bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of immunoglobulin and nuclear protein in synchronized mouse myeloma cells
Authors: Liberti P. , Baglioni C. 
Published: February 2005

AbstractThe synthesis of immunoglobulin and of nuclear proteins has been studied in synchronized mouse myeloma cells of the C1 line. Synchronization has been obtained by a double thymidine block. C1 cells synthesize immunoglobulin at a relatively constant rate throughout the cell cycle except for mitosis, when a decrease in the rate of synthesis of total protein and of immunoglobulin is observed. Cell synchrony around mitosis is not sufficiently good to determine whether immunoglobulin is synthesized at all. Nuclear protein and in particular histones appear to be synthesized synchronously with DNA during the S phase of the cell cycle.
Origin of thymidine kinase deficient (TK−) haploid frog cells via an intermediate thymidine transport deficient (TT−) phenotype
Authors: Lacko L. , Wittke B. , Geck P. 
Published: February 2005

AbstractWild‐type cultured cells of the frog cell line ICR 2A give rise to 5‐bromodeoxyridine (BUdR)‐resistant colonies only when the selecting concentration of the drug is 5 × 10−5 M or lower. The progeny of these colonies multiply in 10−4 M BUdR; resistance is correlated with the absence of a thymidine (TdR)‐specific transport reaction with a Km in the range of 2–7 × 10−4 M. All of the TdR transport‐deficient (TT‐) isolates examined (25) had TdR kinase activity (4% to 100% of wild‐type). Variants deficient in TdR kinase activity (5% of wild‐type) were obtained by exposing TT‐cultures to 10−3 M BUdR. The TK ‐ variants multply continuously in 10−3 M BUdR and retain the phenotype after prolonged culture in the absence of the drug. The frequency with which they occur is increased 20 to 50 fold by prior treatment of the culture with ICR 191, an acridine mustard mutagen.In haploid cells, it would be expected that TK‐ variants would arise in equal numbers from wild‐type and TT‐ cultures if loss TdR kinase occurred independently of loss of the transport reaction. However, wild‐type cells give no colonies resistant to 10−3 M BUdR under conditions the give 1 to 50 colonies per million TT‐ cells. The TT‐ phenotype seems to be a required intermediate state in the origin of the TK‐ phenotype. Therefore, the TK‐ clones described above are unlikely to be products of mutation at a single genetic locus.
DNA synthesis and mitosis in a temperature sensitive Chinese hamster cell line
Authors: Roscoe D. H. , Robinson Hildred , Carbonell A. W. 
Published: February 2005

AbstractViability, DNA synthesis and mitosis have been followed in the temperature sensitive Chinese hamster cell mutant K12 under permissive and non‐permissive conditions. On incubation at 40°C cells retained their ability to form colonies at 33°C for 15 to 20 hours, but viability was lost gradually during the following 20 hours. When random cultures of K12 were shifted to 40°C the rate of DNA synthesis was normal for three to four hours but then decreased markedly, reaching 95% inhibition after 24 hours. Under the same conditions mitosis was inhibited after 15 hours. If cultures which had been incubated at 40°C for 16 hours were placed at 33°C the rate of DNA synthesis increased five hours after the shift down and mitosis 18 hours after. These results can be interpreted on the assumption that K12 at 40°C is unable to complete a step in the cell cycle which is essential for DNA synthesis and which occurs three to four hours before the start of S at 33°C.
Changes in membrane transport function in G0 and G1 cells
Authors: Costlow Mark , Baserga Renato 
Published: February 2005

AbstractConfluent quiescent monolayers of aneuploid and euploid cells in culture can be stimulated to proliferate by appropriate nutritional changes. In confluent monolayers of WI‐38 human diploid fibroblasts the uptake of cycloleucine is increased three hours after these cells are stimulated to proliferate by a change of medium plus 10% serum. No changes in the uptake of cycloleucine are observed in logarithmically‐growing WI‐38 cells exposed to fresh medium plus 10% serum, or in WI‐38 confluent monolayers in which the conditioned medium has been replaced by fresh medium with 0.3% serum (a change that does not cause stimulation of cellular proliferation in WI‐38 cells). In 3T6 cells in the stationary phase stimulated to proliferate by nutritional changes, there is a prompt increase in the uptake of cycloleucine, within one hour after stimulation of cell proliferation. Similar results were obtained with stationary 2RA cells which are SV‐40 transformed WI‐38 fibroblasts. In addition, chromatin template activity which is known to increase in the early stages after stimulation of confluent WI‐38 cells, was unchanged in confluent 3T6 or 2RA cells stimulated to proliferate.These results show that at least two of the very early biochemical events occurring in response to stimulation of cell proliferation are different in WI‐38 diploid cells and in aneuploid 2RA or 3T6 cells. It is proposed that WI‐38 cells in the stationary phase are arrested in the G0 phase of the cell cycle, while 2RA and 3T6 cells are arrested in the G1 phase.
The effect of cytochalasin B on pigment dispersion and aggregation in perfused Xenopus laevis tailfin melanophores
Authors: Fisher Marilyn , Lyerla Timothy A. 
Published: February 2005

AbstractA perfusion technique is described for the study of melanosome response in ventral tailfin melanophores of Xenopus laevis tadpoles. The melanosomes remain aggregated (punctate melanophores) in Ringer's. Theophylline (15 mM) and caffeine (30 mM) cause a reversible dispersion (stellate melanophores) of melanosomes which is partly blocked by cytochalasin B (10 μg/ml). When added with theophylline or caffeine to stellate cells, cytochalasin B causes a disrupted distribution of pigment granules, characterized by a melanosome free central region. C‐AMP (20 mM) and dibutyryl c‐AMP (1 mM) cause a reversible dispersion of melanosomes which is partly inhibited by cytochalasin. When cytochalasin plus a nucleotide are added to stellate cells, some show the disrupted distribution of melanosomes. Colchicine (5 mM) causes irreversible, while griseofulvin (0.2 mM) causes a slight, but reversible dispersion of melanosomes, and cytochalasin has little effect on these reactions. Perfused tailfin melanophores remain capable of responding to reversible reagents for at least 12 hours and are unresponsive to changes in illumination.
Conditional lethal mutants of Chinese hamster cells: Mutants requiring exogenous carbondioxide for growth
Authors: Scheffler I. E. 
Published: February 2005

AbstractA series of Chinese hamster cell lines were tested and found to be able to proliferate in the absence of added bicarbonate and carbondioxide if hypoxanthine and uridine were present in the medium. Conversely, cells incapable of salvaging one of these precursors, such as hypoxanthine‐guanine phosphoribosyltransferase (HGPRT−) deficient cells did not multiply under these conditions.We describe another variant capable of utilizing hypoxanthine and uridine which has an absolute requirement for exogenous CO2/NaHCO3 for growth. These cells appear to be defective in the complete oxidation of pyruvate to carbondioxide, and indications are that the entry of pyruvate into the Krebs cycle is affected.
The separation of different cell classes from lymphoid organs. X. Preparative electrophoretic separation of lymphocyte sub‐populations from mouse spleen and thoracic duct lymph
Authors: v. Boehmer H. , Shortman K. , Nossal G. J. V. 
Published: February 2005

AbstractConditions have been established for the separation of viable mouse lymphoid cells by continuous free‐buffer film preparative electrophoresis. The detailed electrophoretic distribution profiles of T and B lymphocytes from mouse spleen and thoracic duct have been determined. Cell surface θ‐antigen was used as a marker for T cells, and high surface‐density of immunoglobulin as a marker for B cells. Spleen cells from athymic “nude” mice were also studied.In the unselected normal spleen cell populations B lymphocytes are heterogeneous, about 60% being of low mobility with the remainder distributing broadly, and extending into the highest mobility fractions. T lymphocytes are predominantly of high mobility. Lymphoid cells lacking markers of either the B or T lineage are of intermediate mobility. There is only partial separation of T and B cells because of the extensive overlap between the populations.The high mobility B cells, which separate along with T cells, include a substantial proportion of large cells, and include cells with high surface density of immunoglobulin. The majority of these large B cells can be selectively eliminated by their adherence on passage through a glass‐bead column.By pre‐selecting the 50% non‐adherent lymphocytes from spleen as the starting material, a very sharp and more extensive separation of B and T cells can be achieved, with 100% pure B cells and 90% pure T cells in many fractions. However these samples are not representative of the total T and B cell populations of spleen.In thoracic duct lymph high mobility B‐cells are absent, there is little overlap between T and B cell mobility. 100% pure T and B cells can be isolated.
Intracellular conversions of deoxyribonucleosides by Novikoff rat hepatoma cells and effects of hydroxyurea
Authors: Plagemann Peter G. W. , Erbe John 
Published: February 2005

AbstractThe incorporation of 3H‐labeled deoxyadenosine and deoxyguanosine into nucleic acids by cultured Novikoff rat hepatoma cells is about 80% into RNA and 20% into DNA. The pathways of incorporation have been elucidated in studies with whole cells and cell‐free extracts. Deoxyadenosine is very rapidly deaminated to deoxyinosine. Most of the deoxyinosine formed by whole cells is transported out of the cells and accumulates in the medium. A portion of the deoxyinosine, and deoxyguanosine are phosphorolyzed by purine nucleoside phosphorylase to hypoxanthine and guanine, respectively. The latter are subsequently converted by hypoxanthine‐guanine phosphoribosyl transferase to IMP and GMP, respectively. Incorporation of the purine deoxyribonucleosides into DNA is mainly via this pathway and the subsequent reduction of ADP and GDP by ribonucleoside reductase, although a small proportion of the deoxyadenosine and deoxyguanosine taken up by the cells seems to be directly phosphorylated to dAMP and dGMP, respectively. Deoxyguanosine is incorporated only into guanine residues of RNA and DNA. Deoxyadenosine is also mainly incorporated into guanine residues of RNA and DNA, although the radioactivity of deoxyadenosine in the acid‐soluble pool is almost exclusively associated with ATP. A similar labeling pattern is observed with labeled deoxyinosine, inosine or hypoxanthine. The pyrimidine deoxyribonucleosides, on the other hand, are specific precursors for their respective bases in DNA.Hydroxyurea inhibits the incorporation of all deoxyribonucleosides into DNA. Results from pulse‐chase experiments indicate that the inhibition of DNA synthesis is prevented by the presence of high concentrations of deoxyadenosine plus deoxyguanosine in the medium. Either purine deoxyribonucleoside alone or deoxycytidine, hypoxanthine or inosine alone or in combination with deoxyadenosine or deoxyguanosine are ineffective. The results are consistent with the conclusion that the inhibition of DNA synthesis is due to a depletion of the dATP and dGTP pools as a result of the hydroxyurea treatment. On the other hand, hydroxyurea causes an increased incorporation of thymidine and deoxycytidine into the dTTP and dCTP pools, respectively. Evidence is presented to indicate that this effect of hydroxyurea is due to an increased synthesis of dTTP and dCTP rather than to an inhibition of their turnover.
Effect of growth conditions on the activity of ornithine decarboxylase in cultured hepatoma cells. II. Effect of serum and insulin
Authors: Hogan Brigid L. M. , McIlhinney Ann , Murden Susan 
Published: February 2005

AbstractHTC cells incubated in the absence of serum for more than 14 hours have very low levels of ornithine decarboxylase, the first enzyme on the pathway of polyamine synthesis. Readdition of serum causes an increase in the activity of ODC, reaching a maximum on average 17 times above the basal level after five hours. This increase is due in part to a decrease in the apparent rate of degradation of ODC, and also to a stimulation of its synthesis. Within the first two hours the serum induction of ODC is resistant to Actinomycin D. Insulin at 5 μm/ml alsocauses an increase in ODC activity but only after a delay of two hours, in contrast to its more rapid stimulation of tyrosine transaminase activity.
Differences in the subcellular localization of the stimulatory effects of glucose and pyruvate on protein synthesis in rat thymus cells in vitro
Authors: Giddings Stephen J. , Young Donald A. 
Published: February 2005

AbstractThymocytes incubated as cell suspensions in vitro are known to be markedly dependent upon added glucose for maintenance of maximal rates of incorporation of radiolabelled amino acids into protein. This requirement is only partially satisfied by other added substrates, such as pyruvate. Evidence is presented that incorporation of amino acids into protein associated with the nuclear fraction isolated from these cells is more dependent upon added glucose than is labelling of protein found in the rest of the cell.The dependence of the labelling of nuclear protein upon glucose is shown by comparing the ability of glucose and pyruvate to stimulate the incorporation of [14C‐L] valine into the protein of nuclear and cytoplasmic fractions of thymus cells. The fractions are isolated on sucrose gradients after incubating suspensions of cells in substrate‐free medium for two hours, adding carbohydrates and labelled L‐valine for 30 min and then stopping the incubation by breaking the cells with hypotonic shock. When the protein‐synthetic stimulatory effects of glucose and pyruvate are compared, glucose is almost equally capable (90%) at stimulating rates of protein synthesis in nuclear compared to cytoplasmic fractions. Pyruvate is much less effective in nuclear than in cytoplasmic fractions (30%).Evidence is also presented from pulse‐chase experiments that the glucosedependent labelling of protein associated with the nuclear fraction occurs within that fraction, as opposed to migration to the nuclear fraction after being synthesized elsewhere.It is suggested from these and other data that a unique ability of glucose to provide non‐mitochondrial ATP to the nucleus may be central to the dependence of the labelling of nuclear protein on this substrate.
A comparison of ligand‐induced redistribution of surface immunoglobulins, alloantigens, and concanavalin A receptors on mouse lymphoid cells
Authors: Stackpole Christopher W. , DeMilio Lawrence T. , Jacobson Janet B. , Hämmerling Ulrich , Lardis Michael P. 
Published: February 2005

AbstractRedistribution of surface immunoglobulins (Ig), H‐2b, Thy‐1.2 and TL. 1,2,3 alloantigens, and concanavalin A (Con A) receptors on mouse thymus, lymph node and spleen cells into “caps” induced by bivalent antibodies or ligands was compared by immunofluorescence. Surface Ig was capped rapidly following attachment of anti‐Ig antibody at 37°. Capping of alloantigens and Con A receptors occurred very slowly following attachment of alloantibody or Con A, but much more rapidly after addition of a secondary bivalent antibody. An inverse relationship between the number of surface component sites per cell and the extent of capping of that component was observed. Capping of alloantigens sparsely represented on the cell surface was not inhibited by high concentrations of alloantibody, in contrast to capping of alloantigens present in greater quantities. These results suggest that factors in addition to molecular cross‐linking may be involved in ligand‐induced redistribution of cell surface components.
Neoplastic differentiation: Characteristics of cell lines derived from a murine teratocarcinoma
Authors: Lehman J. M. , Speers W. C. , Swartzendruber D. E. , Pierce G. B. 
Published: February 2005

AbstractMonolayer cultures of a mouse teratocarcinoma were established in vitro. These cultures contained embryonal carcinoma, the malignant stem cell, and its differentiated progeny: parietal yolk sac, neuroepithelial, and mesenchymal cells. Tissues such as squamous epithelium, cartilage, striated muscle, neuroepithelium, and glands were produced from embryonal carcinoma that was maintained under conditions of long term culture. Frequent subcultivation with pancreatin allowed the establishment of cell lines of embryonal carcinoma which have been maintained for more than 18 months in vitro and continue to produce differentiated cells under specific culture conditions. Chromosomally these lines of embryonal carcinoma have a stem line of 39 chromosomes. Two lines of parietal yolk sac cells have been established which produce basement membrane, are not tumorigenic, and chromosomally are hypotetraploid. This system may yield information concerning neoplastic differentiation and its possible use in therapy for cancer.
Modification of the proliferative capacity of transplanted bone marrow colony forming units by changes in the host environment
Authors: Beran M. , Tribukait B. 
Published: February 2005

AbstractRegulation of the proliferation of transplanted colony forming units (CFUs) was investigated in lethally irradiated mice, pretreated by methods known to accelerate hemopoietic recovery after sublethal irradiation. Prospective recipients were exposed to either hypoxia, vinblastine or priming irradiation and at different intervals thereafter lethally irradiated and transplanted with bone marrow. Repopulation of CFUs was determined by counting the number of splenic colonies in primary recipients or by retransplantation.Regeneration of grafted CFUs was greatly accelerated and their self‐renewal capacity increased in mice grafted within two days after hypoxia. Also the number of splenic colonies formed by grafted syngeneic CFUs as well as by C57BL parent CFUs growing in BC3F1 hosts was significantly increased. The effect was not dependent on the seeding efficiency of CFUs and apparently resulted from hypoxia induced changes in the hosts physiological environment. Proliferative capacity of grafted CFUs increased remarkably in hosts receiving vinblastine two or four days prior to irradiation. Priming irradiation given six days before main irradiation accelerated, given two days before impaired regeneration of CFUs. The increased rate of regeneration was not related to the cellularity of hemopoietic organs at the time of transplantation. The growth of CFUs in diffusion chambers implanted into posthypoxic mice was only slightly improved which does indicate that the accelerated regeneration of CFUs in posthypoxic mice is mainly due to the changes in the hemopoietic microenvironment. A short conditioning of transplanted CFUs by host factor(s) was sufficient to improve regeneration. The results might suggest that the speed of hemopoietic regeneration depends on the number of CFUs being induced to proliferate shordy after irradiation, rather than on the absolute numbers of CFUs available to the organism.
Cyclic AMP levels in temperature sensitive SV40 transformed cell lines
Authors: Burstin Stuart J. , Renger Hartmut C. , Basilico Claudio 
Published: February 2005

AbstractThe cAMP levels of the 3T3 cell line and its transformed derivatives were determined. The level was found to be lower in transformed cell lines than in parental 3T3 and to decrease at confluence in all cell lines tested. SV40 transformed 3T3 cell lines which are temperature sensitive in growth control were found to have lower cAMP levels than 3T3, but these levels were not temperature dependent. Retransformation of these cell lines by murine sarcoma virus did not markedly affect their cAMP levels.
Some characteristics of myotubes cultured from slow and fast chick muscles
Authors: Purves R. D. , Vrbová Gerta 
Published: February 2005

AbstractExplant cultures were prepared from the slow anterior latissimus dorsi muscle and the fast posterior latissimus dorsi muscle of 15 day chick embryos. The morphology and growth pattern of myotubes from the two types of muscle were very similar. Intracellular microelectrode studies did not reveal consistent differences between the myotube types in regard to resting potential, input resistance, input time constant, or ability to produce active electrogenic responses. It is suggested that specific differentiation of the two muscles is determined by their innervation.
Metabolic heterogeneity of phosphoglyceride classes and subfractions during cell cleavage and early embryogenesis: Model for cell membrane biogenesis
Authors: Barassi Carlos A. , Bazán Nicolás G. 
Published: February 2005

AbstractDuring the early developmental stages of the toad, Bufo arenarum, Hensel. up to the stage of gill circulation (150 hr of development at 20–25°C) the total phospholipids content as well as that of phosphoglycerides of choline and of ethanolamine were found unchanged. The subfraction of both phosphoglycerides were separated according to the number of double bonds on silver‐ion chromatography and were also found to be unchanged up to the tail bud stage. The distribution of non‐polar side chains in the subfractions varied in both phosphoglycerides showing a structural heterogeneity. In the phosphatidylethanolamines predominate the polyenoic containing subfractions.In contrast with the constant concentration of polar lipids, during early embryogenesis a steady increase in 32P incorporation into phospholipids takes place when oocytes labeled during oogenesis are used. These changes were also correlated with the DNA content up to gill circulation stage.It is proposed that most of the nascent membrane polar lipids during early embryogenesis may be derived from a storage site through an active and specific intracellular redistribution process. At the arrival of the polar lipid to the nascent membrane a change in their covalent structure by introduction of a phosphorylbase from a highly labeled pool may explain the raise in specific activity. This change may be necessary to make possible the assembly of the lipid into the membrane structure.
Further studies on the factor in lung‐conditioned medium stimulating granulocyte and monocyte colony formation in vitro
Authors: Sheridan J. W. , Metcalf D. , Stanley E. R. 
Published: February 2005

AbstractThe CSF's extracted from 6‐hour “in vivo” post‐endotoxin mouse lung tissue and 48‐hour “in vitro” lung‐conditioned medium appear to be glyco‐proteins, for like human urinary CSF they were inactivated by proteases and altered in charge but not inactivated by sialidase.Neither endotoxin injection nor length of in vitro incubation significantly affected the apparent S20 W (approximately 2.OS) of the bulk of the CSF in mouse lung‐conditioned medium. The lower apparent molecular weight of CSF in mouse lung‐conditioned medium contrasted with that of monkey lung‐conditioned medium (S20 W approximately 3.3S). CSF's in both monkey and mouse lung‐conditioned media exhibited a much higher apparent MW on gel nitration than one would expect from their sedimentation behavior, a characteristic generally observed with most unpurified CSF preparations.Mouse lung‐conditioned medium CSF was antigenically distinguishable from other CSF's. Failure to demonstrate this form of CSF in the tissue serum or urine of normal or endotoxin‐injected mice suggests that this type of CSF might normally lack in vivo significance.