Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “G2 Phase”

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.

At least 487 records · Page 27Linked to original sources
PubMed1981

A mouse temperature-sensitive mutant defective in H1 histone phosphorylation is defective in deoxyribonucleic acid synthesis and chromosome condensation.

By means of a temperature-sensitive mutant (ts85 strain), we have studied the effect of the decrease in H1 histone phosphorylation on DNA synthesis and chromosome condensation. When ts85 cells were incubated at 39 degrees C (nonpermissive temperature), the rate of H1 histone phosphorylation was decreased gradually and reached half that at 33 degrees C (permissive temperature) by 6-h incubation. Wild-type cells, growth-revertant ts85 cells (ts85R-MN3), and other ts mutants which were arrested mainly at the G2 phase at 39 degrees C had no defects in H1 histone phosphorylation. When ts85 cells were synchronized at the G1/S boundary at 33 degrees C and released from the blockade at 39 degrees C, approximately 70% of cells passed through the S phase and stopped at the G2 phase. The rest were distributed in G1/S to the S phase and mitotic cells were not detected at all. When ts85 cells, synchronized at the G1/S boundary, were further incubated for 8 h at 39 degrees C with a synchronizing agent, the rate of phosphorylation of H1 histone was decreased and the cells were not able to complete DNA synthesis after release from the blockade. Cytofluorometric analysis revealed that the cells had DNA contents of the S phase. Taken together with our earlier data [Matsumoto, Y., Yasuda, H., Mita, S., Marunouchi, T., & Yamada, M. (1980) Nature (London) 184, 181-183], both events, incomplete DNA replication and a defect in chromosome condensation, were thought to be ascribed to the decrease in H1 histone phosphorylation.

Animals↗
PubMed2000

ATM-dependent phosphorylation and accumulation of endogenous BLM protein in response to ionizing radiation.

Bloom's syndrome (BS), a rare genetic disease, arises through mutations in both alleles of the BLM gene which encodes a 3'-5' DNA helicase identified as a member of the RecQ family. BS patients exhibit a high predisposition to development of all types of cancer affecting the general population and BLM-deficient cells display a strong genetic instability. We recently showed that BLM protein expression is regulated during the cell cycle, accumulating to high levels in S phase, persisting in G2/M and sharply declining in G1, suggesting a possible implication of BLM in a replication (S phase) and/or post-replication (G2 phase) process. Here we show that, in response to ionizing radiation, BLM-deficient cells exhibit a normal p53 response as well as an intact G1/S cell cycle checkpoint, which indicates that ATM and p53 pathways are functional in BS cells. We also show that the BLM defect is associated with a partial escape of cells from the gamma-irradiation-induced G2/M cell cycle checkpoint. Finally, we present data demonstrating that, in response to ionizing radiation, BLM protein is phosphorylated and accumulates through an ATM-dependent pathway. Altogether, our data indicate that BLM participates in the cellular response to ionizing radiation by acting as an ATM kinase downstream effector.

Adenosine Triphosphatases↗
PubMed1987

Avian primary erythropoiesis; accessory pathways of erythrocyte maturation in chick yolk sack.

In the population of chick primary erythroblasts the quota of the G2-phase (tetraploid) cells is greatly increased probably due to the fact that a part of erythroblasts is reversibly blocked at this phase. An increased number of G2 cells is also detected in the population of reticulocytes at later stages of embryogenesis and there is no cell-division in about half of the G2 cells until the 8th day the erythrocytes being exclusively diploid. The primary erythrocytes are probably formed from two types of precursors: normally dividing and specialized cells, and cells blocked in the G2-phase some of which do not complete mitosis before they develop into erythrocytes. Haemoglobinization is far more intensive in primary erythroid cells as compared with erythrocytes of definitive normal erythropoiesis.

Animals↗
PubMed1987

Negative control of periodic tubulin gene expression in the mitotic cycle of Physarum polycephalum.

Naturally synchronous syncytial plasmodia of Physarum polycephalum provide an ideal model for studying the eukaryotic cell cycle. The tubulin genes of Physarum provide a striking example of cell cycle-regulated gene expression: synthesis of both tubulin mRNA and the tubulin proteins is limited to the last three hours of G2 phase. Fusion of late G2-phase plasmodia, in which the tubulin genes are actively expressed, and mid-S phase plasmodia, in which the tubulin genes are not expressed, is used to demonstrate the presence of a diffusible negative regulator of tubulin gene expression in S-phase plasmodia. It is inferred that this factor is responsible for the turning-off of tubulin gene transcription that follows mitosis.

DNA Replication↗
PubMed1995

The human immunodeficiency virus type 1 vpr gene arrests infected T cells in the G2 + M phase of the cell cycle.

Human immunodeficiency virus type 1 (HIV-1) infection causes profound immunological defects in afflicted patients. Various mechanisms have been proposed to account for the immune dysfunction in AIDS ultimately leading to loss of CD4+ T cells, including HIV-1 envelope-mediated syncytium formation, apoptosis, and cytokine modulation. Here we present results which suggest a novel hypothesis for T-cell dysfunction. We show, using HIV-1 bearing a novel cell surface reporter gene, that infected cells are unable to progress normally through the cell cycle and became arrested in the G2 + M phase. Furthermore, we identify the HIV-1 vpr gene product as being both necessary and sufficient for eliciting this cell cycle arrest. Cell cycle arrest induced by Vpr correlates with an increase in the hyperphosphorylated (inactive) form of the cyclin-dependent serine/threonine kinase CDC2, consistent with an arrest of cells at the boundary of G2 and M.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Correlation between tubulin mRNA stability and poly(A) length over the cell cycle of Physarum polycephalum.

During the cell cycle of the Physarum polycephalum plasmodium, levels of alpha-tubulin mRNA rise exponentially in G2 phase, reach a peak at metaphase 40-fold above basal levels, and then fall exponentially to basal levels after mitosis. We show that post-mitotic alpha-tubulin mRNA carries poly(A) tracts of less than 30 residues. By contrast, when levels of alpha-tubulin mRNA rise during G2 phase, the mRNA has a poly(A) tract of approximately 80 bases. The length of the poly(A) tract of any mRNA encoding actin is relatively constant at fewer than 30 bases through the cycle. We have estimated the apparent rate of synthesis of alpha-tubulin mRNA at different stages of the cell cycle by short-term labeling in vivo. Transcription of alpha-tubulin mRNA continues even after mitosis, though the rate may be diminished relative to that in late G2 phase. So, the post-mitotic molecular half-life of alpha-tubulin mRNA must be less than the 19 minute half-life by which the levels of this species fall. The fact that the apparent rate of alpha-tubulin mRNA synthesis is not vastly greater in early G2 phase than in post-mitotic plasmodia is consistent with an S-phase destabilization of alpha-tubulin mRNA molecules. Thus, the poly(A) tail is shorter when the alpha-tubulin mRNA is less stable.

Cell Cycle↗
PubMed1989

Centromeric association and non-random distribution of centromeres in human tumour cells.

Centromere arrangement in interphase and metaphase cells of two human tumour cell lines was analysed using anti-kinetochore antibodies as immunofluorescent probes. In GLC1 interphase nuclei, kinetochores were non-randomly positioned around the nucleolus and close to the nuclear membrane. During S and early G2 phase, necklace-like strands of kinetochores were formed in the centre of the nucleus. The duplication of sister kinetochores during the G2 phase was not synchronized. At late G2 phase, a relatively random topological distribution of centromeres was observed with short linear arrays of sister kinetochores. Carefully spread metaphase plates of MDA-MB231 cells generally exhibited a linear alignment of centromeres and large centromeric clusters. In completely pulverized MDA-MB231 cells, centromeres showed a strong tendency to associate with each other.

Breast Neoplasms↗
PubMed1986

Flow cytometry reveals a high degree of genomic size variation and mixoploidy in various strains of the acellular slime mold Physarum polycephalum.

High-resolution flow cytometry, using avian erythrocytes as an internal standard, was employed to study constitutive genome size variation of G2-phase nuclei of Physarum polycephalum strains during the macroplasmodial stage of their life cycle. Our results document a previously unknown extent of genome size variation and mixoploidy in this organism. The unimodal diploid strain Tu 291 displayed the largest genome of the strains tested; in contrast, the Colonia strain displayed only half of the Tu 291 G2-phase fluorescence, confirming its haploid nature. An additional strain, derived from a recent cross between Lu897 and Lu898 amoebae, must have arisen by selfing (propagation of only one of the parental genomes to the macroplasmodial stage), since its nuclei display close to the haploid G2-phase DNA content. The observation of a small fraction of corresponding diploid nuclei within the haploid population of this strain, while maintained as microplasmodia, supports the notion that meiosis in haploid strains may require the presence of diploid nuclei. Two of the descendants of the prototype haploid Colonia strain, which were kept for extended periods of time in submerse culture, proved to be near diploid and mixoploid. Polyploidization and subsequent loss of DNA thus seems to contribute to the extremes of genome size variation in Physarum. In addition to unimodal fluorescence distributions, a number of diploid strains displayed bi- and even trimodal distributions within harvests of a single G2-phase macroplasmodium. Analysis of these mixoploid strains by means of gaussian curve-fitting suggests that the smaller genome size differences in Physarum may arise in step-wise diminution of DNA in approximate units of 3-5% of the original Tu 291 genome.

DNA, Fungal↗
PubMedDate not supplied

[A study of expression of cell cycle genes in Drosophila using an enhancer trap and radioautography].

The phase of expression of genes CycB, CycE, and chb were determined in the cell cycle of neuroblasts of D. melanogaster 3rd instar larvae using the previously described radioautographic method and software. CycB was expressed at G2 phase and upon transition from G2 phase to M phase, while CycE was expressed at the end of G1 phase and upon transition from G1 phase to S phase. The phase of expression of the centrosome-associated protein was determined more precisely in G2 phase. The mean life span of reporter beta-galactosidase in neuroblasts was 4 h. The existence of more than one peak of expression of the gene in question in the cell cycle is discussed.

Animals↗
PubMed1987

The effect of hydrocortisone on the para-aortic body of the newborn mouse: an in vivo fraction of labelled mitoses study.

Information about the cell cycle of the mouse para-aortic body within the first 24 hours of postnatal life was derived from a fraction of labelled mitoses study. The total cell cycle time was 8 1/2 hours, being made up as follows: S phase-2 hours; G2 phase-1 hour; M phase-3 1/2 hours (by analysis of the results, not by assumption) and G1 phase-2 hours (by subtraction). Problems are discussed regarding the length of G2 and M phases and the consequences for G1. After hydrocortisone administration (40 mg/kg/day) to female mice for the last seven days of pregnancy, the pattern in newborn mice was disrupted. Values for G2 and M were similar to those of the untreated group, but no values were obtainable for the other phases of the cell cycle or for the total cell cycle time. These results after hydrocortisone treatment could be explained by the superimposition of the cell cycles of two or more different groups of cells. They are discussed with regard to the life span of the para-aortic body, and their implications are considered in the light of previously reported glucocorticoid-induced transformations of small granule cells from cervical sympathetic ganglia into catecholamine-storing chromaffin cells. The established hyperplastic effect of hydrocortisone on the para-aortic body is therefore not the result simply of an acceleration of the cell cycle, but it may involve the incorporation into the proliferative compartment of cells previously either moribund or nonproliferating.

Animals↗
PubMed1999

Cyclin D1 production in cycling cells depends on ras in a cell-cycle-specific manner.

BACKGROUND: Cellular Ras and cyclin D1 are required at similar times of the cell cycle in quiescent NIH3T3 cells that have been induced to proliferate, but not in the case of cycling NIH3T3 cells. In asynchronous cultures, Ras activity has been found to be required only during G2 phase to promote passage through the entire upcoming cell cycle, whereas cyclin D1 is required through G1 phase until DNA synthesis begins. To explain these results in molecular terms, we propose a model whereby continuous cell cycle progression in NIH3T3 cells requires cellular Ras activity to promote the synthesis of cyclin D1 during G2 phase. Cyclin D1 expression then continues through G1 phase independently of Ras activity, and drives the G1-S phase transition. RESULTS: We found high levels of cyclin D1 expression during the G2, M and G1 phases of the cell cycle in cycling NIH3T3 cells, using quantitative fluorescent antibody measurements of individual cells. By microinjecting anti-Ras antibody, we found that the induction of cyclin D1 expression beginning in G2 phase was dependent on Ras activity. Consistent with our model, cyclin D1 expression during G1 phase was particularly stable following neutralization of cellular Ras. Finally, ectopic expression of cyclin D1 largely overcame the requirement for cellular Ras activity during the continuous proliferation of cycling NIH3T3 cells. CONCLUSIONS: Ras-dependent induction of cyclin D1 expression beginning in G2 phase is critical for continuous cell cycle progression in NIH3T3 cells.

3T3 Cells↗
PubMed2004

Intracellular clusterin induces G2-M phase arrest and cell death in PC-3 prostate cancer cells1.

Enhanced clusterin gene expression has been related frequently to organ remodeling, tissue involution, and cell death. Whether clusterin represents a leading cause or a consequence of apoptosis induction is still a matter of debate. Clusterin is known as an extracellular secreted glycoprotein in the mature form. However, truncated isoforms of the protein and nuclear localization of clusterin have been described recently in association to cell death. Here, we show the biological effects triggered in PC-3 androgen-independent prostate cancer cells by overexpression of an intracellular, not secreted form of clusterin (intracellular-clusterin). Transient transfection of PC-3 cells with intracellular-clusterin resulted in nuclear localization signal-independent massive nuclear localization of the protein leading to G2-M phase blockade followed by caspase-dependent apoptosis. Constitutive expression of intracellular-clusterin (pFLAG- intracellular-clusterin) in recombinant PC-3 cells caused clonogenic toxicity. The rare pFLAG-intracellular clusterin surviving clones showed inhibition of the proliferation rate and altered phenotype with impaired mitosis and endoreduplication. In these cells, caspase-independent cell death was induced. Impaired cell cycle progression in pFLAG-intracellular-clusterin clones was associated to arrest at the G2-M checkpoint by down-regulation of the mitotic complex cyclin B1/cyclin-dependent kinase 1. Intriguingly, intracellular-clusterin was localized exclusively in the cytoplasm in stably transfected cells, suggesting a negative correlation between nuclear clusterin accumulation and cell survival. These findings may possibly explain the conflicting results obtained in different laboratories, suggesting that clusterin might be a proapoptotic or a survival gene, also opening new perspectives for the characterization of androgen-independent and apoptosis-resistant prostate cancer cells.

Amino Acid Sequence↗
PubMed2006

Nocodazole does not synchronize cells: implications for cell-cycle control and whole-culture synchronization.

It has been predicted that nocodazole-inhibited cells are not synchronized because nocodazole-arrested cells with a G2-phase amount of DNA would not have a narrow cell-size range reflecting the cell size of some specific, presumably G2-phase, cell-cycle age. Size measurements of nocodazole-inhibited cells now fully confirm this prediction. Further, release from nocodazole inhibition does not produce cells that move through the cell cycle mimicking the passage of normal unperturbed cells through the cell cycle. Nocodazole, an archetypal whole-culture synchronization method, can inhibit growth to produce cells with a G2-phase amount of DNA, but such cells are not synchronized. Cells produced by a selective (i.e., non-whole-culture) method not only have a specific DNA content, but also have a narrow size distribution. The current view of cell-cycle control that is based on methods that are not suitable for cell-cycle analysis must therefore be reconsidered when results are based on whole-culture synchronization.

Animals↗
PubMed1987

Potentiation of radiation cytotoxicity by recombinant interferons, a phenomenon associated with increased blockage at the G2-M phase of the cell cycle.

Radiation sensitivity of human hypernephroma tumor cells, ACHN, was evaluated in the presence or absence of various recombinant interferons (IFNs): alpha D (rHuIFN-alpha D), beta ser (rHuIFN-beta ser), and gamma (rHuIFN-gamma). Exponentially growing monolayers of ACHN cells were incubated with IFNs (10(3) units/ml) for 2, 6, and 24 h prior to irradiation. The effects of IFNs on the growth inhibition, radiation cell survival, and cell cycle redistribution were determined from growth curves, colony-forming efficiency, and flow cytometric analysis. rHuIFN-alpha D and rHuIFN-beta ser were associated with a modest inhibition in cell growth and the growth delay was reversible upon the removal of IFNs. However, rHuIFN-gamma exhibited the greatest inhibitory effect on both cell growth delay and rate. IFN and radiation have an additive effect on cell growth inhibition. Although IFN treatments alone (0-1000 IU/ml) did not have a significant effect on cell survival, radiation killing was increased by IFN pretreatment. The enhancing factor measured at a survival level of 0.1 for rHuIFN-alpha D, rHuIFN-beta ser, and rHuIFN-gamma was 1.21, 1.28, and 1.44, respectively. In addition, this potentiation effect was dependent on the dose of radiation and exposure time to IFN with the maximal effect observed after 24 h of treatment with IFN at 12 Gy. When the distributions of G1, S, and G2-M cells were measured 24 and 48 h after combined IFN and radiation treatment, there was a significant increase in the accumulation of cells at the G2-M phase of the cell cycle compared to either IFN or radiation treatment alone. We conclude that IFNs and radiation have an additional inhibitory effect on ACHN cell growth, that IFN can potentiate radiation cytotoxicity, and that this phenomenon is associated with an increased blockage at G2-M phase of the cell cycle.

Cell Survival↗
PubMed1995

A UV-responsive G2 checkpoint in rodent cells.

We have studied the effect of UV irradiation on the cell cycle progression of synchronized Chinese hamster ovary cells. Synchronization of cells in S or G2 phase was accomplished by the development of a novel protocol using mimosine, which blocks cell cycle progression at the G1/S boundary. After removal of mimosine, cells proceed synchronously through the S and G2 phases, allowing manipulation of cells at specific points in either phase. Synchronization of cells in G1 was achieved by release of cells after a period of serum starvation. Cells synchronized by these methods were UV irradiated at defined points in G1, S, and G2, and their subsequent progression through the cell cycle was monitored. UV irradiation of G1-synchronized cells caused a dose-dependent delay in entry into S phase. Irradiation of S-phase-synchronized cells inhibited progression through S phase and then resulted in accumulation of cells for a prolonged interval in G2. Apoptosis of a subpopulation of cells during this extended period was noted. UV irradiation of G2-synchronized cells caused a shorter G2 arrest. The arrest itself and its duration were dependent upon the timing (within G2 phase) of the irradiation and the UV dose, respectively. We have thus defined a previously undescribed (in mammalian cells) UV-responsive checkpoint in G2 phase. The implications of these findings with respect to DNA metabolism are discussed.

Animals↗
PubMed2000

Inhibition of eukaryotic DNA replication by geminin binding to Cdt1.

In all eukaryotic organisms, inappropriate firing of replication origins during the G2 phase of the cell cycle is suppressed by cyclin-dependent kinases. Multicellular eukaryotes contain a second putative inhibitor of re-replication called geminin. Geminin is believed to block binding of the mini-chromosome maintenance (MCM) complex to origins of replication, but the mechanism of this inhibition is unclear. Here we show that geminin interacts tightly with Cdt1, a recently identified replication initiation factor necessary for MCM loading. The inhibition of DNA replication by geminin that is observed in cell-free DNA replication extracts is reversed by the addition of excess Cdt1. In the normal cell cycle, Cdt1 is present only in G1 and S, whereas geminin is present in S and G2 phases of the cell cycle. Together, these results suggest that geminin inhibits inappropriate origin firing by targeting Cdt1.

Amino Acid Sequence↗
PubMed1988

Alterations of cell cycle distribution in the bone marrow of aging mice measured by flow cytometry.

The effect of aging on the cell cycle distribution in bone marrow cells was measured by flow cytometry with special reference to the lability in bone marrow physiology. Female C3H mice were examined every 3 h during a 24-h period at the age of 16, 21 and 26 months, vs 3-month-old control mice. Considerable circadian fluctuations were found in the different cell cycle phases in young mice. The rhythmicity patterns were different when comparing different months. In aging mice the variations were dampened, while consistent age-related phase shifts were not seen. The maximal 24-h mean numbers of cells in all three cell phases, but especially the S and G2 phases were reached at 21 months. The relative number of S and G2 phases were significantly reduced in 26-month-old mice, indicating an age-related shift of the proliferative capacity. The present findings are discussed in relation to age-related changes in granulopoiesis and the increase of myelotoxic effects during cancer chemotherapy in aging individuals.

Aging↗
PubMed1999

Adventitious root growth and cell-cycle induction in deepwater rice

Deepwater rice (Oryza sativa) is adapted to survive conditions of severe flooding over extended periods of time. During such periods adventitious roots develop to provide water, nutrients, and anchorage. In the present study the growth of adventitious roots was induced by treatment with ethylene but not auxin, cytokinin, or gibberellin. Root elongation was enhanced between 8 and 10 h after submergence. The population of cells in the S phase and expression of the S-phase-specific histone H3 gene increased within 4 to 6 h. Within 6 to 8 h the G2-phase population increased. Cell-cycle activation was accompanied by sequential induction of a cdc2-activating kinase homolog, R2, of two cdc2 genes, cdc2Os-1 and cdc2Os-2, and of three cyclin genes, cycA1;3, cycB2;1, and cycB2;2, but only induction of the R2 gene expression preceded the induction of the S phase, possibly contributing to cell-cycle regulation in the G1 phase. Both cdc2 genes were expressed at slightly higher levels during DNA replication. Transcripts of the A-type cyclin accumulated during the S and G2 phases, and transcripts of the B-type cyclins accumulated during the G2 phase. Cyclin expression was induced at all nodes with a similar time course, suggesting that ethylene acts systemically and that root primordia respond to ethylene at an early developmental stage.

Journal Article↗