The recovery of normal DNA replication kinetics in ultraviolet-irradiated Chinese hamster cells.
Explore the source record for details and available documents.
Bromodeoxyuridine↗
SEARCH · Search PubMed
Results for “DNA Replication Timing”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Developmental control in animals and a biological role for DNA charge transfer.
A model is developed based on data from diverse lines of inquiry, describing the possible role of charge transfer in the timing and coordination of DNA replication and gene expression in eukaryotic cells. Emphasis is placed on a possible electrical process which participates in the simultaneous base-pair opening in many regions of DNA preceding replication, and a similar coordination of gene expression by simultaneous generation of base-pair openings around promoter and transcriptional start sites. This process could have the character of an ultradian biological clock. There is no specific evidence for such a process, but the argument is presented that such a process is neither unphysical nor unbiological, and its postulation would act as a first-iteration road map for explaining the coordinated nature of eukaryotic organism development.
Animals↗
Chromosomal aberrations induced by caffeine in endoreduplicated Chinese hamster cells.
Explore the source record for details and available documents.
Animals↗
Study of trans-cyclopropylbis (diketopiperazine) and chelating agents related to ICRF 159. Cytotoxicity, mutagenicity, and effects on scheduled and unscheduled DNA synthesis.
The cytotoxicity, mutagenicity, and DNA damaging potential of trans-cyclopropylbis (diketopiperazine) (3) and chelating agents related to ICRF 159 (1) were examined as a function of concentration and duration of exposure in the Chinese hamster cell line V79A. At a concentration of 10(-3) M, 1 and the trans-cyclopropanediamine tetraacid 8 and ester 7 proved to be cytotoxic and mutagenic. The trans-cyclopropyl analogue 3 of ICRF 159 and acyclic tetraacid 6 were less cytotoxic at all concentrations; analogue 3 exhibited no mutagenic activity at any of the concentrations tested. Compounds 1, 7, and 8, at lethal concentrations, exhibited significantly different mutation frequencies with 7 being sixfold more mutagenic than 8 at the same molar concentration. At 10(-3) M compounds 8 was several times more effective blocking DNA replication than other analogues but did not induce unscheduled DNA synthesis as did 1,3, and 6. With the exception of 8, there was an excellent correlation between mutagenesis and the induction of unscheduled DNA synthesis.
Animals↗
The chromatin remodeling complex NoRC controls replication timing of rRNA genes.
The ATP-dependent chromatin remodeling complex NoRC silences a fraction of mammalian ribosomal RNA genes (rDNA) by establishing heterochromatic structures at the rDNA promoter. Here we show that NoRC also plays a role in replication timing of rDNA. rDNA is replicated in a biphasic manner, active genes ( approximately 60%) replicating early and silent ones ( approximately 40%) replicating late in S-phase. The chromatin structure that marks active and silent rDNA repeats is propagated during cell division. To examine the function of NoRC in epigenetic inheritance and replication timing, we have monitored the chromatin structure, transcriptional activity and replication timing of rDNA in a cell line that moderately overexpresses NoRC. NoRC is exclusively associated with late-replicating rDNA arrays. Overexpression of NoRC silences rDNA transcription, reduces the size and number of nucleoli, impairs cell proliferation and resets replication timing from early to late. The results demonstrate that NoRC is an important determinant of replication timing and epigenetic marks are heritably maintained through DNA replication.
Adenosine Triphosphate↗
Effect of an acute exposure of rat testes to gamma rays on germ cells and on Sertoli and Leydig cell functions.
Germ cells and Sertoli and Leydig cell functions were studied from 7 to 180 days after an acute exposure of 2-month-old rat testes to 9 Gy of gamma rays. Body weight, testis and epididymal weights were recorded. Sertoli cell parameters (androgen-binding protein, ABP, in caput epididymis and plasma follicle stimulating hormone, FSH) and Leydig cell parameters (plasma luteinizing hormone, LH, testosterone and prostate and seminal vesicle weights) were determined together with the number of germ cells and Sertoli cells. Irradiation did not affect body weight but significantly reduced testicular and epididymal weights from day 7 and day 15 post-irradiation respectively. The cells killed by irradiation were mainly spermatogonia and preleptotene spermatocytes engaged in replicating their DNA at the time of exposure, but all spermatocytes seemed damaged as they gave abnormal descendent cells. By day 34, only elongated spermatids remained in a few tubules and thereafter very little regeneration of the seminiferous epithelium occurred, except for one rat which showed a better regeneration. Levels of ABP decreased by day 15 when the germ cell depletion had reached the pachytene spermatocytes, whereas FSH and LH levels rose when the number of elongated spermatids decreased. Levels of testosterone and the weight of the seminal vesicles did not change; occasionally, the prostate weight was slightly reduced. These results support our hypothesis that pachytene spermatocytes and elongated spermatids are involved in influencing some aspects of Sertoli cell function in the adult rat.
Animals↗
Regulation of dihydrofolate reductase synthesis in an overproducing 3T6 cell line during transition from resting to growing state.
We have isolated a methotrexate (MTX)-resistant clone of mouse 3T6 cells, designated M50L3, which grows normally in the presence or absence of 50 muM MTX and produces a level of dihydrofolate reductase (DHFR; 5,6,7,8-tetrahydrofolate:NADP(+) oxidoreductase, EC 1.5.1.3) that is increased about 300-fold compared to the parental 3T6 cells. The cells retain the ability to rest in the G(0) state when maintained in medium containing 0.5% calf serum and can be stimulated to reenter the cell cycle by increasing the serum concentration to 10%. The rate of accumulation of DHFR in resting M50L3 cells is about 1/25th of that in exponentially growing cells. When resting cells are stimulated to reenter the cell cycle, the rate of accumulation of DHFR starts to increase at about 8 hr and reaches a maximum (25-fold increase) at about 16 hr after stimulation. Pulse-labeling experiments show that the increase in DHFR accumulation is due to an increased rate of synthesis. This increase occurs at about the same time the cells enter S phase. However, inhibitors of DNA synthesis have no effect on the increase in DHFR accumulation after serum stimulation, indicating that there is no tight coupling of the two events. Actinomycin D inhibits the subsequent increase in DHFR accumulation if added 8 hr after stimulation but has no effect if added 16 hr after stimulation. This is consistent with the idea that the increase in DHFR gene expression depends on transcription of the gene and that DHFR mRNA synthesis begins at about the time the cell initiates DNA replication. DHFR gene expression appears to be regulated in the same manner in the overproducing cells as we found in the parental 3T6 cells [Johnson, L. F., Fuhrman, C. L. & Wiedemann, L. M. (1978) J. Cell. Phys. 97, 397-406]. Therefore, the alterations that are responsible for DHFR overproduction (presumably DHFR gene amplification) do not interfere with the ability of the cell to regulate the rate of synthesis of the enzyme after serum stimulation.
Animals↗
The molecular basis for inhibition of adipose conversion of murine 3T3-L1 cells by retinoic acid.
The effect of retinoic acid (RA) on the adipose conversion of 3T3 cells has been studied. Differentiation of 3T3-L1 cells was initiated by addition of 0.5 mM methylisobutylxanthine, 0.3 microM dexamethasone and 10 micrograms/ml insulin (MDI) to confluent monolayers of preadipocytes for 48 h. During this time, the cells underwent DNA replication and cell division prior to the expression of adipose specific genes. RA administration had no apparent effect on the rate or extent of cell growth, cell division, or DNA replication. However, RA treatment concomitant with MDI addition inhibited triacylglycerol accumulation (I0.5 = 6 nM) and the accumulation of the differentiation-dependent mRNAs encoding the adipocyte lipid-binding protein (ALBP) and stearoyl-CoA desaturase 1 (SCD1). No inhibition occurred with RA addition either prior to or after MDI treatment. Runoff transcription revealed that the inhibitory effects of RA occurred at the level of transcription and were persistent. Cells treated with RA during the MDI regimen did not appreciably transcribe ALBP or SCD1 mRNAs several days following RA withdrawal. The effects of RA were specific for differentiation-dependent transcripts: 10(-6) M RA did not inhibit expression of the mRNAs encoding beta-tubulin or glutamine synthase. Examination of immediate-early transcription factor expression during the MDI regimen revealed that RA mediated an elevated, prolonged expression of c-Jun mRNA accompanied by diminished expression of c-Fos and Jun-B mRNAs. Given the previously demonstrated role of transcription factor AP-1 in ALBP gene expression, our results suggest that the initiation of expression of this and other adipocyte-specific genes during adipose conversion is regulated by the relative composition of transcription factor AP-1.
Adipose Tissue↗
Inactivation of bacteriophage lambda containing semiconserved alkylated deoxyribonucleic acid.
Immediate and delayed inactivation of ethylmethane sulfonate (EMS)-treated lambda phage were studied. Phage particles with one alkylated and one intact deoxyribonucleic acid (DNA) strand were obtained by allowing host-modified, EMS-treated phage to undergo one growth cycle in a nonmodifying host and selecting the progeny with semiconserved parental DNA on a restricting host. The results indicate that particles with one alkylated DNA strand are more sensitive to a second treatment with the alkylating agent. When incubated at 37 C, they are subject to inactivation at a rate which is smaller than that of phages containing two alkylated DNA strands. It appears that depurination events in one of the DNA strands of a phage particle are sufficient to cause death.
Alkylating Agents↗
C/EBPalpha is a DNA damage-inducible p53-regulated mediator of the G1 checkpoint in keratinocytes.
The basic leucine zipper transcription factor, CCAAT/enhancer binding protein alpha (C/EBPalpha), is abundantly expressed in keratinocytes of the skin; however, its function in skin is poorly characterized. UVB radiation is responsible for the majority of human skin cancers. In response to UVB-induced DNA damage, keratinocytes activate cell cycle checkpoints that arrest cell cycle progression and prevent replication of damaged DNA, allowing time for DNA repair. We report here that UVB radiation is a potent inducer of C/EBPalpha in human and mouse keratinocytes, as well as in mouse skin in vivo. UVB irradiation of keratinocytes resulted in the transcriptional up-regulation of C/EBPalpha mRNA, producing a >70-fold increase in C/EBPalpha protein levels. N-Methyl-N'-nitro-N-nitrosoguanidine, etoposide, and bleomycin also induced C/EBPalpha. UVB-induced C/EBPalpha was accompanied by an increase in p53 protein and caffeine, an inhibitor of ataxia-telangiectasia-mutated kinase, and ataxia-telangiectasia-mutated and Rad3-related kinase inhibited UVB-induced increases in both C/EBPalpha and p53. UVB irradiation of p53-null or mutant p53-containing keratinocytes failed to induce C/EBPalpha. UVB irradiation of C/EBPalpha knockdown keratinocytes displayed a greatly diminished DNA damage G(1) checkpoint, and this was associated with increased sensitivity to UVB-induced apoptosis. Our results uncover a novel role for C/EBPalpha as a p53-regulated DNA damage-inducible gene that has a critical function in the DNA damage G(1) checkpoint response in keratinocytes.
Animals↗
The evolution of mutation rate in finite asexual populations.
In this article, we model analytically the evolution of mutation rate in asexual organisms. Three selective forces are present. First, everything else being equal, individuals with higher mutation rate have a larger fitness, thanks to the energy and time saved by not replicating DNA accurately. Second, as a flip side, the genome of these individuals is replicated with errors that may negatively affect fitness. Third, and conversely, replication errors have a potential benefit if beneficial mutations are to be generated. Our model describes the fate of modifiers of mutation rate under the three forces and allows us to predict the long-term evolutionary trajectory of mutation rate. We obtain three major results. First, in asexuals, the needs for both adaptation and genome preservation are not evolutionary forces that can stabilize mutation rate at an intermediate optimum. When adaptation has a significant role, it primarily destabilizes mutation rate and yields the emergence of strong-effect mutators. Second, in contrast to what is usually believed, the appearance of modifiers with large mutation rate is more likely when the fitness cost of each deleterious mutation is weak, because the cost of replication errors is then paid after a delay. Third, in small populations, and even if adaptations are needed, mutation rate is always blocked at the minimum attainable level, because the rate of adaptation is too slow to play a significant role. Only populations whose size is above a critical mass see their mutation rate affected by the need for adaptation.
Adaptation, Physiological↗
B-cell activation by helper T-cell membranes.
Resting B cells can be stimulated to proliferate and differentiate to antibody-producing cells by the combination of cell contact and soluble signals provided by activated primed helper T (Th) cells. The ability of purified plasma membranes from activated Th cell clones and recombinant lymphokines to reconstitute B cell proliferation and differentiation has allowed an increased understanding of B cell activation and characterization of the molecules involved. B cell-Th cell contact appears sufficient for delivering the proliferative signal to B cells in the absence of lymphokines. A receptor ligand pair that plays a critical role in delivery of the contact signal is CD40 on the B cell surface and the ligand for CD40 on activated Th cells. Lymphokines alone do not drive resting B cell differentiation, however, when these soluble signals are delivered during the time of B cell DNA replication, they effect B cell differentiation and isotype switching. Delivery of the CD40-dependent contact signal to resting B cells appears to require a high degree of CD40 crosslinking on the B cell surface. Providing contact signals to naive B cells with recombinant molecules in membrane fractions may allow the generation of methodology to support the production of novel antibodies in vitro.
Animals↗
Inhibition of hepatitis B virus production by Boehmeria nivea root extract in HepG2 2.2.15 cells.
AIM: To explore the anti-hepatitis B virus (HBV) effects of Boehmeria nivea (B. nivea) root extract (BNE) by using the HepG2 2.2.15 cell model system. METHODS: Hepatitis B surface antigen (HBsAg), hepatitis B virus e antigen (HBeAg), and HBV DNA were measured by using ELISA and real-time PCR, respectively. Viral DNA replication and RNA expression were determined by using Southern and Northern blot, respectively. RESULTS: In HepG2 2.2.15 cells, HBeAg (60%, P < 0.01) and particle-associated HBV DNA (> 99%, P < 0.01) secretion into supernatant were significantly inhibited by BNE at a dose of 100 mg/L, whereas the HBsAg was not inhibited. With different doses of BNE, the reduced HBeAg was correlated with the inhibition of HBV DNA. The anti-HBV effect of BNE was not caused by its cytotoxicity to cells or inhibition of viral DNA replication and RNA expression. CONCLUSION: BNE could effectively reduce the HBV production and its anti-HBV machinery might differ from the nucleoside analogues.
Antiviral Agents↗
[Characteristics of DNA replication in the long-term culture of human cells at the stationary phase].
Peculiarities of DNA replication in cultured human diploid fibroblasts in logarithmic and stationary phases were studied using DNA autoradiography. The rate of DNA replication fall from 30-36 mu/hour at active proliferative phase to 18-20 mu/hour at late stationary phase. This phenomenon is characteristic of stationary cultures after stimulation to proliferate by changing medium as well as by culturing without stimulation. Possible mechanisms of DNA replication rate alteration in senescent human cells are discussed.
Autoradiography↗
Deoxyribonucleic acid replication in human diploid fibroblasts stimulated to proliferate.
The elongation of replicating DNA chains was studied in resting (G0) cultures of WI-38 cells stimulated to proliferate. An alkaline sucrose gradient sedimentation method which avoids shear effects was employed. The earliest detected intermediate is a short (4.5 S) piece of DNA which is converted to 11 S and larger (50 to 60 S) pieces within 1 min. The 50 to 60 S pieces are gradually converted to two distinct size classes, 212 S and 275 S, which are in turn converted to a chromosomal aggregate of about 400 S. The overall rate of elongation of DNA is about 1.4 X 10(6) daltons/min.
Cell Line↗
Post-meiotic DNA synthesis in nocodazole-blocked nuclei during conjugation of Tetrahymena thermophila. Induction of polyploidy in the micronucleus.
The formation of single, polyploid micronuclei was induced during conjugation of Tetrahymena thermophila with Nocodazole (ND) according to Kaczanowski et al. The increase in DNA content in these nuclei was measured cytophotometrically in conjugating pairs continuously exposed to the drug. ND-treated micronuclei ('restitution nuclei') undergo two complete rounds of DNA replication and enter the third at the time of pair separation. The DNA content of these micronuclei in late pairs was in the range 16-30C (mean 20C). This amount was similar to the sum of the DNA content of all post-meiotic products during normal conjugation at about the same stage. Thus the increase in DNA content in 'restitution' nuclei reflects some intrinsic ability of nuclei in pairing cells to replicate DNA independently of nuclear division.
Animals↗
Transcription of genes encoding DNA replication proteins is coincident with cell cycle control of DNA replication in Caulobacter crescentus.
DNA replication in the dimorphic bacterium Caulobacter crescentus is tightly linked to its developmental cell cycle. The initiation of chromosomal replication occurs concomitantly with the transition of the motile swarmer cell to the sessile stalked cell. To identify the signals responsible for the cell cycle control of DNA replication initiation, we have characterized a region of the C. crescentus chromosome containing genes that are all involved in DNA replication or recombination, including dnaN, recF, and gyrB. The essential dnaN gene encodes a homolog of the Escherichia coli beta subunit of DNA polymerase III. It is transcribed from three promoters; one is heat inducible, and the other two are induced at the transition from swarmer to stalked cell, coincident with the initiation of DNA replication. The single gyrB promoter is induced at the same time point in the cell cycle. These promoters, as well as those for several other genes encoding DNA replication proteins that are induced at the same time in the cell cycle, share two sequence motifs, suggesting that they represent a family whose transcription is coordinately regulated.
Amino Acid Sequence↗
The temporal program of DNA replication: new insights into old questions.
During the last decades it has been shown that the replication timing program in metazoans is related to chromosome structure, the nuclear positioning and AT/GC content of chromosomal loci, their patterns of histone modifications, and their transcriptional regulation. Here, the current state of knowledge concerning these relationships is reviewed. An integrated view on structure-function relationships in the nucleus is provided and the determination and functional role of the replication timing program is discussed in this context. A corresponding comprehensive model is developed and a key aspect of this model is the suggestion that mammalian chromosomes are organized into stable units equivalent to replicon clusters. It is proposed that the nuclear positions of these units would depend on their histone modifications and determine the replication timing of the whole unit. It is furthermore predicted that replication timing is only indirectly linked to transcriptional regulation and contributes to the maintenance of gene expression patterns. These clear predictions, and the fact that the tools are at hand now to further test them, open an avenue towards solving the long standing problem on how replication timing is determined in metazoan cells.
Animals↗