bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemotactic peptide-induced exocytosis in neutrophils: granule fusion patterns depend on the source of messenger calcium
Authors: Chandler Douglas E. , Kazilek Charles J. 
Published: April 2021

ABSTRACT
Rabbit neutrophils, exposed either to partially purified human C5a or to formylmethionyl-leucyl-phenylalanine in the presence of 5μgml-1 cytochalasin B underwent a rapid, compound exocytosis. The pattern of granule fusion, as visualized in freeze-fracture replicas, differed depending on the source of messenger calcium. In the presence of extracellular calcium, a linearly directed pattern, consisting of finger-like invaginations converging at the cell centre, was prominent at 10–20 s after stimulation. After stimulation for 20–40 s, further fusion of granule membranes created extremely convoluted surfaces, some consisting of up to a dozen granule membranes connected by narrow pores or flat ribbons of membrane. In many cells the peripheral cytoplasm was constricted to form lobes or finger-like protrusions. Neutrophils stimulated in the absence of extracellular calcium exhibited granule fusion in the directed pattern, with only occasional involvement of the convoluted patterns seen when calcium is present. In contrast, neutrophils depleted of intracellular calcium before stimulation (and thereby forced to use extracellular calcium for triggering secretion) exhibited the convoluted pattern of granule fusion almost exclusively. These results suggest that the directed pattern of fusion is initiated by release of intracellular calcium or a calcium-independent pathway and that the non-directed, convoluted pattern of fusion is initiated by entry of extracellular calcium.
Elemental content of mast cell granules measured by x-ray microanalysis of rat thymic tissue sections
Authors: Kendall Marion D. , Warley Alice 
Published: April 2021

ABSTRACT
Mast cell granules were examined by fully quantitative X-ray microanalysis of 20 cells in freeze-dried cryosections. The mast cells were situated mainly in the connective tissue of the thymic capsule of five adult male Carworth Sprague Europe rats. In addition 30 red blood cells were analysed from the same sections.
Nineteen of the mast cells had granules rich in S and K. One cell had smaller granules, and in this cell the granules contained high [Ca] and [P] instead of high [S] and [K], In the majority of cells (13) the S: K ratio was highly correlated and less than 2–2, whereas in the remaining six cells the individual granule ratios were very variable in any one cell and much higher. The mean granule [K] (994 ± 57 mmol kg-1 dry wt) was about four times the mean cytoplasmic level of 227 ±81 mmol kg-1 dry wt. The existence of this difference in concentration between the granules and the cytoplasm suggests that the K in the granules must be bound.
The relationship between the [K] and [S] is discussed with regard to the possible binding of heparin and amines in the granules.
Chromosome condensation activity in ovulated metaphase ii mouse oocytes assayed by fusion with interphase blastomeres
Authors: Czołowska Renata , Waksmundzka Małgorzata , Kubiak Jacek Z. , Tarkowski Andrzej K. 
Published: April 2021

ABSTRACTFusion of large and small karyoplasts produced from metaphase II mouse oocytes with interphase blastomeres from 2-cell and 8-cell embryos (volume ratio of partners, 1:1) results in premature chromosome condensation (PCC) of the interphase nucleus in the majority of the fusion products (hybrids). Fused under the same experimental protocol, oocyte-derived cytoplasts also induce PCC of the blastomere nucleus in the fusion products (cybrids) provided they originate from recently ovulated oocytes (14½ −15h after injection of human chorionic gonadotrophin (HCG)). In cytoplasts derived from older oocytes (16–20 h post-HCG) chromosome condensation activity gradually decreases with time as can be inferred from the increasing proportion of cybrids retaining interphase blastomere nuclei. However, even the oldest cytoplasts (19–20 h post-HCG) can induce PCC if the cytoplast volume significantly exceeds the volume of the interphase partner (7:1)-We postulate that the condensation activity is predominantly bound to the nuclear apparatus (most probably to the chromosomes), and that in the cytoplasm of metaphase II mouse oocyte it decreases with post-ovulatory age.
Neutrophil leucocyte chemotaxis is not induced by a spatial gradient of chemoattractant
Authors: Vicker Michael G. , Lackie John M. , Schill Walter 
Published: April 2021

ABSTRACT
Chemotaxis and directed locomotion of neutrophil leucocytes are generally thought to be determined by the directed response of the cell to stable, spatial gradients of chemoattractants. In most cases, however, cells are also exposed to characteristic temporal changes in the attractant concentration during the lifetime of the gradient, especially as it develops. We have attempted to test whether neutrophils can respond to a spatial gradient in which these temporal changes are essentially absent. Gradients of formyl-peptides were made across a narrow barrier of agarose gel that separated two fluid reservoirs, and the cells were observed cinematographically as they moved between gel and glass. In gradients predeveloped at low temperature, at which cell motion and responses to attractant were inhibited, neutrophils showed no tendency to accumulate up-gradient when warmed to 37°C. Yet their speed and turning behaviour was related to the local concentration of formyl-peptide. However, gradients that developed at 37°C, whilst the cells were responsive, elicited directed locomotion. We also tested populations that were either spreading into or already evenly distributed across micropore filters to see how cells might sense directional cues. We reasoned that evenly distributed populations could accumulate in a spatial gradient only if cells were able to ‘read’ it. However, no redistribution occurred without an applied impulse of attractant. It seems that the oriented, temporal component of an attractant signal is essential if a directed response (i.e. non-random turning) is to occur; a spatial gradient of soluble attractant alone does not induce neutrophil accumulation or taxis. This finding has implications for the termination of the acute inflammatory response, for clinical tests of leucocyte behaviour and for morphogen signal interpretation by cells in developing tissues.
Actin during pollen germination
Authors: Heslop-Harrison J. , Heslop-Harrison Y. , Cresti M. , Tiezzi A. , Ciampolini F. 
Published: April 2021

ABSTRACT
The cytoplasm of the vegetative cell of the ungerminated pollen grain of Endymion non-scriptus and other angiosperm species contains numerous fusiform bodies sometimes exceeding 15 gm in length and 2-5 gm in width, which bind fluorescent-labelled phalloidin and are likely therefore to constitute a storage form of actin. The bodies are dispersed during the activation of the pollen, being replaced by aggregates of slender phalloidin-binding fibrils, which converge towards the germination apertures and are present in the emerging pollen tube. The storage bodies appear to be homologous with crystalline-fibrillar structures, shown in an earlier paper to be abundantly present in the vegetative cells of Nicotiana pollen. These are composed of massive aggregates of linearly disposed units with individual widths of 4–7 nm, probably to be interpreted as actin microfilaments.
Vegetative-cell protoplasts from mature but ungerminated pollen disrupted in osmotically balancing medium release extended phalloidin-binding fibrils of a kind not observed in the intact grain. It is suggested that these are derived by the rapid dissociation of the compact actin storage bodies present in the vegetative cell at this stage of development.
Presumptive mesoderm cells from Xenopus laevis gastrulae attach to and migrate on substrata coated with fibronectin or laminin
Authors: Nakatsuji Norio 
Published: April 2021

ABSTRACT
During amphibian gastrulation, presumptive mesoderm cells migrate from the blastopore towards the animal pole along the inner surface of the ectodermal layer. Their natural substratum is a network of anastomosing extracellular matrix fibrils, which contains fibronectin and laminin, as shown by immunostaining. If the fibril network is transferred onto a coverslip from the ectodermal layer, dissociated mesodermal cells readily attach to such conditioned surfaces and show active migration in a medium of high pH and low calcium ion concentration.
In the present study, the surface of tissue culture dishes was coated with fibronectin, laminin, collagen type IV or heparan sulphate, to examine the effects on cell attachment and movement. The presumptive mesoderm cells from Xenopus laevis gastrulae showed rapid adhesion and active movement on the fibronectin- or laminin-coated surfaces. Cell adhesion was stronger and the mean rate of movement was higher on the fibronectin-coated surface than on the laminin-coated surface. The dissociated ectodermal cells did not attach to the fibronectin- or laminin-coated surfaces. The mesodermal cells did not attach to the collagen-, or heparan sulphate-coated surfaces, showing that these components of the basement membrane cannot serve as an adequate substratum for the mesoderm cells, at least by themselves.
Invasive behaviour of mouse primordial germ cells in vitro
Authors: Stott David , Wylie Christopher C. 
Published: April 2021

ABSTRACT
We have isolated migrating primordial germ cells (PGCs) from 10-5-day mouse embryos and studied their behaviour when cultured on a mouse embryo fibroblast (STO) cell line. Living and fixed PGCs were identified by fluorescent labelling with a monoclonal antibody specific for PGCs in the culture system used. The behaviour of the cells was studied using interference reflexion microscopy (IRM) and time-lapse video cinematography. The IRM pattern displayed by PGCs is typical of highly motile cell types, the cells lack focal contacts and possess large areas of close contacts indicative of weak membrane to substrate interaction. The PGCs exhibit relatively high rates of translocation and lack contact inhibition. They were observed to underlap STO cells in subconfluent monolayers and to penetrate between the cells of confluent monolayers, becoming located between the monolayer and its substrate. These observations support the hypothesis that migrating mouse PGCs are inherently motile and are able transiently to disrupt the adhesion of surrounding cells. These results suggest that PGCs actively migrate to the developing gonad in vivo.
Algal endosymbiosis in brown hydra: Host/symbiont specificity
Authors: Rahat M. , Reich V. 
Published: April 2021

ABSTRACT
Host/symbiont specificity has been investigated in non-symbiotic and aposymbiotic brown and green hydra infected with various free-living and symbiotic species and strains of Chlorella and Chlorococcum. Morphology and ultrastructure of the symbioses obtained have been compared. Aposymbiotic Swiss Hydra viridis and Japanese H. magnipapillala served as controls.
In two strains of H. attenuata stable hereditary symbioses were obtained with Chlorococcum isolated from H. magnipapillata. In one strain of H. vulgaris, in H. oligactis and in aposymbiotic H. vtrtdis chlorococci persisted for more than a week. Eight species of free-living Chlorococcum, 10 symbiotic and 10 free-living strains of Chlorella disappeared from the brown hydra within 1-2 days.
In H. magnipapillata there was a graded distribution of chlorococci along the polyps. In hypostomal cells there were &gt;30 algae/cell while in endodermal cells of the mid-section or peduncle &lt;10 algae/cell were found. In H. attenuata the algal distribution was irregular, there were up to five chlorocci/cell, and up to 20 cells/hydra hosted algae.
In the dark most cells of Chlorococcum disappeared from H. magnipapillata and aposymbiotic hydra were obtained. Chlorococcum is thus an obligate phototroph, and host-dependent heterotrophy is not required for the preservation of a symbiosis. The few chlorococci that survived in the dark seem to belong to a less-demanding physiological strain.
In variance with known Chlorella/H. viridis endosymbioses the chlorococci in H. magnipapillata and H. attenuata were tightly enveloped in the vacuolar membrane of the hosting cells with no visible perialgal space. Chlorococcum reproduced in these vacuoles and up to eight daughter cells were found within the same vacuole.
We suggest that the graded or scant distribution of chlorococci in the various brown hydra, their inability to live in H. viridis and the inability of the various chlorellae to live in brown hydra are the result of differences in nutrients available to the algae in the respective hosting cells.
We conclude that host/symbiont specificity and the various forms of interrelations we show in green and brown hydra with chlorococci and chlorellae are based on nutritional-ecological factors. These interrelations demonstrate successive stages in the evolution of stable obligatoric symbioses from chance encounters of preadapted potential cosymbionts.
Cytoplasmic organization during pattern formation in the alga Micrasterias
Authors: Mcnally James G. , Swift Hewson 
Published: April 2021

ABSTRACT
Using an improved fixation for electron microscopy, we have observed an ordered cytoplasmic organization during pattern formation in the alga Micrasterias. At the earliest stages of morphogenesis (the bulge to 3-lobe stage), as observed previously, electron-dense vesicles and endoplasmic reticulum were found towards the cell periphery, while mitochondria and Golgi material were located internally. In contrast to previous studies, which found no organization in the cytoplasm of growing lobes, we observed a single cluster of electron-dense vesicles at the tip of each lobe at or beyond the 5-lobe stage. In lobes about to branch, two separate clusters of electron-dense vesicles were present in each lobe, apparently foreshadowing the sites of new lobe outgrowth. Individual lobes also possessed an ordered distribution of organelles. Immediately basal to the lobe tip, the concentration of electron-dense vesicles decreased and rough endoplasmic reticulum was more prevalent, followed more deeply in the cytoplasm by increased concentrations of mitochondria and then Golgi material. This cytoplasmic organization in individual lobes is characteristic of tip growth, thus suggesting that individual lobes elongate by this process. We have also investigated the effect of the ionophore A23187 on this cytoplasmic organization. The polarization of rough endoplasmic reticulum, mitochondria and Golgi material was destroyed by ionophore treatment in the presence of 2mM-MgCl2 or 2mM-CaCl2. The tip-associated clusters of electron-dense vesicles were dispersed by A23187 in 2mM-CaCl2 but not significantly affected by A23187 in 2mM-MgCl2. The latter observation indicates that the vesicle pattern can be disrupted by high calcium, but not high magnesium concentrations.
Characterization of a spontaneously transformed pulmonary embryonic rat (PER) epithelial cell line
Authors: Paye M. , Etievant CH. , Michiels F. , Pierard D. , Nusgens B. , Lapière CH. M. 
Published: April 2021

ABSTRACT
A spontaneously transformed pulmonary embryonic rat epithelial cell line (PER) is described in terms of growth, tumorigenicity, growth factor responsiveness and biosynthetic capacity. At low-passage subcultures, PER cells grew as a monolayer and did not form colonies in soft agar. After long-term subcultivation, they lost contact inhibition, became anchorage-independent and formed tumours in nude mice. Low concentrations of foetal calf serum permit the maximum growth rate. The multiplication and metabolic activity, assessed by 2-deoxy-D-glucose uptake, was significantly stimulated by growth factors. PER cells synthesized collagen types I, III, IV and V, laminin and fibronectin, and organized a pericellular matrix made up of only basement membrane components (type IV collagen and laminin) and fibronectin. These data enabled us to define PER cells as a transformed epithelial cell line evolving towards malignancy with long-term subcultivation. These cells appeared to be a valuable tool in studies of tumour cell-matrix interactions and regulation of growth factor receptors in tumorigenesis.
Kinesin from pig brain studied by electron microscopy
Authors: Amos L. A. 
Published: April 2021

ABSTRACT
Kinesin, a protein that transports particles along microtubules, has been purified from pig brain, following published methods. By electron microscopy of both shadowed and negatively stained specimens, it appears to be a rod with a large branched structure at one end and a small fork at the other. The total length of the structure is about 100 nm. The rod has a diameter of 2–4 nm. Close to the middle of the rod there may be a flexible joint. The molecules appear to be attached to microtubules most often by their forked ends in the presence of AMP · PNP. However, the large branched end can also attach to microtubules and individual molecules occasionally have been seen cross-linking two microtubules.
Further characterization of the defects of skin fibroblasts from cancer patients
Authors: Azzarone B. , Macieira-Coelho A. 
Published: April 2021

ABSTRACT
We have previously shown that skin fibroblasts from breast cancer patients display abnormal growth properties when compared with cells from patients with benign breast lesions. In the present study, we shown that it is possible to define, within the patients previously analysed, a subgroup whose fibroblasts exhibit a significant fraction of cells still synthesizing DNA when growth curves reach a plateau. The phenomenon can also be detected in skin fibroblasts from patients with other types of cancer. In two instances detection of this defect preceded the discovery of the disease.
The high percentage of labelled interphases when cell counts reach a plateau is not due to an increased duration of S phase, relative to total cell cycle duration. The data suggest that these cells are delayed in the G2 phase.
This assay buttresses our previous results, which suggested that at least in some instances cancer is a systemic disease; it could be used for the screening of patients at high risk of cancer.
Research on the patients’ somatic cells could shed more light on the process leading to neoplasia, rather than the study of the tumour cells that have already gone through several steps of the evolution to malignancy.
A simple microcomputer-based system for real-time analysis of cell behaviour
Authors: Dow Julian A. T. , Lackje John M. , Crocket Kenneth V. 
Published: April 2021

ABSTRACT
An image analysis package based on a BBC microcomputer has been developed, which can simultaneously track many moving cells in vitro. Cells (rabbit neutrophil leucocytes, BHK C13 fibroblasts, or PC12 phaeochromocytoma cells) are viewed under phase optics with a monochrome TV camera, and the signal digitized. Successive frames are acquired by the computer as a 640 × 256 pixel array. Under controlled lighting conditions, cells can readily be isolated from the background by binary filtering. In real-time tracking, the positions of a given cell in successive frames are obtained by searching the area around the cell’s centroid in the previous frame. A simple box-search algorithm is described, which proves highly successful at low cell densities. The resilience of different search algorithms to various exceptional conditions (such as collisions) is discussed. The success of this system in real-time tracking is largely dependent upon the leisurely speed of movement of cells, and on obtaining a clean, high quality optical image to analyse. The limitations of this technique for different cell types, and the possible configurations of more sophisticated hardware, are outlined. This system provides a versatile and automated solution to the problem of studying the movement of tissue cells.
Induced stabilization of the transmembrane potential of Drosophila cells by heat shock and periodic applications of chloramphenicol
Authors: Jürgen Behnel H. , Weckbart G. 
Published: April 2021

ABSTRACT
The transmembrane potential of Drosophila salivary gland cells is largely decreased (by 78% within 120 min) in response to the application of 5 mM-chloramphenicol (CAP), with an initial slope of 0 ·5 mV min−1. This depolarization is reversed immediately after the CAP concentration is reduced to 0 ·06 mM by step-wise dilution with normal medium. At the same concentration, thiamphenicol (TAP) induces only a small reversible depolarization by less than 30% within 120 min. These results are in agreement with the different effects of CAP and TAP on respiration and induction of the heat-shock genes, as known from previous data.
The extent of induced membrane depolarization decreases with the number of repeated applications of CAP to the same cell, alternating with 75-min periods of recovery. Moreover, reduced sensitivity to CAP is also observed in cells recovering from a transient heat shock (30 min, 36°C) 45 min prior to the addition of CAP. This phenomenon is inhibited by cycloheximide (0 ·lmM), which suggests an involvement of heat-induced proteins in the stabilization of certain membrane functions.
Structure and function of the nematosome
Authors: Ockleford C. D. , Nevard C. H. F. , Indans I. , Jones C. J. P. 
Published: April 2021

ABSTRACT
The ultrastructural morphology of human placental and mouse placental nematosomes has been investigated. The description includes a three-dimensional analysis of the shape of the organelles based on serial sectioning, measurements of the repeat distance of the subunit fibre of the organelle derived by optical diffraction analysis and the results of an ultrastructural cytochemical study designed to test whether the organelle contains nucleic acid.
The distribution of a ‘mitosis-specific’ antigen during Drosophila development
Authors: Millar Sarah E. , Freeman Matthew , Glover David M. 
Published: April 2021

ABSTRACT
We have used MPM-2, a monoclonal antibody raised against mitotic HeLa cells, to stain a Drosophila cell line, whole mounts of Drosophila embryos, and sectioned tissue from embryonic and larval stages of development. MPM-2 recognizes a major phosphoprotein of approximately 125 ×103Mr in Drosophila tissue culture cells that, like the mammalian MPM-2 antigen, appears to be recognized only in mitotic cells. During early embryogenesis, when the embryonic nuclei divide as a syncytium with a very short nuclear division time, MPM-2 antigen is observed within the spindle compartment at all stages of the nuclear division cycle. Upon cellularization of the embryo and lengthening of the duration of the cycle, the antigen is predominantly seen in mitotic cells. Drosophila larvae contain both diploid and polytene tissues: in diploid tissue MPM-2 staining is specifically observed over mitotic cells, as expected from its distribution in cellu-larized embryos. Surprisingly, antigen is also detected in the nuclei of polytene cells that replicate their DNA but do not undergo mitosis.