bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early changes in the synthesis of acidic nuclear proteins in human diploid fibroblasts stimulated to synthesize DNA by changing the medium
Authors: Rovera Giovanni , Baserga Renato 
Published: February 2005

AbstractWhen resting WI‐38 cells in a confluent monolayer were stimulated to proliferate by changing the medium, the incorporation of leucine‐3H into nuclear acidic proteins was promptly stimulated, although its incorporation into total cellular proteins was unchanged or even decreased. Three fractions, all acidic by aminoacid analysis, were extracted from the nuclei: (1) ribonucleoproteins (RNP); (2) a fraction extractable with 0.15 M NaC1; and (3) a fraction tenaciously bound to the insoluble residue (residual fraction). A first increase occurred between one and three hours after stimulation in all three fractions. The synthesis of NaCl‐soluble proteins then returned to control levels, while the synthesis of residual and RNP proteins remained high between 6 and 12 hours and increased even further at 18 hours, the peak of DNA synthesis. Pulse chase experiments indicated that the proteins synthesized in the first hour after stimulation have a turnover time of less than four hours, while the same fractions in non‐proliferating cells were stable for at least 12 hours. 2‐mercapto‐1‐(β‐4‐pyridethyl) benzimidazole, when added at the same time as the fresh medium, produced an inhibition of the increase in nuclear protein synthesis at one hour, but, if added at five hours after stimulation, it did not inhibit the increase in nuclear protein synthesis occurring at six hours. Actinomycin D (0.01 μg/ml) inhibited both the stimulation of DNA synthesis and the increases in nuclear acidic protein synthesis occurring at one and six hours after stimulation. These results seem to indicate that the serum factors responsible for the stimulation of WI‐38 cells, after binding to cells, induce an early synthesis of acidic nuclear proteins which is sensitive to very low doses of actinomycin D. In turn, the newly synthesized proteins could in some way activate in the nuclei the genes that control DNA synthesis and cell division.
Biochemistry of the bioluminescence of colonial hydroids and other coelenterates
Authors: Morin James G. , Hastings J. W. 
Published: February 2005

AbstractThe biochemical system responsible for the bioluminescent flashing in a number of coelenterates has been isolated and partially characterized. The system involves a molecule termed a “photoprotein,” which emits a brief (1 second) flash of light when reacted with calcium. A chelating agent such as EDTA must be used at all times to maintain the activity intact. The activity of reacted photoprotein is not restored if the calcium is removed by EDTA.
Formation of extracellular adenosine triphosphate by normal and neoplastic human cells in culture
Authors: Ågren G. , Ponten J. , Ronquist G. , Westermark B. 
Published: February 2005

AbstractNormal and neoplastic human cells in culture were suspended under isotonic conditions and incubated for one minute with the substrates, including 32P‐labelled inorganic phosphate, and cofactors of the glyceraldehyde‐3‐phosphate dehydrogenase and phosphoglycerate kinase reactions (complete medium), as well as with an incomplete medium lacking ADP, NAD+ and glyceraldehyde‐3‐phosphoric acid. The neoplastic cell types incubated in the complete medium synthesized three to six times more labelled ATP than the corresponding normal cells. In the incomplete medium only insignificant amounts of labelled ATP were formed during one‐minute incubation by all types of cells. From other types of experiments it could be concluded that the labelled ATP, isolated from the cells incubated in the complete medium, was formed at the surface of the cell membranes. Only negligible amounts of enzymes engaged in the synthesis of ATP have leaked out from the cells.
Studies on the mechanism of interaction between rabbit transferrin and reticulocytes
Authors: Baker Erica , Morgan E. H. 
Published: February 2005

AbstractThe two stages in the uptake of transferrin by rabbit reticulo‐cytes were investigated using radioiodine‐labeled rabbit transferrin and albumin. The first stage of rapid, temperature‐insensitive uptake of transferrin was similar to albumin uptake: uptake of both proteins increased linearly with increasing protein concentration of the incubation medium up to at least 60 mg/ml, was maximal at low ionic strength and pH, and increased in the presence of basic polyamino acids. Transferrin uptake was in part dependent on the reticulocyte concentration of the blood, but albumin uptake was independent of reticulocyte concentration.The second slower, temperature‐sensitive stage of transferrin uptake was linearly related to reticulocyte concentration, and was not found with albumin, α1‐macroglobulin or γ‐globulin. Transferrin uptake was optimal at physiological pH and ionic strength and was unaffected by basic polyamino acids. When the transferrin concentration was raised, uptake increased to reach a maximum at a concentration of 15 mg/ml.It was concluded that the first stage of transferrin uptake was in part or wholly due to non‐specific adsorption of transferrin to erythrocytes, while the second stage of uptake was specific for transferrin and reticulocytes and depended upon normal function of the cells.
Comparative studies on the interaction of benzpyrene with cells derived from poikilothermic and homeothermic vertebrates. II. Effect of temperature on benzpyrene metabolism and cell multiplication
Authors: Fred Clark H. , Diamond Leila 
Published: February 2005

AbstractThe effect of incubation temperature on cell multiplication and on the efficiency of benzpyrene (BP) metabolism to water‐soluble derivatives was compared in cell cultures derived from three poikilothermic and three homeo‐thermic vertebrate species. The fish cells grew optimally at about 20°C and the amphibian and reptilian cells at about 30°C, and in general, these cells multiplied over broader ranges of temperature than the mouse, hamster or chick cells. In each cell system, the maximum temperature supporting efficient BP metabolism exceeded the maximum temperature supporting cell growth by 4 to 8°, but the range of temperatures supporting near‐maximal BP metabolism was also considerably broader in the poikilothermic than in the homeothermic vertebrate cultures.
The time of DNA replication in the cell cycle in relation to RNA synthesis in frog embryos
Authors: Remington J. A. , Flickinger R. A. 
Published: February 2005

AbstractVariations in the rates of DNA and RNA synthesis during the DNA synthetic (S) period of the cell cycle have been determined in explants of early Rana pipiens embryos.Cells of dorsal axial ectoderm‐mesoderm regions and belly endoderm regions of the embryo were partially synchronized using 5‐fluorodeoxyuridine. The partially synchronized explants were incubated continuously or at intervals during the S period with radioactive nucleic acid precursors. Autoradiographic and biochemical evidence indicates that at the gastrula, neurula and tailbud stages the DNA is replicated discontinuously in two maxima with a slowing in the synthetic rate in the middle of the S period. There is an increase in the proportion of the DNA which replicates late as development proceeds from gastrulation. At the neurula and tailbud stages the proportion of late replicating DNA is greater in the belly endoderm than in the dorsal axial ectoderm‐mesoderm.Experiments utilizing H3‐5‐uridine indicate that RNA is synthesized discontinuously in two maxima during the S period in both dorsal axial and belly regions at the earlier neurula stage. By the tailbud stage, however, a significant decrease in the second maximum of RNA transcription occurs. RNA extraction experiments indicate that these changes can be attributed, in part, to changes in the synthesis of DNA‐like RNA. These findings are discussed in relation to cell determination.
Changes in the functional efficiency of flight muscle sarcosomes during heat death of adult Calliphora erythrocephala
Authors: Davison T. F. , Bowler K. 
Published: February 2005

AbstractThe temperature sensitivity of flight muscle mitochondria from adult Calliphora erythrocephala has been studied. Intact flies were treated to sublethal and lethal high temperatures, their sarcosomes were isolated and the efficiency of the coupling of oxidation and phosphorylation was measured. The temperature sensitivity of sarcosomes is correlated with the heat death point of the intact animal and the impairment of oxidative phosphorylation with α‐glycerophosphate suggests that a breakdown in ATP synthesis may be one of the causes of heat death. Restitution of enzyme activity was observed in mitochondria isolated from flies recovering from sublethal heat treatment. The results suggest that the impairment of membrane‐enzyme complexes may be important lesions in heat death.
Viral‐induced fusion of human cells. I. Quantitative studies on the fusion of human diploid fibroblasts induced by sendai virus
Authors: Velázquez Antonio , Payne Francis E. , Krooth Robert S. 
Published: February 2005

AbstractHuman diploid fibroblasts in monolayer cultures underwent cyto‐plasmic fusion in the presence of UV‐inactivated Sendai virus. The proportion of nuclei in the cultures which were in polykaryocytes (“polykaryocytic index”) under the conditions used in the present study, was about 0.50. When the cells were fused by the methods developed for the present study, the polykaryocytic index was substantially higher than when the conventional method was employed. The extent of fusion obtained was dependent, up to a certain degree, on the concentration of the virus and on the cell population density. The polykaryocytic index reached a maximum four to six hours after the cells were exposed to virus, but the frequency of cells with very high numbers of nuclei continued to increase for at least two days. Evidence is presented which suggests that the population of mononucleate cells is heterogeneous as regards their ability to fuse. The distribution of multinucleate cells with various numbers of nuclei roughly fits the Poisson distribution, although the frequency of cells with very large numbers of nuclei is substantially greater than the Poisson would predict.
The effect of hypertransfusion on the growth of mouse foetal liver cells transplanted into irradiated, adult recipients: Failure to detect a differential effect between cells from early and late foetuses
Authors: Tarbutt R. G. , Cole R. J. 
Published: February 2005

AbstractErythropoiesis can be reinstated in lethally irradiated mice by transplantation of adult bone marrow or liver cells from foetuses at any stage of gestation beyond the eleventh day. Hypertransfusion of the recipients abolishes erythropoiesis resulting from the transplants, even when the transplants are derived from foetuses at a very early stage of development. This suggests that erythropoietin is necessary for the successful growth of these early foetal transplants, at least in the environment of the irradiated recipient. These results are at variance with an earlier report on the susceptibility of early foetal liver transplants to suppression by hypertransfusion.
Innervation and acetylcholine sensitivity of skeletal muscle cells differentiatedin vitrofrom chick embryo
Authors: Kano Masaakira , Shimada Yutaka 
Published: February 2005

AbstractTrypsin‐dissociated myoblasts from leg muscle of 12‐day chick embryos have been cultured in monolayers. After four days the muscle cultures have been confronted with fragments of the spinal cord of six‐day chick embryos.Electrophysiological and morphological analysis demonstrate that characteristic neuromuscular transmission can develop in these cultures. Electrical stimulation of the cord fragment evokes contractions of innervated muscle fibers, from which end plate potentials and miniature end plate potentials with average frequency around one per second or more can be recorded. D‐tubocurarine (1 μg/ml) suppresses reversibly these synaptic potentials.Non‐innervated muscle fibers are sensitive to acetylcholine over all their surface, while innervated muscle fibers are sensitive at the regions where structures suggestive of motor end plate (“bulb‐type”) are found.We can conclude that neuromuscular connections developedin vitroin our experiments are functional in respect of transmission of impulses but also in respect of neurotrophic influences for restriction of chemosensitivity.
The rate of sedimentation of individual human red blood cells
Authors: Canham Peter B. , Jay Alfred W. L. , Tilsworth Eva 
Published: February 2005

AbstractThe sedimentation of individual cells was investigated in the context of the Stokes' equation for sedimenting spheres. Blood obtained from a finger prick was diluted 104 times by volume in Tris buffered Ringer solution (pH 7.4, 310 milliosmolar). A small sample of the suspension was put in a plastic, flat bottomed depression slide which was then closed with a coverslip. Thirty‐six runs were done in which a cell was kept in focus on an inverted microscope. The 250 μm descent was monitored on a two channel chart recorder. The orientation, determined by the observer as edge, oblique, or flat, and the verticle displacement, indicated by a ten turn potentiometer connected to the fine focussing knob, were recorded simultaneously. The cells studied indicated that cells are more frequently in the edge‐on orientation, that larger cells sediment faster than smaller cells despite the lower density for larger cells, and that cells wobble considerably. The biconcave cells made approximately three orientation changes per minute where one change in orientation was considered to be a rotation of 45° in any direction. Brownian motion is thought to be responsible for the wobble, or random rotations of the sedimenting cell. The edge‐to‐flat velocity ratio was 1.38 ± 0.30 S.D. which is significantly less than 1.5, the theoretical and experimental value for thin discs. There was a moderate dependence of sedimentation velocity on the square of the diameter (R = +0.5) in accordance with Stokes' Law. The variance in this relation can be accounted for by the known variation of cellular density within a normal population of red cells, and by the inherent errors of measurement.
Density dependent regulation of growth in suspension cultures of L‐929 cells
Authors: Glinos André D. , Werrlein Robert J. 
Published: February 2005

AbstractSuspension cultures of L‐929 fibroblasts grown to densities of 6 to 10 × 106 cells/ml through daily centrifugation and resuspension in fresh media, have been maintained for periods up to five months without change in viability or cell size. DNA synthesis and mitosis in these cultures is limited to 5% of the cells per day, a fraction very nearly equal to the fraction of cells rendered nonviable, most likely during the manipulations associated with medium renewal. The kinetics of the flow of cells into the S and M periods following (a) renewal of the medium and (b) dilution of the high density cultures, suggest that the large majority of the cells are in a G0 or early G1 phase, resuming growth readily in response to decreased cell density. This is further indicated by the sequence of the marked shifts occurring in the cell volume distribution spectrum of the high density cultures after dilution. Long term, steady state regulation of growth with retention of intact viability was thus demonstrated in the case of a long established aneuploid cell line. The fact that this occurs in suspension but not in attached cultures, supports the concept that impairment of growth control in such cells affects predominantly regulatory mechanisms located at the cell surface rather than those concerned with intracellular synthesis and metabolism.
Density‐dependent resistance to puromycin in cell cultures
Authors: Cass Carol E 
Published: February 2005

AbstractPig kidney cells exhibit resistance to puromycin when cultured at high cell densities, growing progressively in otherwise lethal concentrations of drug. Comparison of population growth of cultures inoculated at different densities indicates that survival in puromycin is a function of cell density. Uptake of puromycin from culture media is less at higher cell densities resulting in decreased inhibition of protein synthesis by puromycin. Enhanced survival in puromycin at high population densities is attributed to reduced accumulation of puromycin from the culture media.
Genetics of somatic mammalian cells. XIV. Genetic analysis in vitro of auxotrophic mutants
Authors: Kao Fa‐Ten , Fuck Theodore T. 
Published: February 2005

AbstractGenetic analysis has been carried out on auxotrophic mutants produced by treatment of Chinese hamster ovary and the Chinese hamster lung cells with mutagenic agents in vitro. Thirty‐six different mutants were subjected to complementation analysis and biochemical tests. The different mutations studied result in growth requirements for proline; glycine; glycine or folinic acid; adenine or several of its precursors; inositol; adenine plus thymidine; and glycine plus adenine plus thymidine.The mutants which require glycine fall into four different complementation classes while those requiring adenine or hypoxanthine form two different complementation classes. The biochemical blocks of the latter two classes both occur somewhere in the steps involved in conversion of 5‐phosphoribosyl‐1‐pyrophosphate to 5‐aminoimidazole 4‐carboxylic acid ribonucleotide.The auxotrophic mutants described exhibit all‐or‐none responses to their specific nutrilite supplements and are stable with respect to reversion. They involve alterations in ten different genes, and hence form a useful set of mutants for a variety of genetic studies. All the auxotrophies produced in a single exposure to a mutagen are due to single gene mutations, even when multiple nutritional requirements were produced. All the mutations studied are recessive.
Control of macromolecular synthesis in proliferating and resting syrian hamster cells in monolayer culture. III. Electrophoretic patterns of newly synthesized proteins in synchronized proliferating cells and resting cells
Authors: Becker H. , Stanners C. P. 
Published: February 2005

AbstractElectrophoretic patterns of newly synthesized proteins have been compared for hamster embryo fibroblasts in asynchronous cultures, mitotically synchronized cultures, and stationary phase cultures. Only proteins with molecular weight between 30,000 and 150,000, comprising 60–70% of the total cell proteins and excluding histones and collagen were included in the comparison. Although no significant differences could be detected between such patterns for cells at different stages of the cell cycle, significant differences were detected between patterns for cells in stationary phase and for proliferating asynchronous or synchronous cells in any stage of the cell cycle. These differences amounted to at least 5% of the newly synthesized cellular proteins. Much larger differences were detected between patterns from a nuclear fraction of proliferating and resting cells. These results indicate that normal cells in stationary phase are arrested in a state distinct from any phase of the normal cell cycle and may provide a biochemical marker for resting cells.
Synthesis of nuclear acidic proteins in density‐inhibited fibroblasts stimulated to proliferate
Authors: Tsuboi Atsushi , Baserga Renato 
Published: February 2005

AbstractPrevious work from this laboratory (Rovera and Baserga, 1971) has shown that, when density‐inhibited WI‐38 human diploid fibroblasts are stimulated to proliferate by a change of medium, the synthesis of nuclear acidic proteins increases within 30 minutes after stimulation; several hours before DNA synthesis begins to increase. Similar results have now been obtained with density‐inhibited 3T6 mouse fibroblasts, also stimulated by a change of medium.Gel electrophoretic analysis of nuclear acidic proteins in both WI‐38 human diploid fibroblasts and 3T6 mouse fibroblasts stimulated to proliferate indicates that the increased synthesis of nuclear acidic proteins is limited to certain classes of proteins while other classes are totally unaffected.The increase in nuclear acidic proteins synthesis is inhibited when WI‐38 cells or 3T6 cells are stimulated in the presence of 5‐azacytidine (10 μg/ml), a treatment which also inhibits the subsequent stimulation of DNA synthesis.These results, confirming and extending similar findings previously reported in other models of stimulated DNA synthesis, lend further support to the hypothesis that nuclear acidic proteins may play a critical role in the control of DNA synthesis and cell division in mammalian cells.
Transport changes in synchronously growing CHO and L cells
Authors: Sander Greta , Pardee Arthur B. 
Published: February 2005

AbstractA reduced rate of transport of 2‐amino‐isobutyric acid (AIB), was found to be associated with M and early G1 periods in synchronized populations of CHO and L cells. A doubling of the transport rate occurred with progress of CHO cells further into G1, and the specific transport activity remained constant during the rest of the cycle, The rate of uridine and thymidine transport also doubled at this point in the cell cycle. There was no change in Km values. The rise in transport rate was blocked by cycloheximide, or when the cells were prevented from leaving metaphase by colcemid.
Opposite effects of dibutyryl adenosine 3′:5′ cyclic monophosphate and serum on growth of Chinese hamster cells
Authors: Rozengurt Enrique , Pardee Arthur B. 
Published: February 2005

AbstractThe effect of dibutyryl adenosine cyclic 3′:5′ monophosphate and testosterone on growth, response to serum and transport properties of Chinese hamster ovary cells was studied. There was a marked depression of growth in the presence of both compounds. A change of medium was sufficient to permit a partially synchronized burst of growth of the treated cells either in the presence or absence of dibutyryl adenosine cyclic 3′:5′ monophosphate plus testosterone. However, in the presence of these compounds a second round of cell division was prevented. Initiation of the cell cycle by cells exposed to dibutyryl adenosine cyclic 3′:5′ monophosphate plus testosterone displayed a greater serum requirement than untreated cells. It is concluded that serum and cyclic AMP could have antagonistic interactions in growth regulation.The treated cells had a reduced ability to accumulate amino‐isobutyrate and glutamine, but no difference was observed with uridine uptake. The data suggest that a functional alteration of the membrane is induced by the exposure to dibutyrl adenosine cyclic 3′:5′ monophosphate plus testosterone.
Separation of mouse spermatogenic cells by velocity sedimentation
Authors: Meistrich Marvin L. 
Published: February 2005

AbstractImprovements have been made in methods of preparation of single cell suspensions from mouse testes for separation by sedimentation at unit gravity. Mechanical means of preparation specifically damage spermatogonia, young primary spermatocytes, and spermatids at various stages of development, resulting in apparent sedimentation velocities which correspond closely to those of free nuclei. Trypsin has been used to release these cells from the seminiferous tubules allowing measurement of the sedimentation properties of the intact cell. The exclusion of trypan blue from the cells, resistance to trypsin, and the persistence in vitro of the highly differentiated forms of macromolecular synthesis demonstrate the integrity of the cells in the suspensions prepared with trypsin. Differentiation pathways in terms of sedimentation velocities of the cells and nuclei have been constructed and are in agreement with morphological changes.