bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of cytochalasin b on the aggregation, electrophoretic mobility and surface morphology of chick neural retina cells
Authors: Jones G. E. 
Published: April 2021

ABSTRACT
Over a concentration range of 0 · 5–10 μg/cm3, cytochalasin B caused a biphasic change in the electrophoretic mobility of disaggregated neural retina cells. An initial rise in anodal mobility at low concentrations of the drug was transformed into a reduction in the mobility below that of the control at a concentration of 10 μg/cm3.
The effect of cytochalasin B was found to be reversible by washing treated cells in cytochalasin B-free media. This was investigated at a concentration of cytochalasin at which the greatest difference existed between the mobilities of the control and experimental cell suspensions.
Reaggregation of cell dispersions failed to show any significant difference in the rate of aggregation between cytochalasin B-treated cells and the control. Scanning electron microscopy of cells fixed while in suspension also showed little significant change in the surface morphology upon application of cytochalasin B. In high concentrations of the drug cells appeared somewhat smoother in outline, but no correlation was found between changes in surface morphology and the variations in cell electrophoretic mobility.
It is concluded that the observed changes in electrophoretic mobility may be attributed to a binding of cytochalasin B to the cell membrane. This lends support to the hypothesis that the primary site of action of cytochalasin B may be the plasma membrane.
Cytoplasmic induction of changes in the ultrastructure of the Acetabularia nucleus and perinuclear cytoplasm
Authors: Berger S. , Schweiger H. G. 
Published: April 2021

ABSTRACT
The ultrastructure of the cell nucleus and perinuclear cytoplasm in Acetabularia is quite different in young and old cells. When a nucleus of an old cell was implanted into the cytoplasm of a young cell the nucleus assumed the morphology typical of a young cell within less than 10 days. The cytoplasm of an old cell was able to induce the reverse change in an implanted nucleus from a young cell. This cytoplasmic induction of nuclear ageing appeared to proceed more rapidly than rejuvenation.
Inability to detect Chlamydomonas microtubule assembly in vitro: Possible implications to the in vivo regulation of microtubule assembly
Authors: Farrell K. W. , Burns R. G. 
Published: April 2021

ABSTRACT
It has been demonstrated that the in vitro assembly of microtubules from Chlamydomonas preparations does not occur under a wide range of conditions, including those efficacious for mammalian brain tubulin. This incompetence of Chlamydomonas extracts to form microtubules is independent of the tubulin concentration, the presence of added nucleotides or an added seed, temperature, or the concentration of divalent cations. However, an amorphous aggregate was observed under certain conditions, whose composition was mainly tubulin.
The in vitro reassembly of microtubules in gerbil brain extracts is inhibited by Chlamydomonas preparations. Fractionation of the Chlamydomonas extracts by column chromatography suggests that the inhibitory component is Chlamydomonas tubulin itself. The mechanism of this inhibition is unknown, but reassembly experiments indicate that the 2 types of tubulins cannot copolymerize. We suggest that the Chlamydomonas tubulin, derived from a cytoplasmic pool, requires to be activated prior to its in vivo polymerization into microtubules.
Ultrastructural characteristics of the non-immune rosette-forming cell
Authors: Levy J. D. , Knieser M. R. , Briggs W. A. 
Published: April 2021

ABSTRACT
Non-immune rosette formation, where a non-sensitized lymphocyte is surrounded by three or more sheep red blood cells, is an in vitro technique which is thought to be specific in the identification of thymus-dependent (T) lymphocytes. Using the electron microscope and tissue culture techniques, we have studied the ultrastructure of the rosette-forming lymphocyte which has been stimulated by various cellular mitogens. Non-sensitized but stimulated lymphocytes, which form rosettes, have a morphology similar to that of previously identified T cells, adding further credence to the concept that non-sensitized rosette-forming cells represent a population of T cells. Changes in the binding pattern of the sheep red cell membrane to the lymphocyte have been identified which may represent an early phase of cell ‘activation.’ This marker of activation offers a potential method of studying membrane responses in attempts to localize cellular defects involving the T lymphocyte. In addition, preliminary studies using fluorescein-labelled sheep red blood cell fragments suggest specific attachment of labelled membrane to the T lymphocyte, allowing rapid identification of T cells in smears or tissue preparations.
Supercoils in human dna
Authors: Cook P. R. , Brazell I. A. 
Published: April 2021

ABSTRACT
The three-dimensional structure of a double-stranded DNA molecule may be described by distinguishing the helical turns of the DNA duplex from any superhelical turns that might be superimposed upon the duplex turns. There are characteristic changes in the hydrodynamic properties of superhelical DNA molecules when they interact with intercalating agents. The hydrodynamic properties of nuclear structures released by gently lysing human cells are changed by intercalating agents in this characteristic manner. The characteristic changes are abolished by irradiating the cells with γ-rays but may be restored by incubating the cells at 37 °C after irradiation. These results are interpreted as showing that human DNA is supercoiled. A model for the structure of the chromosome is suggested.
Effects of adenosine 5′-monophosphate and adenosine 3′,5′-cyclic monophosphate on l cells
Authors: Taylor-Papadimitriou J. , Karemfyllis T. , Eukarpidou A. , Karamanlidou G. 
Published: April 2021

ABSTRACT
The adenine nucleotides, 5′-AMP and 3′5′-cyclic AMP block L cells in the S-phase of the cell cycle. The intracellular level of cyclic AMP is reduced after incubation of cells with 5′-AMP, and rates of uridine transport are increased after incubation with either 5′-AMP or cyclic AMP. On the contrary, cyclic AMP levels are increased and uridine transport decreased in cells treated with an inhibitor of the cyclic AMP phosphodiesterase. This inhibitor partially reverses the growth-inhibitory effect of cyclic AMP, indicating that a breakdown product is the effective inhibitor of growth. The inhibition of cell growth induced by the adenine nucleotides is prevented by uridine, suggesting that the block in S is due to a lack of availability of pyrimidines.
Immaturity substances: Material basis for immaturity in Paramecium
Authors: Miwa Isoji , Haga Nobuyuki , Hiwatashi Koichi 
Published: April 2021

ABSTRACT
Cells of Paramecium caudatum in the immaturity period of the life cycle contain substances which repress the expression of mating ability when introduced into mature cells. When 5 × 103μm3 of immature cytoplasm were injected into mature cells, loss of mating ability occurred and it continued for more than 15 fissions after the injection. The effective substances are contained in the soluble fraction of immature cells and have the properties of heat-labile macromolecules.
Studies on intercellular invasion in vitro using rabbit peritoneal neutrophil granulocytes.: II. Adhesive interaction between cells
Authors: Lackie J. M. , Armstrong P. B. 
Published: April 2021

ABSTRACT
A possible mechanism for intercellular invasion is that the strength of adhesion between host and invading cells is greater than the average of the strengths of homotypic adhesions. This hypothesis has been examined by a study of the kinetics of aggregation of dispersed populations of an invasive cell type (the rabbit peritoneal neutrophil granulocyte) and a host cell type (the chick embryo heart fibroblast) in shaken suspension culture. Since aggregation in mixed populations of the 2 cell types demonstrated tissue specificity, the hypothesis is not supported by these studies, heterotypic adhesions seem in fact to be weaker than homotypic adhesions.
An electron-microscope study of capsule formation by insect blood cells
Authors: Grimstone A. V. , Rotheram Susan , Salt G. 
Published: April 2021

ABSTRACT
Haemocytes of Ephestia kuehmella adhere to foreign objects introduced into the haemocoel and form capsules around them. The fine structure of these capsules, and the blood cells which form them, has been studied by electron microscopy. By 72 h the capsule is a compact tissue, about 50–60 cells thick. The cells retain their integrity and do not form a syncytium. Cells nearest the implant develop large numbers of cytolysomes and appear necrotic. Peripheral to this the cells, which are initially more or less spherical and about 6 μ across, are flattened into thin sheets, on average about o·3 μ thick. Capsule cells adhere closely to each other, and a conspicuous electron-dense material may be present between them. The structure of developing capsules 24 h old and of capsules retrieved from adult insects following metamorphosis is described. The formation of capsules is discussed in relation to general problems of cell recognition and adhesion.
Quantitative investigation on the effect of puromycin on the aggregation of trypsin- and versene-dissociated chick fibroblast cells
Authors: Kemp R. B. , Jones B. M. , Cunningham I. , James M. C. M. 
Published: April 2021

AbstractEmbryonic chick fibroblast cells were used to test the effects of puromycin on cell adhesion and aggregation. Single cell suspensions were prepared by dissociating the muscle tissues of 5- and 9-day-old chick embryos with either trypsin or versene according to standard cell dissociation procedures.’ Cell aggregation was quantitatively estimated by a turbidimetric method.Quantitative analyses of the components in cell-free supernatants revealed that both trypsin and versene when used as cell dissociating agents removed substantial amounts of protein from the surfaces of the cells and the intercellular regions. Trypsin removed larger quantities of protein and of N-acetylneuraminic acid than did versene. Nucleic acids were also released during trypsin and versene dissociation, and estimations of these nucleic acids gave a measure of the extent of cell lysis. The proteins and peptides were separated by gel filtration. The solubilized proteins removed by versene treatment were separated into three peaks on Sephadex G.200. The tryptic digest gave one main peptide peak on Sephadex G.50.Both trypsin- and versene-dissociated cells, on rotation in Hanks’s balanced salts solution with or without serum, began to adhere to one another at the start of the test period, indicating that the cell dissociation procedures had not impaired the adhesive properties of the separated cells.When puromycin at a final concentration of 10 μg/ml was introduced at zero time into a cell suspension with or without serum, it did not delay the adhesion of cells to one another, and did not prevent the formation in the first hour of initial aggregates ; it succeeded only in preventing progress in aggregation beyond the initial stages. Adding puromycin at the 2nd or 3rd hour of the 4-h test period, when aggregation had already taken place, produced results of a similar pattern, progress in aggregation being brought to a halt an hour later. Puromycin at the above concentration effectively blocked protein synthesis by more than 90 % as measured by the incorporation of L-[α-14C]leucine into the proteins of the rotated cells. These results implied that aggregation was not dependent on the synthesis of ‘cell aggregating ‘material to replenish the loss of such material from the surfaces of the cells owing to the trypsin treatment. It is significant that 2,4-dinitrophenol, which is known to suppress cellular metabolism by inhibiting the production of ATP, also brought cell aggregation to a halt only after a lag period during which initial aggregates were formed.It is suggested, as evidenced in the results of our investigations, that puromycin may well be exerting its inhibitory effect by ultimately depressing cellular metabolism below the level at which certain basic adhesive mechanisms at the cell surface can operate.
The Localization of [3H]Thymidine Incorporation in the DNA of Replicating Spinach Chloroplasts by Electron-Microscope Autoradiography
Authors: Rose R. J. , Possingham J. V. 
Published: April 2021

ABSTRACT
Electron-microscope autoradiography has been used to obtain information on the localization of DNA labelled with [®H]thymidine in chloroplasts known to be replicating and concomitantly synthesizing and segregating DNA, in cultured leaf disks. The studies were made using both Microdol-X developer and a ‘compact’ developer which gave a smaller grain size. About 80 % of the grains were associated with the granal membranes and with presumptive DNA regions (3-nm fibril material in clear areas). Few grains occurred in association with the chloroplast envelope. We suggest that the DNA of chloroplasts is associated with the grana lamellae and extends into the stroma. Some light-microscope autoradiographs of whole chloroplasts show spiral or helical-like labelling patterns. We interpret these patterns as demonstration of the possibility that DNA occurs along the length of a continuous lamellar membrane system. Chloroplast fractionation experiments provided data consistent with the electron-microscope autoradiographic studies as most of the label was associated with chlorophyll-containing lamellae.
We consider an association of chloroplast DNA molecules along the length of a continuous lamellar system would ensure an orderly segregation of DNA to daughter chloroplasts, during the binary fission of spinach chloroplasts by constriction division.
Goblet Cell Membrane Differentiations in the Midgut of a Lepidopteran Larva
Authors: Flower N. E. , Filshie B. K. 
Published: April 2021

ABSTRACT
So-called goblet cells are present in the midgut of lepidopteran larvae. They are thought to be involved in the active transport of potassium out of the haemolymph and into the gut lumen. A number of plasma membrane differentiations within the goblet cell cavity has been investigated using conventional staining, lanthanum tracer and freeze-etch techniques. Of particular interest are junction-like inter- and intra-membrane differentiations found on the villus-like cytoplasmic projections present at the apical tip of the goblet cell cavities. These cytoplasmic projections appear to act as a valve; in some cases they seem to close off the top of the goblet cell cavity, so isolating it from the gut lumen, while in other cases they are spread apart leaving a wide channel from the cavity into the lumen. The junction-like structures on these cytoplasmic projections are different in structure from the septate-type junctions which seal the midgut cells together at their apical borders, and the 2 types are present on the same plasma membrane, often within one micron of each other. The need for a different type of junction may possibly be related to the fact that it occurs between 2 areas of the same plasma membrane. The morphology of this unusual junction-like structure is discussed and 2 diagrams are presented to illustrate our interpretation of its structure.
The Secretion of Collagen by Insects: Uptake of [3H] Proline by Collagen-Synthesizing Cells in Locusta Migratoria and Galleria Mellonella
Authors: Ashhurst Doreen E. , Costin Natalie M. 
Published: April 2021

ABSTRACT
The uptake of [3H]proline by collagen-secreting cells of the locust, Locusta migratoria, and wax-moth, Galleria mellonella, has been investigated by electron autoradiography. The locust cells are around the ejaculatory duct and they secrete collagen in the young adult male, while the wax-moth cells are those which produce the dorsal mass of connective tissue on the abdominal nerve cord during the late pupal stage. The cells were exposed to [3H]proline either by injection of the [3H]proline into the insect, or as a pulse while the tissue was maintained in a culture medium. The tissues were fixed at differing experimental times after exposure to the [3H]proline. The resulting electron autoradiographs were subjected to quantitative analysis, and the silver grain distribution was determined as the relative number of grains per unit area over a series of tissue compartments. When the results of this analysis for the matrix, rough endoplasmic reticulum and Golgi complexes of the two tissues were plotted against experimental time, it was seen that the relative number of grains per unit area over the rough endoplasmic reticulum decreases while that over the matrix increases; statistical analysis has shown that these changes are significant. For the Golgi complexes, however, the theoretical variances are much greater, due to the small relative area occupied by this organelle. There is little evidence for anything other than random sampling fluctuations in the relative numbers of grains per unit area, and hence it is unlikely that the time course of the label over the Golgi complexes follows that over the rough endoplasmic reticulum.
The conclusions drawn from these experiments are firstly that a large portion of the labelled protein passes straight from the rough endoplasmic reticulum to the matrix, but that a smaller portion of the labelled material might pass from the rough endoplasmic reticulum to the Golgi complexes and thence to the matrix. It is assumed that collagen comprises most of the protein which passes straight from the rough endoplasmic reticulum to the matrix, and while there is no evidence to exclude collagen from the material passing through the Golgi complexes, it is probable that other proteins and glycosaminoglycans are also present in this labelled material. These conclusions about the intracellular pathway for collagen secretion are similar to those derived from recent studies of some vertebrate fibroblasts. There is, however, conflicting opinion about the intracellular pathway of collagen and it is pointed out that there is diversity in collagen-synthesizing cells, which may account for the differences in the intracellular pathways for collagen secretion which have been proposed.
Phagocytosis of concanavalin a in normal and enucleated cultures of mammalian cells
Authors: Wise Gary E. 
Published: April 2021

ABSTRACT
The fate of concanavalin A (Con A) bound to normal and enucleated L cells was followed at the ultrastructural level over a 20-h period. In both enucleates and normal cells the Con A is seen to be distributed in a uniform manner over the entire cell surface following a 30-min pulse with a low concentration of Con A. In the subsequent chase period the cells then aggregate the Con A and Con A sites into large clusters on the cell membrane. The cells then phagocytoze the Con A and large phagocytic vacuoles containing it are observed. Thus, enucleated cells are capable of phagocytozing Con A and its sites in the same manner as normal cells.
Signal emission and signal propagation during early aggregation in Dictyostelium discoideum
Authors: Gross J. D. , Peacey M. J. , Trevan D. J. 
Published: April 2021

ABSTRACT
Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum are of 2 kinds, concentric waves produced by cells that emit cyclic AMP signals spontaneously, and spirals generated by excitations relayed continuously around loops of excitable cells. The period of a spiral wave is the time taken for the excitation to make one complete circuit of the pacemaker loop. We have compared signal emission from the 2 types of source in time-lapse films made at a variety of temperatures. Our results show that spiral waves have a characteristic period length throughout most if not all of the early phase of aggregation, and that the period of concentric waves is generally longer and more variable. Temperature has a pronounced effect on period length and a lesser effect on propagation velocity. We find that each individual wave is propagated at constant velocity over distances of 1–2 cm but that the velocity of successive waves declines. This decline probably reflects some cumulative effect of the chemotactic excitations on the excitable properties of the aggregating cells.
The analysis of malignancy by cell fusion. VIII. evidence for the intervention of an extra-chromosomal element
Authors: Jonasson J. , Harris H. 
Published: April 2021

ABSTRACT
Diploid human, fibroblasts and lymphocytes were fused with the cells of a malignant mouse melanoma and a range of hybrid clones selected for study. The ability of these clones to produce progressive tumours was assayed in nude mice. Although human chromosomes were preferentially eliminated in all the hybrid clones, the human diploid cells were as effective as mouse diploid cells in suppressing the malignancy of the mouse melanoma cells. The suppression produced by fibroblasts was again more profound than that produced by lymphocytes. Malignancy was also found to be suppressed in a hybrid clone in which a single X was the only human chromosome present; and this clone continued to give a very low take incidence even after the human X had been eliminated by back selection. Hybrids were made between the melanoma cells and diploid human fibroblasts that had been given 100 J kg−1 of gamma radiation before cell fusion. These hybrids contained no recognizable human chromosomes, but their ability to produce progressive tumours was greatly reduced compared to that of the melanoma parent cells. The take incidences given by the crosses between the melanoma cells and the irradiated human fibroblasts were, however, substantially higher than those given by the crosses between the melanoma cells and unirradiated fibroblasts. These findings suggest that the suppression of malignancy involves the activity of some extra-chromosomal element and that this element is radio-sensitive.
The isolation of plasma membrane from protoplasts of soybean suspension cultures
Authors: Galbraith David W. , Northcote D. H. 
Published: April 2021

ABSTRACT
A procedure for the isolation of plasma membranes from protoplasts of suspension-cultured soybean is described. Protoplasts were prepared by enzymic digestion of the cell wall and the plasma membrane was labelled with radioactive diazotized sulphanilic acid. The membrane systems from broken protoplasts were separated by continuous isopycnic sucrose gradient centrifugation. Radioactivity was localized in a band possessing a buoyant density of 1·14 g ml−1. The activities of NADPH- and NADH-cytochrome c reductase, fumarase, Mg2+-ATPase, IDPase and acid phosphodiesterase in the various regions of the density gradient were determined. A plasma membrane fraction was selected which was relatively uncontaminated with membranes derived from endoplasmic reticulum, tonoplasts and mitochondria. The results indicated that Mg2+-ATPase and possibly acid phosphodiesterase were associated with the plasma membrane.