bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of colonies developing in vitro from mouse bone marrow cells stimulated by kidney feeder layers or leukemic serum
Authors: Metcalf D. , Bradley T. R. , Robinson W. 
Published: February 2005

AbstractAn analysis has been made of cell colonies developing in agar cultures from mouse bone marrow cells following stimulation either by neonatal kidney cell feeder layers or AKR lymphoid leukemia serum. Colonies arose by cell proliferation and were mixtures of granulocytic and mononuclear cells.Colonies stimulated by kidney feeder layers reached a mean size of 2000 cells by day 10 of incubation and remained predominantly granulocytic in nature. When bovine serum was substituted for fetal calf serum, cell colonies grew to a smaller size and lost their granulocytic nature, finally becoming almost pure populations of mononuclear cells.Colonies stimulated by AKR leukemic serum reached a mean size of 350 cells by day 10 of incubation. Although these colonies initially were granulocytic in nature, they finally became almost pure populations of mononuclear cells.The colony mononuclear cells actively phagocytosed carbon, and contained metachromatic granules probably derived from ingestion of agar.The mononuclear cells in these colonies may not have been members of the original colony, but may have been incorporated in the colony as it expanded in size, subsequently proliferating in the favourable environment of the colony.
Some physicochemical factors relevant to cellular interactions
Authors: Brooks D. E. , Millar J. S. , Seaman G. V. F. , Vassar P. S. 
Published: February 2005

AbstractColloidal stability theory is discussed to accomodate the conditions imposed by biological systems. It is shown that to obtain potential curves with secondary minima, Hamaker's constant must be in the range of 1–5 × 10−14 ergs. The effect of increasing the dielectric constant is shown in theory to lower the surface potential and electrophoretic mobility but to increase the total energy of interaction. Calculations made from the theory predict the forces between model cells to be ca. 4.0 × 10−7 dynes.By cone‐plate shearing of cell aggregates, the most successful of several techniques tried and discussed, at shear rates approaching 1 × 10−4 second−1 (1.5 × 10−4 dynes) semi‐complete disaggregation was achieved although cell disruption was apparent; analysis of blood viscosity data indicates 5–10 × 10−7 dynes are required to separate red cells suspended in plasma. Colloidal stability theory, while not applicable to cell systems associated by special areas of attachment, seems to describe the physicochemical interaction of freely moving or reversibly adherent cells.
Observations and measurements of sea urchin eggs with a centrifuge microscope
Authors: Hiramoto Y. 
Published: February 2005

AbstractEggs of the sea urchins, Arbacia punctulata and Lytechinus variegatus were observed with a centrifuge microscope. The protoplasmic viscosity calculated from the displacement velocity of the nucleus in a centrifugal field is about 30 poises. The surface forces of the unfertilized egg, which were determined from the relationship between the deformations of the egg in centrifugal fields and the magnitudes of the centrifugal forces, are 0.046 dyne/cm in Arbacia and 0.087 dyne/cm in Lytechinus (mean values). Both of these values increase as the deformation of the egg increases. The cleavage plane of the first cleavage of the egg in the centrifugal field (35–140 × g) is parallel to the direction of the centrifugal force. The flattening of the fertilized egg in a constant centrifugal field changes during development, probably owing to the change in the surface force. The flattening attains a minimum shortly before the onset of cleavage and another minimum during the cleavage, corresponding to a peak of the surface before the cleavage and another peak during the cleavage.
DNA synthesis in the giant salivary chromosomes of Drosophila virilis prior to pupation
Authors: Pettit Barbara J. , Rasch Robert W. , Rasch Ellen M. 
Published: February 2005

AbstractBoth two‐wavelength microspectrophotometry of Feulgen‐stained whole nuclei and autoradiography of H3‐thymidine incorporation by giant salivary chromosomes in Drosophila virilis demonstrate a net decrease in the relative rate of salivary DNA synthesis during the late third instar and prepupal stages of development. Amounts of DNA‐Feulgen per nucleus were distributed into several classes, the means of which closely approximated values projected as geometric multiples of the basic somatic DNA level estimated from hemocyte nuclei of the same larvae. Comparison of DNA polytene class frequencies showed no statistical difference between male larvae of different development stages, although female prepupae showed a greater frequency of nuclei in higher polytene classes when compared to male prepupae of the same age. Comparison of chromosomal H3‐thymidine incorporation with previously described H3‐histidine incorporation suggests that the amino acid labeling, which reaches a maximum during the prepupal period, has a physiological significance distinct from chromosomal endoreplication.
Effect of ribonuclease and neuraminidase on the electrophoretic mobility of tissue culture cells in parasynchronous growth
Authors: Mayhew E. 
Published: February 2005

AbstractCultured mammalian cells (RPMI no. 41) in parasynchronous growth were treated, at different stages of the mitotic cycle, with neuraminidase and ribonuclease, separately and sequentially, and their electrophoretic mobilities determined. Changes in the electrophoretic mobility of these cells are probably mainly due to variations in the density of negatively charged groups susceptible to neuraminidase, although variations in groups susceptible to ribonuclease may occur. It is suggested that the observed variations in electrophoretic mobility of different cells may be due to differences in the relative lengths of different life‐cycle phases. Where G2 phase is relatively long or G1 relatively short the cell populations will hve higher mean electrophoretic mobilities.
Calcium binding by subcellular fractions of bovine adrenal medulla
Authors: Borowitz J. L. 
Published: February 2005

AbstractSignificantly more calcium per gram protein was found in a relatively pure granule fraction isolated from fresh bovine adrenal medulla than in predominantly mitochondrial fractions isolated from the same tissue. Sixty‐four and 55% of the calcium associated with chromaffin granule and mitochondrial fractions, respectively, was released into the supernatant upon lowering the tonicity of the medium. The per cent calcium released by this procedure was significantly greater for granules than for mitochondria (p < 0.05). The amount of calcium per gram protein released into the supernatant also was greater in granule fractions than in mitochondrial fractions (p < 0.05). These data, coupled with a previous report that 10−3 M EDTA does not markedly decrease the calcium content of whole granules, indicate that the excess calcium of the granule fractions relative to the mitochondrial fractions is maintained within the particles of that fraction. The functional significance of the relatively large amount of calcium in chromaffin granules is not clear.The presence of 150 mM sodium chloride or potassium chloride decreases calcium binding by granule or mitochondrial fragments incubated in 2.2 mM calcium chloride in 0.2 M Tris, pH 7, by about 50%. EDTA, 10−3 M, removes all but a small residual of the calcium associated with the granule or mitochondrial fragments whereas lowering the concentration of Tris increases calcium binding to about the same extent in both these subcellular fractions. The calcium‐binding properties of granule and mitochondrial fragments therefore appear to be quantitatively and qualitatively similar. Inhibition of catecholamine release by relatively high concentrations of sodium may be explained by competitive inhibition of calcium binding. Calcium binding by granule fragments decreases with an increase in hydrogen ion concentration.
The relation of karyotypic change to loss of contact inhibition of division in human diploid cells after SV40 infection
Authors: Weinstein David , Moorhead Paul S. 
Published: February 2005

AbstractFollowing in vitro infection of human cell cultures with simian virus 40, karyotypic analyses were performed on the earliest serial culture in which cells were released from contact inhibition of division. In these cultures of diploid fibroblast‐like cells, normal karyotypes were found in excess of the statistical expectation for the number of background dividing cells. Thus, loss of contact inhibition of cell division occurs prior to the alteration of chromosome morphology. These events are two of the prime alterations in the series of steps comprising transformation by this virus. The chromosomal changes which were present represent the first cytological alteration detectable. Their distribution in the human karyotype was examined, but was found to have no relation to any specific chromosome or chromosome group.
Properties of mitotic cells prepared by mechanically shaking monolayer cultures of chinese hamster cells
Authors: Tobey R. A. , Anderson E. C. , Petersen D. F. 
Published: February 2005

AbstractA technique has been developed for the selective detachment of mitotic cells from monolayer cultures of Chiness hamster cells with a simple reciprocating shaking machine. Cultures prepared by the shake treatment and placed in spinner flasks are routinely obtained, in which the mitotic fraction drops from 0.95–0.05 in 19 minutes. Some properties of mitotic cells prepared by this technique are described, along with a simple procedure for producing large quantities of mitotic cells. Cells chilled immediately after collection from a series of shake treatments complete mitosis synchronously upon subsequent resuspension in warm medium.
The incorporation of microinjected 14C‐amino acids into TCA insoluble fractions of the giant axon of the squid
Authors: Fischer S. , Litvak S. 
Published: February 2005

AbstractGiant squid axons were microinjected with serine, valine and leucine‐C14 under controlled electrophysiological conditions. These amino acids are incorporated into TCA insoluble fraction in the isolated axon.This incorporation is higher in the stimulated axons as compared to non‐stimulated ones. By processing separately the axoplasm and axon sheath, it was found that the last one is responsible almost entirely for the observed incorporation.Through differential centrifugation of homogenates of microinjected axons was shown that the highest incorporation occurred in the 1500 × g sediment, which probably corresponds to membranes.The incorporation of amino acids in stimulated axons, is strongly inhibited by chloramphenicol and actinomycin D.
Electrophysiological studies of the isolated posterior moiety of the electroplax of the electric eel
Authors: Webb George D. 
Published: February 2005

AbstractIntracellular microelectrodes were used to measure resting and action potentials of electric eel electroplax cells from which the middle portion of the anterior moiety had been removed. External electrode studies of this preparation have been described by Chagas and Esquibel (C. R. Acad. Sc., Paris, 260: 3172 ('65)). In the present studies it was found that the resting and action potentials were almost as large as normal in the intact portion of the preparation, whereas these potentials were greatly reduced in the areas from which the anterior moiety had been removed. The reduction in amplitude was greater the farther the microelectrode was from the intact portion, indicating the possibility of decremental spread from the intact portions. The action potentials measured with external electrodes appeared to be an average of potentials from the various areas of the preparation. In other experiments the entire anterior moiety of the electroplax was removed, leaving only the innervated plasma membrane plus some adhering cytoplasm and extracellular material. Various high K+ solutions were used to bathe the inner surface. No action potentials could be elicited from these preparations, but resting potentials as high as 51 mV were observed using external electrodes. The resting potential could be reduced reversibly by carbamylcholine applied to the outer surface. Carbamylcholine applied to the inner surface had no effect.
A change in growth potential of cells after conversion by Rous sarcoma virus
Authors: Bader John P. 
Published: February 2005

AbstractChick embryo cells transformed by Rous sarcoma virus (RSV) were able to grow in suspension, either as colonies when trapped in nutrient agar, or in spinner cultures using liquid medium. Two strains of RSV, RSV (RAV‐1) and Schmidt‐Ruppin RSV, were able to increase the ability of chick embryo cells to grow in suspension but Rous‐associated virus (RAV‐1) and polyoma virus were not. Cells growing in suspension supported high levels of RSV production and a simple method for propagating large amounts of virus is suggested. Suspended noninfected cells, which do not grow extensively, lose their ability to be infected by RSV, suggesting that cellular divisions must be in progress for successful infection by RSV.
The need for direct cell contact in “contact” inhibition of cell division in culture
Authors: Schutz Leonard , Mora Peter T. 
Published: February 2005

AbstractNon‐dividing mouse embryo fibroblasts which grew to a confluent cell density on one side of an ultra‐thin filter did not inhibit the active multiplication of the same type of cells growing at low cell density on the other side of the filter directly opposite the confluent side. The close proximity of the cells across the filter was not sufficient to cause inhibition of cell division. The phenomenon of “contact” or “density dependent” inhibition of cell division is therefore probably not mediated by a cellular product which remains concentrated near the cell surface.The degree of contact inhibition of cell division was correlated with the local cell density on the same side of the filter. This relationship was found to be influenced strongly by the surface on which the cells were growing.
Growth of mouse fibroblasts in the presence of irradiated and lyophilized monolayers of the same type of cells
Authors: Schutz Leonard , Mora Peter T. 
Published: February 2005

AbstractCertain cells, such as 3T3 mouse embryo fibroblasts, are inhibited from dividing when they grow to a characteristic cell density on a surface in tissue culture. We asked whether the inhibition of cell division could be attributed to the inert chemical composition of neighboring cells, that is, whether the residues of lyophilized cells retained the ability to inhibit the division of normal cells. In addition, we wanted to know whether cells in which DNA synthesis was imparied by irradiation would retain the capacity to effectively inhibit normal cells.To answer these questions, confluent and non‐confluent layers of 3T3 cells were prepared in tissue culture dishes and the cells were either lyophilized or irrariated in situ. Fresh 3T3 cells were then added to these prepared layers and their growth was followed using radioactive label. There was no growth of added cells on the confluent monolayers of either untreated or irradiated cells. Growth was unimpeded on the monolayers of lyophilized cells. When cells were added to non‐confluent cultures of either normal or irradiated cells the added cells grew until they had covered the remaining surface of the culture dish and had come into contact with the pre‐existing cells. In the discussion, consideration is given to the role of available surface over which the cells can spread as well as to the possible interactions between neighboring cells.
Potentiation of bone marrow colony growth in vitro by the addition of lymphoid or bone marrow cells
Authors: Metcalf Donald 
Published: February 2005

AbstractColony formation and growth in vitro by C57B1 mouse bone marrow cells were analysed following stimulation by a standard dose of serum colony stimulating factor. Under restricted conditions, colony crowding was observed to potentiate colony growth rates. The addition of thymic or lymph node lymphoid cells or nonviable bone marrow cells also potentiated colony growth. Extensive reutilisation of nuclear material by bone marrow colony cells was observed when labeled lymphoid and bone marrow cells were added to the culture system. The results provide evidence that lymphocytes can exert trephocytic effects on proliferating hematopoietic cells.
Myogenesis of striated muscle in vitro: Hormone and serum requirements for the development of glycogen synthetase in myotubes
Authors: De La Haba Gabriel , Cooper George W. , Elting Virginia 
Published: February 2005

AbstractThe fusion in vitro of embryonic myoblasts to form multinucleated myotubes requires the addition of serum to a basal nutrient medium. The serum requirement for fusion can be satisfied by insulin with somatotropin potentiating its effect. Myotubes formed under these conditions fail to differentiate to cross‐striated, spontaneously contractile muscle fibers. This arrest of development is reversible if serum is restored to the medium.Development of the enzyme glycogen synthetase was studied as an additional indicator of muscle differentiation. In cultures developing in the presence of serum, this enzyme was demonstrated by autoradiography to be highly concentrated in myotubes as compared to mononuclear cells. The activity of the enzyme remains low in (1) cultures formed in response to insulin and somatotropin in the absence of serum, as well as (2) in cultures formed in unsupplemented basal medium which are virtually lacking in myotubes. The addition of serum to (1) restores the development of this enzyme. Serum which has been extensively digested with the proteolytic preparation, pronase, and subjected to boiling temperature, when combined with insulin and somatotropin is also capable of promoting the development of glycogen synthetase to a specific activity which exceeds the control. The serum factor is not lost on exhaustive dialysis, nor can enzyme promoting activity be liberated by heat denaturation of serum proteins.
Regulation of melanin synthesis in mammalian cells, as studied by somatic hybridization. I. Evidence for negative control
Authors: Davidson Richard , Ephrussi Boris , Yamamoto Kohtaro 
Published: February 2005

AbstractSomatic hybrids between pigmented Syrian hamster cells and unpigmented mouse cells were isolated and propagated in vitro. These hybrids are unpigmented and lack dopa oxidase (and tyrosinase) activity, which is correlated with the pigmentation of the Syrian hamster cells. In contrast, the presence of three other enzymes (LDH, MDH, and thymidine kinase) also specified by the hamster genome but unrelated to pigment synthesis is observed in the hybrid cells. This suggests that the repression of dopa oxidase in these cells is a specific effect on the enzyme associated with the differentiated state of pigment cells. It is concluded that the genetic control of differentiation in this case involves a diffusible regulator substance which functions negatively.
Persistent synthesis of 5S RNA when production of 28S and 18S ribosomal RNA is inhibited by low doses of actinomycin D
Authors: Perry Robert P. , Kelley Dawn E. 
Published: February 2005

AbstractTo determine whether transcription of the genes coding for 5S ribosomal RNA depends upon the concurrent activity of the genes for 28S and 18S ribosomal RNA we studied the synthesis of 5S RNA in cultured L cells when the synthesis of the 45S precursor of 28 and 18S RNA was inhibited with low doses of actinomycin D. Synthesis of 5S RNA was measured by following the incorporation of 3H uridine into components which, upon acrylamide gel electrophoresis, co‐migrated with markers of 5S RNA obtained from 32P labeled ribosomes. We observed that the synthesis of 5S RNA persists in the absence of detectable 28S and 18S RNA synthesis, continuing at the normal rate for several hours and at a reduced rate for at least a generation time. This strongly supports the concept that 45S RNA is not a precursor of 5S RNA, and indicates furthermore that neither the 45S component, nor any of the intermediates involved in its transition to 28S and 18S RNA, are involved in controlling the output of the 5S genes The 5S RNA which is made during actinomycin treatment is retained predominantly in the nucleoplasm and undergoes a turnover of about 3.5% per hour. It apparently cannot be utilized when ribosome synthesis resumes following removal of the actinomycin.
The retinal rod outer segment of the frog: Detachment, isolation, phosphorus fractions and enzyme activity
Authors: Lolley Richard N. , Hess Helen H. 
Published: February 2005

AbstractFrog retinal rod outer segments were detached from dark adapted retinas by (1) agitation in frog Ringer's solution or (2) by crushing between two glass surfaces. The resulting suspensions were further purified by low and high speed centrifugation procedures in Ficoll density gradients. The density of the outer segments in Ficoll solutions was found to be 1.09. The large frog outer segments, unlike bovine outer segments, are not readily separated from nuclei, which were estimated to comprise 2.6–8% of the material, based on DNA analyses. The RNA/DNA ratio was 0.4–0.5, like that of neuronal nuclei. Representative enzymes of glycolysis (lactic dehydrogenase and glyceraldehyde phosphate dehydrogenase), phosphogluconate oxidation (glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase), the citric acid cycle (malic dehydrogenase) and ATP degradation (ATPase) were assayed. A major part of the malic dehydrogenase activity was probably due to inner segments attached to some of the outer segments. Glyceraldehyde phosphate dehydrogenase and glucose‐6‐phosphate dehydrogenase (but not lactic dehydrogenase) activities were lower in detached outer segments purified on Ficoll gradients than in samples of outer segment layer microdissected from freeze‐dried sections of frog retina, as well as in whole retina. The data suggest that the activities of all the enzymes studied are intrinsically low in rod outer segments.
Separation of cells by velocity sedimentation
Authors: Miller Richard G. , Phillips R. A. 
Published: February 2005

AbstractA system for fractionating populations of living cells by velocity sedimentation in the earth's gravitational field is described. The cells start in a thin band near the top of a shallow gradient of 3% to 30% fetal calf serum in phosphate buffered saline at 4°C. Cell separation takes place primarily on the basis of size and is approximately independent of cell shape. A sharply‐defined upper limit, called the streaming limit, exists for the cell concentration in the starting band beyond which useful cell separations cannot be achieved. This limit, which varies with the type of cell being sedimented, can be significantly increased by proper choice of gradient shape. For sheep erythrocytes (sedimentation velocity of 1.6 mm/hour) it is 1.5 × 107 cells/ml. Measured and calculated sedimentation velocities for sheep erythrocytes are shown to be in agreement. The technique is applied to a suspension of mouse spleen cells and it is shown, using an electronic cell counter and pulse height analyzer, that cells are fractionated according to size across the gradient such that the sedimentation velocity (in mm/hour) approximately equals r2/4 where r is the cell radius in microns. Since cells of differing function also often differ in size, the system appears to have useful biological applications.