bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reconstruction of complexes of histone and superhelical nuclear dna
Authors: Levin Jeremy M. , Cook Peter R. 
Published: April 2021

ABSTRACT
When HeLa cells are lysed in solutions containing a non-ionic detergent and 2 M-NaCl, structures are released that retain many of the morphological features of nuclei. These nucleoids contain all the nuclear RNA and DNA but few of the proteins characteristic of chromatin. Their DNA is supercoiled and so intact. Using a simple and rapid procedure we have reconstructed nucleohistone complexes from nucleoids and the ‘core’ histones without breaking the DNA. We have probed the integrity and structure of the reconstructed complexes using a non-destructive fluorometric approach, which provides a general method for detecting agents that bind to DNA and alter its supercoiling. The βuperhelical status of the DNA in the reconstructed complexes is indistinguishable from that found in control nucleoids containing core histones. Experiments with micrococcal nuclease confirm that the DNA in the reconstructed complexes is organized into nucleosome-like structures. These, however, are spaced 145 base-pairs apart and not 200 base-pairs apart as is found in native chromatin.
Contraction and organization of collagen gels by cells cultured from periodontal ligament, gingiva and bone suggest functional differences between cell types
Authors: Bellows C. G. , Melcher A. H. , Aubin J. E. 
Published: April 2021

ABSTRACT
Monkey periodontal ligament fibroblasta (MPLF cells), human gingival fibroblasts (HGF cells), rat embryonic calvaria cells (REC cells), porcine periodontal ligament epithelial cells (PPLE cells) and rat osteosarcoma 17/2 cells (ROS cells) were incorporated into 3-dimensional collagen gels plated in 60 mm Petri dishes in order: first, to measure the capacity of these cell types to contract; second, to investigate cell-collagen and intercellular relationships during contraction; and third, to define the cellular contribution to tissue contraction in an in vitro system. Measurements at times up to 72 h on 3 ml gels containing 5×105 cells and with a collagen concentration of 1·20 mg/ml showed that MPLF cells contracted the gels at a significantly greater rate (P &lt; 0·001) than did the other cell types. In addition, contraction started sooner and was of greater extent than with the other cells. HGF cells contracted the gels more rapidly than REC and PPLE cells, while ROS cells caused no contraction. Several stages of gel compaction could be defined: (1) the attachment of cells to collagen; (2) cellular spreading within the collagen fibre matrix; (3) organization and alignment of collagen fibres by cell processes; (4) cell migration; (5) establishment of intercellular contacts; and (6) the development of a cellular reticular arrangement within the gel and the extension of this arrangement into a 3-dimensional, tissue-like, honeycomb network. Electron microscopic observations on 0·1 ml gels containing MPLF cells showed that, in the early contractile phase, numerous cell processes attached to or enclosed collagen fibrils. These processes contained micro-filamentous material and few organelles. In compacted gels, the cells contained an increased amount of distended rough endoplasmic reticulum and Golgi membranes. Since MPLF cells have the capacity for vigorous contraction of the collagen gels and since they develop a reticular, 3-dimensional structure in compacted gels that is reminiscent of the relationship of periodontal ligament fibroblasts to collagen fibres in vivo, it is suggested that they could provide the major force necessary for tooth eruption in vivo. This system also provides a well-defined in vitro model to study the sequential stages that occur during contraction processes.
Effect of hyaluronic acid on neutrophil adhesion
Authors: Forrester John V. , Lackie J. M. 
Published: April 2021

ABSTRACT
The effects of hyaluronate on rabbit neutrophil adhesion were studied using a variety of techniques. Exogenous hyaluronate inhibited neutrophil aggregation under conditions of both turbulent flow and constant shear rate. Hyaluronate also inhibited neutrophil adhesion to glass. Inhibition was dose-dependent above 100 μg ml−1 and a minimum molecular weight for hyaluronate of 1 × 104 was required. These effects were not simply the result of increased bulk viscosity of the hyaluronate-containing medium, nor did they appear to be mediated by putative cell-surface receptor mechanisms. Instead, physical factors such as steric hindrance and/or changes in the interfacial free-energy exchange at the cell surface due to the unusual hydrodynamic properties of the hyaluronate molecule were considered to be more important.
Since neutrophil migration in vivo occurs through hyaluronate-rich connective tissue matrices, the relevance of these findings for processes such as inflammation and wound healing is clear.
Variability in individual cell cycles of Saccharomyces cerevisiae
Authors: Lord P. G. , Wheals A. E. 
Published: April 2021

ABSTRACT
The kinetics of cell proliferation of Saccharomyces cerevisiae were studied at 4 growth rates using time-lapse cinephotomicrography. Cells were grown on media with a high refractive index to reveal greater intracellular detail under the phase-contrast microscope. The morphological cell-cycle events scored were: bud emergence, nuclear migration, nuclear division, onset of cytokinesis and cell separation. Cell size was measured at cell separation and at bud emergence. The daughter-cycle time was always longer than the parent-cycle time mainly due to the large difference in the lengths of the unbudded phases. Parent cells had a shorter budded period than daughter cells. The large variance in daughter-cycle times was accounted for by the large variance in the lengths of the unbudded phase of daughter cells. The duration and variability of the periods in the cycle from nuclear migration onwards were equivalent for parent and daughter cells. Daughter cells were always smaller than parent cells at division. There was wide variation in cell size at both division and bud emergence. The results indicated that a modified deterministic model could best explain cell proliferation kinetics in yeast. The data were used to evaluate 2 different models. The * sloppy size control’ model of Wheals (1981a) was more consistent with the data than the ‘tandem’ model of Shilo, Shilo & Simchen (1976). The distribution of unbudded periods of daughter cells suggested that there was an additional incompressible period not present in parent cells.
Mitochondrial morphology in the spermatozoa of the mexican axolotl, Ambystoma mexicanum
Authors: Keyhani Ezzatollah , Lemanski Larry F. 
Published: April 2021

ABSTRACT
Thin-section and freeze-fracture electron microscopy of immature and mature spermatozoa of the Mexican axolotl, Ambystoma mexicanum, revealed numerous small spherical mitochondria with diameters ranging from 0·15 to 0·22 μm. Both the spherical form and the small size of these mitochondria were confirmed by serial thin-section studies. In mature spermatozoa, the mitochondria are located in the midpiece region, in tight contact with each other, exhibiting an almost crystalline arrangement. They do not surround the midpiece, but form a semicircular sheet over the sustained filament. The portion of the midpiece on the side of the undulating membrane and the flagellum is devoid of mitochondria. The plasma membrane in the midpiece region is tightly apposed to the mitochondria, so that in freeze-fracture or scanning electron microscopy the mitochondria seem to protrude through the plasma membrane. We suggest that the unusual organization of mitochondria in axolotl sperm facilitates the oxidative processes and increases the efficiency of ATP production and/or distribution within the cell.
Bs i-b4 isolectin as a probe for an investigation of membrane alterations and transformation phenotypes of mouse l cells
Authors: Stanley Wayne S. , Chu E. H. Y. 
Published: April 2021

ABSTRACT
BS I-B4, an α-D-galactopyranosyl-binding isolectin from Bandeiraea simplicifolia seeds, was found to interact differently with transformed mouse L cells and non-transformed mouse 3T3 cells. The lectin induces detachment of 3T3 cells but increases adhesiveness and clustering of L cells. However, the induced cell aggregation does not lead to cell fusion.
A variant clone of L cells, resistant to BS I-B4, which had lost the capacity for agglutination in the presence of the lectin, was isolated. Fluorescence binding studies of this variant suggest a lesion involving a and β-D-galactopyranosyl units on its cell-surface structures. Although the variant cells form colonies in a methylcellulose medium, they do not produce tumours, as do the parental cells, when transplanted in athymic nude mice. The results demonstrate that alterations in cell membrane glyco-conjugates play an important role in tumourigenesis of animal cells, but anchorage-independent growth in vitro, as one of the transformation phenotypes, cannot be correlated absolutely with tumourigenicity in vivo.
Nuclear bodies in the maturing egg cell of a fern, Pteridium aquilinum
Authors: Bell P. R. 
Published: April 2021

ABSTRACT
Nuclear bodies about 250 nm in diameter, and with a strong affinity for uranium and acriflavine, appear in the nuclei of maturing egg cells of Pteridium. Many enter well-defined evaginations of the nucleus. The nuclear bodies are almost wholly digested by Pronase, but are resistant to ribonuclease and deoxyribonuclease. Radioactive labelling gives no evidence of the presence of nucleic acids, but X-ray microprobe analysis indicates phosphorus. It is concluded that the bodies consist entirely of acidic protein, possibly phosphorylated. This protein may be a structural component of the nucleus, temporarily displaced and aggregated as a consequence of the fine dispersal of the chromatin.
Immunocytochemistry of the acellular slime mould Physarum polycephalum: I. Preparation, morphology, and reliability of results concerning cytoplasmic actomyosin patterns in sandwiched plasmodia
Authors: Naib-Majani Wallid , Osborn Mary , Weber Klaus , Wohlfarth-Bottermann Karl-Ernst , Hinssen Horst , Stockem Wilhelm 
Published: April 2021

ABSTRACT
Small phaneroplasmodia of Physarum polycephalum migrate, under sandwich conditions between two agar sheets and a membrane of cellophane, as thin protoplasmic sheets. This method suitably simulates the situation in the natural habitat of acellular slime moulds; i.e. the narrow clefts of the forest soil. The highly differentiated system of cytoplasmic fibrils displayed under these conditions survives both long-term extraction with glycerol and fixation with methanol, procedures that remove the strong inherent autofluorescence, thus allowing the use of immunocytochemical studies. The complicated fibrillar system of sandwiched plasmodia consists of: (1) a membrane-associated cortical filament layer in the anterior region; (2) a more or less regular polygonal fibrillar network in the intermediate region; and (3) a helically twisted fibrillar system encircling endoplasmic pathways as well as isolated strands in the posterior region. So far, three different cytoskeletal proteins have been identified immunocytochemically as constituents of the fibrillar structures: actin, myosin and AM-protein (fragmin). No positive identification of α-actinin, filamin and tropomyosin was obtained using antibodies against vertebrate proteins. Electron microscopy of glycerol-extracted specimens treated with antibodies against actin and myosin revealed that the 6 nm filaments consist of actin, whereas the electron-dense material between single actin filaments appears to be myosin. The AM-protein modulating the polymer status of actin is located in all fibrillar structures.
Bacillus thuringiensis var israelensis crystal δ-endotoxin: effects on insect and mammalian cells in vitro and in vivo
Authors: Thomas Wendy E. , Ellar David J. 
Published: April 2021

ABSTRACT
Bacillus thuringiensis var israelensis parasporal crystal ô-endotoxin was purified by ultracentrifugation on a discontinuous sucrose gradient. Native δ-endotoxin crystals showed no detectable toxicity in the in vitro and in vivo systems that are described. By contrast alkali-solubilized crystal δ-endotoxin caused rapid cytological and cytopathological changes in Aedes albopictus, Choris-toneura fumiferana 63 CF1, Spodoptera frugiperda and Trichoplusia ni cell lines as observed by phase-contrast microscopy and vital staining.
Mouse fibroblasts, primary pig lymphocytes and three mouse epithelial carcinoma cell types showed a similar response to the alkali-soluble crystal δ-endotoxin. In addition the soluble crystal δ -endotoxin protein caused haemolysis of rat, mouse, sheep, horse and human erythrocytes.
Intravenous administration of the alkali-soluble crystal δ-endotoxin to Balb.c mice at a dose rate of 15-30μg of protein per gram body weight resulted in rapid paralysis followed by death within 12h. Subcutaneous inoculation of 15–30μg of protein per gram body weight resulted in death of suckling mice in 2-3 h. The alkali-solubilized crystal δ-endotoxin was not toxic however, when administered per os.
A comparison is made with a similar alkali-soluble fraction from the parasporal crystal δ-en-dotoxin of B. thuringiensis var kurstaki. With the exception of the Lepidopteran cell line, Choris-toneura fumiferana 63 CF1, this soluble crystal δ-endotoxin protein showed no in vitro or in vivo toxicity, and no haemolytic activity.
X-ray microanalysis of hela s3 cells I. Instrumental calibration and analysis of randomly growing cultures
Authors: Warley Alice , Stephen J. , Hockaday A. , Appleton T. C. 
Published: April 2021

ABSTRACT
Cryo-ultramicrotomy and X-ray microanalysis were used to study the elemental composition of HeLa S3 cells. Quantitation was achieved by reference to elemental standards of known concentration made up in 25% gelatin. Analysis of standards showed linear calibration for each of the elements studied: Na, P, S, Cl, K. Standardization was validated by comparing flame-photometric analysis of gelatin containing sodium potassium tartrate with that of X-ray microanalysis. Freeze-dried sections of cells showed good morphology and analysis of whole sections of the cells showed that K/Na varied in individual cells. Low K/Na could not be ascribed to cell damage or to the sequestering of Na in any particular subcompartment of the cells. Treatment with ouabain caused changes in levels of all the elements studied and resulted in a low K/Na ratio in all cells.
Modification of flagellar waveform and adenosine triphosphatase activity in reactivated sea-urchin sperm treated with N-ethylmaleimide
Authors: Cosson Marie Paule , Tang Wen-Jing Y. , Gibbons I. R. 
Published: April 2021

ABSTRACT
Treatment of demembranated aea-urchin sperm for 1-2 min with 10μMW-cthylmaleimide (Mall-NEt) at pH80 prior to reactivation with 1 mM-ATP causes the asymmetry of the flagellar waveform to become desensitized to the presence or absence of Ca2+ in the reactivating medium. In such sperm, changes in concentration of free Ca2+ between 10−7M and 10−3M have no effect on the asymmetry of the waveforms as measured by the turning rate of the sperm in radians per beat cycle, while the beat frequency and the propulsive efficiency of the waves remain unchanged from the values observed in control preparations not treated with MalNEt. A somewhat more prolonged treatment with MalNEt causes a progressive decrease in the bend angles of the flagellar waves, while the beat frequency and the wavelength still remain largely unchanged. Further extension of the treatment with MalNEt causes complete loss of motility.
Little ATP-induced sliding of the doublet tubules is observed upon treatment with trypsin of sperm flagella that have been rendered non-motile with MalNEt. However, the preparations of solubilized dynein 1 obtained by 0·6M-NaCl extraction of axonemes treated with MalNEt appear almost identical to those obtained from untreated axonemes, both in terms of the amount solubilized and in the specific ATPase activities of their latent and Triton-activated forms. These preparations also appear capable of restoring much of the beat frequency of dynein-1-depleted flagella. These results suggest that the observed desensitization to Ca2+ and decrease in bend angle result from the reaction of MalNEt with axonemal polypeptides that are not part of the dynein 1 particle extracted with 0·6M-NaCl.
The rate of ATP hydrolysis by demembranated sperm rendered non-motile with MalNEt remains relatively high, and it decreases about 50% when the flagella are broken by brief homogenization. This ‘homogenizer-sensitive’ ATPase activity appears to be derived from some flagellar regulatory mechanism, which controls the ATPase activity of intact non-motile axonemes.
Identification of the cohesion molecule, contact sites B, of Dictyostelium discoideum
Authors: Chadwick C. M. , Garrod D. R. 
Published: April 2021

ABSTRACT
Polyspecific antibodies were raised against vegetative cells of Dictyostelium discoideum, strain Ax2. Monovalent (Fab′) fragments of antibodies CMC 1, 5, 7 and 12 blocked completely the cohesion of vegetative cells. Antibody CMC 1 was studied in detail. The Fab′ of this blocked the cohesion of aggregation-competent cells by 40%. It also caused some loss of cell contact in aggregation streams. In so doing the contacts that remained were mostly at the ends of the cells. Immunofluorescence showed that CMC 1 Fab′ bound to both the cytoplasm and the surface of fixed cells. It also bound to the surface of live cells. A control (N Fab′) also bound to the cell surface but did not block vegetative cell cohesion.
An extract of vegetative cells was obtained using the detergent Triton X-100. D. discoideum proteins were immunoprecipitated from this extract using protein A-Sepharose and CMC 1 immunoglobulin G (IgG). These immobilized proteins absorbed the cohesion-blocking activity of CMC 1 Fab′.
About 30 proteins were obtained when the Triton-soluble fraction was immunoprecipitated with IgG of CMC 1, 5, 7 and 12. Five of these were found to be cell surface proteins by the technique of lactoperoxidase-catalysed radio-iodination. These proteins had molecular weights of 178 000, 166 000, 126 000 and 64 000. CMC 12 IgG immunoprecipitated an additional cell surface protein of 46000 molecular weight.
Slices of polyacrylamide gel containing each of the five proteins identified as possible contact sites were fixed, washed and incubated with CMC 1 Fab′. Gel that contained protein of 178 000, 166 000 and 64 000 molecular weight had no effect on the activity of CMC 1 Fab′. However, Fab′ that had been incubated with gel containing protein of 126000 molecular weight no longer blocked cell cohesion.
Behaviour and structure of the leading lamella in moving fibroblasts: I. Occurrence and centripetal movement of arcshaped microfilament bundles beneath the dorsal cell surface
Authors: Heath Julian P. 
Published: April 2021

ABSTRACTArc-shaped bundles of microfilaments are frequently found beneath the dorsal surface of the leading lamella of chick embryo fibroblasts. These structures, called arcs, form parallel to, and 2 – 10μm from the leading edge of the lamella and they then move centripetally through the lamella and disappear in front of the cell nucleus. Arcs move centripetally at a mean speed of 1 · 33 (±0 · 08 S.E.) μm min − 1 relative to the substratum.Arcs are specifically associated with cells that are actively protrusive. They are common in fanshaped fibroblasts and in those cells that are newly spreading on a substratum. Arcs are absent from fibroblasts that have only small lamellae or that are polygonal. The correlation between arc formation and protrusive activity is also clearly shown by the locomotory behaviour of fan-shaped cells. When protrusion of the lamella is increased by tail detachment, fibroblasts often develop numerous arcs, which chase each other backwards through the lamella. Conversely, arc formation ceases during contact inhibition of locomotion.In cells with large convex-edged lamellae there is a dorsal submembraneous sheath of microfilaments. All of the filaments comprising the sheath are oriented parallel to the margin of the lamella. Arcs are regions of the sheath where the microfilaments are more densely packed and hence visible by phase-contrast microscopy. There is no obvious relationship between the dorsally situated arcs and microfilament sheath, and the stress fibres that are associated with the ventral cell surface.The similarities between the movement and behaviour of arcs and the centripetal transport of particles on the surface of the lamella suggest a role for the microfilament sheath in the movement of particles.
Nucleoside diphosphokinase and cell cycle control in the fission yeast Schizosaccharomyces pombe
Authors: Dickinson J. Richard 
Published: April 2021

ABSTRACT
Centrifugal elutriation was used to prepare synchronous cultures of Schizosaccharomycespombe. Nucleoside diphosphokinase activity was measured throughout the cell cycle. In the wild-type strain (972) nucleoside diphosphokinase activity doubled in a stepwise fashion. The midpoint of the rise in enzyme activity was at 0 ·65 of a cycle, 0·29 of a cycle before the next S phase. Synchronous cultures of the mutant wee l ·6 were also prepared. In this strain S phase is delayed, occurring about 0·3 cycle later than in the wild-type. In wee 1 ·6 the midpoint of the stepwise doubling in nucleoside diphosphokinase activity occurred at 0 · 084; showing that the rise in enzyme activity is also delayed.
Addition of cycloheximide to an exponentially growing culture caused an immediate inhibition of protein synthesis, yet nucleoside diphosphokinase activity continued to increase exponentially for a further 300 min. This indicates that the stepwise doubling of nucleoside diphosphokinase activity during the cell cycle is not achieved by a simple control on protein synthesis.
Two temperature-sensitive cdc− mutants were also used: cdc2-33, a mutant whose single genetic lesion results in the twin defects of a loss of mitotic control and a loss of commitment to the cell cycle; and cdc10-129, which has a defect in DNA replication. In both mutants a temperature shift-up of an asynchronously growing culture from the permissive (25 °C) to the restrictive temperature (36·5°C) results in a rapid inhibition of DNA replication. In both mutants nucleoside diphosphokinase continues to increase exponentially. Therefore, although nucleoside diphosphokinase is required for DNA replication, apparently DNA replication is not required for an increase in nucleoside diphosphokinase activity.
Microspectrophotometric and autoradiographic study of the timing and duration of pre-meiotic DNA synthesis in Paramecium caudatum
Authors: Fujishima Masahiro 
Published: April 2021

ABSTRACT
Timing and duration of pre-meiotic G1, S and G2 phases in Paramecium caudatum have been clarified by microspectrophotometry of DNA content and autoradiography with [H]thymidine ([H]dThd) and [3H]deoxyuridinemonophosphate ([3H]dUMP). Microspectrophotometric measurement of DNA content showed that cells in stationary phase have a G| micronucleus, and that pre-meiotic DNA synthesis begins with the micronuclear swelling and ends immediately before the nucleus enters meiotic prophase. The results indicate that the micronucleus is in G1 during the first T5 h after onset of mating reaction at 25 °C and in pre-meiotic S phase during the following 1 h, and that Gl phase is very short or lacking. Therefore, in P. caudatum, the transition point from pre-meiotic interphase to meiotic prophase is at or very close to the end of pre-meiotic DNA synthesis.
Autoradiographic study showed that although [3H]dThd and [3H]dUMP were well utilized in pre-mitotic DNA synthesis, only [3H]dUMP was well utilized in pre-meiotic DNA synthesis. [3H]dThd was utilized very little in pre-meiotic DNA synthesis even if the precursor was taken into the cell, suggesting that the activity of thymidine kinase is low in these cells.