The Inifiation, Maintenance and Termination DNA Synthesis: A Study of Nuclear DNA Replication Using Amoeba Proteus As a Cell Model

1971 ◽  
Vol 9 (1) ◽  
pp. 1-21
Author(s):  
M. J. ORD
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Nuclear Dna ◽  
Thymidine Incorporation ◽  
Cell Model ◽  
Amoeba Proteus ◽  
Early Prophase ◽  
Precursor Pool ◽  
Endogenous Precursor ◽  
The Individual

By means of the nuclear transfer technique for amoeba, combinations of nuclei and cytoplasma from all parts of the cell cycle were available for examining the individual roles of the nucleus and cytoplasm in nuclear DNA replication. Neither S-phase nor division sphere cytoplasm proved capable of initiating a new round of nuclear DNA synthesis in the G2 nucleus. There was some indication that G2 nuclei which were transferred into early prophase cells, i.e. before the formation of a regular division sphere, did incorporate more [3H]thymidine than control G2 nuclei. Positive proof of the induction of DNA synthesis in ‘immature’ nuclei was observed in only two cases. When young G2 nuclei were transplanted into late G2 amoebae, the addition of the donor nucleus generally resulted in the older nucleus being held in a late G2 phase until the younger nucleus passed through its G2. Division of 90% of heterophasic homokaryons was synchronous, with a subsequent synchrony of DNA synthesis. A study of variance in [3H]thymidine incorporation by S nuclei sharing the same cytoplasm - using binucleate, trinucleate and multinucleate homokaryons - showed that nuclei through the peak-S period synthesized DNA at approximately similar rates. The large differences in [3H]thymidine incorporation by nuclei of amoebae of equal age appear due to differences in endogenous precursor pools. These would vary both with differences in food intake and with the draining of remote precursor pools for simultaneous cellular activities, particularly RNA synthesis. When sharing the same cytoplasm nuclei in peak S incorporated similar amounts of [3H]thymidine. Though cytoplasm did not influence the progress of DNA replication by a nucleus, it did influence the use of exogenous [3H]thymidine by the cell, and in so doing caused much of the variation observed in the labelling of nuclei during S. Nuclei sharing the same cytoplasm, and so subject to the same precursor pool changes, incorporated similar amounts of exogenous thymidine. Once DNA synthesis had been initiated it continued to completion regardless of the cytoplasm which surrounded it. Thus neither the maintenance nor termination of DNA synthesis required a special cytoplasmic state.

Timing of nucleolar DNA replication in Amoeba proteus

1976 ◽  
Vol 22 (3) ◽  
pp. 521-530
Author(s):  
I. Minassian ◽  
L.G. Bell
Keyword(s):  
Electron Microscope ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Central Region ◽  
Thymidine Incorporation ◽  
Tritiated Thymidine ◽  
Amoeba Proteus ◽  
Electron Microscope Autoradiography ◽  
Microscope Autoradiography ◽  
G2 Phase

Light- and electron-microscope autoradiography have been used to follow the incorporation of [3H]thymidine at different stages during the interphase of synchronously growing populations of Amoeba proteus. Two main patterns were found for tritiated thymidine incorporation, i.e. DNA synthesis. The major incorporation was in the central region of the nucleus, but a lesser degree of incorporation occurred in the nucleolar region. The bulk of this nucleolar DNA was found to be late replicating, i.e. it replicated during the G2 phase.

scholarly journals LIMITED DNA SYNTHESIS IN THE ABSENCE OF PROTEIN SYNTHESIS IN PHYSARUM POLYCEPHALUM

1966 ◽  
Vol 31 (3) ◽  
pp. 577-583 ◽  
Author(s):  
J. E. Cummins ◽  
H. P. Rusch
Keyword(s):  
Protein Synthesis ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Physarum Polycephalum ◽  
Nuclear Dna ◽  
S Phase ◽  
Early Prophase ◽  
Late Prophase ◽  
Removal Experiments ◽  
Inhibitor Of Protein Synthesis

Actidione (cycloheximide), an antibiotic inhibitor of protein synthesis, blocked the incorporation of leucine and lysine during the S phase of Physarum polycephalum. Actidione added during the early prophase period in which mitosis is blocked totally inhibited the initiation of DNA synthesis. Actidione treatment in late prophase, which permitted mitosis in the absence of protein synthesis, permitted initiation of a round of DNA replication making up between 20 and 30% of the unreplicated nuclear DNA. Actidione treatment during the S phase permitted a round of replication similar to the effect at the beginning of S. The DNA synthesized in the presence of actidione was replicated semiconservatively and was stable through at least the mitosis following antibiotic removal. Experiments in which fluorodeoxyuridine inhibition was followed by thymidine reversal in the presence of actidione suggest that the early rounds of DNA replication must be completed before later rounds are initiated.

The effect of aerated hydration on DNA synthesis in embryos of Brassica oleracea L.

1993 ◽  
Vol 3 (3) ◽  
pp. 195-199 ◽  
Author(s):  
J. M. Thornton ◽  
A. R. S. Collins ◽  
A. A. Powell
Keyword(s):  
Dna Damage ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Brassica Oleracea ◽  
Thymidine Incorporation ◽  
Recovery Process ◽  
Time Difference ◽  
Brussels Sprouts ◽  
Brassica Oleracea L

AbstractAgeing causes a delay in the onset of DNA replication in seeds. Aerated hydration for 8 h, a treatment to invigorate seeds, resulted in a reduction of about 12 h in the time difference in the onset of DNA synthesis between unaged and aged embryos of brassica seed. This effect is consistent with a recovery process occurring during aerated hydration of the seed involving the repair of accumulated DNA damage. The occurrence of hydroxyurea-resistant 3H-thymidine incorporation in aged Brussels sprouts embryos during the period 16–32 h from the start of hydration supports this interpretation.

scholarly journals Aphidicolin does not inhibit DNA repair synthesis in ultraviolet-irradiated HeLa cells. A radioautographic study

1981 ◽  
Vol 199 (2) ◽  
pp. 453-455 ◽  
Author(s):  
N Hardt ◽  
G Pedrali-Noy ◽  
F Focher ◽  
S Spadari
Keyword(s):  
Dna Repair ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Dna Polymerase ◽  
Hela Cells ◽  
Nuclear Dna ◽  
Detectable Effect ◽  
Repair Synthesis ◽  
Dna Polymerase Alpha ◽  
Dna Repair Synthesis

A radioautographic examination of nuclear DNA synthesis in unirradiated and u.v.-irradiated HeLa cells, in the presence and in the absence of aphidicolin, showed that aphidicolin inhibits nuclear DNA replication and has no detectable effect on DNA repair synthesis. Although the results establish that in u.v.-irradiated HeLa cells most of the DNA repair synthesis is not due to DNA polymerase alpha, they do not preclude a significant role for this enzyme in DNA repair processes.

scholarly journals MACROMOLECULAR EVENTS LEADING TO CELL DIVISION IN TETRAHYMENA PYRIFORMIS AFTER REMOVAL AND REPLACEMENT OF REQUIRED PYRIMIDINES

1965 ◽  
Vol 25 (2) ◽  
pp. 9-19 ◽  
Author(s):  
Ivan L. Cameron
Keyword(s):  
Cell Division ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Nuclear Dna ◽  
Early Period ◽  
Tetrahymena Pyriformis ◽  
Cell Number ◽  
Cellular Protein ◽  
Cellular Content ◽  
Endogenous Protein

Tetrahymena pyriformis were brought to a non-growing state by removal of pyrimidines from their growth medium. During pyrimidine deprivation cell number increased 3- to 4 fold, and this increase was accompanied by one or more complete cycles of macronuclear DNA replication. Autoradiographic studies show that endogenous protein and RNA were turning over throughout starvation and that RNA breakdown products were used to support the DNA synthesis that occurred during the early period of starvation. However, after 72 hours of starvation all DNA synthesis and cell division had ceased. Feulgen microspectrophotometry shows the macronuclei of these cells to have been stopped at a point prior to DNA replication (G1 stage). After pyrimidine replacement the incorporation of H3-uridine, H3-adenosine, and H3-leucine was measured by the autoradiographic grain counting method. The results indicate that RNA synthesis began to increase almost immediately, but that there was a lag of almost an hour before an increase in protein synthesis. In agreement with the autoradiographic data, chemical data also show that cellular content of RNA began to increase shortly after pyrimidine replacement but that cellular protein content did not increase until about one hour later. Pulse labeling of the cells with H3-thymidine at intervals after pyrimidine replacement shows that labeled macronuclei first began to appear at 150 minutes; that 98 per cent of the macronuclei were in DNA synthesis at 240 to 270 minutes; and that the percentage then began to decrease from 300 to 390 minutes, at which time only 25 per cent of the macronuclei were labeled. Cellular content of DNA did not increase for at least 135 minutes after pyrimidine replacement; however, just before the first cells divided (360 minutes) the DNA content had doubled. After pyrimidine replacement the cells first began to divide at 360 minutes, and 50 per cent had divided at 420 minutes; however, all cells had not divided until 573 minutes. This technique of chemical synchronization of cells in mass cultures makes feasible detailed biochemical analysis of events leading to nuclear DNA replication and cell division.

Benzyladenine-stimulation of nuclear DNA synthesis and cell division in germinating maize

1991 ◽  
Vol 1 (2) ◽  
pp. 113-117 ◽  
Author(s):  
J. Reyes ◽  
L. F. Jiménez-García ◽  
M. A. Gonzalez ◽  
J. M. Vázquez-Ramos
Keyword(s):  
Cell Division ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Mitotic Index ◽  
Nuclear Dna ◽  
Fold Increase ◽  
Mechanisms Of Action ◽  
Dna Metabolism ◽  
Stimulation Of

AbstractWe have studied by means of cytology and autoradiography the effect of benzyladenine (BA, a synthetic cytokinin) on DNA metabolism during early maize germination.The data indicate that BA stimulates nuclear DNA replication. The doubling of the amount of nuclear DNA in BA-treated axes occurs earlier than in nontreated axes, and there is a three-fold increase in the mitotic index at 24 h of germination. These results provide further corroboration for the suggestion that the stimulation of DNA synthesis observed relates to a nuclear replicative type of synthesis. Possible mechanisms of action of BA are discussed.

Mitochondrial DNA synthesis in mouse L cells temperature sensitive in nuclear DNA replication

1977 ◽  
Vol 55 (5) ◽  
pp. 543-547 ◽  
Author(s):  
Rose Sheinin ◽  
Pamela Darragh ◽  
Margaret Dubsky
Keyword(s):  
Mitochondrial Dna ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Nuclear Dna ◽  
Temperature Sensitive ◽  
Chromosomal Dna ◽  
Mt Dna ◽  
L Cells ◽  
Mitochondrial Dna Synthesis

Temperature-sensitive (ts) A1S9 mouse L cells continue to synthesize double-stranded covalently closed mitochondrial (mt) DNA at a temperature (38.5 °C) which is nonpermissive for chromosomal DNA replication. The amount of mt DNA made appears to be quantitatively linked to nuclear DNA synthesis. Nuclear DNA replication proceeds normally for 6–8 h after the cells are shifted to 38.5 °C, and then declines to reach a minimum at 20–24 h. The level of mt DNA synthesis remains high during this period and decreases once the ts lesion has been established.

scholarly journals Relationship between the timing of DNA replication and the developmental competence in Acanthamoeba castellanii

1988 ◽  
Vol 91 (3) ◽  
pp. 389-399
Author(s):  
H. Jantzen ◽  
I. Schulze ◽  
M. Stohr
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Nuclear Dna ◽  
Defined Medium ◽  
Reciprocal Relationship ◽  
Developmental Competence ◽  
Replication Phase ◽  
G2 Phase ◽  
D Cells

In Acanthamoeba, two different cell types are known. Trophozoites are generated in the mitotic division cycle, whereas cells committed at late G2 phase of the cell cycle develop into cysts in response to starvation. In this paper we study the role of timing of DNA replication in regulating development. The investigation was performed with cultures growing in a non-defined medium (ND cells) that show a high encystation competence and with cultures that have been growing in a chemically defined medium (D cells) for several years and show a low encystation competence. Bivariate DNA/BrdUrd distributions show that ND cells progress through a cycle in which the short replication phase occurs immediately and exclusively after prior completion of mitosis. These cells arrest at late G2 phase of the cell cycle during the stationary stage. In D cells, DNA replication and mitosis seem to be uncoupled, since replication takes place before as well as after mitosis. These cells arrest within their replication phase during the stationary stage. These findings indicate that D cells do not progress into late G2 phase of the cell cycle and hence do not have the competence for commitment. The alternate timing of DNA replication and the low encystation competence of D cells can be reversed by cultivation of these cells in ND medium. Synchronization experiments reveal that late G2 phase ND cells exhibit a low capacity for BrdUrd incorporation and growth after transfer into D medium, whereas ND cells of earlier phases of the cell cycle show premitotic incorporation of BrdUrd into nuclear DNA and growth. These findings suggest on the one hand that premitotic DNA synthesis is a prerequisite for growth of cells in D medium, and that there is a dependence of the induction of premitotic DNA synthesis on the cell cycle, and on the other hand that a reciprocal relationship exists between the capacity of premitotic DNA synthesis and commitment to differentiation.

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