bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fine structure and radiation resistance in Acinetobacter: studies on a resistant strain
Authors: Thornley Margaret J. , Glauert Audrey M. 
Published: April 2021

ABSTRACT
An electron-microscope study of thin sections and negatively stained preparations of intact cells and isolated cell walls of a bacterium which is moderately resistant to ionizing radiation, Acinetobacter strain 199 A, showed that it is similar to other Gram-negative bacteria except for its mode of division and for the fine structure of some of the surface layers. During division the cells form a fairly thick septum similar to those observed in Gram-positive bacteria. An examination of the appearance and chemical composition of isolated cell walls before and after treatment with enzymes, detergents and lipid solvents revealed that three layers, each with a characteristic fine structure, are present in the cell wall: (1) an outer membrane with an array of peg-like subunits; (2) a layer of wrinkled material which is digested by proteolytic enzymes; and (3) a smooth, rigid layer, which contains the mucopeptide components of the cell wall. These observations are compared with the results of other workers for various Gram-negative bacteria. From comparisons with the structure of more radiation-sensitive strains of Acinetobacter, it appears that layer (2) may be associated with the radiation resistance of the organism.
A radioautographic study of the time course of male meiosis in the newt Triturus vulgaris
Authors: Callan H. G. , Taylor J. H. 
Published: April 2021

ABSTRACT
In male Triturus vulgaris at 16 °C the pre-meiotic synthesis of DNA (S-phase) takes 9–10 days. The S-phase starts 1–2 days after completion of the ultimate spermatogonial mitosis, and extends into leptotene. Heterochromatic regions, most of which lie close to the centromeres, start and finish replicating about 1 day later than other parts of the chromosomes. Synapsis starts 6 days after the end of pre-meiotic S and is completed 8 days later. Pachytene lasts for 4 or 5 days, diplotene for 1 or 2 days, and first metaphase occurs 20 or 21 days after the end of pre-meiotic S. Label distribution at first metaphase in spermatocytes stemming from spermatogonia which incorporated [3H]thymidine during the penultimate intennitotic S shows that random segregation and assortment of labelled and unlabelled chromatids took place at the ultimate spermatogonial mitosis.
Reaction of surface lamella of moth spermatozoa to vinblastine
Authors: Friedländer Michael , Gershon Janine 
Published: April 2021

ABSTRACT
Previous ultrastructural studies appear to indicate that the lacinate appendages (highly elaborated laminar structures which cover the surface of moth spermatozoa) may be intra-cellular derivatives of transient microtubules found in the elongating spermatids of these insects. Additional support for this theory is supplied by the present study in which testes of the warehouse moth Ephestia cantella were treated in vivo with the antimitotic agent vinblastine sulphate. Solutions containing 10−5 M vinblastine caused the lacinate appendages to become poorly resolved, and at 10−3 M they disappeared. This concentration-dependent response of the appendages to vinblastine resembles that of tubulin-containing structures.
Mutual cohesion and cell sorting-out among four species of cellular slime moulds
Authors: Nicol A. , Garrod D. R. 
Published: April 2021

ABSTRACT
Interspecific cell cohesion among 4 species of cellular slime moulds, Dictyostelium discoideum, D. mucoroides, D. purpureum and Polysphondylium violaceum has been studied. Binary mixtures of aggregation-stage cells of the 4 species were shaken in suspension, one species of each pair being labelled with PH]thymidine. Cell aggregates were sampled at intervals over 24 h and their composition examined by autoradiography. The following results were obtained: (i) Cells of each species were capable of cohesion with those of the other 3 species, (ii) In general cells of both species in any mixture were present in aggregates after 1 h, but were not localized according to species, (iii) Within 8-h aggregates cells of different species were regionally localized, i.e. sorting-out appeared to have taken place, (iv) 24-h aggregates were more varied: in mixtures of Dictyostelium species, the different species were localized within the aggregates; in mixtures of Dictyostelium species with Polysphondylium, there was a tendency for cells of the different species to become segregated into completely separate aggregates.
The significance of these results in relation to both previous descriptive work and recent biochemical studies on the mechanism of slime mould cell cohesion is discussed.
The distribution of actin cables and microtubules in hybrids between malignant and non-malignant cells, and in tumours derived from them
Authors: Watt Fiona M. , Harris H. , Weber K. , Osborn Mary 
Published: April 2021

ABSTRACT
Cell fusion provides a genetic test for linkage between cellular phenotypic markers and malignancy. We have examined hybrid cells in which malignancy is suppressed and malignant segregants derived from them, to test whether the reappearance of malignancy is regularly associated with loss or abnormality of actin cables or microtubules. Immunofluorescence studies did not reveal any difference between the malignant and non-malignant hybrids in the number and distribution of microtubules that they contained. All the hybrids, whether tumorigenic or not, contained elaborate patterns of cytoplasmic microtubules. Furthermore, no consistent relationship was observed between the absence of actin cables and malignancy.
Divalent cation stimulation of in vitro fibre assembly from epidermal keratin protein
Authors: Fukuyama Kimie , Murozuka Takashi , Caldwell Russell , Epstein William L. 
Published: April 2021

ABSTRACT
Keratin was extracted from purified cornified cells of newborn rats in Tris-HCl-buffered 8 M urea containing β-mercaptoethanol. Microfilaments were assembled in vitro by reducing the ionic strength of buffer and the urea concentration.
One millimolar concentration of KC1 and NaCl did not affect filament formation, but the same concentration of divalent cations greatly altered this process. CaCl2 and MgCl2 induced gelation of keratin by formation of bundles of biréfringent macrofilaments. ZnCl2, CuSO4 and HgCl2 formed greater numbers of macrofilaments and the protein aggregated.
Stimulation of dendritogenesis in the epidermal melanocytes of newborn mice by melanocyte-stimulating hormone
Authors: Hirobe Tomohisa 
Published: April 2021

ABSTRACT
The number of dendrites and the total length of dendrites in the epidermal melanocytes positive for the dopa reaction were shown to increase when newborn mice were injected with α-MSH or DBc-AMP. Moreover, both indices of the degree of dendritogenesis increased when skin expiants of newborn mice were cultured in medium containing α-MSH or DBc-AMP. Electron-microscopic observation showed that the number of melanosomes was also increased by α-MSH treatment. Many mature melanosomes were observed in the dendrites of the epidermal melanocytes of α-MSH-injected mice. Highly dendritic melanocytes seem to be the cells stimulated by MSH to form melanosomes and translocate them to dendrites. Dendritogenesis stimulated by the hormone was suppressed by actinomycin D or cycloheximide, suggesting that the dendritogenesis in the epidermal melanocytes requires de novo transcription and translation.
Unidirectional regeneration is an intrinsic property of longitudinal microtubules in Tetrahymena-an in vivo study
Authors: NG Stephen F. 
Published: April 2021

ABSTRACT
The cortex of Tetrahymena contains a regular array of longitudinal microtubular bands (lms) next to basal body rows running from pole to pole. The lm exhibits a predominant unidirectionality in assembly. The direction of regeneration following breakage of the microtubules is from posterior to anterior of the cell. When the lm and the accompanying basal body row are rotated 180 ° (inverted), so that their polarity is opposite to that of the cell, the predominant direction of regeneration exhibited by the inverted lm is from anterior to posterior. This shows that the lm has an inherent direction of regeneration independent of cellular polarity. This implies that the microtubules constituting the lm have an intrinsic property which controls the direction of assembly. This finding is in accord with the in vitro demonstration using Chlamydomonas flagellar fragments. On the basis of this finding and also the possible pattern of arrangement of the microtubules constituting the lm, it is suggested that growth of the lm involves both elongation of pre-existing microtubules constituting the lm and also laying down of new ones.
Preaggregative cell motion in Dictyostelium
Authors: Potel Michael J. , Mackay Steven A. 
Published: April 2021

ABSTRACT
The motions of a large number (495) of preaggregative D. discoideum NC-4 cells in sparse fields are recorded on time-lapse film and analysed using a specially constructed computer graphics system. All films are produced under a standard set of conditions, so that the range of cell behaviours under given conditions can be characterized. The mean velocity of preaggregative D. discoideum NC-4 is 7·19 μm/min. The mean velocity time course has a significant early peak at about 3 h. The distribution of mean velocities is fairly broad with a long high velocity tail. A modified random walk model using the parameters diffusion constant and persistence time describes well the changes in cell direction with time. Persistence can be described as an exponentially distributed ‘memory’ of movement direction, with a mean of 4·89 min. High velocity cells never have long persistence times, and persistence time shows no relationship with age. A nearest neighbour model of cell spacing shows that cells are randomly (Poisson) distributed at low densities. Measurements of cell contacts are compared to a simple model of contact frequency based on the kinetic theory of gases to show that cells at low densities have an affinity for making collisions. The length of contact durations is indicative of some mechanical adhesion between cells, and cells in contact move significantly though not dramatically slower. A cross-correlation analysis shows that the various parameters of motion are significantly interrelated in numerous ways. Finally mutants and strains related to D. discoideum NC-4 exhibit a number of new behaviours, suggesting that motion is a distinctive characteristic of cell type.
Effect of concanavalin A dose, unbound concanavalin A, temperature, ca2+ and mg2+, and vinblastine on capping of concanavalin A receptors of human peripheral blood lymphocytes
Authors: Bhalla D. K. , Hunt C. V. , Kapur S. P. , Anderson W. A. 
Published: April 2021

ABSTRACT
The capping of Concanavalin A (Con A) receptors induced by Con A was studied using human peripheral blood lymphocytes. The effects of Con A dose (5–100 μg/ml), pretreatment at 4 °C, unbound Con A, extracellular Ca2+ and Mg2+ and vinblastine were evaluated using Con A-horseradish peroxidase and electron microscopy. Lymphocytes incubated with Con A at 4 °C and fixed with glutaraldehyde exhibited Con A-horseradish peroxidase around the entire cell periphery. After raising the temperature to 37 °C, the Con A-horseradish peroxidase moved to form a cap at one pole of the cell and subsequently underwent endocytosis. Capping of Con A receptors induced by Con A at 37 °C was observed only at low Con A concentrations in the presence of unbound Con A and extracellular Ca2+ and Mg2+. Increased capping was found after pretreatment of cells with Con A at 4 °C, removing unbound Con A and/or removing extracellular Ca2+ and Mg2+, and by treatment with vinblastine. Following removal of both unbound Con A and extracellular Ca2+ and Mg2+, the percentage of capped cells at 37 °C was the same as on pretreatment at 4 °C under the same conditions. While pretreatment at 4 °C caused the breakdown of microtubules, removal of unbound Con A and/or extracellular Ca2+ and Mg2+ had no morphological effect on microtubules or microfilaments. Following exposure of lymphocytes to vinblastine and removal of unbound Con A, capping of Con A receptors by Con A was observed in over 90 % of cells at all Con A dosages. However, when cells were exposed to vinblastine in the presence of unbound Con A the formation of Con A caps was either partially or completely inhibited.
Plasmalemma invaginations of Physarum dependent on the nutritional content of the plasmodial environment
Authors: Achenbach Friedhelm , Naib-Majani Wallid , Wohlfarth-Bottermann Karl Ernst 
Published: April 2021

ABSTRACT
Quantitative estimates of plasmalemma invaginations in plasmodial veins of Physarum polycephalum were made under different conditions of nutrition. Pronounced differences were observed dependent on the nutritional content of the substrate. There was a decided increase in the number of plasmalemma invaginations in plasmodial veins grown on substrates containing absorbable food substances compared to veins migrating on non-nutrient substrates. This observation supports the proposition that the nutritional content, rather than the physical properties, of the substrate is the decisive factor for the formation of plasmalemma invaginations. The invaginations are believed to be concerned with the uptake of non-particulate food substances.
Increase in macromolecular amounts during the cell cycle of tetrahymen a a contribution to cell cycle control*
Authors: Cleffmann Günter , reuter Wolf-otto , seyfert Hansmartin 
Published: April 2021

ABSTRACT
Increases in RNA, protein and cell size were determined cytophotometrically during the cell division cycle of Tetrahymena. For these parameters different patterns were found. RNA accumulates slowly during G1 period and faster during macronuclear S. This agrees with the changing uridine incorporation rate which is at least partly related to the varying macronuclear DNA amount. Increases in protein content and cell size occur mainly during G1and G2. This pattern was confirmed by determining the RNA : protein ratio in individual cells. It is minimal at the end of the G, period. These findings and evidence from the literature suggest that initiation of DNA replication is under negative control by the relative RNA content of the cell.
Survival of cells implanted in the embryonic chick limb bud: A difference between normal and malignant rat brain cells
Authors: Tickle C. , Crawley A. , Roscoe J. P. 
Published: April 2021

ABSTRACT
Cells from normal rat brain tissue did not survive and few cells could be found 1 d after grafting. In contrast, cells from a glioma and a carcinogen-treated rat brain survived well and many mitoses were observed. These malignant cells also invaded the limb. The behaviour of normal and malignant cells was followed at shorter times after grafting and some invasion by the normal cells was detected. The first signs of degeneration of normal cells were apparent around 7 h after grafting, and after this the grafts progressively deteriorated. These results support the idea that the ability of cells to survive and grow in embryonic tissues is a characteristic of malignant cells. The findings are discussed in relation to mechanisms of tumour formation.
A ligand-receptor model for the cohesive behaviour of Dictyostelium Discoideum axenic cells
Authors: Jaffe Alida R. , Swanf Alma P. , Garrod D. R. 
Published: April 2021

ABSTRACT
Axenically grown cells of D. discoideum Ax-2 harvested in the log phase of growth, cohere rapidly when shaken in phosphate buffer. After 3.5 days in the stationary phase of growth, cells become completely non-cohesive. Although they do not stick to each other, stationary phase cells do stick to both log phase cells and aggregation-competent cells. The cohesion of stationary phase cells with these other 2 cell types is inhibited by both EDTA and the low-molecular-weight factor which we have previously demonstrated in stationary-phase growth medium.
There is a decline in the sensitivity of slime mould cell cohesion to the low-molecular-weight inhibitory factor as the cells become aggregation-competent. This effect parallels the developmentally-regulated decline in sensitivity to EDTA. The low-molecular-weight inhibitor is not a chelating agent, however. The effect of the inhibitor seems to be specifically against contact sites-B mediated cohesion. We suggest that the simplest cohesive mechanism which can explain our results, is that the EDTA-sensitive cohesion of log phase cells could be dependent on a ligand-receptor system.
Dibutyryl cyclic amp suppresses mobility of embryonic chick heart cells in aggregates
Authors: Gershman Howard , Weis Geri , Barstow Nancy 
Published: April 2021

ABSTRACT
The intermixing of chick embryonic heart ventricle cells was studied in cellular aggregates as a function of embryonic age of the cells. Cell mobility, as measured by intermixing of radiolabelled and unlabelled cells, was high in cells derived from young embryos: 5.36 ± 1.05 cell diameters per 2.5 days for 6-day-old heart ventricle cells. During development, mobility steadily declined to 1.56 ±0 24 cell diameters per 2.5 days for 18-day old cells. Treatment of aggregates with 1.0 mM theophylline plus 1.2 mM dibutyryl cyclic AMP resulted in greatly decreased mobility, particularly in aggregates of the more mobile younger cells. Depending on the embryonic age of the heart ventricle cells, this treatment reduced mobility by 45.3 to 89.4%. These data are consistent with an age-dependent decrease in intrinsic mobility superimposed upon a contact-paralysis mediated inhibition of movement present in solid tissues. In addition, the sensitivity of heart ventricle cells to inhibition by agents that increase intracellular cyclic AMP levels suggest that this is another possible inhibitory mechanism, although its physiological significance has not been established.
Stem cell growth and differentiation in Hydra attenuata: II. Regulation of nerve and nematocyte differentiation in multiclone aggregates
Authors: Sproull Frederick , David Charles N. 
Published: April 2021

ABSTRACT
The differentiation of nerve cells and nematocytes from interstitial stem cells in Hydra has been investigated under conditions of changing stem cell density. Interstitial stem cells were cultured in a feeder layer system consisting of aggregates of nitrogen mustard-inactivated tissue. The aggregates were seeded with varying numbers of stem cells from 10 to 400 per aggregate; between 4 and 7 days later the rates of nerve and nematocyte differentiation were measured. Nerve differentiation was scored by labelling the stem cell population with [3H] thymidine and counting labelled nerve cells after 48 h. Nematocyte differentiation was scored by counting nests of 4 proliferating nematoblasts. In both cases the numbers of differentiating cells were normalized to the size of the stem cell population.
The results indicate that the rate of nematocyte differentiation increases as the concentration of stem cells increases in aggregates; under the same conditions the rate of nerve differentiation remains essentially constant. To calculate the numbers of stem cells entering each pathway per generation, a computer was programmed to simulate the growth and differentiation of interstitial stem cells. Standard curves were prepared from the simulations relating the rates of nerve and nematocyte differentiation to the fraction of stem cells committed to each pathway per generation. The rates of nerve and nematocyte commitment were then estimated from the experimentally observed rates of differentiation using the standard curves. The results indicate that nerve commitment remains constant at about 0·13 stem cells per generation over a wide range of stem cell concentration. Nematocyte commitment, by comparison, increases from 0·15 to 0·21 stem cells per generation as stem cell concentration increases in aggregates. The fact that the ratio of nerve to nematocyte commitment changes under our conditions suggests that stem cell commitment is not a stochastic process but subject to control by environmental stimuli.
Immaturity substances in paramecium primaurelia and their specificity
Authors: Miwa Isoji 
Published: April 2021

ABSTRACT
Cells of Paramecium primaurelia in the immaturity period of the life cycle contain substances which repress the expression of mating ability when introduced into mature cells. When the immature cytoplasm of P. primaurelia was injected into mating-reactive cells of P. tetraurelia, P. caudatum and P. timicronucleatum, immaturity was also induced in them. But the immature cytoplasm of P. primaurelia was ineffective when injected into mature cells of P. bursaria. When the immature cytoplasm of P. bursaria was injected into mating-reactive cells of P. primaurelia and P. tetraurelia, no difference from the control was observed. When the immature cytoplasm of P. caudatum was injected into mating-reactive cells of P. pri maurelia and P. tetraurelia, immaturity was induced in cells of the latter 2 species.
Vesicles in guard-cell walls and their possible roles in the stomatal mechanism
Authors: Cork Robert John , Nelmes Brenda J. 
Published: April 2021

ABSTRACT
A variety of vesicular inclusions have been, observed in guard-cell walls. They have been seen in a number of species and are mostly membrane-bound. They appear confined to the upper and ventral walls of the guard cell. A number of possible origins and functions are discussed. They may be involved in wall deposition or cuticle formation possibly in a role similar to ectodesmata. They also may serve to increase the wall-plasmalemma interface to enhance the movement of ions during the stomatal mechanism.
A cytochemical and radioautographic study of the ultrastructural organization of puff-like fibrillar structures in plant interphase nuclei (Allium porrum)
Authors: Lafontaine J. G. , Luck B. T. , Dontigny D. 
Published: April 2021

ABSTRACT
Loose, fibrillar, spherical structures have been observed during recent years in interphase nuclei of both animal and plant cells. These nuclear formations have been referred to as karyosomes, fibrillar bodies, micropuffs and centromeres. In order to gain further information on the nature of these structures, a cytochemical and radioautographic investigation was undertaken using plant meristematic cells (Allium porrum). For that purpose roots were fixed with either formaldehyde or glutaraldehyde in order to carry out cytochemical tests for DNA, RNA and proteins. Certain of the preparations were also first digested with DNase, RNase or proteinase K and then stained according to different procedures. Other specimens were labelled with thymidine for high-resolution radioautographic observations. Staining with diaminobenzidine (DAB) revealed that these nuclear puff-like formations consisted partly of a loose fibrillar meshwork containing nucleic acids. Part of this fine fibrillar reticulum persisted whether the preparations were digested with DNase or RNase before staining with DAB, thus indicating that these nuclear structures contained both DNA and RNA. The fact that these formations incorporate thymidine furnished additional support for the view that they correspond to specific chromosome segments. Staining with ethanolic phosphotungstic acid or digestion of specimens with proteinase K showed that these loose fibrillar structures also consisted of proteins.
Judging from their ultrastructure, their association with the chromatin reticulum as well as from their cytochemical characteristics, these nuclear formations most likely correspond to centromeres.
In view of the presence of DNA within these structures, it is possible to distinguish them from other equally spherical nuclear formations, observed in certain plant species, that have generally been referred to as karyosomes or micronucleoli and that appear to consist of ribonucleoproteins.