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1.
Summary
Saccharomyces cells induced to undergo meiosis when in late G
1 or early S-phase, proceed mitotically until a point between completion of the S-phase and nuclear division. From that point, the cells start meiotic development without intervention of a round of premeiotic DNA replication. Cells induced at any other point in the cell cycle, enter meiosis from G
1. 相似文献
2.
An improved mathematical method to estimate DNA synthesis time of bromodeoxyuridine-labelled cells, using FCM-derived data 总被引:1,自引:0,他引:1
M. C. Johansson B. Baldetorp P. O. Bendahl R. Johansson S. M. Oredsson† 《Cell proliferation》1994,27(8):475-488
Abstract. Chinese hamster ovary cells in vitro were pulse-labelled with bromodeoxyuridine (BrdUrd and were then allowed to progress through the cell cycle. Every half hour after labelling, cells were harvested and prepared for simultaneous flow cytometric determination of DNA content and incorporated BrdUrd, with the intercalating dye propidium iodide and with a monoclonal antibody against incorporated BrdUrd, respectively. The relative movement (RM), i.e. the relative mean DNA content of the moving cohort of BrdUrd-labelled cells in relation to that of G1 and G2 cells, was calculated. RM was then used to calculate DNA synthesis time (TS), at all post-labelling times (t). Since labelled cells in G2 and mitosis (M) in addition to S phase cells, are included in the cohort of moving labelled cells, and since the time of G2 and M (Tg2+M) phases is finite, a non-linear relationship exists between RM and post-labelling time. Because of this, the use of a linear formula in the calculation of TS yields results that are affected by t. We found that RM data can be corrected with regard to TG2+M resulting in the derivation of a non-linear TS formula. This non-linear TS formula gave results that were nearly independent of t. Moreover, windows were set in the mid DNA distributions for G1, S and G2+ M cells in the bivariate DNA v. BrdUrd cytograms, to estimate the fraction of BrdUrd-labelled cells in each window at every post-labelling time. Plots of the fraction of BrdUrd-labelled cells v. post-labelling time were then made for each window. TS obtained in this way was in agreement with TS obtained with the corrected RM method. In conclusion, we present a method to calculate Ts which theoretically first makes the determination of RM independent of TG2+M, and secondly compensates for the non-linear function of RM with post-labelling time caused by accumulation of BrdUrd-labelled cells in G2+ M. 相似文献
3.
SYNOPSIS. Relationships between the cell cycle and the beginning of conjugation were analyzed for 3 hypotrichs: Diophrys scutum, Oxytricha bifaria, and Euplotes crassus. The first 2 species enter conjugation with micronuclei in G1; the latter species with a micronucleus in G2. The 1st micronuclear division of conjugating E. crassus is mitotic. Thus meiotic DNA replication occurs when the cells of each species have already entered the mating process. Cells from asynchronous populations start conjugation with their macronuclei primarily in G1 or more rarely at the beginning of the S stage in a percentage significantly different from that expected on the basis of random mating among all cells in the population. Also, macronuclear replication, when already begun, was blocked in cells undergoing conjugation. Therefore only the G1 or the very early S stages of the cell cycle are compatible with conjugation in the 3 analyzed species. 相似文献
4.
Suspension cultures of Chinese hamster cells (line CHO), which had stopped dividing and were arrested in G1 following growth to high cell concentrations in F-10 medium, could be induced to reinitiate DNA synthesis and to divide in synchrony upon addition of the appropriate amounts of isoleucine and glutamine. Both amino acids were required to initiate resumption of cell-cycle traverse. Deficiencies in other amino acids contained in F-10 medium did not result in accumulation of cells in G1, indicating a specific action produced by limiting quantities of isoleucine and glutamine. In the presence of sufficient glutamine, approximately 2 x 10-6
M isoleucine was required for all cells to initiate DNA synthesis in a population initially containing 1.5 x 105 cells/ml. Under similar conditions, about 4 x 10-6
M isoleucine was required for all G1-arrested cells to progress through cell division. In contrast, 1 x 10-4
M glutamine was necessary for maximum initiation of DNA synthesis in G1 cells, along with sufficient isoleucine. A technique for rapid production of G1-arrested cells is described in which cells from an exponentially growing population placed in F-10 medium deficient in both isoleucine and glutamine or isoleucine alone accumulated in G1 after 30 hr. 相似文献
5.
Sixty to eighty per cent of the cells in a culture of human diploid fibroblasts may be stimulated from the state of density dependent inhibition of replication to active DNA synthesis and division. The maximum response is effected by 50% serum within the pH range 7.2–8.0. The proportion of cells responding depends on the concentration of serum protein in the medium which may be effectively substituted by crystalling serum albumin. There is a differential sensitivity to the stimulus of cells in the densely packed centers of whorls and in the less dense areas between the whorls. The cell response is parasynchronous and the median durations of the various phases of the cell cycle are: G1I 6 β ?æ® ¿ ∞ 8 hours, G2 = 6 hours and doubling time = 30 hours. The stimulatory effect of fresh medium is lost during contact with dense cultures so that it has only 50% of its initial capacity after 14 hours. It can be restored by dialysis against serum-free medium. The stimulus must be applied for at least ten hours to be effective in inducing DNA synthesis. During the latter half of ten hour induction period subsequent DNA synthesis becomes exquisitely sensitive to actinomycin D. After this time an increasing number of cells become irreversibly committed to replicate. The data are interpreted to indicate that during contact with serum proteins (including albumin) changes in the cell surface, if continued long enough, trigger a mechanism which involves the synthesis of a unique RNA species during the fifth to tenth hours. After this RNA has been synthesized the cells are then committed to DNA synthesis. 相似文献
6.
Cultures of Euglena gracilis (strain Z from French CNRS collection) can be made cadmium resistant if grown in a medium with 5x10-4M cadmium chloride. This resistance is reflected by the appearance of a second exponential growth phase. The development of this resistance was studied at the cellular level by determining the relative content of DNA at different stages of the cell cycle in an asynchronously grown culture. The culture was followed until the second, cadmium resistant, growth phase had reached its stationary state. During the first exponential growth phase, cells were mostly in the late period of DNA synthesis (stage S of the cell cycle), or in the gap preceding mitosis (stage G2 of the cell cycle). In addition, some cells contained high multiples of the normal amount of DNA. In the beginning of the second exponential growth phase, a few cells were again in G1 (the post mitotic stage of the cell cycle preceding DNA synthesis). These G1 cells were predominant at the end of the second growth period. During the second stationary phase the DNA content of the cadmium treated cells was similar to the stationary phase of the control culture. Cells had stopped growing in G1 with an unreplicated genome. The implications of these data are discussed. 相似文献
7.
In flow microfluorometry (FMF) analysis cells stained with a fluorescent dye that binds specifically to DNA are passed through the instrument. The number of cells in the population having a fluorescence intensity is recorded in a single channel of a multichannel pulse height analyzer. The result is a DNA fluorescence histogram for the population.A method for decomposing an FMF histogram into its G1, S and G2 + M components, corresponding to similarly designated phases of the cell cycle is given. This technique can also be applied to find the parameters in all of the previous approaches. The parameters are calculated by iteration which eliminates the need for non-linear optimization procedures. 相似文献
8.
M. Wierzbicka 《Protoplasma》1999,207(3-4):186-194
Summary
Allium cepa (L.) adventitious roots were treated with lead (2.5 mg of Pb2+ [from Pb(NO3)2] per dm3) for 30–72 h. The cell cycle was studied by pulse labeling with [3H]thymidine. Mitotic activity kinetics, occurrence of disturbed mitoses (c-mitoses), and level of DNA synthesis were examined. It was found that lead prolonged the cell cycle and that cells in two phases of the cycle, G2 and S, differed in their sensitivity to lead. Cells in G2 were more sensitive; lead lengthened their cycle by 216% and disturbed the course of cell division by causing c-mitoses. Cells in S phase were less sensitive. Their cell cycle was longer by 55%. They went through their G2 phase without major disturbances, mitosis in these cells was normal. During treatment ofA. cepa with lead, its destructive effects on cells were exerted only during the first few hours (around 6 h) of incubation. That is when the inhibition of mitotic activity, numerous disturbances of cell division, a decline in the number of cells synthesizing DNA, and a lower level of DNA synthesis were observed. As the incubation continued, the above processes were found to return to normal. In the discussion, data are presented supporting the hypothesis that during the initial period of exposure ofA. cepa to lead, this metal enters both the root apoplast and symplast, exerting a destructive effect on cells, while later, lead penetrates only into the root apoplast, and in this way remains harmless to cells. 相似文献
9.
Summary Following X-irradiation of exponentially growing L929 cells two major phenomena have been observed. First, there was a delay in cell division which can be ascribed to the arrest of cells in theG
2-phase (G
2-block), and, second, the cellular content of the O6-alkylguanine-DNA alkyltransferase (AGT) was markedly increased. Flow cytometrical DNA-measurements revealed that cells began to accumulate in theG
2-phase 4 h after irradiation (p.r.) irrespective of the X-ray dose, while both the fraction of cells blocked inG
2 and the time period the cells persisted inG
2 increased with the radiation dose. About 24 h past release from theG
2-block the distribution of cells in the cell cycle was similar to that of untreated control cells. In comparison with control cells the AGT content in irradiated cells (4 Gy) was highest at about 48 h p.r. (3.4-fold increase). The highest ratio of increase in AGT was, however, observed to occur between about 4 and 13 h p.r. (2.6-fold increase). As shown by flow cytometrical measurements using a BrdUrd/DNA double labeling technique, this rapid primary increase in AGT coincides very well with the entrance of cells into theG
2-phase. This indicates that the cellular AGT content in X-irradiated (parental) cells started to exceed the basal level at the beginning of theG
2-phase, but not before or during theS-phase. Once the AGT level was elevated it continued to increase for 2 to 3 cell doubling times.Paper given at the Workshop Molecular Radiation Biology. German Section of the DNA Repair Network, München-Neuherberg, 21.-23.3.1990 相似文献
10.
Reversible accumulation of plant suspension cell cultures in g(1) phase and subsequent synchronous traverse of the cell cycle 总被引:1,自引:0,他引:1
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Conia J Alexander RG Wilder ME Richards KR Rice ME Jackson PJ 《Plant physiology》1990,94(4):1568-1574
The induction of DNA synthesis in Datura innoxia Mill. cell cultures was determined by flow cytometry. A large fraction of the total population of cells traversed the cell cycle in synchrony when exposed to fresh medium. One hour after transfer to fresh medium, 37% of the cells were found in the process of DNA synthesis. After 24 hours of culture, 66% of the cells had accumulated in G2 phase, and underwent cell division simultaneously. Only 10% of the cells remained in G0 or G1. Transfer of cells into a medium, 80% (v/v) of which was conditioned by a sister culture for 2 days, was adequate to inhibit this simultaneous traverse of the cell cycle. A large proportion of dividing cells could be arrested at the G0 + G1/S boundary by exposure to 10 millimolar hydroxyurea (HU) for 12 to 24 hours. Inhibition of DNA synthesis by HU was reversible, and when resuspended into fresh culture medium synchronized cells resumed the cell cycle. Consequently, a large fraction of the cell population could be obtained in the G2 phase. However, reversal of G1 arrested cells was not complete and a fraction of cells did not initiate DNA synthesis. Seventy-four percent of the cells simultaneously reached 4C DNA content whereas the frequency of cells which remained in G0 + G1 phase was approximately 17%. Incorporation of radioactive precursors into DNA and proteins identified a population of nondividing cells which represents the fraction of cells in G0. The frequency of cells entering G0 was 11% at each generation. Our results indicate that almost 100% of the population of dividing cells synchronously traversed the cell cycle following suspension in fresh medium. 相似文献
11.
Arrangement and association of somatic chromosomes induced by chloramphenicol in barley 总被引:1,自引:0,他引:1
Chromosome number in the cells of the first division cycle in the root tip of Hordeum vulgare (2n=14) was apparently reduced from 2n to n by the chloramphenicol (CAP) treatments in early S, S late and/or early G
2 stages. Morphological observations and measurements of relative DNA content per cell indicated that such reduction was due to tight alignment of chromosomes in pairs. —It was supposed that homologous chromosomes are close together in the interphase nucleus, and their successive association up to mitotic prometaphase was induced by the CAP treatment. 相似文献
12.
Frank Traganos Jianping Gong Barbara Ardelt Zbigniew Darzynkiewicz 《Journal of cellular physiology》1994,158(3):535-544
Staurosporine (SSP) is an inhibitor of a variety of protein kinases with an especially high affinity towards protein kinase C. Whereas SSP has been shown to halt the cell cycle progression of various normal, nontransformed cell types in G1, most virus transformed or tumor cells are unaffected in G1 but arrest in G2 phase. SSP has also been observed to increase the appearance of cells with higher DNA content, suggestive of endoreduplication, in cultures of tumor cells. Using multivariate flow cytometry (DNA content vs. expression of cyclin B, nucleolar p120 protein, or protein reactive with Ki-67 antibody) which makes it possible to discriminate cells with identical DNA content but at different phases of the cycle, we have studied the cell cycle progression of human lymphocytic leukemic MOLT-4 cells in the presence of 0.1 μM SSP.MOLT-4 cells did not arrest in G1 or G2 phase in the presence of the inhibitor. Rather, they failed to undergo cytokinesis, entering G1 phase at higher DNA ploidy (tetraploidy; G1T), and then progressed through ST (rereplication) into G2T and MT. The rates of entrance to G2 and G2T were essentially identical, indicating that the rates of cell progression through S and ST as well as through G2 and G2T, respectively, were similar. Cells entrance to mitosis and mitotic chromatin condensation were also similar at the diploid and tetraploid DNA content level and were unaffected by 0.1 μM SSP. No evidence of growth imbalance (altered protein or RNA to DNA ratio) was observed in the case of tetraploid cells. The data show that, in the case of MOLT-4 cells, all events associated with the chromosome or DNA cycle were unaffected by SSP; the only target of the inhibitor appears to be kinase(s) controlling cytokinesis. © 1994 Wiley-Liss, Inc. 相似文献
13.
The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) exerts a dose-dependent effect on Daudi cell proliferation. A low concentration has a slight mitogenic effect but higher concentrations inhibit proliferation. The inhibitory effect is associated with increases in cell size, macromolecular content, and incorporation of precursors into RNA and protein. Cell cycle analysis indicates that TPA at 1–10 nM leads to an apparent accumulation of cells in G2/M phase. However, within this population a significant proportion of cells undergo nuclear division but fail to carry out cytokinesis, giving rise to cells with two or more nuclei. Consistent with this, DNA synthesis continues in cells which cease to divide in the presence of TPA. The ability of the phorbol ester to inhibit proliferation can thus be attributed mainly to an inhibition of cytokinesis rather than DNA replication 相似文献
14.
Synchronized cultures of mammalian cells were labeled with 14C-methyl methionine. Labeled methionine methyl groups were incorporated into certain histone fractions, forming methyl lysine. Incorporation of labeled methyl group into histone fractions as 14C-methyl lysine was followed through the cell cycle from late G1 into early M. The 14C-methyl lysine contents of fractions F2a and F3 began to rise in S and reached maxima after termination of DNA and histone synthesis, coincident with the beginning of mitosis, and began to fall by mid-M. The 14C-methyl lysine content of fraction F2b rose to a maximum early in S, coincident with initiation of DNA synthesis, and rapidly decreased to its original unmethylated level by late S. Fraction F1 remained unmethylated during the period G1-M. Evidence is presented to demonstrate differential methylation of histone fractions and to substantiate differential temporal coupling of the methylation of specific histone fractions with histone and DNA biosynthesis. 相似文献
15.
V. V. Shaposhnikova L. N. Kublik A. A. Narimanov M. Kh. Levitman O. E. Orlova A. A. Kudryavtsev V. V. Leshchenko Yu. N. Korystov 《Biology Bulletin》2001,28(2):202-205
We studied the effect of arachidonic acid metabolism inhibitors in a wide concentration range on the proliferation and death of lympholeukemia cells P-388. Proliferation of the cells was estimated by metaphase frequency and the proportion of cells in S phase; cellular death was determined by their lysis, trypan blue staining, damaged nuclei, the proportion of cells with subdiploid DNA content, and DNA fragmentation. Low concentrations of phospholipase A2 and lipoxygenase inhibitors were shown to stimulate cell division, while higher concentrations inhibited it by blocking G
1–S transition and inducing apoptotic cellular death. Indomethacin, a cyclooxygenase inhibitor, had no effect on proliferation and induced no cell death at concentrations up to 10 M. Inhibitors of phospholipase A2 and lipoxygenase also inhibited tumor growth in mice. 相似文献
16.
Millie Hughes-Fulford 《Journal of cellular biochemistry》1994,54(3):265-272
Our previous studies have implied that prostaglandins inhibit cell growth independent of cAMP. Recent reports, however, have suggested that prostaglandin arrest of the cell cycle may be mediated through protein kinase A. In this report, in order to eliminate the role of c-AMP in prostaglandin mediated cell cycle arrest, we use the-49 lymphoma variant (cyc?) cells that lack adenylate cyclase activity. We demonstrate that dimethyl prostaglandin A1 (dmPGA1) inhibits DNA synthesis and cell growth in cyc? cells. DNA synthesis is inhibited 42% by dmPGA1 (50 μM) despite the fact that this cell line lacks cellular components needed for cAMP generation. The ability to decrease DNA synthesis depends upon the specific prostaglandin structure with the most effective form possessing the α,β unsaturated ketone ring. Dimethyl PGA1 is most effective in inhibiting DNA synthesis in cyc? cells, with prostaglandins PGE1 and PGB1 being less potent inhibitors of DNA synthesis. DmPGE2 caused a significant stimulation of DNA synthesis. S-49 cyc- variant cells exposed to (30–50 μm) dmPGA1, arrested in the G1 phase of the cell cycle within 24 h. This growth arrest was reversed when the prostaglandin was removed from the cultured cells; growth resumed within hours showing that this treatment is not toxic. The S-49 cyc? cells were chosen not only for their lack of adenylate cyclase activity, but also because their cell cycle has been extensively studied and time requirements for G1, S, G2, and M phases are known. Within hours after prostaglandin removal the cells resume active DNA synthesis, and cell number doubles within 15 h suggesting rapid entry into S-phase DNA synthesis from the G1 cell cycle block. The S-49 cyc? cells are known to have a G1/S boundary through M phase transition time of 14.8 h, making the location of the prostaglandin cell cycle arrest at or very near the G1/S interface. The oncogenes, c-fos and c-myc which are normally expressed during G1 in proliferating cells have a 2–3 fold enhanced expression in prostaglandin G1 arrested cells. These data using the S-49 variants demonstrate that dmPGA1 inhibits DNA synthesis and arrests the cell cycle independent of cAMP-mediated effects. The prostaglandin arrested cells maintain the gene expression of a G1 synchronous cell which suggests a unique molecular mechanism for prostaglandin action in arresting cell growth. These properties indicate that this compound may be an effective tool to study molecular mechanisms of regulation of the cell cycle. 相似文献
17.
P. O. Vardevanyan A. P. Antonyan G. A. Manukyan A. T. Karapetyan A. K. Shchyolkina O. F. Borisova 《Molecular Biology》2000,34(2):272-276
Isotherms of the EtBr adsorption on native and denatured poly(dA)poly(dT) in the temperature interval 20–70°C were obtained.
The EtBr binding constants and the number of binding sites were determined. The thermodynamic parameters of the EtBr intercalation
complex upon changes of solution temperature 20–48°C were calculated: 1.0·106 M−1≤K≤1.4·106 M−1, free energy ΔG
o=−8.7±0.3 kcal/mol, enthalpy ΔH
o≅0, and entropy ΔS
o=28±0.5 cal/(mol deg). UV melting has shown that the melting temperature (T
m) of EtBr-poly(dA)poly(dT) complexes (μ=0.022,4.16·10−5 M EtBr) increased by 17°C as compared with the ΔT
m of free homopolymer, whereas the half-width of the transition (T
m) is not changed. It was shown for the first time that EtBr forms complexes of two types on single-stranded regions of poly(dA)poly(dT)
denatured at 70°C: strong (K
1=1.7·105 M−1; ΔG
o=−8.10±0.03 kcal/mol) and weak (K
2=2.9·103 M−1; ΔG
o=−6.0±0.3 kcal/mol).The ΔG
o of the strong and weak complexes was independent of the solution ionic strength, 0.0022≤μ≤0.022. A model of EtBr binding
with single-stranded regions of poly(dA)poly(dT) is discussed. 相似文献
18.
Variations in Several Responses of HeLa Cells to X-Irradiation during the Division Cycle 总被引:15,自引:0,他引:15
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Several responses of synchronized populations of HeLa S3 cells were measured after irradiation with 220 kev x-rays at selected times during the division cycle. (1) Survival (colony-forming ability) is maximal when cells are irradiated in the early post-mitotic (G1) and the pre-mitotic (G2) phases of the cycle, and minimal in the mitotic (M) and late G1 or early DNA synthetic (S) phases. (2) Markedly different growth patterns result from irradiation in different phases: (a) Prolongation of interphase (division delay) is minimal when cells are irradiated early in G1 and rises progressively through the remainder of the cycle. (b) Cells irradiated while in mitosis are not delayed in that division, but the succeeding division is delayed. (c) Persistence of cells as metabolizing entities does not depend on the phase of the division cycle in which they are irradiated. (3) Characteristic perturbations of the normal DNA synthetic cycle occur: (a) Cells irradiated in M suffer a small delay in the onset of S, a slight prolongation of S, and a slight depression in the rate of DNA synthesis; the major delay occurs in G2. (b) Cells irradiated in G1 show no delay in the onset of S, and essentially no alteration in the duration or rate of DNA synthesis; G2 delay is minimal. (c) Cells irradiated in S suffer an appreciable S prolongation and a decreased rate of DNA synthesis; G2 delay is shorter than S delay. 相似文献
19.
Relationship between double fertilization and the cell cycle in male and female gametes of tobacco 总被引:4,自引:2,他引:2
Nuclear DNA content of male and female gametes of tobacco was determined using 4,6-diamindino-2-phenylindole and quantitative microfluorimetry. Pollen grains are released with generative cells containing 2C DNA. Mitotic division occurs in the pollen tube 8–12 h after germination. The resulting sperm cells have 1C DNA content during pollen tube elongation in the style. Sperm cells deposited in the degenerated synergid have a DNA content between 1C and 2C, indicating that sperm are in S-phase in the synergid. Concomitant with pollen tube arrival, the egg cell increases in DNA quantity from 1C to between 1C and 2C at 48 h after pollination. In the absence of pollination, S-phase in the egg cell is delayed by up to 36 h. Newly formed zygotes contain nuclear DNA concentrations of 4C at karyogamy and remain at 4C until zygote division. Tobacco displays cell fusion after the completion of S-phase, apparently during G2. Failure to achieve an optimized system for in vitro fertilization in Nicotiana may reflect the challenges of achieving cell cycle synchrony in gametes isolated from pollen tubes. Receptive gametes are presumably those that pass through the protracted S-phase, reaching G2 receptivity and cell cycle congruity before fusion. 相似文献
20.
M. E. Fernández-Gómez 《Histochemistry and cell biology》1968,12(4):302-306
Summary The microspectrophotometric study of the amount of DNA in the course of the interphase of synchronous binucleate cells, experimentally induced in the roots of the onion (Allium cepa), at 30° C, showed that the rate of DNA synthesis does not appear to be constant throughout the interphase, being greater at the beginning and end of the S period and slower during the middle part of the period.We found that the G
1 period occupies from 0% at 10% of the cell cycle, the S period about 81% and G
2 period plus mitosis about 14%.Contrary to our expectations, highly significant differences were found in the DNA content of the two nuclei of more than 1% of the binucleate cells, which suggests that DNA synthesis may be asynchronous in the two nuclei within a common cytoplasm. 相似文献