bluuebunny/crossref_metadata_2025_split huggingface dataset:
The kinetics of DNA methylation in cultures of a mouse adrenal cell line
Authors: Kappler John W. 
Published: February 2005

AbstractDirect measurements of the methylation of newly‐synthesized DNA were made in cultures of a clonal mouse adrenal cortex cell line, Y129OS3, by (1) following the incorporation of radioactivity from methionine‐(methyl)‐C14 into a segment of DNA which had been density‐labeled with bromouracil and (2) labeling DNA cytosine with C14‐deoxycytidine and then following the appearance of radioactivity in DNA 5‐methylcytosine. The results establish that during exponential growth the DNA of this cell line is methylated entirely within a few minutes of its synthesis. Using the second technique described above accurate, sensitive measurements of DNA methylation levels can be made by comparing radioactivity in 5‐methylcytosine to radioactivity in cytosine plus 5‐methylcytosine. In this cell line 5‐methylcytosine accounts for 4.3 ± 0.2% of the DNA cytosine. Some apparent contradictions between these results and those of other workers are discussed.
Flattening, movement and control of division of epithelial‐like cells
Authors: Castor Laroy N. 
Published: February 2005

AbstractThe kinetics of cell division and movement in four epithelial‐like cell lines, grown in continuously perfused culture medium, were studied by time‐lapse cinemicrography. One line exhibited “contact regulation of cell division,” so that the rate of mitosis per cell decreased steadily as population density increased. In the other three lines mitosis was not controlled as a function of population density until the cells became very crowded. An explanation for this difference was sought in terms of the hypothesis that the rate of division depends on the area of the cell membrane.Cells of the contact‐regulated line flattened uniformly on the substrate. Their motility was restrained by adhesion between their borders. As they crowded together, contact inhibition of cell overlap caused a steady decrease in average surface area per cell. All three of the non‐controlled lines also had contact inhibition of overlap. Cells of two of them flattened on the substrate; but these cells had little mutual adhesion and were highly motile, so that they continually changed their shapes. The areas of their cell membranes were therefore not subject to a restraint that could control the rate of division. Cells of the fourth line remained rounded or only slightly flattened during culture growth, so that no change in cell membrane area occurred that could change the rate of division.
Strain‐specific mitotic inhibition in large mononucleate amoebae
Authors: Jeon K. W. , Lorch I. J. 
Published: February 2005

AbstractA strain‐specific antimitotic substance is present in large mononucleate amoebae. It inhibits mitosis when injected into amoebae of heterologous strains. The antimitotic substance has been isolated from homogenized cells, and some of its properties have been studied. The results obtained show that the active factor is a protein(s) of molecular weight between 200,000 and one million. The activity of this substance differs from other known antimitotic agents in that its action is strain‐specific.
Stimulation of DNA synthesis in cultures of mouse embryo fibroblast‐like cells
Authors: Vasiliev Ju. M. , Gelfand I. M. , Guelstein V. I. , Fetisova E. K. 
Published: February 2005

AbstractStimulation of the DNA synthesis and mitoses in stationary cultures of mouse embryo fibroblast‐like cells was induced by various agents such as ribonuclease, digitonin, fresh medium and commercial preparations of hyaluronidases. Time sequence of stimulation was similar in experiments with all these agents. Cells were activated to enter S phase from GI phase. The rise of the number of DNA‐synthesizing cells was preceded by a latent period of about 8–12 hours with the maximal number of DNA‐synthesizing cells being observed at 16–24 hours. Mitotic wave was observed after the wave of DNA synthesis. Stimulation of DNA synthesis and mitosis was not preceded by any significant decrease of an average cell density in the culture. The progeny of activated cells had no greater chance than other cells to be activated again when stimulation was repeated.It is concluded that similar proliferative reactions can be induced in stationary cultures by a variety of diverse agents. Possible role of cell surface changes in the induction of these reactions is discussed.
Induction of fatty acid synthesis in cultured mammalian cells: Effects of cycloheximide and x‐rays
Authors: Raff R. A. 
Published: February 2005

AbstractIt was found that L cells deprived of exogenous fatty acids responded adaptively by increased synthesis of fatty acids. This adaptive increase was found to be sensitive to cycloheximide presented at the time of removal of exogenous lipids, but was not sensitive to cycloheximide added six hours after removal of lipids. It was concluded that the adaptive increase in fatty acid synthesis represents a case of enzyme induction. The effect of x‐rays on this process was studied. It was found that induction was inhibited to a greater extent than total protein synthesis. Factors of potential importance to such an effect are discussed.
An analysis of the recovery of Tetrahymena from effects of cycloheximide
Authors: Frankel Joseph 
Published: February 2005

AbstractWhen cycloheximide (0.2 μg per ml) was added to synchronized cultures of Tetrahymena pyriformis GL‐C, the initial rate of incorporation of 14C‐leucine was reduced to about 20% of the rate observed in control cells. After one hour, the rate increased fairly abruptly to about 60% of the control rate. The cells in cycloheximide underwent synchronous division about three hours after addition of cycloheximide. A second addition of cycloheximide had little effect on either the rate of incorporation or on the time of cell division in the drug. The medium in which cells had recovered brought about full inhibition of 14C‐leucine incorporation in fresh cells, indicating that recovery was not accompanied by appreciable degradation of the cycloheximide. It was therefore concluded that during recovery the cells were either adapting to the cycloheximide or excluding it. The recovery process shows some specificity, since cells which had recovered from cycloheximide, and had become insensitive to a second dose of this drug, still retained full sensitivity to another drug, colchicine. Conversely, cells recovering in colchicine became insensitive to fresh colchicine but remained sensitive to cycloheximide.
The possible mediation by cyclic AMP of the stimulation of thymocyte proliferation by vasopressin and the inhibition of this mitogenic action by thyrocalcitonin
Authors: Whitfield J. F. , MacManus J. P. , Gillan D. J. 
Published: February 2005

AbstractLysine vasopressin (antidiuretic hormone), like cyclic adenosine 3',5'‐monophosphate (cyclic AMP), rapidly (in less than 1 hour) stimulates the initiation of deoxyribonucleic acid synthesis and thereby increases the flow of cells into mitosis in rat thymic lymphocyte populations in vitro. This mitogenic action of vasopressin, again like that of cyclic AMP, is potentiated by caffeine, an inhibitor of the intracellular phosphodiesterase which catalyzes the degradation of cyclic AMP. On the other hand, vasopressin's mitogenic action (also like that of cyclic AMP) is blocked by imidazole, an activator of cyclic nucleotide phosphodiesterase activity. The hormone, thyrocalcitonin (calcitonin) which is known to block the cyclic AMP‐mediated mitogenic effect of parathyroid hormone by interfering with cyclic AMP action, also blocks the mitogenic action of vasopressin. The inhibitory effects of imidazole and thyrocalcitonin on vasopressin's mitogenic action are both overcome by the phosphodiesterase inhibitor, caffeine. It is concluded from these observations that the mitogenic action of vasopressin is mediated by cyclic AMP.
Variations in the synthesis and assembly of immunoglobulins by mouse myeloma cells: A genetic and biochemical analysis
Authors: Scharff M. D. , Bargellesi A. , Baumal R. , Buxbaum J. , Coffino P. , Laskov R. 
Published: February 2005

AbstractThe synthesis, assembly, and secretion of gamma globulin has been examined using cells from a mouse plasma cell tumor. The cells were then adapted to continuous culture and individual clones were obtained which differed from each other in the relative amounts of heavy and light chains synthesized, in the absolute amounts of gamma globulin being produced, and in the details of the assembly process. Finally, the kinetics, pathway, and completeness of assembly were examined in a variety of tumors and variants of these tumors.
Changes in ribosome‐polyribosome balances in chick muscle cells during tissue dissociation, development in culture, and exposure to simplified culture‐medium
Authors: Hosick Howard L. , Strohman Richard C. 
Published: February 2005

AbstractThe populations of polyribosomes, monomeric ribosomes, and ribosomal subunits are described from the time of tissue explantation to the time of complete muscle differentiation in primary cultures of chick muscle cells. There is extensive degradation of polyribosomes, and a net loss of ribosomes recovered, as cells of embryonic muscle are dissociated with proteolytic enzymes. The cells rapidly restore a high polysome: monomeric ribosome ratio. This recovery of the polyribosome population occurs before there is any detectable net increase in ribosome number. Ribosome production begins after a lag of approximately 15 hours in culture. Number of ribosomes/cell triples by 60 hours, at which time cell fusion (myotube formation) is complete. Unlike developing muscle in vivo, cultured cells have a very reduced pool of monomeric ribosomes. Medium simplification experiments done with fully differentiated cultures show, however, that monomers accumulate during starvation. These monomers reassociate to form polyribosomes during medium replenishment. Subunit complements are maintained at a constant level regardless of nutritional conditions. These features of cultured muscle are discussed as possible tools for further study of muscle development.
Nucleotide pools of Novikoff rat hepatoma cells growing in suspension culture. I. Kinetics of incorporation of nucleosides into nucleotide pools and pool sizes during growth cycle
Authors: Plagemann Peter G. W. , Erbe John 
Published: February 2005

AbstractResults from kinetic studies on the incorporation of 3H‐5‐uridine and 3H‐8‐adenosine into the acid‐soluble nucleotide poor and nucleic acids by Novikoff hepatoma cells (subline N1S1‐67) in suspension culture indicate that the uridine transport reaction is saturated at about 100 μM and that for adenosine at about 10 μM nucleoside in the medium, and that above 100 μM simple diffusion becomes the predominant mode of entry of both nucleosides into the cell. The Km of the transport reactions is approximately 1.3 × 10−5 M for uridine and 6 × 10−6 M for adenosine. The incorporation of these nucleosides into both the nucleotide pool and into nucleic acids seems to be limited by the rate of entry of the nucleic acid synthesis from the rate of incorporation of nucleosides. Other complicating factors are a change with time of labeling in the relative proporation of nucleoside incorporated into DNA and into the individual nucleotides of RNA, the splitting of uridine to uracil by th ecells, the deamination of adenosine kto inosine and the subsequent cleavage of inosine to hypoxanthine.Various lines of evidence are presented which indicate that the overall nucleotide pools of the cells are very small under normal growth conditions. During growth in the presence of 200 μM uridine or adenosine, however, the cells continue to convert the nucleosides into intracellular nucleotides much more rapidly than required for nucleic acid synthesis. This results in an accumulation of free uridine and adenosine nucleotides in the cells, the maximum amounts of which are at least equivalent to the amount of these nucleotides in total cellular RNA.
Nucleotide pools of Novikoff rat hepatoma cells growing in suspension culture. II. Independent snucleotide pools for nucleic acid synthesis
Authors: Plagemann Peter G. W. , Erbe John 
Published: February 2005

AbstractNovikoff rat hepatoma cells (subline NlSl‐67) in suspension culture incorporate 3H‐5‐uridine into the acid‐soluble nucleotide pool more rapidly than into RNA, resulting in the accumulation of labeled UTP in the cells. When labeled uridine is removed from the medium after 20 minutes or 4.75 hours of labeling, the rate of incorporation of label from the nucleotide pool into RNA decreases to less than 10% of the original rate within five to ten minutes, in spite of the presence of a large pool of labeled UTP in the cells, and incorporation ceases completely if an excess of unlabeled uridine is present during the chase. Upon addition of 14C‐uridine to 3H‐uridine pulse‐labeled, chased cells, the 14C begins to be incorporated into RNA without delay and at a rate predetermined by the concentration of 14C‐uridine in the medium and without affecting the fate of the free 3H‐nucleotides labeled during the pulse‐period. The results are interpreted to indicate that uridine is incorporated into at least two different pools, only one of which serves as primary source of nucleotides for RNA synthesis. During active synthesis of RNA, the latter pool of free nucleotides is very small and rapidly exhausted when uridine is removed from the medium. However, UTP accumulates in this pool when cells are labeled at 4–6°, since at this temperature RNA synthesis is blocked while uridine is still phosphorylated by the cells, and the UTP is rapidly incorporated into RNA during a subsequent ten‐minute chase at 37°. From these types of experiments it is estimated that only 20–25% of the total uridine nucleotides formed in the cells from uridine in the medium is directly available for RNA synthesis and that the remainder becomes available only at a slow rate. Evidence is presented which suggests that one uridine nucleotide pool is located in the cytoplasm and another in the nucleus and that mainly the nuclear pool supplies nucleotides for RNA synthesis. The size of the latter pool is under strict regulatory control, since preincubation of the cells with 0.5 mM unlabeled uridine has little or no effect on the subsequent incorporation of 3H‐uridine, although it results in an increase of the overall cellular uridine nucleotide content to at least 5 mM. Other results indicate that adenosine is also incorporated into two independent nucleotide pools, whereas the cells normally appear to possess a single thymidine nucleotide pool.
Hemolysis in several animal species after rapid freezing of blood
Authors: Rapatz G. , Luyet B. 
Published: February 2005

AbstractThe effect of various freezing rates on the extent of hemolysis in human, bovine and ovine erythrocytes, which are known to have different cell volumes, water contents and permeabilities, was investigated. Blood in stainless steel capillary tubes was frozen at various rates by abrupt immersion of the capillaries into cooling baths at temperatures ranging from −20° to −130°C. Minimum lysis values were obtained at freezing temperatures of −40°, −50° and −70°C with, respectively, human, bovine and ovine blood. The smallest, highly permeable sheep erythrocytes were the least damaged at the highest freezing rates; the largest human cells with the highest water content, suffered the greatest damage; intermediate values were obtained with ox blood. At the lower freezing rates, the largest, human cells were the least damaged; the highest hemolysis values were obtained with the smallest, highly permeable sheep erythrocytes; ox blood again gave intermediate values. These results are in agreement with current views that, (1) very rapid freezing results in the formation of damaging intracellular ice; (2) injury associated with slow freezing is related to the extent of dehydration or to the increase in electrolyte concentration which accompanies ice formation; (3) minimum hemolysis is obtained under those freezing conditions in which osmotic dehydration has been sufficient to prevent the formation of intracellular ice, but has left enough water in the cells to prevent the damaging effects of dehydration and high electrolyte concentrations.
Distribution of UDP‐glucuronyl transferase among cell fractions of rat liver
Authors: Nyquist S. E. , Morre D. James 
Published: February 2005

AbstractMicrosomal UDP‐glucuronyl transferases (uridine‐5′‐diphosphate‐glucuronate glucuronyl transferase, acceptor unspecific, EC 2.4.1.17) function in detoxification of a wide range of aglycons containing phenolic, alcoholic, carboxylic or amino acceptor groups through formation of water‐soluble glucuronic acid derivatives. To localize this activity within a specific cell component, purified rough‐surfaced endoplasmic reticulum and Golgi apparatus fractions from rat liver were compared with total homogenates. The UDP‐glucuronyl transferase specific activity of the Golgi apparatus fractions was less than or approximately equal to that of the total homogenate whereas this activity was concentrated 3–8 fold in the rough‐surfaced endoplasmic reticulum fraction depending upon substrate. We conclude that the rough‐surfaced endoplasmic reticulum is the major site of glucuronide formation within the microsome fraction of normal rat livers.
The 5‐methylcytosine content of DNA: Tissue specificity
Authors: Kappler John W. 
Published: February 2005

AbstractUsing a new technique for the determination of the extent of DNA methylation by comparing the incorporation of radioactivity from deoxycytidine‐2‐C14 into DNA cytosine and 5‐methylcytosine (5MC), the 5MC content of DNA was found to be a tissue specific property in two systems: (1) mouse tissue culture cell lines, in which the level of 5MC varied from 2.97 ± 0.03% conversion of cytosine to 5MC in the DNA of a mouse melanoma line to 4.58 ± 0.18% in a primary teratoma line, and (2) the organs of the developing chick embryo, in which the level of 5MC varied from 3.60 ± 0.04% conversion of cytosine to 5MC in the DNA of the chorioallantoic membrane to 4.19 ± 0.02% in the brain.
Ultrastructural changes in sarcosomes after exposure of adult Calliphora erythrocephala to lethal and sub‐lethal high temperatures
Authors: Davison T. F. 
Published: February 2005

AbstractThe effects of lethal and sub‐lethal high temperatures on the morphology of intact flight muscle sarcosomes of adult Calliphora erythrocephala are described. Treatment of adult flies to lethal temperatures results in ultrastructural changes in the organisation of the cristae and the appearance of electron opaque inclusions. These changes have not been observed after sub‐lethal heat treatment, when 50% of the animals recover. It is suggested that changes in the ultrastructure of the intact sarcosomes may be correlated with changes in their ability to couple oxidative phosphorylation with α‐glycerophosphate. Age‐dependent changes in the sensitivity of sarcosomes are related to changes in the heat death point of the animal and suggest that the impairment of sarcosomal function may be one of the primary lesions in heat death of adult C. erythrocephala.
The effect of environment on lactate dehydrogenase isozymes of cultured somatic cells
Authors: Cribbs Richard M. , Kline Edward S. 
Published: February 2005

AbstractThe lactate dehydrogenases of HeLa cells grown in an anaerobic environment with either glucose or L‐lactate have a higher ratio of A to B sub‐units than do the same cells grown in an aerobic environment. This ratio is decreased when the anaerobic environment is made aerobic during cell growth, or when the cells are cultured for the entire growth period in aerobic conditions.
Effects of acronycine on nucleic acid synthesis and population growth in mammalian tumor cell cultures
Authors: Gout P. W. , Dunn B. P. , Beer C. T. 
Published: February 2005

AbstractAcronycine — an alkaloid with antineoplastic activity against a wide range of experimental tumors — at concentrations of 0.5‐12 μg/ml rapidly inhibits RNA synthesis in L5178Y mouse lymphoma and IRC rat monocytic leukemia cultures. Culture growth is arrested only at acronycine concentrations which markedly inhibit RNA synthesis. DNA synthesis is inhibited at rather higher concentrations but this is not a prerequisite of the arrest of growth. It is suggested that the arrest of growth may be a consequence of the inhibition of RNA synthesis.In both cultures arrest of growth coincides with the appearance of many cells with two apparently normal nuclei. Cells are not arrested in mitosis. It is shown these binucleated cells very probably arise from an inhibition of cell cleavage. Studies with synchronized cultures show that at low drug concentrations, more than one cell cycle may elapse before growth is arrested and binucleated cells appear, indicating the effect on cytokinesis is not immediate. The results suggest that the arrest of growth may be a result of a slow depletion of a component essential for cell cleavage. The disturbance at division is a major factor in arresting growth at low drug concentrations. At higher acronycine concentrations, when RNA synthesis may be inhibited by 80–90%, the cytotoxic effects appear earlier and are less specifically directed at cytokinesis; DNA synthesis is then also rapidly and markedly inhibited.
Demonstration of an ATPase at the cell surface of intact normal and neoplastic human cells in culture
Authors: Ågren G. , Pontén J. , Ronquist G. , Westermark B. 
Published: February 2005

AbstractAn ATPase reaction has been studied at the surface of intact normal and neoplastic human cells in culture. For this purpose a sensitive method has been developed which permits repeated monitoring of enzyme activity without interference with cellular viability.Experiments could be performed with the cells cultured in a single dish. The cells were firmly attached to the supporting medium throughout the experiment. The incubation medium could easily be separated from the cells at the end of the reaction. There was no diffusion of the surface‐located ATPase into the incubation medium. Another advantage was the possibility of microscopic control of the appearance of the cells during the reaction.High ATPase activity was found in glia‐like cells derived from normal adult brain cells while lines from gliomas had very low activity. One SV40 transformed glia line had an extremely low ATPase activity in contrast to the uninfected cells. Normal fibroblasts and sarcoma cells had about the same low activity as the glioma cells.
Regulation of specific functions of glial cells in somatic hybrids. I. Control of S100 protein
Authors: Benda Philippe , Davidson Richard L. 
Published: February 2005

AbstractHybrids were isolated between rat glial cells and mouse fibroblasts. Micro complement (C′) fixation was used to assay S100, a highly acidic protein specific for nervous tissues. The glial cells contain large amounts of S100. Extracts of the fibroblasts contain some C′ fixing material which is detected only at very high protein concentrations and which fixes C′ only weakly. The identity of this material is not known. The hybrids contain some C′ fixing material, but the concentrations of protein necessary to reach the point of antigen‐antibody equivalence is ten times greater with an extract of hybrids than with an extract of glial cells. This increase in the concentration of protein is associated with a decrease in the amount of C′ fixed. The possible significance of the C′ fixing material in the hybrids is discussed.