bluuebunny/crossref_metadata_2025_split huggingface dataset:
The ultrastructural organization of proteoglycans and collagen in human and rabbit scleral matrix
Authors: Young Robert D. 
Published: April 2021

ABSTRACT
The distribution of proteoglycans and their association with collagen fibrils were studied in human and rabbit sclera following fixation of tissue in glutaraldehyde containing Cuprolinic Blue, a specific stain for proteoglycans when used in the presence of critical concentrations of electrolytes. Proteoglycans were visualized by electron microscopy as fine filaments, approximately 54 nm in length and 5 nm in diameter, associated with the d band in the gap zone of the periodic collagen banding pattern. Filaments were present in three orientations: (1) radiating from the d band to associate with corresponding sites on adjacent collagen fibrils; (2) encircling the collagen fibril at the d band position; and (3) lying along the fibril axis, often linking consecutive d bands.
No difference was apparent between the proteoglycan-collagen organization in human and rabbit sclera. A similar arrangement of proteoglycan filaments in association with the collagen d band was also evident throughout all levels of the sclera in spite of considerable variations in fibril diameter from inner to outer stroma.
Furthermore, the specific relationship of proteoglycans with the collagen fibrils in sclera closely resembled that previously described in tendon and in articular cartilage, lending support to the view that the association of proteoglycans with collagen may be consistent in a majority of connective tissues, irrespective of their diverse functional specializations.
Changes occurring in chloroplasts of Phaseolus following infection by Sclerotinia: A cytochemical study
Authors: Tariq V. N. , Jeffries P. 
Published: April 2021

ABSTRACT
Dramatic changes occur in the ultrastructure of chloroplasts within host tissues during the infection of Phaseolus by the plant pathogenic fungus Sclerotinia. Electron-opaque deposits develop initially in the peripheral region of the chloroplast stroma, in cells in advance of the hyphal front. As infection continues, the amount and intensity of deposition increases and spreads throughout the chloroplast. The deposits possess a high degree of structural integrity in the form of a crystalline square lattice with 10 nm periodicity. Enzyme digestion studies have been used to show that the deposits are proteinaceous. Similar deposits are also induced by treatment with oxalic and citric acids, but not by the potassium salts of these acids buffered at pH7·2. It is suggested that a pH change within the chloroplasts, resulting from oxalic acid secretion by the fungus, is responsible for induction of protein deposition. The likelihood that the deposits are ribulose, 1,5-bisphosphate carboxylase-oxygenase is discussed.
The alteration of mitotic events by ionophore a23187 and carbonyl cyanide N-chlorophenylhydrazone
Authors: Ziegler Michael L. , Sisken Jesse E. , Vedbrat Sharanjit 
Published: April 2021

ABSTRACT
A large quantity of published work indicates that calcium ions may be involved in the regulation of mitotic events and recent reports suggest that the onset of chromosome movement is dependent upon a transient increase in free cytosolic calcium ions. In this paper we examine the effects of two agents known to perturb intracellular calcium pools on mitosis in HeLa cells. These were the calcium-selective ionophore A23187 and carbonyl cyanide n-chlorophenylhydrazone (CCCP), which is a protonophoric inhibitor of oxidative phosphorylation. Owing to a stimulation of glycolysis, the latter agent does not decrease intracellular ATP in HeLa but does cause mitochondria to release calcium ions. Our data show that, at low concentrations, both agents prolong metaphase but differ in their effects on anaphase and cytokinesis. Studies with chlorotetracycline, a commonly used probe for membrane-associated calcium, verify that these agents do affect calcium pools under the conditions of our experiments. The data presented are consistent with the idea that increased cytosolic calcium levels can directly or indirectly affect mitotic events but, contrary to other suggestions, cause a prolongation of metaphase, i.e. they delaythe onset of chromosome movement.
X-ray microanalysis of synchronized hela s3 cells infected with vaccinia virus
Authors: Warley Alice , Stephen J. 
Published: April 2021

ABSTRACT
X-ray microanalysis has been used to study changes in concentration of P, S, Cl Na and K in synchronized HeLa S3 cells in G1phase infected with Vaccinia virus. No dramatic redistribution of elements between nucleus and cytoplasm was demonstrated during the first 6h post-infection, during which time viral shut-off of host protein synthesis occurred. [Cl] increased relative to [Na] and [K] during the first 3 h post-infection. The magnitude and direction of change in [K] and [Na] (from approximately 10 cells/analysis) was compared with data previously obtained by flame photometry (from approximately 106 cells/analysis) and found to be remarkably parallel.
Fine structure and radiation resistance in Acinetobacter: A comparison of a range of strains
Authors: Glauert Audrey M. , Thornley Margaret J. 
Published: April 2021

ABSTRACT
Nine strains of the Gram-negative bacterium, Acinetobacter, showed a wide variation in resistance to ionizing radiation; all gave sigmoid survival curves, with D10 values for the ex- ponential portion ranging from 70 to 460 J kg;−1 (7–46 krd). The fine structure of these strains was studied by electron microscopy. Results for a resistant strain were described earlier and the present paper gives comparative results for the other 8 strains.
The mode of division varied, 5 strains dividing predominantly by constriction of all the layers of the cell wall, while the other 4strains showed ingrowth of thick septa. These 4 included the 3 most resistant strains and 1 strain of intermediate resistance.
The arrangement of surface layers was the same as that usually found in Gram-negative bacteria. In 1 strain an extra layer was visible outside the outer membrane; this layer does not appear to influence radiation resistance since it is lacking in another strain of similar resistance.
The layer of wrinkled material, previously observed in the resistant strain between the outer membrane and the intermediate dense layer of the cell wall, in negatively stained preparations of isolated cell walls, was seen in 5 other strains of intermediate and high resistance, while in 3 sensitive strains finely granular material appeared to occupy a corresponding position in the cell wall.
These observations suggest that morphological features, such as the wrinkled layer of the cell wall, and possibly the mode of cell division, may influence the radiation resistance of Acinetobacter strains, but their function is not yet known.
Systemic viral material in the cells of the freshwater red alga Sirodotia tenuissima (holden) skuja
Authors: Lee R. E. 
Published: April 2021

ABSTRACT
A cytoplasmic inclusion consisting of polygonal viral particles surrounding a spherical viroplasm is described in the cells of Sirodotia tenuissima but not in other species of Sirodotia and Batracliospermum investigated. Some polygonal viral particles are also found associated with nucleolar material in the nucleus of S. tenuissima. The viral material is present in the apical cell and appears to be distributed to the daughter cells during division of the apical cell.
The uptake of vitamins by mouse fibroblast cells (strain LS) during growth in a chemically defined medium
Authors: Blaker G. J. , Pirt S. J. 
Published: April 2021

ABSTRACT
The uptake of biotin, choline, folic acid, hypoxanthine, inositol, nicotinamide, pantothenic acid, pyridoxine, riboflavin, thiamine and vitamin B12 by mouse LS cells in suspension culture was determined by microbiological assay methods. Based on the extent of uptake during cell growth, vitamin growth yields (cells produced/unit mass of vitamin utilized) were estimated for all of the vitamins, except folic acid, thiamine and B12. The growth yields were lower during the early phases of culture. No uptakes of folic acid or B12 could be demonstrated. During the period of incubation about half of the thiamine was irretrievably lost through spontaneous decomposition.
Effect of temperature on the mutual adhesion of preaggregation cells of the slime mould, Dictyostelium discoideum
Authors: Garrod D. R. , Born G. V. R. 
Published: April 2021

ABSTRACT
The mutual adhesion of slime-mould cells was investigated at 24 and 1 °C in stirred and unstirred medium. Adhesion was induced by adding sodium chloride and followed by recording the diminution in optical density of the cell suspension associated with the formation of cell aggregates. It was found that: (1) when cells, previously stored at 1 °C, were stirred in distilled water at 24 °C the optical density of the suspension increased; (2) when sodium chloride was added after this increase, the optical density fell as cells adhered to each other; (3) both the increase in optical density and subsequent adhesion were reversibly inhibited at 1 °C; and (4) the rise in optical density was a prerequisite for adhesion.
Comparison of cell shape and volume at the 2 temperatures suggested that the rise in optical density was due to (a) extension of pseudopodia and a consequent change from a spherical to an irregular shape, and (b) an increase in mean cell volume of about 17%.
Observations on the formation of adhesions in still medium at 24 °C showed that initial contacts were formed either by microspikes or by rounded parts of the cell surface. The cell surfaces then flattened against each other, thereby increasing the area of contact. No flattening occurred at 1 °C. Microspikes were present on the surfaces of both cold and warm cells and contained longitudinal fibrils.
It is suggested that adhesion of these cells is inhibited in the cold in stirred medium because the cells are unable to expand areas of mutual contact. Cold adhesions are, therefore, weak and easily disrupted by shearing forces. The inability to expand adhesive contacts may be due to the inhibition of cell motility at low temperature.
The role of microfilaments in cytoplasmic streaming in Drosophila follicles
Authors: Gutzeit Herwig O. 
Published: April 2021

ABSTRACT
During the last phase of oogenesis in Drosophila, nurse cell cytoplasm can be seen to be streaming into the growing oocyte when visualized in time-lapse films. This process can be reversibly inhibited by cytochalasins. The distribution of F-actin filaments in the nurse cells has been studied by staining with rhodamine-conjugated phalloidin. At the beginning of cytoplasmic streaming (stage 10B) increasingly thick bundles of microfilaments formed, many of *which spanned the nurse cell cytoplasm from the cell membrane to the nuclear membrane. The association of F-actin with the nuclear membrane persisted when nurse cell nuclei were isolated mechanically. The experimental evidence suggests that microfilament contraction in the nurse cells leads to cytoplasmic streaming by pressure flow.
Biosynthesis of nuclear proteins after stimulation of quiescent swiss mouse 3t3 cells
Authors: O’Farrell Minnie K. , Dixon Cynthia 
Published: April 2021

ABSTRACT
Stimulation of quiescent Swiss mouse 3T3 fibroblasts either by serum or by the low molecular weight hormones, prostaglandin and insulin, induces DNA synthesis after a lag period of about 15 h. Following restimulation by serum or these pure hormones there is an overall increase of two-to fourfold in the rate of biosynthesis of nuclear proteins. In addition, there is a relative decrease in some proteins (Mr = 200×103, pI 6·0—6’5), while others increase (e.g. actin). Two polypeptides show specific correlations with the exit from Go-The synthesis of p30 (Mr = 30×103, pI 5·2) is at a maximum within 5 h of restimulation, while the synthesis of p36 (Mr = 36×103, pI = 4#x00B7;25) is first seen at 10— 20 h after restimulation. Synthesis of p36 correlates well with the initiation of DNA synthesis. The synthesis of both proteins is stimulated by serum and by the hormones. Thus there are common biosynthetic responses to different stimuli indicating convergent pathways leading to DNA biosynthesis. Addition of hydrocortisone with the growth-stimulatory hormones inhibits both entry into the S phase and biosynthesis of p36. In contrast, hydrocortisone does not alter the biosynthesis of p30. This ‘early’ protein, p30, is different from the products of both c-fos and c-myc. Therefore, we have identified two specific components that might participate in the regulation of cell proliferation.
Either exogenous or endogenous fibronectin can promote adherence of human endothelial cells
Authors: Clark Richard A. F. , Folkvord Joy M. , Nielsen Larry D. 
Published: April 2021

ABSTRACT
Recently, we have presented evidence that proliferating blood vessels produce and deposit fibronectin in situ during the angiogenesis of wound repair. This report extends these observations by demonstrating that human endothelial cells from both large and small vessels depend on fibronectin for their adherence in vitro. Endothelial cells were grown from human umbilical veins (HUVEC) by the method of Gimbrone and from the microvasculature of human omentum by the method of Kern, Knedler and Eckel. Second-passage cells were plated into microtitre wells that had been coated with 100/tgml−1 of fibronectin, types I and III collagen, type IV collagen or laminin. After a 3-h incubation, adherent cells were solubilized with Zap-Isoton and quantified on a Coulter Counter. Under normal culture conditions HUVEC showed no preference for fibronectin substrates while microvascular cells always demonstrated a striking preference for fibronectin substrates. However, when HUVEC were exposed to 2·5 or 25μgml−1 of cycloheximide for 4h before and during the adherence assays, the adherence to fibronectin was 50—200% greater than to types I and III collagen. Immunofluorescence studies showed that while HUVEC expressed a large quantity of surface fibronectin, microvascular cells expressed very little. Metabolic labelling studies confirmed that HUVEC cultures had substantial quantities of fibronectin in their cell layer while microvascular cells did not. In antibody blocking experiments, preincubation of fibronectin-coated surfaces with anti-fibronectin antibodies totally blocked microvascular cell adhesion but only abrogated HUVEC adherence by 50%, presumably since these latter cells were able to deposit additional fibronectin onto the surface during the 3 h assay period. In the presence of cycloheximide anti-fibronectin antibodies totally blocked HUVEC adherence. These results demonstrate that both endothelial cell types rely, at least in part, on fibronectin for adherence in vitro. HUVEC can synthesize, secrete and deposit enough fibronectin for their adherence in vitro, while microvascular cells rely on an exogenous source of fibronectin under these culture conditions. Thus, the increased blood vessel fibronectin observed during angiogenesis in vivo may mediate adherence of the proliferating and migrating endothelial cells.
Tight and gap junctions in the intestinal tract of tunicates (urochordata): A freeze-fracture study
Authors: Lane Nancy J. , Dallai R. , Burighel P. , Martinucci G. B. 
Published: April 2021

ABSTRACT
The intestinal tracts from seven different species of tunicates, some solitary, some colonial, were studied fine-structurally by freeze-fracture. These urochordates occupy an intermediate position phylogenetically between the vertebrates and the invertebrates. The various regions of their gut were isolated for examination and the junctional characteristics of each part investigated. All the species examined exhibited unequivocal vertebrate-like belts of tight-junctional networks at the luminal border of their intestinal cells. No septate junctions were observed. The tight junctions varied in the number of their component strands and the depth to which they extended basally, some becoming loose and fragmented towards that border. The junctions consisted of ridges or rows of intramembranous particles (IMPs) on the P face, with complementary, but offset, E face grooves into which IMPs sometimes fractured. Tracer studies show that punctate appositions, the thin-section correlate of these ridge/groove systems, are sites beyond which exogenous molecules do not penetrate. These junctions are therefore likely to represent permeability barriers as in the gut tract of higher chordates. Associated with these occluding zonular junctions are intermediate junctions, which exhibit no identifiable freeze-fracture profile, and macular gap junctions, characterized by a reduced intercellular cleft in thin section and by clustered arrays of P face particles in freeze-fractured replicas; these display complementary aggregates of E face pits. The diameters of these maculae are rarely very large, but in certain species (for example, Ciona), they are unusually small. In some tissues, notably those of Diplosoma and Botryllus, they are all of rather similar size, but very numerous. In yet others, such as Molgula, they are polygonal with angular outlines, as might be indicative of the uncoupled state. In many attributes, these various junctions are more similar to those found in the tissues of vertebrates, than to those in the invertebrates, which the adult zooid forms of these lowly chordates resemble anatomically.
The presence of epidermal growth factor binding sites in the intracellular organelles of term human placenta
Authors: Ramani N. , Chegini N. , Rao Ch. V. , Woost P. G. , Schultz G. S. 
Published: April 2021

ABSTRACT
Highly purified lysosomes, rough and smooth endoplasmic reticulum, and Golgi apparatus, as well as microvillus plasma membranes, bound 125I-labelled epidermal growth factor ([125I]EGF) with similar affinity. Scatchard plots for all the organelles were curvilinear. The apparent number of available binding sites per mg protein of intracellular organelles was 27–71% of that found in microvillus plasma membranes. The bound and free [125I]EGF were not degraded by any of the organelles.
Binding and dissociation of [125I]EGF in all organelles were dependent on the time and temperature of incubation. The specificity of [125I]EGF binding was similar in all organelles. The optimal pH for binding to lysosomes was 6·0, in contrast to 7·0 for all the other organelles. Exposure of different organelles to enzymes and protein-modifying reagents resulted in numerous binding differences between the intracellular organelles and microvillus plasma membranes. Covalent affinity labelling with [125I]EGF revealed two major proteins of 155 and 140(×103)Mr in all the organelles. The 155×103Mr protein was labelled predominantly in all organelles except rough endoplasmic reticulum, where both proteins were equally labelled. Addition of proteolytic inhibitors during isolation of organelles did not alter the pattern of [125I]EGF-labelled binding proteins found in the organelles.
EGF also stimulated phosphorylation of the 155 and 140(× 103)Mr proteins in all the organelles. The 155×103Mr protein was phosphorylated more than the 140×103Mr protein in microvillus plasma membranes and smooth endoplasmic reticulum, whereas the 140×103Mr protein was phosphorylated more than the 155×103Mr protein in lysosomes and both proteins were equally phosphorylated in rough endoplasmic reticulum. Several organelles also contained minor [125I]EGF-binding proteins that did not show phosphorylation response and proteins that showed phosphorylation response but did not bind [125I]EGF.
Thus, the present study demonstrates by a number of different criteria, that several intracellular organelles of term human placenta also contain EGF-binding and kinase activities.
Three-dimensional reconstruction of the chondriome of the unicellular red alga Rhodella reticulata
Authors: Broadwater Sharon , Scott Joe 
Published: April 2021

ABSTRACT
Three cells of the unicellular red alga Rhodella reticulata were serially sectioned and photographed in a transmission electron microscope in order to analyse the organization of the mitochondrial system, or chondriome, which, on the basis of cursory examination, appeared to consist of an interconnected network of one to a few organelles. The chondriome of all three cells was traced and superimposed on acetate paper and a three-dimensional model using balsa wood was constructed of one cell. The chondriome was found to consist primarily of one large, anastomosing mitochondrion located principally at the cell periphery. In addition, it appears that some cells can contain a few small mitochondria that are not connected to the main body of the chondriome. This is the first study to reveal the three-dimensional nature of the chondriome in a red alga.
Large-scale selection synchrony of Tetrahymena thermophila
Authors: Hill Robin J. , Kroft T. , Zuker M. , Smith Ian C. P. 
Published: April 2021

ABSTRACT
A method is described, based on the phagocytosis of colloidal ferrite particles, which gives highly synchronous populations of Tetrahymena thermophila. To ensure a successful synchrony, the cell culture doubling time, the limits of the phagocytic period and the distribution of cell stages must first be determined. Once these parameters are known, synchrony can be achieved under a variety of growth conditions and with cultures ranging in volume from a few millilitres to 12 litres or more.
The main advantages of the method are that the apparatus required is simple, large volumes of cells can tie handled easily, and the synchronous populations can be prepared within a few hours. In principle, the method should be applicable to any cell population in which phagocytosis occurs discontinuously over the cell cycle.
Quantitative electron microscopic autoradiographic studies on internalization of 125I-labelled epidermal growth factor in term human placenta
Authors: Chegini N. , Rao Ch. V. 
Published: April 2021

ABSTRACT
The electron microscopic autoradiographic studies described here revealed the presence of specific silver grains over nuclei, lysosomal vesicles, rough endoplasmic reticulum and Golgi apparatus after incubation of placental tissue for 2h at 38°C with 1 nM-[125I]EGF. Three-step mask analysis, which corrects for radiation spread, showed that the relative grain density was the highest in nuclei, followed by lysosomal vesicles, then Golgi and rough endoplasmic reticulum, equally. The nuclear grain density, however, was lower than that in microvillus plasma membranes. There were very few grains in basolateral plasma membranes, none in the basement membrane area and a considerable number in capillary endothelial cells. The present results demonstrating the association of internalized [125I]EGF with a variety of intracellular organelles raise the possibility of EGF acting on the intracellular sites in addition to cell surface sites.
Direct cell-to-cell transmission of vesicular stomatitis virus
Authors: Vassalli J.-D. , Lombardi T. , Wohlwend A. , Montesano R. , Orci L. 
Published: April 2021

ABSTRACT
Vesicular stomatitis virus (VSV) infection of kidney-derived, LLC-PK1 epithelial cells resulted in the budding of new viral particles into the basolateral space of the cultures. In lateral regions where cells were in close apposition, the majority of assembling viral particles in the process of budding from the producing cell had their apex already engaged in clathrin-coated pits of the neighbouring cell surface. These observations suggest that the viral envelope-plasma membrane interaction triggers the focal formation of clathrin-coated pits; they also show how VSV infection could spread throughout a tissue with only minimal exposure to a host’s extracellular environment.