and free ribosomes appear first (stage 2), followed by scarce elements of RER (stage 3). The step preceding the secretion period (stage 4) is characterized by a conspicuous increase in volume of RER and Golgi complex. From stage 7 to stage 10, the cell undergoes a dramatic involution. After a transient hypertrophy of the RER, numerous autophagic vacuoles invade the cytoplasm. This degeneration can lead to a complete lysis of the cell and to its rebuilding after elimination of the greatest part of the cytoplasm. The volume of the epithelium falls to 15.6% of the total volume. With antibodies raised against the protein family which constitutes the main part of the secretion (L proteins of 19 kDa), it is shown by immunohistochemistry that these proteins are concentrated into secretory granules which are discharged into the lumen to finally bind to the heads of the spermatozoa.

Assessment of ultrastructure in isolated cochlear hair cells using a procedure for rapid freezing before freeze-fracture and deep-etching.

Abstract: Separated cochlear outer hair cells and isolated strips of organ of Corti containing hair cells and supporting cells have been rapidly frozen before freeze-fracture and deep-etching by immersion of samples sandwiched between two copper plates into liquid nitrogen-cooled propane: isopentane. Assessment of this procedure has shown that no significant freezing damage occurs. The ultrastructure of the hair cells revealed by freeze-fracture of these non-chemically fixed preparations was generally very similar to that seen in fixed material. This indicates that the processing of cochlear tissue normally used for electron microscopy produces few obvious structural artefacts. It also demonstrated that procedures for isolating cochlear hair cells generally do not affect cell structure significantly. However, some isolated hair cells did show abnormalities within the membranes of the lateral cisternae. Such membrane alterations, which would not be identified by light microscopy, occurred to a variable extent but were more commonly present after prolonged periods in maintenance medium. Deep-etching of the preparations to examine extracellular features around stereocilia revealed clearly lateral cross-links between stereocilia. However, tip-links could not be positively identified in either unfixed or prefixed preparations.

Cuticle development and ultrastructure: evidence for a procuticle of high osmium affinity

Abstract: Transmission electron microscopy was used to investigate the development and ultrastructure of the cuticles of the bladder primordium and other parts of Utricularia, the stem of Cuscuta gronovii, and the leaves of Athanasia parviflora. In all materials investigated, except the apical meristem of Cassytha pubescens, the first-formed cuticle, named the procuticle, was very electron dense and apparently amorphous in texture. Later, the procuticle changed its ultrastructural appearance: in all species having a procuticle it lost much of its electron density. Simultaneously, it developed into a lamellar structure in U. lateriflora and Cuscuta, and became part of a lamellar cuticle proper. In U. sandersonii and Athanasia the procuticle generally remained without visible structure. The velum of the pavement epithelium of Utricularia is considered to be a slightly modified procuticle which has become loosened from the epithelial cells and stretched.

Ultrastructure of the septal pore apparatus and early septum initiation in Auricularia auricula-judae

Abstract: The septal pore apparatus and septum initiation in vegetative hyphae of Auricularia auricula-judae were studied by light and electron microscopy for phylogenetic comparisons. Both freeze substituti...