SOMATIC-CELL EXPRESSION OF THE MOS PROTOONCOGENE IS CELL-CYCLE REGULATED - HIGHEST RNA EXPRESSION IN THE G2 PHASE

1993 ◽  
Author(s):  
LV TSUI ◽  
LS RAMAGLI ◽  
B SINGH ◽  
M NASH ◽  
RB ARLINGHAUS
Keyword(s):  
Cell Cycle ◽  
Somatic Cell ◽  
Rna Expression ◽  
G2 Phase ◽  
Cell Expression

Efficient reactivation of Xenopus erythrocyte nuclei in Xenopus egg extracts

1995 ◽  
Vol 108 (6) ◽  
pp. 2187-2196 ◽  
Author(s):  
L.J. Wangh ◽  
D. DeGrace ◽  
J.A. Sanchez ◽  
A. Gold ◽  
Y. Yeghiazarians ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Somatic Cell ◽  
Nuclear Transplantation ◽  
Optimal Time ◽  
Genome Replication ◽  
Cell Nuclei ◽  
Egg Extracts ◽  
Xenopus Egg ◽  
Xenopus Egg Extracts

Rapid genome replication is one of the hallmarks of the frog embryonic cell cycle. We report here that complete reactivation of quiescent somatic cell nuclei in Xenopus egg extracts depends on prior restructuring of the nuclear substrate and prior preparation of cytoplasmic extract with the highest capacity to initiate and sustain DNA synthesis. Nuclei from mature erythrocytes swell, replicate their DNA efficiently, and enter mitosis in frozen/thawed extracts prepared from activated Xenopus eggs, provided the nuclei are first treated with trypsin, heparin, and an extract prepared from unactivated, meiotically arrested, eggs. Optimal replicating extracts are prepared from large batches of unfertilized eggs that are synchronously activated into the cell cycle for 28 minutes (at 20 degrees C). Because the Xenopus cell cycle progresses so rapidly, extracts prepared just a few minutes before or after this time have substantially lower DNA synthetic capacities. At the optimal time and temperature, eggs have just reached the G1/S boundary of the first cell cycle. This fact was revealed by injecting and replicating an SV40 plasmid in intact unfertilized eggs as described previously. We estimate that under optimal conditions approximately 6.14 × 10(9) base pairs of DNA/per nucleus are synthesized in 30–40 minutes, a rate that rivals that observed in the zygotic nucleus. The findings reported here are one step in our long term effort to develop a new in vitro/in vivo approach to nuclear transplantation. Nuclear transplantation in amphibian embryos has been used to establish that the genomes of many types of differentiated somatic cells are pluripotent. But very few such nuclei have ever developed into advanced tadpoles or adult frogs, probably because somatic nuclei injected directly into activated eggs fail to reactivate quickly enough to avoid being damaged during first mitosis. We have already shown that unfertilized eggs can be injected prior to activation of the first cell cycle. Future experiments will reveal whether in vitro reactivated somatic cell nuclei transplanted into such eggs reliably reach advanced stages of development.

Excision and replication of extrachromosomal DNA of pea (Pisum sativum)

1983 ◽  
Vol 3 (2) ◽  
pp. 172-181
Author(s):  
J Van't Hof ◽  
C A Bjerknes ◽  
N C Delihas
Keyword(s):  
Cell Cycle ◽  
Pisum Sativum ◽  
S Phase ◽  
Velocity Sedimentation ◽  
Extrachromosomal Dna ◽  
Chromosomal Dna ◽  
Root Tips ◽  
Dividing Cells ◽  
G2 Phase ◽  
Pea Roots

Experiments with cultured pea roots were conducted to determine (i) whether extrachromosomal DNA was produced by cells in the late S phase or in the G2 phase of the cell cycle, (ii) whether the maturation of nascent DNA replicated by these cells achieved chromosomal size, (iii) when extrachromosomal DNA was removed from the chromosomal duplex, and (iv) the replication of nascent chains by the extrachromosomal DNA after its release from the chromosomal duplex. Autoradiography and cytophotometry of cells of carbohydrate-starved root tips revealed that extrachromosomal DNA was produced by a small fraction of cells accumulated in the late S phase after they had replicated about 80% of their DNA. Velocity sedimentation of nascent chromosomal DNA in alkaline sucrose gradients indicated that the DNA of cells in the late S phase failed to achieve chromosomal size. After reaching sizes of 70 X 10(6) to 140 X 10(6) daltons, some of the nascent chromosomal molecules were broken, presumably releasing extrachromosomal DNA several hours later. Sedimentation of selectively extracted extrachromosomal DNA either from dividing cells or from those in the late S phase showed that it replicated two nascent chains, one of 3 X 10(6) daltons and another of 7 X 10(6) daltons. Larger molecules of extrachromosomal DNA were detectable after cells were labeled for 24 h. These two observations were compatible with the idea that the extrachromosomal DNA was first replicated as an integral part of the chromosomal duplex, was cut from the duplex, and then, once free of the chromosome, replicated two smaller chains of 3 X 10(6) and 7 X 10(6) daltons.

scholarly journals Cell-cycle phase-dependence of drug-induced cycle progression delay.

1979 ◽  
Vol 27 (1) ◽  
pp. 470-473 ◽  
Author(s):  
W Göhde ◽  
M Meistrich ◽  
R Meyn ◽  
J Schumann ◽  
D Johnston ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Chromosomal Abnormalities ◽  
Cell Cycle Phase ◽  
Cycle Phase ◽  
Drug Induced ◽  
Phase Dependence ◽  
Cycle Progression ◽  
G2 Phase ◽  
Phase Progression ◽  
Pulse Cytophotometry

The effect of adriamycin on cell cycle phase progression of CHO cells synchronized into the various phases of the cell cycle by elutriation was investigated by high resolution pulse cytophotometry. Cells treated in all phases of the cell cycle showed delay in their subsequent progression. In addition to the wellknown block of cells in the G2-phase, a delay in passage of cells from G1 to S and a decreased rate of transit through the S-phase were observed. A broadening of the DNA distributions of the treated cells was observed after cell division indicating induction of chromosomal abnormalities.

scholarly journals Enhancement of DNA-mediated gene transfer by high-Mr carrier DNA in synchronized CV-1 cells

1985 ◽  
Vol 225 (2) ◽  
pp. 529-533 ◽  
Author(s):  
A J Strain ◽  
W A H Wallace ◽  
A H Wyllie
Keyword(s):  
Cell Cycle ◽  
Gene Transfer ◽  
Transfection Efficiency ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
S Phase ◽  
Sv40 Virus ◽  
G2 Phase ◽  
Cycle Dependent ◽  
Sv40 Dna

Synchronized CV-1 cells were transfected with SV40 (simian virus 40) DNA-calcium phosphate co-precipitates. In the presence of carrier DNA, the transfection efficiency of SV40 DNA was decreased 5-fold in S-phase cells and was increased 4-fold in preparations of mitotically enriched cells as compared with asynchronous controls. No difference was observed when carrier DNA was omitted, when cells had progressed through S-phase and into G2-phase, or when the infectivity of cells to intact SV40 virus was tested. These results highlight the importance of cell-cycle-dependent factors on DNA-mediated gene transfer.

scholarly journals Cell cycle arrest of cdc mutants and specificity of the RAD9 checkpoint.

Genetics ◽  
1993 ◽  
Vol 134 (1) ◽  
pp. 63-80 ◽  
Author(s):  
T A Weinert ◽  
L H Hartwell
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Dna Replication ◽  
Cell Cycle Control ◽  
Dna Lesions ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
A Cell ◽  
G2 Phase ◽  
Rad Mutants

Abstract In eucaryotes a cell cycle control called a checkpoint ensures that mitosis occurs only after chromosomes are completely replicated and any damage is repaired. The function of this checkpoint in budding yeast requires the RAD9 gene. Here we examine the role of the RAD9 gene in the arrest of the 12 cell division cycle (cdc) mutants, temperature-sensitive lethal mutants that arrest in specific phases of the cell cycle at a restrictive temperature. We found that in four cdc mutants the cdc rad9 cells failed to arrest after a shift to the restrictive temperature, rather they continued cell division and died rapidly, whereas the cdc RAD cells arrested and remained viable. The cell cycle and genetic phenotypes of the 12 cdc RAD mutants indicate the function of the RAD9 checkpoint is phase-specific and signal-specific. First, the four cdc RAD mutants that required RAD9 each arrested in the late S/G2 phase after a shift to the restrictive temperature when DNA replication was complete or nearly complete, and second, each leaves DNA lesions when the CDC gene product is limiting for cell division. Three of the four CDC genes are known to encode DNA replication enzymes. We found that the RAD17 gene is also essential for the function of the RAD9 checkpoint because it is required for phase-specific arrest of the same four cdc mutants. We also show that both X- or UV-irradiated cells require the RAD9 and RAD17 genes for delay in the G2 phase. Together, these results indicate that the RAD9 checkpoint is apparently activated only by DNA lesions and arrests cell division only in the late S/G2 phase.

scholarly journals Cubic Membranes Formation in Synchronized Human Hepatocellular Carcinoma Cells Reveals a Possible Role as a Structural Antioxidant Defense System in Cell Cycle Progression

2020 ◽  
Vol 8 ◽  
Author(s):  
Deqin Kong ◽  
Rui Liu ◽  
Jiangzheng Liu ◽  
Qingbiao Zhou ◽  
Jiaxin Zhang ◽  
...  
Keyword(s):  
Hepatocellular Carcinoma ◽  
Cell Cycle ◽  
Cell Cycle Progression ◽  
S Phase ◽  
Carcinoma Cells ◽  
Human Hepatocellular Carcinoma ◽  
Cycle Progression ◽  
Hepatocellular Carcinoma Cells ◽  
G2 Phase ◽  
Human Hepatocellular Carcinoma Cells

Cubic membranes (CMs) represent unique biological membrane structures with highly curved three-dimensional periodic minimal surfaces, which have been observed in a wide range of cell types and organelles under various stress conditions (e. g., starvation, virus-infection, and oxidation). However, there are few reports on the biological roles of CMs, especially their roles in cell cycle. Hence, we established a stable cell population of human hepatocellular carcinoma cells (HepG2) of 100% S phase by thymidine treatment, and determined certain parameters in G2 phase released from S phase. Then we found a close relationship between CMs formation and cell cycle, and an increase in reactive oxygen species (ROS) and mitochondrial function. After the synchronization of HepG2 cells were induced, CMs were observed through transmission electron microscope in G2 phase but not in G1, S and M phase. Moreover, the increased ATP production, mitochondrial and intracellular ROS levels were also present in G2 phase, which demonstrated a positive correlation with CMs formation by Pearson correlation analysis. This study suggests that CMs may act as an antioxidant structure in response to mitochondria-derived ROS during G2 phase and thus participate in cell cycle progression.

scholarly journals Maximal binding levels of an H1 histone gene-specific factor in S-phase correlate with maximal H1 gene transcription.

1988 ◽  
Vol 8 (10) ◽  
pp. 4576-4578 ◽  
Author(s):  
S Dalton ◽  
J R Wells
Keyword(s):  
Cell Cycle ◽  
Nucleic Acids ◽  
Gene Transcription ◽  
S Phase ◽  
Histone Gene ◽  
Specific Factor ◽  
Synchronized Cells ◽  
Phase Regulation ◽  
G2 Phase ◽  
Binding Component

Levels of trans-acting factor (H1-SF) binding to the histone H1 gene-specific motif (5'-AAACACA-3' [L. S. Coles and J. R. E. Wells, Nucleic Acids Res. 13:585-594, 1985]) increase 12-fold from G1 to S-phase in synchronized cells and decrease again in G2 phase of the cell cycle. Since the H1 element is required for S-phase expression of H1 genes (S. Dalton and J. R. E. Wells, EMBO J. 7:49-56, 1988), it is likely that the increased levels of H1-SF binding component play an important role in S-phase regulation of H1 gene transcription.

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