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At least 37 records · Page 2Linked to original sources
PubMed1978

Oxygen-sensitive stages of the cell cycle of human diploid cells.

We had established that growth of human diploid WI-38 cells is reversibly inhibited by elevated partial pressures of oxygen (PO2) and we were interested in determining where in the cell cycle growth was delayed. A technique combining cytospectrophotometry and autoradiography was used to determine cell cycle parameters. Confluent cells that were subcultivated and exposed to a PO2 of 365 +/- 8 mm Hg were delayed primarily after DNA synthesis but before metaphase. At a PO2 of 590 +/- 35 mm Hg, most cells did not initiate DNA synthesis, and the few that did, failed to complete the process. When exponentially growing cells that had already begun DNA synthesis were exposed to a PO2 of 590 p 35 mm Hg, they accumulated after completing DNA synthesis but before initiating mitosis. The rate at which (3H)thymidine was incorporated into DNA was inversely correlated with oxygen tension (PO2 of 135--590 mm Hg). These results suggest that the process most sensitive to oxygen causes cells to be delayed after DNA synthesis but before metaphase. Slightly higher PO2's were needed to inhibit the initiation of DNA synthesis. Further, the rate of DNA synthesis is decreased by elevated oxygen tensions.

Cell Cycle↗
PubMed1976

DNA and the cell cycle.

The cell cycle and its significance for pathology is reviewed. The molecular basis and questions of regulation in the cell cycle are discussed, along with deviations from the normal cycle in the form of polyploidy formation and aneuploidy in tumor cells. Automated prescreening processes may play a role in the future in daily routine diagnosis. Methods of cytophotometry with the possibility for objective pattern recognition will become significant in pathology in many ways, both in research and in routine work.

Aneuploidy↗
PubMed1979

[Autoradiographic investigations on the effect of city smog extract on DNA synthesis and cell cycle of mammalian cells in vitro. I. Effect of city smog extract on DNA synthesis of kidney- and embryonic cells of the golden hamster in vitro (author's transl)].

We analysed the effect of city smog extract from Düsseldorf on DNA synthesis of mammalian cells in vitro. Airborne dust was extracted with aceton and thereafter transferred to dimethylsulfoxide. Dosage was calculated according to the benzo(a)pyrene content. We used logarithmically growing cultures of hamster kidney and embryonic cells. DNA synthesis was determined autoradiographically by incorporation of 3H-Thymidine. We found that city smog extract exerted a dose-dependent cytotoxic effect leading to a decrease of DNA synthesizing cells. High concentrations of city smog extract induced cell necrosis and suppressed DNA synthesis completely. Moderate doses of extract caused a dose-dependent, but temporary cessation of DNA synthesis. Cells resumed DNA synthesis after a certain delay. Low concentrations of city smog extract induced no detectable effects. Inhibition of DNA synthesis was evident already one hour after addition of extract. Therefore a direct effect on DNA metabolism could be supposed. Furthermore, exposed cultures demonstrated a delay in entrance of new cells into the DNA synthesis. Alterations in DNA synthesis could be of great importance for carcinogenesis, especially if we take in consideration the content of carcinogens in city smog extract.

Animals↗
PubMed1978

The cell cycle of an established cell line of the mosquito Aedes aegypti.

The duration of the cell cycle and its four phases was determined for a cell line of the mosquito, Aedes aegypti (L.), using high-resolution autoradiography. The total cell cycle time is 12.5 h, with G1 comprising 1.66 h, S--4.5 h, M--3 h, and G2 3.33 h. These results are compared with those of other mosquito species.

Aedes↗
PubMed1976

Cell-cycle analysis of perturbed cell populations: computer simulation of sequential DNA distributions.

A mathematical model is presented that permits simulation of a time sequence of DNA distributions with a single set of cell-cycle parameters. The method is particularly suited to the quantitative analysis of sets of sequential DNA distributions from perturbed cell populations. The model permits determination of the durations and associated dispersions of the phases of the cell cycle as well as the point in the cell cycle at which the perturbing agent exerts its effect. The mathematical details of the simulation technique are presented, and the technique is applied to the analysis of DNA distributions from perturbed cell populations. Three cell populations are modeled: CHO-line cells released from a block at the interface of the G1-and S-phases, 3T3 cells released from a G1-phase block produced by serum starvation, and S49 mouse lymphoma cells responding to a block in the G1-phage produced by N6,02'-dibutyryl adenosine 3':5'-cyclic monophosphate (Bt2cAMP).

Autoradiography↗
PubMed1975

Induction potential for glyoxylate cycle enzymes during the cell cycle of Euglena gracilis.

In light/dark synchronized cultures of Euglena gracilis Klebs Z the enzymes malate synthase, isocitrate lyase and acetate thiokinase were induced upon addition of acetate at all stages of the cell cycle. Cycloheximide and p-fluorophenylalanine inhibited the development of enzyme activity, showing that induction was dependent on protein synthesis. The maximum rate of induction for all three enzymes was constant for much of the cell cycle but doubles in a single step during the period of DNA replication. Although these data indicate that enzyme potential was regulated by gene dosage and that the structural gene for each enzyme was continuously available for transcription during the cell-cycle it was not possible by using inhibitors of RNA synthesis, to demonstrate concurrent transcription during enzyme induction.

Acetate-CoA Ligase↗
PubMed1979

Variation of two forms of DNA polymerase-alpha during a HeLa cell cycle.

HeLa cells contain two forms of DNA polymerase-alpha (P-I and P-II) with varied affinity to DNA, separable on a DNA-cellulose column. The activity of each form was followed during a cell cycle of synchronized culture of the HeLa cells. P-I was recovered from the nuclear extract and P-II from the cytoplasmic fraction. The P-I activity remained at a low level during M to G1 phase until a marked increase between late G1 and S phases, while P-II activity increased gradually throughout the period. Both activities attained their highest level at mid-S phase and then the P-I activity declined more rapidly than the P-II. Addition of hydroxyurea at mid-S phase inhibited the decrease of both enzyme activities. The enzyme activity of nuclear extract from S phase cells was not inhibited by mixing with extract from M phase cells. When the cytoplasmic fraction from M phase cells was chromatographed on a DNA-cellulose column, single activity peak was observed at the position of P-II. These results suggest that the decrease in P-I activity is neither due to the presence of an inhibitor nor to mere release of the enzyme from chromosomes.

Cell Cycle↗
PubMed1978

Ultrastructural localization of transcription sites and of RNA distribution during the cell cycle of synchronized CHO cells.

The ultrastructural localization of [3H]uridine-labelled RNA synthesized in the course of the cell cycle of synchronized CHO cells is studied using high resolution autoradiography combined with a differential staining for nucleoproteins. It is shown that sites of RNA transcription can already be visualized on the periphery of chromosomes of apparently late metaphase-early anaphase cells with no visible association with the reforming nuclear membrane. In interphase cells they are associated with the border of intranucleolar chromatin or condensed nucleoplasmic chromatin, wherever this localization is made possible by the degree of chromatin dispersion. In cells labeled for 1 or 3 h, the rate of RNA synthesis is higher in S and G2 than in G1. When cells fixed immediately after a [3H]uridine pulse are compared with those post-incubated for 13 h in isotope-free medium, there is a clear difference in intensity of labelling between the nucleus and the cytoplasm. However, the localization pattern of radioactive RNA in the nucleus is similar for all incubation periods as well as for all phases of interphase. The groups of interchromatin granules are generally labeled weakly with radioactivity associated rather with the periphery of their clusters, or remain unlabelled. These results are discussed in the context of other recent findings concerning the distribution of RNA and RNP-structures in the nucleus.

Animals↗
PubMed1978

Effect of interferon on the cell cycle of BALB/c 3T3 cells.

The effect of interferon on the exponential growth phase of BALB/c 3T3 cells was studied. Although interferon reduced the growth rate and the proportion of cells in both the M and S phases (mitotic index and labelling index), there were no appreciable differences in the duration of these phases between control and interferon-treated cells. Moreover, the shape of the first peak of the fraction of labelled mitoses (FLM) curve was not altered by treatment with interferon, which indicates that the duration of the S and G2 phases was not affected. However, the height of the second peak of the curve in interferon-treated cells was extremely reduced as compared to control culture. These results are compatible with the idea that the suppressive effect of interferon is exerted mainly in the G1 phase (A-state) of the cell cycle of BALB/c 3T3 cells.

Animals↗
PubMed1979

[Thiophosphamide induction of sister chromatid exchanges at various phases in the cell cycle of a Chinese hamster cell culture].

Influence of three concentrations of thiophosphamide (thioTEPA) on the formation of sister chromatid exchanges (SCE) has been studied at different phases during 2 cell cycles in cultured Chinese hamster cells. It is shown that the frequency of SCE does not differ from the control level under the effect of the mutagen on cells in the G2 phase of the first cell cycle from the moment of harvesting. Thiophosphamide induces the same number of SCE at S, G1 stages of the first cell cycle and G2 of the second one till the moment of harvesting. The number of SCE correlates in a direct proportion with a concentration of thiophosphamide. A scheme of forming SCE is proposed.

Animals↗
PubMed1975

Studies on changes in DNA polymerase activity during the cell cycle in synchronized KB cells.

We have demonstrated the presence of two DNA polymerases in KB cells and studied the variation of their activities in a synchronous cell population. During the cell cycle we observed in nuclei, only one DNA dependent DNA polymerase, the 3.4 S or minipolymerase, and similarly in the cytoplasm only one enzyme, the 8.3 S or maxipolymerase. The former shows preference for native DNA and the latter for denatured DNA. Their Mg++ and K+ requirements are different and their pH optima are 8.5 and 7 for nuclear polymerase and cytoplasmic polymerase respectively. The cytoplasmic polymerase activity remains stable from one cell cycle to the other with each cell reconstituting its stock at the start of the following cycle (G1 and early S phases). On the contrary nuclear activity decreases in G2, M and early G1, then increases to a maximum in the middle of the S phase. This fluctuation in enzyme activity could be due to degradation, transfer to the cytoplasm or the association of the enzyme with the chromatin and/or the nuclear membrane after completion of DNA synthesis. Our results do not permit us to choose between these three hypotheses. However their significance is discussed in the light of the results obtained by some authors who, on the contrary, have tended to minimise the role of the minipolymerase in DNA duplication, whereas we, from our findings, ascribe a preponderant role to this enzyme. The cytoplasmic maxipolymerase (8.3 S) may simply be a storage form of the enzyme from which minipolymerase can be formed as needed.

Animals↗
PubMed1977

Studies on the cell cycle of Myxobacter AL-1. II. Activities of seven enzymes during the cell cycle.

The properties of seven enzymes were studied in extracts from Myxobacter AL-1. The enzymes were isocitrate dehydrogenase (E.C.1.1.1.42), succinate dehydrogenase (E.C.1.3.99.1), alkaline phosphatase (E.C.3.1.3.1), alpha-glucosidase (E.C.3.2.1.20), beta-glucosidase (E.C.3.2.1.21), beta-galactosidase (E.C.3.2.1.23), and N-acetyl-glucosaminidase (E.C. 3.2.1.30). Four of these enzymes: isocitrate dehydrogenase, alpha-glucosidase, beta-glucosidase, and beta-galactosidase are cytosolic enzymes. Succinate dehydrogenase was found to be located on the cytoplasmic membrane system, whereas alkaline phosphatase and N-acetylglucosaminidase were considered as enzymes which bind the outer membranes resp. the cell wall. During the cell cycle, all enzymes have a pattern of discontinuous activity increase. Succinate dehydrogenase and isocitrate dehydrogenase exhibit a stepwise increase of activity, whereas the other enzymes follow the pattern of a peak enzyme.

Acetylglucosaminidase↗
PubMed1978

Regulation of cell cycle events in asymmetrically dividing cells: functions required for DNA initiation and chain elongation in Caulobacter crescentus.

To study the regulation of cell cycle events after asymmetric cell division in Caulobacter crescentus, we have identified functions that are required for DNA synthesis in the stalked cell produced at division and in the new stalked cell that develops from the swarmer cell 60 min after division. The initiation of DNA synthesis in the two progeny cells is dependent upon at least two common functions. One of these is a requirement for protein synthesis and the other is a gene product identified in a temperature-sensitive cell cycle mutant. DNA chain elongation requires a third common function. The characteristic pattern of DNA synthesis in C. crescentus appears to be controlled in part by the expression of these functions in the two stalked cells at different times after cell division. The age distribution for Caulobacter cells in an exponential population has been calculated (Appendix by Robert Tax) and used to analyze some of the results.

Bacteria↗
PubMed1977

A change in the oxygen effect throughout the cell-cycle of human cells of the line NHIK 3025 cultivated in vitro.

NHIK 3025 cells were synchronized by repeated mitotic selection. The S-phase was determined by 3H-thymidine incorporation and scintillation counting. By comparing the age-response surves of aerobic cells irradiated with 500 rad with those of extremely hypoxic (less than4 p.p.m. O2) cells irradiatedwith 1500 rad, it was found that the sensitizing effect of oxygen was not constant throuhgout the cycle. It was significantly higher in S, G2 and mitosis than in G1. No significant sensitizing effect of 120 p.p.m. O2 (compared with less than4 p.p.m.O2) was found on cells in G1 when the cells were irradiated with 1500 rad. In S, G2 and mitosis, however, the sensitizing effect of oxygen at 120 p.p.m. is considered to be significant. Experiments performed with cells irradiated with 2000 rad incontact with either less than4 p.p.m. O2 or 80 p.p.m. O2 showed the same trend, little sensitizing effect in G1 and higher in S, G2 andmitosis. Dose-response curves for cells in mid-G1 and mid-S under aerobic and extremely hypoxic conditions were well fitted by the formula S=exp (-alphaD-betaD2). From the dose-response curves it was conculded that the change in the sensitizing effect of oxygen throughout the cell-cycle only appeared for low doses (in the dose region where alpha dominates). The sensitizing effect of oxygen on cells in mid-G1 was found to be increasing with increasing dose.

Cell Division↗