bluuebunny/crossref_metadata_2025_split huggingface dataset:
X-Ray Microanalysis Of HeLa S3 Cells II. Analysis of elemental levels during the cell cycle
Authors: Warley Alice , Stephen J. , Hockaday A. , Appleton T. C. 
Published: April 2021

ABSTRACT
HeLa S3 cells were synchronized using hydroxyurea. Cryoultramicrotomy and X-ray microanalysis were used to study changes occurring in concentrations of elements during the cell cycle of the synchronized cells. Three subcellular compartments were studied: cytoplasm, nucleus and nucleolus. Potassium concentrations showed little fluctuation in all of the cell compartments during the cell cycle. Sodium concentrations increased during S and M phases, returning to lower levels in the G1 phase. Chlorine concentrations were highest during the S and G2 phases. At all stages of the cell cycle respective concentrations of potassium, sodium, sulphur and chlorine were similar in the cytoplasm and nucleus. Concentrations of phosphorus increased in the nucleus during S, G2 and M, and also showed fluctuations in the nucleolus during the cycle; these were not seen in the cytoplasm. In S, M and M/G1 sodium concentrations were highest in the nucleolus compared with the other compartments. In the cytoplasm these changes resulted in an increase in total monovalent cation concentration (i.e. sodium-t-potassium) during S, G2 and M, which returned to base levels after mitosis. This increase in monovalent cation concentration is due almost entirely to the increase in sodium, with little change occurring in the concentration of potassium.
Kinetic Parameters Of Hexose Transport In Hybrids Between Malignant And Non-Malignant Cells
Authors: White M. K. , Bramwell M. E. , Harris H. 
Published: April 2021

ABSTRACT
Matched pairs of isogeneic hybrid cells, in which one member of the pair was malignant and the other not, were used to examine the linkage between malignancy and functional alterations in hexose transport. The kinetic parameters of uptake of 2-deoxy-D-glucose were measured in a range of such hybrids, both human and murine. Some other malignant cell lines were also examined and were compared with non-tumorigenic derivatives of tumour cells selected by exposure to the lectin, wheat-germ agglutinin. In every case, malignancy, as defined by the ability of cells to grow progressively in vivo, was found to be linked to a decrease in the Michaelis constant of hexose uptake. Independent measurement of the transport and phosphorylation reactions involved in hexose uptake revealed that this decrease was determined by the membrane transport system. The difference in Michaelis constant between malignant and non-malignant cells was observed with 3–0-methylglucose, a hexose that is transported into the cell but not further metabolized. The activity of hexokinase in cell homogenates was higher than the level that would be required to cope with transport and showed no correlation with tumorigenicity. Measurement of the uptake of D-glucose itself, by a rapid filtration centrifugation method, gave results similar to those obtained with 2-deoxy-D-glucose.
A sharp cell surface conformational transition at low ionic strength changes the nature of the adhesion of enzyme-treated red blood cells to a hydrocarbon interface
Authors: Donath E. , Gingell D. 
Published: April 2021

ABSTRACT
Aldehyde-fixed human red cells have previously been used to assess the roles of electrostatic and electrodynamic forces in adhesion. We have attempted to test the prediction that enzymic removal of cell surface negative charges should increase adhesion in dilute salt solutions by reducing electrostatic repulsion. While this is indeed the case for neuraminidase-treated cells and also for Pronase- and trypsin-treated cells over much of the low ionic strength range, the latter two treatments cause very strong adhesion over a remarkably narrow range of ionic strength centred on 1 mM-NaCl. At 0·5 and 1·5 mM adhesion is negligible. After Pronase treatment a further adhesive peak occurs at 2·5 mM. Electrophoresis of protease-treated cells shows small but clear reductions in mobility at precisely these peak adhesion values. These electrophoretic potential changes are almost certainly not large enough to cause increased adhesion directly, and it is thought that they are second-order changes, symptomatic of a structural rearrangement of the cell surface. How this causes such vastly augmented adhesion is an intriguing problem.
Coated pits and pinocytosis in Tetrahymena
Authors: Nilsson Jytte R. , Deurs Bo Van 
Published: April 2021

ABSTRACT
The possible role in pinocytosis of coated pits at the parasomal sacs of Tetrahymena has been studied using cationized ferritin (CF; pl = 8·5) as a marker of membrane and content. It is shown that CF binds evenly to the surface, including the coated pits, of Tetrahymena in an inorganic salt medium (to avoid formation of food vacuoles) at the normal growth temperature. Moreover, CF is internalized by coated vesicles (shown to be truly free by thin serial-section analysis) and delivered initially (1–5 min of incubation) to cisterns near the cell surface. Later (5–10 min) CF occurs also in autophagic vacuoles, formed as a result of starvation, and eventually (15–90 min) it is present in preformed (old) food vacuoles. These observations indicate that the coated pits at the parasomal sacs of Tetrahymena function in adsorptive pinocytosis in much the same manner as coated pits at the surface of mammalian cells.
The complexity of poly(a)+ RNA in the alga Chlorella fusca
Authors: McBride N. K. , Thurston C. F. 
Published: April 2021

ABSTRACT
RNA excess hybridization with radioactively labelled complementary DNA (cDNA) was used to reveal the complexity of poly(A)+ RNA from Chlorellafusca var. vacuolata. RNA was tested from cells during photosynthetic exponential growth and during adaptation to heterotrophic growth in the dark on acetate. Both RNA populations were resolved into abundant, intermediate and rare sequence classes. Abundant sequences (200—400 copies per cell) constituted a significantly larger proportion of total poly(A)+ RNA in acetate-adapting cells than in exponentially growing autotrophic cells. Both types of RNA contained a rare sequence class of complexity consistent with a composition of about 20 000 different sequences. This indicated a substantially greater complexity of genes expressed in this alga and Euglena than in fungi and slime moulds. Heterologous hybridization, and hybridization with fractionated cDNA, showed that the majority of differences between RNA populations from exponentially growing and adapting cells were changes in relative abundance of groups of sequences, rather than presence of different sets of sequences in the two populations.
Junction formation between cultured normal rat hepatocytes an ultrastructural study on the presence of cholesterol and the structure of developing tight-junction strands
Authors: Feltkamp Constance A. , Waerden Alexandra W. M. Van Der 
Published: April 2021

ABSTRACT
In cultures of normal rat hepatocytes, isolated by collagenase perfusion, formation of junctions started 4—7 h after seeding. The junctional complexes were localized at two preferential sites of the contiguous membrane : apically and on both sides of open spaces with microvilli at some distance from the free upper surface.
The domains of early contact formation are characierized by a flattening of the membranes, a decrease in intercellular space, a depletion of intramembrane particles (IMPs) and a concentration of electron-dense and of fine fibrillar material in the cytoplasm immediately adjacent to the membrane. We were able to demonstrate the presence of cholesterol in these domains by formation of cholesterol-filipin complexes that deformed the membrane. However, membrane-deformation in these domains was often inhibited. This inhibition appeared to be due to the presence of pepsinsensitive material, since full deformation was induced after mild proteolysis. The arrangement of IMPs into small gap junctions and short tight-junction strands is synchronous in the membranes of the neighbouring cells. The tight junctions are composed of two strands arranged in a slightly offset configuration. The possibility that the strands are lipidie in nature is not excluded.
Fibronectin-independent adhesion of fibroblasts to extracellular matrix material: Partial characterization of the matrix components
Authors: Harper P. A. , Brown Patricia , Juliano R. L. 
Published: April 2021

ABSTRACT
Fibroblasts can adhere to extracellular matrix (ECM) material by fibronectin-dependent (type I) and fibronectin-independent (type II) mechanisms. In this report we investigate the biochemical characteristics of ECM that contribute to type II adhesion. ECM capable of mediating type II adhesion is produced primarily by normal diploid fibroblasts, but not by transformed cells or epithelial cells. Treatment of fibroblast ECM under conditions that result in the removal of most of the ECM lipid or most of the ECM glycosaminoglycan does not impair type II adhesion. Likewise, treatment of the ECM with large amounts of purified collagenase does not block type II adhesion. However, treatment of ECM with low doses of trypsin or with an agent that reacts with tyrosine residues, results in complete ablation of the ability of the ECM to support type II adhesion. On the basis of these observations we suggest that the matrix component(s) mediating type II adhesion are non-collagenous proteins or glycoproteins.
Differential effect of arginine modification with 1,2-cyclohexanedione on the capacity of vimentin and desmin to assemble into intermediate filaments and to bind to nucleic acids
Authors: Traub Peter , Vorgias Constantin E. 
Published: April 2021

ABSTRACT
When the intermediate filament proteins vimentin and desmin were reacted for a short period of time with the arginine-specific reagent 1,2-cyclohexanedione, the modification had a severe, inhibitory effect on the assembly of intermediate filaments and on the susceptibility of the basic, aminoterminal polypeptide of both proteins to degradation by the intermediate filament-specific, Ca2+-acti vated proteinase. However, it had only a slightly inhibitory effect on the binding of vimentin and desmin to ribosomal RNA from Ehrlich ascites tumour cells. Since the Ca2+-activated proteinase is very likely to be a trypsin-like enzyme, with a preference for arginyl and lysyl peptide bonds, the results indicate that the arginine residues of the amino-terminal polypeptide of vimentin and desmin are highly essential for filament assembly but largely dispensable for the binding of both proteins to nucleic acids. This was supported by the observation that two breakdown products of vimentin lacking a 5 × 103Mr and an 8 × 103Mr polypeptide from the amino terminus, respectively, did not assemble into intermediate filaments but were still capable of binding to rRNA. Both polypeptides also bound to single-stranded DNA-cellulose under non-denaturing conditions, but passed the affinity column in the presence of 6m-urea. Thus, the binding of vimentin to nucleic acids appears to be based on two components: a non-specific electrostatic interaction mediated by the positively charged arginine residues of the amino-terminal polypeptide that is insensitive to denaturation by urea, and a specific interaction that is sensitive to denaturation by urea.
Identification of a laminin-like substance on the surface of high-malignant murine fibrosarcoma cells
Authors: McCoy J.P. , Lloyd R. V. , Wicha M. S. , Varani J. 
Published: April 2021

ABSTRACT
High- and low-malignant murine fibrosarcoma cells were stained with anti-laminin antibodies using immunoperoxidase techniques and examined by electron microscopy. With the high malignant cells, specific staining was observed along the cell surface. Use of normal rabbit serum in place of the rabbit anti-laminin or pretreatment of the anti-laminin with soluble laminin complete ly eliminated this staining. No immunoperoxidase staining was observed with the low-malignant cells. In additional studies, membrane fractions were prepared from the high- and low-malignant cells and used to immunize rabbits. The animals immunized with the membrane fractions from the high-malignant cells produced antibodies that reacted by enzyme-linked immunosorbent assay (ELISA) with murine laminin obtained from the EHS sarcoma. The animals immunized with membrane fractions from the low-malignant cells did not. These studies provide strong evidence that the high-malignant cells (but not the low) express on their cell surface a substance that is immunologically cross-reactive with laminin. In addition, the high-malignant cells (but not the low) secreted a material into the cell culture fluid that could be specifically immunoprecipitated with anti laminin antibodies. The immunoprecipitated material co-migrated with purified laminin when examined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis under reducing con ditions. The existence of this substance associated with the surface of the high-malignant cells and its absence from that of the low-malignant cells may explain the previously noted difference between these cells in their ability to attach to type IV collagen. This difference may also contribute to the dissimilarity between these cells in their metastatic potential.
Control of cell mobility by cyclic AMP
Authors: Katzin William E. , Gershman Howard 
Published: April 2021

ABSTRACT
Cyclic AMP concentrations have been measured in a number of different cell types under a variety of culture conditions in an attempt to define the relationship between the endogenous concentration of cyclic AMP and cell mobility. In previous work it was shown that agents that increase the intracellular concentration of cyclic AMP can effectively suppress cell movement. In Balb/c 3T3 cells, which have a very low mobility in cellular aggregates, the intracellular concentration of cyclic AMP was elevated only transiently soon after the formation of the three-dimensional cell masses. In contrast, in the highly mobile virally transformed counterpart of Balb/c 3T3 cells, called SVT- 2, the concentration of cyclic AMP was relatively low soon after the cell masses were formed, but later rose to a level that was higher than that in Balb/c 3T3 cells. Using NIL B cells, SV40- transformed NIL B cells, and several lines of tumour cells derived from NIL B cells, it was found that the average intracellular concentration of cyclic AMP did not vary significantly from one population of cells to another. Finally, the intracellular concentration of cyclic AMP was measured in chick embryo ventricle cells. The mobility of these cells had previously been found to decrease as embryonic development progressed; furthermore, it had been shown that dibutyryl cyclic AMP plus theophylline produced nearly complete inhibition of their movement in cell masses. In the series of experiments reported here we found that the endogenous concentration of cyclic AMP in aggregates and fragments of chick embryo ventricle cells decreases as development proceeds; these data are consistent with preliminary experiments reported by other investigators. In a separate set of experiments, the intracellular concentration of cyclic AMP was measured in cells that had been cultured in a medium containing 1 · 2 mM-dibutyryl cyclic AMP plus 1 · 0 mM-theophylline. This drug treatment has previously been shown to inhibit the movement of cells both in aggregates and in monolayers; it also produces striking effects on cell shape and ultrastructure. In aggregates of chick embryo ventricle cells, treatment with these drugs resulted in increases in the intracellular concentrations of cyclic AMP from approximately 10 picomol/mg protein to approximately 500 picomol/mg protein. In Balb/c 3T3 and SVT-2 cells this treatment increased cyclic AMP con centrations from 3 · 7 to 160 and from 6 · 4 to 470 picomol/mg protein, respectively.
The polar ring of coccidian sporozoites: A unique microtubule-organizing centre
Authors: Russell D. G. , Burns R. G. 
Published: April 2021

ABSTRACT
The infective stages, or’zoites, of coccidian parasites possess an organized network of spirally arranged microtubules that closely follow the helical body shape of these vermiform cells. These subpellicular microtubules are anchored anteriorly by insertion into a highly structured circular microtubule-organizing centre (MTOC) known as the polar ring.
This MTOC has been examined both in situ and in isolated, critical-point-dried whole cytoskeletons. The 24 microtubules attach laterally to the MTOC through shallow depressions on the inner face of the ring: the ends do not appear to be physically capped. The polar ring has no obvious or regular substructure, although it has a faintly fibrous appearance. The polarity of the microtubules, determined by ‘hook decoration’, is such that the plus or fast-growing end is distal to the MTOC.
The coccidian’zoite MTOC is unique both in its highly defined structure and in the degree of organization it confers upon the developing cell in terms of the number, spacing, orientation and polarity of the subpellicular microtubules.
Identification of spermatogenic cell plasma membrane glycoproteins by twodimensional electrophoresis and lectin blotting
Authors: Millette Clarke F. , Scott B. Keyes 
Published: April 2021

ABSTRACT
Plasma membrane glycoproteins present in purified mouse spermatogenic cells have been identified by two-dimensional polyacrylamide gel electrophoresis and lectin blotting techniques. Four membrane glycoproteins labelled with Bandeiraea simplicifolia lectin (I) have been detected, ranging in Mr from 55 000 to 76000 and in pl from 6·0 to 6·3. Only one of these proteins, p76/6·3, is synthesized by short-term in vitro cultures of spermatogenic cells, as determined by the incorporation of [35S]methionine. Approximately 20 surface glycoproteins labelled with concanavalin A have been identified, ranging in Mr from 50000 to 151000 and in pl from 5·7 to 7·0. None of the components detected with B. simplicifolia lectin (I) are labelled significantly with concanavalin A. A major concanavalin A-binding protein in the membranes of both pachytene spermatocytes and round spermatids is pl51/6·0. This glycoprotein has been previously shown to be exposed on the outer surface of spermatogenic cell membranes and may represent a mediator of germ cell-Sertoli cell interactions. Furthermore, two constituents identified in the present study represent stagespecific markers. Component p73/5·7 is detected with concanavalin A only in the membranes of pachytene spermatocytes. Conversely, p84/6·3 is found only in round spermatid membranes. These results, then have: (a) provided a map of membrane glycoproteins in developing mouse male germ cells; (b) identified p151/6·0 as a membrane constituent of possible functional significance; and (c) identified the first reported glycoprotein surface differentiation markers for mouse spermatogenesis.
Intracellular infection of aposymbiotic Hydra viridis by a foreign free-living Chlorella sp.: Initiation of a stable symbiosis
Authors: Rahat M. , Reich V. 
Published: April 2021

ABSTRACT
An aposymbiotic strain of Hydra vin’dis became infected with free-living Chlorella sp. A stable symbiosis formed that differed in its characteristics from other known Chlorella/Hydra symbioses. The algae reproduced and formed clusters in host endodermal cells, inside large vacuoles filled with an electron-dense substance. A few algae were found to be digested by the hydra, but the apparently uncontrolled reproduct10n rate of the algae more than compensated for this loss. Surplus algae were expelled into the coelenteron and eventually into the surrounding medium. The expelled algae were repeatedly re-engulfed by the hydra during its feeding, forming a process of continuous reinfection.
We suggest that such repeated reinfection of the hydra by the expelled algae provides the host with an endless number of Ch/ore/la from which it might in time select a suitable adapted, controllable symbiont. The present newly formed symbiosis might serve as a model for the study of evolution of algal endosymbioses.
Ultrastructural localization of nucleolar organizers during oogenesis in xenopus laevis using a silver technique
Authors: Boloukhère M. 
Published: April 2021

ABSTRACT
Silver staining at the electron microscopic level of the nucleolar organizers was carried out on Xenopus laevis oocytes at various stages of oogenesis.
The results indicate that a positive reaction takes place exclusively in the dense fibrillar component of the extrachromosomal nucleoli. This constituent undergoes morphological changes of distribution and architecture, which have been correlated with modifications of the transcriptional activity of the nucleoli. When nucleolar activity is reduced, during previtellogenesis, this constituent appears as dense homogeneous spherules well-segregated from the granular component. In contrast, when nucleolar activity is high, during vitellogenesis, it forms an heterogeneous area with an ill-delimited outline: it is organized into a fibrillar core with emerging skein-like strings. It thus seems that this constituent remains silver-stained throughout oogenesis.
These findings suggest that the method used would allow one to follow the evolution of the nucleolar organizer region (NOR) topography during oogenesis. Moreover, they point out facts that have relevance to the problem of the correlation between Ag stainability of NORs and nucleolar transcriptional activity.
The mononuclear phagocyte system of the mouse defined by immunohistochemical localization of antigen f4/80: Macrophages of bone and associated connective tissue
Authors: Hume David A. , Loutit John F. , Gordon Siamon 
Published: April 2021

ABSTRACT
The macrophage-specific antigen F4/80 has been localized in adult mouse bone and connective tissue. F4/80 positive cells form the centre of haemopoietic islands, line the periosteal and subendosteal bone surfaces and are a major component of connective tissue and the synovial membrane (presumptive type A cells). F4/80 is absent from fibroblasts, chondrocytes, osteoblasts, osteocytes, osteoclasts and a subpopulation of synovial lining cells (presumptive type B cells).
The cell cycle and sorting behaviour in Dictyostelium discoideum
Authors: Mcdonald S. A. , Durston A. J. 
Published: April 2021

ABSTRACT
Synchronized cells of the cellular slime mould Dictyostelium discoideum were prepared by mitotic wash-off. Cell counts and DNA synthesis measurements indicated a high degree of synchrony. Cells from each phase of the cell cycle were fluorescently labelled and mixed with unlabelled asynchronous cells. Cells that were in S-phase and very early G2 at the onset of starvation demonstrated a strong tendency to sort to the tip of the subsequent slugs. With reference to these results and published evidence, we discuss the possible role of cell-cycle-related adhesion differences in cell sorting.