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1.
Summary Under hypoxia (10 and 5% partial oxygen tension) meristematic cells ofAllium cepa L. roots acquired new cycle kinetics, characterized by reduced but constant rates of root growth. Under these conditions, there was preferential lengthening of G1 and of the last third of the S period, S3. Since hyperoxygenation shortened S3 but not G1 in these cells, the high sensitivity of late replication to environmental oxygen is demonstrated. The preferential depression of the replication rate when those cells replicated the last third of their DNA was not associated with diminished cell size. Rather, the lower the oxygen level the larger the mean size of the cycling cells. Under anoxia (0% oxygen tension) the rate of growth slowed, accompanied by preferential accumulation of cells in G1. However, steady state kinetics of root growth was not achieved under these extreme conditions.Abbreviations Mean
cell length
- LI
labelling index or frequency of cells with labelled nuclei after [3H]thymidine
- G1, S, G2
pre-replicative, replicative, and post-replicative periods of the interphase of cycling cells
- M
mitosis 相似文献
2.
The duration of the cell generation, the chronology, and the pattern of chromosome duplication was studied in the bone marrow of Gallus domesticus. The duration of the phases of the cell cycle is: cell generation 17.5 hours, S period 9 hours. G2 period plus prophase stage 2.5 hours, G1 period 6 hours. Chromosome replication begins at many sites. During middle S it extends to the whole complement and finally finishes in small, late replicating regions of the macrochromosomes. Interchromosomal asynchrony of duplication at the initiation or at the end of the S period was not observed. Z-chromosomes begin and finish DNA synthesis synchronously with the other macrochromosomes. The W-chromosome in females is the last microchromosome to finish replication. However it ends DNA synthesis at about the same time as the macrochromosomes. Similarities and differences between chromosome replication in Aves and Mammalia are considered. 相似文献
3.
Derepression of the cell cycle by starvation is involved in the induction of tobacco pollen embryogenesis 总被引:1,自引:0,他引:1
V. Žárský D. Garrido L. Říhová J. Tupý O. Vicente E. Heberle-Bors 《Sexual plant reproduction》1992,5(3):189-194
Summary Microspectrophotometry following Feulgen staining and autoradiography following (3H)-thymidine labelling were used to study cell-cycle events during pollen development in tobacco (Nicotiana tabacum L.). During normal gametophytic pollen development in the anther and in vitro the generative nucleus passes through the S phase to the G2 phase soon after microspore mitosis, while the vegetative nucleus remains arrested in G1 (=G0). During embryogenie induction by an in vitro starvation treatment of immature pollen ongoing DNA replication in the generative nucleus is completed and followed by DNA replication in the vegetative cell in a large fraction of the pollen grains. Addition of the DNA replication inhibitor hydroxyurea to the starvation medium postpones S phase entry until the pollen is transferred to a rich medium and does not affect embryo formation. These results demonstrate that one of the crucial events of embryogenic induction is the derepression of the G1 arrest in the cell cycle of the vegetative cell. 相似文献
4.
《Cell cycle (Georgetown, Tex.)》2013,12(10):1423-1432
We report evidence suggesting that methyltransferase SET8 plays a novel role in regulating cell cycle by suppressing DNA replication through histone binding. First, the distribution of SET8 is strongly cell cycle-dependent. SET8 was concentrated in the nucleus during G1 and G2 phases, and was excluded from the nucleus during S phase. Second, at G1/S transition, SET8 was degraded through ubiquitination via SCF/Skp2. Third, it was evident that the SET8 binds to the H4 N-terminal tail (H4NT) and blocks the acetylation of lysine residues K5, K8 and K12 of histone H4 during G1. Such a blockage can hinder DNA replication. Fourth, SET8 binds to hypoacetylated but not hyperacetylated H4NT. Finally, overexpressing the histone-binding domain of SET8 appeared to suppress DNA replication and arrest the cell cycle before the G1/S transition. Taken together, these findings suggest that SET8 can be a negative regulator of DNA replication and the destruction of SET8 is required for the onset of S phase. 相似文献
5.
W. Nagl 《Protoplasma》1977,91(4):389-407
Summary The structure and ultrastructure of nuclei in the S period and other phases of the mitotic cell cycle have been studied in semi- and ultrathin sections of root tips ofAllium carinatum. Significant structural differences have been found and classified by means of DNA measurements by scanning photometry of Feulgen-stained squash preparations. In G1 and early S (S1 and S2) the euchromatin forms small, compact and electron-dense patches, while the heterochromatin is condensed into a number of chromocenters of the same electron-density as the euchromatin. In middle S (S3) the euchromatic elements become larger and more thread-like. In late S (S4) the euchromatin appears in the form of thick and uniform strands as in G2, and the heterochromatin decondenses into strands of the same, or a little higher, diameter, as the euchromatin. DNA replication starts in the condensed heterochromatin (S1, becomes shifted to euchromatin (S2), continues over both eu- and heterochromatin during middle S (S3), and is restricted to decondensed heterochromatin in late S (S4). Quantitative data of various nuclear parameters are given for the different stages. The results are discussed in relation to the species-specific nuclear ultrastructure, its molecular basis, and its variation during the mitotic interphase, as well as with respect to the timing and structural expression of DNA replication. 相似文献
6.
AUGUST RUTHMANN 《The Journal of eukaryotic microbiology》1972,19(4):661-666
The hypotrichous ciliate Keronopsis rubra has ~10 micronuclei and ~100 small macronuclei. DNA synthesis proceeds synchronously in all macronuclei in the 2nd half of the cell cycle which takes about 24 hr at room temperature. A G2 phase is virtually absent, each nucleus dividing as soon as the replication band has passed over it. The micronuclear S phase falls within macronuclear G1 and is followed by immediate division. Comparative cytophotometric measurements of Feulgen-stained preparations indicate that the DNA content of G1 macronuclei is scattered widely in a skewed normal distribution, with a peak corresponding to the DNA content of a G1 micronucleus. Measurements of dividing macronuclei indicate unequal distribution of DNA between daughter nuclei and lead to the conclusion that the units of assortment must be smaller than whole genomes unless the micronucleus is polyploid. After conjugation, a large macronuclear anlage with threads resembling split prophase chromosomes is formed. The threads condense and pass singly into the cytoplasm where they are thought to give rise to the numerous small macronuclei of the vegetative cells. 相似文献
7.
INTERMITTENT DNA SYNTHESIS AND PERIODIC EXPRESSION OF ENZYME ACTIVITY IN THE CELL CYCLE OF WI-38 总被引:2,自引:0,他引:2
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Synchronous cultures of WI-38 were obtained using an automated system for detachment and partitioning of mitotic cells which operates without the use of inhibitors, altered medium, or lowered temperatures. The generation time in synchronous WI-38 is 19.5 h and the duration of S phase when determined from the percentage of labeled metaphase cells or nuclei is 12 h. DNA replication in WI-38 occurs in three temporally distinct and rapid bursts separated by intervals of greatly reduced synthesis within what is nominally described as the DNA synthetic (S) period. Lactate dehydrogenase (LDH) displayed maxima in G1 between 2 and 4 h and again at 10 and 16 h. Peaks in LDH activity were coordinated with DNA replication in a fashion similar to that reported for diploid Chinese hamster cells. Oscillations in LDH activity are more pronounced in normal diploid fibroblasts than in established and neoplastic lines. 相似文献
8.
José L. Díez Consuelo de la Torre Gonzalo Giménez-Martín 《Histochemistry and cell biology》1973,35(2):137-141
Summary We have been able to follow the increase in nuclear histones along the division cycle, using a natural synchronous meristematic cell population labelled by caffeine as binucleate. We have thus found a parallel increase in DNA and histone along the S period. Some increase in nuclear histones during the G1 and G2 has also been detected. At the same time a high rise of stainable histone in the nuclei in prophase has been found.Changes in the composition of nuclear histones have been followed counting the percentage of arginine-rich histones in the total histone content. Two peaks located at the beginning and at the end of the S period as well as a sharp descent of the percentage of arginine-rich histone in the prophasic nucleus have been found. 相似文献
9.
In a generation time of 8 hr in Paramecium caudatum, the bulk of DNA synthesis detected by thymidine-3H incorporation takes place in the latter part of the cell cycle. The micronuclear cycle includes a G1 of 3 hr followed by an S period of 3–3½ hr. G2 and division occupies the remaining period of the cycle. Macronuclear RNA synthesis detected by 5'-uridine-3H incorporation is continuous throughout the cell cycle. Micronuclear RNA synthesis is restricted to the S period. Ribonuclease removes 80–90% of the incorporated label. Pulse-chase experiments showed that part of the RNA is conserved and released to the cytoplasm during the succeeding G1 period. 相似文献
10.
Olav Karsten Vintermyr Gunnar Mellgren Roald Be Stein Ove Dskeland 《Journal of cellular physiology》1989,141(2):371-382
Analogs of cyclic adenosine monophosphate (cAMP) (N6benzoyl cAMP and N6monobutyryl cAMP) as well as agents that increased the intracellular level of cAMP (glucagon and isobutylmethylxanthine) inhibited the EGF-stimulated DNA replication of adult rat hepatocytes in primary culture independently of cell density. This inhibition was strongly potentiated by the glucocorticoid dexamethasone. The effect of cAMP (and dexamethasone) was not due to toxicity, because the inhibition was reversible and the cell ultrastructure preserved. cAMP acted by decreasing the rate of transition from G1- to S-phase, the duration of G2- and S-phase of the hepatocyte cell cycle being unaffected. DNA replication started in the extranucleolar compartment of the nucleus and ended in the nucleolar compartment as described earlier for cells grown in the absence of cAMP (O.K. Vintermyr and S.O. Døskeland, J. Cell. Physiol., 1987, 132:12-21). The action of cAMP was very rapid: significant inhibition of the transition was noted 2 hr after the addition of glucagon/IBMX and half-maximal inhibition after 4 hours. The determination of extranucleolarly labelled nuclei in cells pulse-labelled with [3H]thymidine allowed precise analysis of rapid changes in the probability of transition from G1- to S-phase. The extranucleolar labelling index could also be determined in cells continuously exposed to [3H]thymidine. 相似文献
11.
Abstract. In a previous study the epidermal cell kinetics of hairless mice were investigated with bivariate DNA/anti-bromodeoxyuridine (BrdU) flow cytometry of isolated basal cells after BrdU pulse labelling. The results confirmed our previous observations of two kinetically distinct sub-populations in the G2 phase. However, the results also showed that almost all BrdU-positive cells had left S phase 6–12 h after pulse labelling, contradicting our previous assumption of a distinct, slowly cycling, major sub-population in S phase. The latter study was based on an experiment combining continuous tritiated thymidine ([3H]TdR) labelling and cell sorting. The purpose of the present study was to use a mathematical model to analyse epidermal cell kinetics by simulating bivariate DNA/BrdU data in order to get more details about the kinetic organization and cell cycle parameter values. We also wanted to re-evaluate our assumption of slowly cycling cells in S phase. The mathematical model shows a good fit to the experimental BrdU data initiated either at 08.00 hours or 20.00 hours. Simultaneously, it was also possible to obtain a good fit to our previous continuous labelling data without including a sub-population of slowly cycling cells in S phase. This was achieved by improving the way in which the continuous [3H]TdR labelling was simulated. The presence of two distinct sub-populations in G2 phase was confirmed and a similar kinetic organization with rapidly and slowly cycling cells in G1 phase is suggested. The sizes of the slowly cycling fractions in G1 and G2 showed the same distinct circadian dependency. The model analysis indicates that a small fraction of BrdU labelled cells (3–5%) was arrested in G2 phase due to BrdU toxicity. This is insignificant compared with the total number of labelled cells and has a negligible effect on the average cell cycle data. However, it comprises 1/3 to 1/2 of the BrdU positive G2 cells after the pulse labelled cells have been distributed among the cell cycle compartments. 相似文献
12.
Dynamics of association of origins of DNA replication with the nuclear matrix during the cell cycle 总被引:3,自引:0,他引:3
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DNA of replication foci attached to the nuclear matrix was isolated from Chinese hamster ovary cells and human HeLa cells synchronized at different stages of the G1 and S phases of the cell cycle. The abundance of sequences from dihydrofolate reductase ori-β and the β-globin replicator was determined in matrix-attached DNA. The results show that matrix-attached DNA isolated from cells in late G1 phase was enriched in origin sequences in comparison with matrix-attached DNA from early G1 phase cells. The concentration of the early firing ori-β in DNA attached to the matrix decreased in early S phase, while the late firing β-globin origin remained attached until late S phase. We conclude that replication origins associate with the nuclear matrix in late G1 phase and dissociate after initiation of DNA replication in S phase. 相似文献
13.
Replication and G2 checkpoints: their response to caffeine 总被引:2,自引:0,他引:2
Under long hydroxyurea treatments, evidence was obtained for the sequential activation of four checkpoints located between
the onset of S phase and mitosis in Allium cepa L. root meristems. Bi-parametric flow cytometry (Br-DNA/total DNA) showed that cells initially accumulated at early S phase
but, after a delay, they resumed replication and paused again at mid S phase. Cells not only overrode this second replication
block but also any G2 checkpoint they encountered. Thus, a late mitotic wave was produced in the presence of hydroxyurea. The wave was formed by
cells that had apparently completed their replication (normal mitoses), while others displayed anaphases/telophases with less
than the expected DNA content and with chromosomal breaks (aberrant mitoses). The presence of aberrant mitoses is direct evidence
for the undue override of the two G2 checkpoints responsible for surveillance of completion of DNA synthesis and repair, respectively. Caffeine selectively abrogated
the G2 block produced by the checkpoint that controls post-replication DNA repair, as it advanced the entry of cells into an aberrant
mitosis. However, caffeine proved not to be the universal checkpoint-evading agent as postulated. Caffeine did not modify
the spontaneous override of the replication checkpoints. Moreover, it seems to enforce the checkpoint that controls the completion
of DNA synthesis, as the appearance of the late wave of normal mitoses produced in the presence of hydroxyurea was prevented
by the use of caffeine.
Received: 21 February 2000 / Accepted: 31 July 2000 相似文献
14.
Takayoshi Hiramatsu Osami Misumi Tsuneyoshi Kuroiwa Soichi Nakamura 《Journal of phycology》2006,42(5):1048-1058
Morphological changes in the organellar nucleoids and mitochondria of living Chlamydomonas reinhardtii Dang were examined during the cell cycle under conditions of 12:12 light:dark. The nucleoids were stained with SYBR‐Green I, and the mitochondria were stained with 3,3‐dihexyloxacarbocyanine iodide. An mocG33 mutant, which contains one large chloroplast nucleoid throughout the cell cycle, was used to distinguish between the mitochondrial and chloroplast nucleoids. Changes in the total levels of organellar DNA levels were assessed by real‐time PCR. Each of the G1, S, M, and Smt,cp phases was estimated. At the start of the light period, the new daughter cells were in G1 and contained about 30 mitochondrial and 10 chloroplast nucleoids, which were dispersed and had diameters of 0.1 and 0.2 μm, respectively. During the G1 phase of the light period, and at the start of the S phase, both nucleoids formed short thread‐like or bead‐like structures, probably divided, and increased continuously in number, concomitantly with DNA synthesis. The nucleoids probably became smaller due to the decrease in DNA of each particle and were indistinguishable. The cells in the S and M phases contained extremely high numbers of scattered nucleoids. However, in the G1 phase of the dark period, the nucleoids again formed short thread‐like or bead‐like structures, probably fused, and decreased in number. The mitochondria appeared as tangled sinuous structures that extended throughout the cytoplasm and resembled a single large mitochondrion. During the cell cycle, the numbers of mitochondrial nucleoids and sinuous structures varied relative to one another. 相似文献
15.
Taizo Motomura 《Phycological Research》1996,44(1):11-17
The cell cycle (nuclear division cycle) of a multinucleate green alga, Boergesenia forbesii (Harvey) Feldmann was studied using microspectrophotometry and BrdU incorporation techniques. Mitosis was observed frequently 1-4 h after the beginning of the light period, on a 16:8 h LD cycle at 25°C. Mitotic nuclei formed discrete patches. Other nuclei remained in the G1 period. The DNA synthetic phase (S phase) was estimated to last about 12 h from microspectrophotometric study using aphidicolin inhibition just before the S phase and release from it. The G2 period was estimated to be about 2 h, because a labeled prophase nucleus could be detected when the samples were labeled with BrdU continuously over 3 h. The incorporation pattern of BrdU changed through the S phase nucleus. In early S phase, BrdU staining was detected as many dots in the entire nucleus, while in late S phase, it was detected as several discrete regions along the nuclear membrane. Almost all nuclei in B. forbesii were in the G1 stage after nuclear division, and the nuclei in several patches of the cell simultaneously initiated DNA synthesis. Once the nuclei entered into S phase, these nuclei continued into G2 and mitosis. In other words, the cell cycle regulation of entrance into S phase from G1 is an important factor in the growth and morphogenesis in B. forbesii. 相似文献
16.
JosL. Cnovas Antonio Cuadrado Mariano Escalera Matilde H. Navarrete 《Experimental cell research》1990,191(2)
The distribution of cell surface area projection (cell size) has been measured at birth and at initiation of DNA synthesis in steady-state populations of Allium cepa root meristems. The conditional probability, P(I/G1), that initiation occurs given that the event of being in g1 also occurs has been estimated from these data. p(I/G1) was found to increase when cells became larger. The distribution of G1 duration has been constructed from indicated cell size distributions. The absolute frequencies of G1 times showed a maximum in the zone of cells with short G1 periods; about 14% of cells appear to enter into S with G1 - 1 h. These results suggest that the increase of p(I/G1) was due to cell enlargement and not to cell aging. By comparing the cell size distribution at initiation of S and at the end of this period, a drastic reduction of cell size variability during DNA replication was observed and both curves were seen as rather similar in shape although they obviously had different modal points. These observations support that there is a negative correlation between the initiation size and the duration of genome duplication, and that cells which initiate DNA synthesis with the same size have a similar replication time. From this hypothesis, a plot of S duration versus cell size at initiation of this period was constructed by comparing the distributions of cell size at start and end of replication; this plot was also consistent with the existence of a negative correlation between cell initiation size and S length. 相似文献
17.
Identification and functional characterization of a new member of the human Mcm protein family: hMcm8 总被引:7,自引:1,他引:6
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Gozuacik D Chami M Lagorce D Faivre J Murakami Y Poch O Biermann E Knippers R Bréchot C Paterlini-Bréchot P 《Nucleic acids research》2003,31(2):570-579
The six minichromosome maintenance proteins (Mcm2–7) are required for both the initiation and elongation of chromosomal DNA, ensuring that DNA replication takes place once, and only once, during the S phase. Here we report on the cloning of a new human Mcm gene (hMcm8) and on characterisation of its protein product. The hMcm8 gene contains the central Mcm domain conserved in the Mcm2–7 gene family, and is expressed in a range of cell lines and human tissues. hMcm8 mRNA accumulates during G1/S phase, while hMcm8 protein is detectable throughout the cell cycle. Immunoprecipitation-based studies did not reveal any participation of hMcm8 in the Mcm3/5 and Mcm2/4/6/7 subcomplexes. hMcm8 localises to the nucleus, although it is devoid of a nuclear localisation signal, suggesting that it binds to a nuclear protein. In the nucleus, the hMcm8 structure-bound fraction is detectable in S, but not in G2/M, phase, as for hMcm3. However, unlike hMcm3, the hMcm8 structure-bound fraction is not detectable in G1 phase. Overall, our data identify a new Mcm protein, which does not form part of the Mcm2–7 complex and which is only structure-bound during S phase, thus suggesting its specific role in DNA replication. 相似文献
18.
19.
Fractionated replicating DNA from pea was obtained from both synchronized cells just starting replication and from carbohydrate-starved cells ending replication. Benzoylated naphthoylated DEAE-cellulose chromatography of pulse-labeled DNA digested with EcoR I gave evidence that a family of replicons initiated replication 45 to 60 min after synchronized cells were released from the G1/S phase boundary. DNA from cells labeled in late S phase, on the other hand, showed no signs of additional replication initiations before entering G2 phase. Results with DNA from both early and late S phase cells comply with a model based on the premise that with short pulses of [3H]-thymidine the isotope is localized at replication forks and that longer pulses label both replication forks and recently replicated segments of double-stranded DNA. The model applies only to DNA subjected to fragmentation before chromatography.The results also suggest that benzoylated naphthoylated DEAE-cellulose chromatography is a useful means to isolate origins and replication forks from synchronized plant cells. 相似文献
20.
Cell Cycle-Dependent Regulation of Human DNA Polymerase α-Primase Activity by Phosphorylation
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Christian Voitenleitner Christoph Rehfuess Melissa Hilmes Lynda ORear Pao-Chi Liao Douglas A. Gage Robert Ott Heinz-Peter Nasheuer Ellen Fanning 《Molecular and cellular biology》1999,19(1):646-656
DNA polymerase α-primase is known to be phosphorylated in human and yeast cells in a cell cycle-dependent manner on the p180 and p68 subunits. Here we show that phosphorylation of purified human DNA polymerase α-primase by purified cyclin A/cdk2 in vitro reduced its ability to initiate simian virus 40 (SV40) DNA replication in vitro, while phosphorylation by cyclin E/cdk2 stimulated its initiation activity. Tryptic phosphopeptide mapping revealed a family of p68 peptides that was modified well by cyclin A/cdk2 and poorly by cyclin E/cdk2. The p180 phosphopeptides were identical with both kinases. By mass spectrometry, the p68 peptide family was identified as residues 141 to 160. Cyclin A/cdk2- and cyclin A/cdc2-modified p68 also displayed a phosphorylation-dependent shift to slower electrophoretic mobility. Mutation of the four putative phosphorylation sites within p68 peptide residues 141 to 160 prevented its phosphorylation by cyclin A/cdk2 and the inhibition of replication activity. Phosphopeptide maps of the p68 subunit of DNA polymerase α-primase from human cells, synchronized and labeled in G1/S and in G2, revealed a cyclin E/cdk2-like pattern in G1/S and a cyclin A/cdk2-like pattern in G2. The slower-electrophoretic-mobility form of p68 was absent in human cells in G1/S and appeared as the cells entered G2/M. Consistent with this, the ability of DNA polymerase α-primase isolated from synchronized human cells to initiate SV40 replication was maximal in G1/S, decreased as the cells completed S phase, and reached a minimum in G2/M. These results suggest that the replication activity of DNA polymerase α-primase in human cells is regulated by phosphorylation in a cell cycle-dependent manner. 相似文献