bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional characterization of an adhesive component from the embryonic chick neural retina
Authors: Rutz Richard , Lilien Jack 
Published: April 2021

ABSTRACT
We have developed a quantitative assay for tissue-specific adhesive components which is based on the agglutination of glutaraldehyde-fixed cells. At least 2 components are required for fixed-cell agglutination: a cell-surface ligand which is obtained from tissue culture-conditioned medium, and a soluble ‘agglutinin’ which accumulates in conditioned medium from monolayer cultures. Our results suggest that the surface-binding ligand and the agglutinin interact directly, resulting in tissue-specific agglutination of cells. The agglutination reaction exhibits divalent cation, temperature, and pH dependence. Several models of cell adhesion are described; the simplest of these which can account for the data is a multicomponent model in which the 2 adhesive components have structural roles.
Studies of membrane fusion.: V. fusion of erythrocytes with non-haemolytic sendai virus
Authors: Knutton S. 
Published: April 2021

ABSTRACT
The fusion of human erythrocytes with non-haemolytic ‘1 -day’ Sendai virus has been studied by electron microscopy. The mechanism of viral envelope-cell fusion is the same as that described previously for haemolytic ‘3-day’ Sendai virus except that fusion is frequently arrested at an initial stage when 2 segments of smooth linear viral membrane fuse and become incorporated into the erythrocyte membrane. After longer periods of incubation at 37 °C, in addition to many partly fused virus particles, long (up to 4 μm) lengths of smooth linear viral membrane are seen within the erythrocyte membrane which arise by linear aggregation of shorter (∼ 0·25 μm long) segments of smooth linear membrane derived from individual fused viral envelopes. Cell-Cell fusion, as a result of the fusion of a viral envelope with 2 adjacent erythrocytes also occurs but, in the absence of cell swelling, fusion is arrested at this stage with cells joined by one (or more) small cytoplasmic bridges. Typical fused cells are produced if such cells are swollen with hypotonic buffer. These observations provide further evidence that membrane fusion and cell swelling are distinct events in cell fusion and that cell swelling is the driving force both for completing the incorporation of the viral envelope into the cell membrane and for expanding cells connected by small cytoplasmic bridges to form spherical fused cells. Little lateral diffusion of viral envelope components occurs in the absence of cell swelling; in fact, some aggregation of components occurs. Comparison with previous studies using haemolytic ‘3-day’ Sendai virus suggests that virally induced cell swelling perturbs membrane structure so as to allow the rapid lateral diffusion of integrated viral envelope components.
Arrest of cell membrane movements by In Vitro incubation with polycation reversed by poly anion
Authors: Ebbesen Peter , Güttler Flemming 
Published: April 2021

ABSTRACT
A total arrest of cell membrane movement occurred after incubation for 2 h of cultured fibroblasts with the polycation DEAE-dextran. The immobilized cells resumed normal membrane undulations after exposure for 5 min to the polyanion dextran-sulphate. The influence of DEAE-dextran on the electrophoretic mobility, which was seen after 10 min of incubation was also erased by a subsequent incubation with dextran-sulphate. No influence on growth of the culture was seen.
Kinetics of the regeneration of sea-urchin cilia : II regeneration of animalized cilia
Authors: Burns Roy G. 
Published: April 2021

ABSTRACT
The kinetics of the regeneration of cilia of Arbacia punctulata animalized by treatment with trypsin have been examined. The cilia regenerate with biphasic kinetics: an initial linear phase which changes abruptly to a second, slower linear rate. Inhibition of protein synthesis with 10 μM emetine has little effect on the first phase but totally abolishes the second, suggesting that the first phase represents the utilization of a pre-existing precursor pool while the second reflects de novo protein synthesis. However, cilia will regenerate again following a second deciliation in the presence of emetine, to half the plateau value of the first regeneration, indicating that only a fraction of the pool of the limiting precursor can be assembled into the regenerating cilium. It is proposed that a residual pool of this precursor is required to maintain the assembly-disassembly equilibrium in favour of the assembled organelle.
Morphological alterations in the mitochondria of Amoeba Proteus induced by uncoupling agents
Authors: Smith Robert A. , Ord M. J. 
Published: April 2021

ABSTRACT
Ultrastructural changes in mitochondrial morphology were observed in amoebae exposed to the uncoupling agents dinitrophenol (DNP), pentachlorophenol (PCP), and m-chlorocarbonyl cyanide phenylhydrazone (CCCP). These alterations occurred with rapidity and were present before whole-cell activity changes could be detected. They included changes in profile shape and overall dimensions, matrix density changes, and alterations to the cristal membranes, so that distinction between control Type I and Type II conformations was eliminated and a form with intermediate characters generated. It is proposed that, in producing these altered forms, the uncoupling agents are acting by suppressing the control functional states of the mitochondria.
At the end of the uncoupler treatment all alterations were shown to be reversible, i.e. in cells transferred back to normal culture medium, mitochondrial profiles identical to those in control cells were again evident with time. These effects on the mitochondria could be produced whether the uncoupler was introduced externally by total cell exposure, or to the inside of the cell by microinjection. The importance of precisely defining conditions for treatments aimed at disrupting cell activity was evident. Thus, an uncoupler, which is a weak acid, proved to be more effective in whole cell treatments if applied at a pH near to its pK2 - so ensuring its penetration across the outer cell membrane.
The effect of local anaesthetics and barbiturates on myogenesis and myotube integrity in rat skeletal muscle cultures
Authors: Stygall Katie , Mirsky Rhona , Mowbray John 
Published: April 2021

ABSTRACT
Several cationic anaesthetics and barbiturates including bupivacaine, lignocaine and pentobarbital reversibly inhibit myoblast fusion in rat primary muscle cultures. The same drugs also cause disruption of myotube structure, which is normally complete within 2 h; fusion of myoblasts and reformation of myotubes takes place on removal of the drugs. The disruption of myotubes caused by tertiary amine anaesthetics observed in vitro appears to mimic muscle fibre disruption caused by the same drugs in vivo. The effects of temperature, culture age, medium constitution and calcium flux on anaesthetic-induced myotube breakdown have been examined.
Capping of variable antigen on Trypanosoma Brucei, and its immunological and biological significance
Authors: Barry J. David 
Published: April 2021

ABSTRACT
Pathogenic trypanosomes undergo antigenic variation, whereby the glycoprotein molecules constituting the cell surface coat are changed, the parasite thus evading the host’s immune response. On application of homologous antiserum in indirect immunofluorescence to a given variable antigen type of Trypanosoma brucei, the surface variable antigen moves to the flagellar pocket region, which overlies the Golgi apparatus. This redistribution, or capping, is temperature-dependent, occurring at 37 °C but not at 0–4 °C. Patching does not occur at either temperature. Immediately after capping no homologous or heterologous variable antigen, or host plasma or blood cell antigens, can be detected by immunofluorescence on the cell surface outside the cap; only trypanosome membrane common antigens can be found.
It seems unlikely for two reasons that this antibody-induced redistribution is relevant to antigenic variation. Capping of the coat requires the indirect, rather than the direct, irnmunofluorescent method; a single layer of antibody, as available in nature, would appear to be ineffective. Also, capping of variable antigen of one type is followed within 3 h by appearance of antigen of the same, and not another, type.
The necessity for 2 antibody layers is usually thought of as meaning that the individual molecules of the cell surface antigen are spaced further apart than the binding sites of an individual antibody molecule, so that the necessary cross-linked lattice cannot be formed, but on T. brucei the surface variable antigen molecules are very closely packed. It is proposed that one layer of antibody is ineffective for steric reasons; the dimensions of the exposed face of each variable antigen molecule may not permit the binding of more than one molecule of immunoglobulin, or perhaps the antigen molecules are so closely packed that most of the antigenic determinants are hidden from antibodies. To test this hypothesis, an attempt was made to cap variable antigen on trypanosomes transforming in vitro from the bloodstream to the procyclic (insect midgut) stage; such forms have a much less densely packed surface coat. Patching was observed, indicative of lattice formation, but these trypanosomes did not survive the in vitro manipulation long enough to permit any possible capping.
T. brucei differs structurally from most other eukaryotic cells. It has no detectable microfilaments under the plasma membrane, except at the desmosomes in the region of flagellar binding, and it also has a pellicular cortex of microtubules. Capping of its surface antigen would appear then to differ from that on mammalian cells, either in the cellular components involved or in that specialized areas of the plasma membrane are involved.
Actin in spindles of Haemanthus Katherinae endosperm :IX. general results using various glycerination methods
Authors: Forer Arthur , Jackson W. T. 
Published: April 2021

ABSTRACT
We have studied actin-containing filaments in spindles in Haemanthus endosperm cells glycerinated by various methods; the actin-containing filaments were identified by their reaction with rabbit skeletal muscle heavy meromyosin (HMM) to form ‘decorated’ filaments. Actin-containing filaments in the spindle were seen in amongst microtubules in bundles (both non-kinetochore microtubule bundles and kinetochore microtubule bundles) and were also seen not associated with microtubules. There were very few extra-spindle actin-containing filaments in these cells. Actin-containing filaments seemed to interact with microtubules, because the filaments remained close to and parallel to microtubules even when the microtubules were sharply curved. Because of the close association between microtubules and actin-containing filaments we could not identify all the actin-containing filaments present in microtubule bundles: microtubules obscured actin-containing filaments.
We studied Haemanthus endosperm cells as they were glycerinated. For some of these observations we used phase-contrast microscopy. Glycerination caused the cells to shrink, initially, and this was followed by rapid expansion, but the cells did not expand to as large a volume as before glycerination. Spindle structure was maintained despite these changes in cell size. Evidences for this are that relative chromosome positions were maintained during glycerination, that spindle birefringence was maintained during glycerination, and that individual chromosomal spindle fibres remained biréfringent during glycerination. Electron-microscopic observations supported this in that kinetochore microtubule bundles and non-kinetochore microtubule bundles were maintained during glycerination, as was the helical arrangement of spindle ribosomes into polyribosomes.
One-step glycerination procedures were used (cells were treated with mixtures containing 25% glycerol, Triton-X-100, and HMM), and such procedures might be of general use. Living cells were embedded in fibrin clots in making light-microscopic observations; this procedure, too, might be of general use.
An ultrastructural study of the effects of wheat germ agglutinin (WGA) on cell cortex organization during the first cleavage of Xenopus Laevis eggs II. cortical wound healing
Authors: Geuskens M. , Tencer R. 
Published: April 2021

ABSTRACT
Uncleaved fertilized eggs of Xenopus laevis treated with wheat germ agglutinin (WGA) have been pricked at the animal pole both inside and outside the regressed furrow region. The wounded cortex of both regions has been studied with the electron microscope and compared with the same region of wounded, untreated eggs. In all 3 cases, filaments are organized in an annular zone in the damaged cortex. When the surface is pricked outside the regressed furrow of WGA-treated embryos, bundles of microfilaments radiate from the ring and extend in deep folds which form a ‘star’ around the wound at the surface of the embryo. However, when the surface is pricked in the new membrane of the regressed furrow, filaments are intermingled with internalized portions of the plasma membrane. It is suggested that, when the surface is pricked outside the furrow region, more filaments are mobilized to counteract the tangential retraction of the membrane which has acquired more rigidity after WGA binding.
Probing the free space within rat and chicken chromatin with active and passive probes
Authors: Burgoyne Leigh A. , Skinner Jennifer D. 
Published: April 2021

ABSTRACT
The cavity systems within chicken erythrocyte nuclei and rat liver nuclei were compared using passive probes of radioactive glycogen and active probes of nuclease-armed-glycogen. The passive probe curves have a form that indicates that they are due to passive occupation of spaces and not due to the effects of a limiting membrane.
The technique of probing nuclei with glycogen armed with a small enzyme is described.
The chicken erythrocytes appeared to have 11–15-nm and 4–5-nm cavity systems similar to those we have previously reported in rat nuclei. Evidence is presented to show that the bridge DNA is enclosed within the 4-5-nm cavities in both rat liver and chicken erythrocyte nuclei.
Minor differences between the rat liver and chicken erythrocyte nuclear cavity systems are noted in the region of 5–8 nm. A relatively mild procedure is described for preparing chicken erythrocyte nuclei.
A crystalline inclusion in sieve element nuclei of Amsinckia: I. The inclusion in differentiating cells
Authors: Esau Katherine , Magyarosy Andrew C. 
Published: April 2021

ABSTRACT
The presence of usually single, elongated, compound crystalloids in nuclei of sieve elements is an outstanding characteristic of the phloem of Amsinckia douglasiana A. DC. (Boraginaceae). The crystalloid consists of two components forming alternating panels, or blocks, that extend through the entire length of the crystalloid and radiate from the centre where one of the components predominates. Three to seven panels for each component were recorded. One component consists of 4-sided tubules closely packed in highly ordered aggregates, the other of wider 6-sided tubules rather loosely arranged in paracrystalline aggregates. The crystalloid arises at the beginning of sieve clement differentiation. Aggregates of 4-sided tubules appear first. In plants infected with the curly top virus, the crystalloids do not differ from those in non infected controls in structure and conformation. But because the phloem in infected plants is hypcrplastic, with most of the cells differentiating as sieve elements, the crystalloids are far more abundant in diseased than in healthy plants.
Granulocyte migration through endothelium in culture
Authors: Beesley Julian E. , Pearson Jeremy D. , Hutchings Amanda , Carleton J. Susan , Gordon John L. 
Published: April 2021

ABSTRACT
Using a model system with which we have previously investigated the adhesion of granulocytes to cultured endothelium, we have now shown that adherent granulocytes migrate through cultured endothelium in a manner closely resembling that found during the acute inflammatory response in vivo. The migration of granulocytes was markedly enhanced in the presence of erythrocytes, whereas blood platelets did not affect migration. Several test agents, including Paroven and some prostaglandins, had different effects upon migration and adhesion. We conclude that the adhesion of granulocytes to endothelium and their migration through it are responses that are, at least in part, separately controlled, and that migration does not depend exclusively upon extravascular stimuli.
The interaction of lectins with the surface of differentiating erythroleukaemic cells
Authors: Hunt Richard C. , Marshall Linda M. 
Published: April 2021

ABSTRACT
Friend erythroleukacmic cells can be induced to mature along the erythroid differentiation pathway when an inducing agent such as dimethyl sulphoxide is included in the medium. In the absence of the inducing agent, the 707B line of Friend erythroleukaemic cells is highly agglutinable by the lectins concanavalin A or wheat germ agglutinin. However, 48 h after the induction of differentiation, there is a marked decrease in the agglutination of the cells in the presence of either lectin. This suggests that early in differentiation a change occurs in the cell membrane preceding the onset of globin synthesis which starts approximately 72 h after induction. The change in agglutination by concanavalin A also occurs in the presence of reagents which do not induce haemoglobin synthesis in the 707B line of Friend erythroleukaemic cells but which are able to stimulate the synthesis of this protein in other erythroleukaemic cell lines.
The reduction in the agglutinability of the differentiating cells does not seem to result from a reduction in the number of concanavalin A receptors on the cells, nor does it reflect a change in the clustered distribution of concanavalin A receptors in the differentiating cells. Both the control and dimethyl sulphoxide-induced cells show a similar patchy distribution of ferritin-labelled concanavalin A when examined by electron microscopy.
Polyacrylamide gel electrophoresis shows little change in the total pattern of protein synthesis by control and differentiating cells when pulse-labelled with [35S] methionine. However, use of 125I-labelled concanavalin A to stain polyacrylamide gels, on which the total proteins of control and differentiating cells had been separated, revealed a profound change in the composition of the concanavalin A-binding proteins. The control, undifferentiated cells contained eleven or more classes of concanavalin A-binding glycoproteins, many of which stained to a lesser degree as the cell density increased. After the onset of differentiation, 2 new concanavalin A-binding glycoproteins appeared within 48 h. One of these proteins has a molecular weight in excess of 180000 while the other migrated with an apparent molecular weight of approximately 100000. After erythroid differentiation had progressed for 120 h, these newly synthesized glycoproteins became the major concanavalin A-binding proteins of the erythroleukaemic cells.
Co-operativity of lectin binding to fibroblasts and its relation to cellular actomyosin
Authors: Thom David , Cox Diana S. , Safford Richard , Rees David A. 
Published: April 2021

ABSTRACT
We have investigated the binding of 125 I-concanavalin A (125 I-Con A) and 125 I-succinyl concanavalin A (125 I -s-Con A) to rat fibroblasts (16C line) as a function of the concentration of added lectin, and the alterations to this binding behaviour caused by drugs which modify the cytoskeleton. The changes in cell behaviour which occur at different levels of binding have also been studied. As shown previously for some other systems, the binding of Con A is complex and partly co-operative. Three phases can be distinguished in our system: (i) prenucleation binding, (ii) binding which shows a small positive slope in a Scatchard plot and a Hill coefficient greater than unity, and which therefore is incipiently co-operative, and (iii) post-co-operative binding.
The co-operative phase of binding is paralleled by progressive inhibition of EGTA-mediated cell detachment from substrata, with inhibition being complete when this phase of binding is complete. Likewise, the phagocytosis of latex spheres is progressively inhibited up to a threshold which coincides with the completion of co-operative binding. Thirdly, cells pretreated with Con A round up with colchicine (10− 5 M) if co-operative binding is complete, but adopt broad epithelial shapes if it is not. r-Con A does not show co-operative binding, and correspondingly does not inhibit EGTA-mediated cell detachment, or show a distinct threshold in the inhibition of phagocytosis, or promote the 2 types of shape change with colchicine.
The pattern of Con A binding is drastically altered by pretreatment of cells with cytochalasin B or azide. The Scatchard and Hill plots show that the co-operative phase remains and is complete at about the same level of binding, but that it is more readily nucleated and takes place against a changed number and/or distribution of receptors. Pretreatment of cells with colchicine causes changes in the pattern of binding which are different from those observed with cytochalasin B or azide and are more difficult to interpret.
We conclude that a reciprocal relationship exists between the cellular actomyosin and the state of cell surface receptors. Perturbation of actomyosin by cytochalasin B or azide can enhance the freedom of some receptors to participate in a co-operative rearrangement which facilitates the binding of further molecules of lectin. Vice versa, the co-operative event has a feedback influence on the cellular actomyosin to cause alterations of cellular response.
The behaviour of fibroblasts migrating from chick heart explants: changes in adhesion, locomotion and growth, and in the distribution of actomyosin and fibronectin
Authors: Couchman John R. , Rees David A. 
Published: April 2021

ABSTRACT
Fibroblasts migrating from heart explants of chick embryos at first have a high rate of locomotion but lack focal contacts or adhesions and also lack substantial actin-containing bundles. A meshwork of 7-nm filaments is present particularly in submembranous regions and is proposed to be directed towards efficient locomotion whilst maintaining a high degree of spreading. Also during the first 48 h there is little production of extracellular fibronectin and the growth rate is low. Later, these fibroblasts develop focal contacts and focal adhesions together with actomyosin bundles, with a parallel increase in fibronectin expression. We propose that progressive immobilization by the development of focal adhesions and actomyosin structures occurs to set these cells up for growth.