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.

The cell cycle and its relationship to development in Acanthamoeba castellanii

1987 ◽  
Vol 88 (5) ◽  
pp. 579-590
Author(s):  
MICHAEL STÖHR ◽  
KURT BOMMERT ◽  
INGRID SCHULZE ◽  
HELGA JANTZEN
Keyword(s):  
Cell Cycle ◽  
Stationary Phase ◽  
Nuclear Dna ◽  
Acanthamoeba Castellanii ◽  
Nuclear Dna Content ◽  
Defined Medium ◽  
G2 Phase ◽  
D Cells ◽  
High Degree ◽  
The Relationship

The cell cycle and the relationship between particular cell cycle phases and the differentiation of trophozoites into cysts were reinvestigated in Acanthamoeba castellanii using flow fluorometric measurements of nuclear DNA content and synthesis and synchronization of cells by release from the stationary phase. The investigation was performed with cultures growing in non-defined medium (ND cells) showing a high degree of encystation in response to starvation and with subcultures growing in chemically defined nutrient medium (D cells) exhibiting a very low encystation competence. In both cultures the cell cycle starts with a short S phase taking place simultaneously with cytokinesis followed by a long G2 phase. A G1 phase seems to be either absent or very short. Synchronization experiments reveal that in ND cells encystation is initiated from a particular position of late G2. The high encystation competence of stationary phase ND cells seems to be due to arrest of cells at this particular cell cycle position. The lack of encystation competence of stationary phase D cells correlates with the loss of accumulation of cells at this particular stage of the cell cycle. This change of the property of cells is related to the growth condition and not to an irreversible loss of encystation competence of D cells.

scholarly journals Distinct replication-independent and -dependent phases of histone gene expression during the Physarum cell cycle.

1987 ◽  
Vol 7 (5) ◽  
pp. 1933-1937 ◽  
Author(s):  
J J Carrino ◽  
V Kueng ◽  
R Braun ◽  
T G Laffler
Keyword(s):  
Gene Expression ◽  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
S Phase ◽  
Histone Gene ◽  
Histone Mrna ◽  
Histone Gene Expression ◽  
Tightly Coupled ◽  
G2 Phase

During the S phase of the cell cycle, histone gene expression and DNA replication are tightly coupled. In mitotically synchronous plasmodia of the myxomycete Physarum polycephalum, which has no G1 phase, histone mRNA synthesis begins in mid-G2 phase. Although histone gene transcription is activated in the absence of significant DNA synthesis, our data demonstrate that histone gene expression became tightly coupled to DNA replication once the S phase began. There was a transition from the replication-independent phase to the replication-dependent phase of histone gene expression. During the first phase, histone mRNA synthesis appears to be under direct cell cycle control; it was not coupled to DNA replication. This allowed a pool of histone mRNA to accumulate in late G2 phase, in anticipation of future demand. The second phase began at the end of mitosis, when the S phase began, and expression became homeostatically coupled to DNA replication. This homeostatic control required continuing protein synthesis, since cycloheximide uncoupled transcription from DNA synthesis. Nuclear run-on assays suggest that in P. polycephalum this coupling occurs at the level of transcription. While histone gene transcription appears to be directly switched on in mid-G2 phase and off at the end of the S phase by cell cycle regulators, only during the S phase was the level of transcription balanced with the rate of DNA synthesis.

Periodic expression of nuclear and mitochondrial DNA replication genes during the trypanosomatid cell cycle

1994 ◽  
Vol 107 (12) ◽  
pp. 3515-3520
Author(s):  
S.G. Pasion ◽  
G.W. Brown ◽  
L.M. Brown ◽  
D.S. Ray
Keyword(s):  
Cell Cycle ◽  
Mitochondrial Dna ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Cell Cycle Progression ◽  
Nuclear Dna ◽  
Protein A ◽  
Mrna Levels ◽  
Gene Encoding ◽  
Genes Encoding

In trypanosomatids, DNA replication in the nucleus and in the single mitochondrion (or kinetoplast) initiates nearly simultaneously, suggesting that the DNA synthesis (S) phases of the nucleus and the mitochondrion are coordinately regulated. To investigate the basis for the temporal link between nuclear and mitochondrial DNA synthesis phases the expression of the genes encoding DNA ligase I, the 51 and 28 kDa subunits of replication protein A, dihydrofolate reductase and the mitochondrial type II topoisomerase were analyzed during the cell cycle progression of synchronous cultures of Crithidia fasciculata. These DNA replication genes were all expressed periodically, with peak mRNA levels occurring just prior to or at the peak of DNA synthesis in the synchronized cultures. A plasmid clone (pdN-1) in which TOP2, the gene encoding the mitochondrial topoisomerase, was disrupted by the insertion of a NEO drug-resistance cassette was found to express both a truncated TOP2 mRNA and a truncated topoisomerase polypeptide. The truncated mRNA was also expressed periodically coordinate with the expression of the endogenous TOP2 mRNA indicating that cis elements necessary for periodic expression are contained within cloned sequences. The expression of both TOP2 and nuclear DNA replication genes at the G1/S boundary suggests that regulated expression of these genes may play a role in coordinating nuclear and mitochondrial S phases in trypanosomatids.

Distinct replication-independent and -dependent phases of histone gene expression during the Physarum cell cycle

1987 ◽  
Vol 7 (5) ◽  
pp. 1933-1937
Author(s):  
J J Carrino ◽  
V Kueng ◽  
R Braun ◽  
T G Laffler
Keyword(s):  
Gene Expression ◽  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
S Phase ◽  
Histone Gene ◽  
Histone Mrna ◽  
Histone Gene Expression ◽  
Tightly Coupled ◽  
G2 Phase

During the S phase of the cell cycle, histone gene expression and DNA replication are tightly coupled. In mitotically synchronous plasmodia of the myxomycete Physarum polycephalum, which has no G1 phase, histone mRNA synthesis begins in mid-G2 phase. Although histone gene transcription is activated in the absence of significant DNA synthesis, our data demonstrate that histone gene expression became tightly coupled to DNA replication once the S phase began. There was a transition from the replication-independent phase to the replication-dependent phase of histone gene expression. During the first phase, histone mRNA synthesis appears to be under direct cell cycle control; it was not coupled to DNA replication. This allowed a pool of histone mRNA to accumulate in late G2 phase, in anticipation of future demand. The second phase began at the end of mitosis, when the S phase began, and expression became homeostatically coupled to DNA replication. This homeostatic control required continuing protein synthesis, since cycloheximide uncoupled transcription from DNA synthesis. Nuclear run-on assays suggest that in P. polycephalum this coupling occurs at the level of transcription. While histone gene transcription appears to be directly switched on in mid-G2 phase and off at the end of the S phase by cell cycle regulators, only during the S phase was the level of transcription balanced with the rate of DNA synthesis.

Continuous Nucleolar DNA Synthesis in Late-Interphase Nuclei of Physarum Polycephalum after Transplantation into Postmitotic Plasmodia

1974 ◽  
Vol 15 (1) ◽  
pp. 131-143
Author(s):  
E. GUTTES
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Physarum Polycephalum ◽  
Nuclear Dna ◽  
S Phase ◽  
Interphase Nuclei ◽  
G2 Phase

In the myxomycete, Physarum polycephalum, nuclear DNA synthesis commences immediately upon completion of mitosis. While the synthesis of extranucleolar DNA is completed within a few hours, nucleolar DNA synthesis occurs during most of the S-phase and the entire G2 phase of the intermitotic period. When large (polyploid), late-interphase nuclei were allowed to bypass mitosis by transplantation into recipient plasmodia which were at early interphase and which belonged to a strain having smaller nuclei, the nucleolar DNA of the transplanted nuclei continued to be labelled (autoradiographs) after incubation of the host plasmodia with [3H]thymidine until they entered prophase along with the nuclei of the host plasmodium, approximately one intermitotic period later. This labelling was DNase-sensitive and RNase-resistant. When late-interphase nuclei were labelled with [3H]thymidine just prior to transplantation, there was no decrease of label after transplantation during the additional intermitotic period. We conclude from these experiments that there is no obligatory alternation between nucleolar DNA duplication and mitosis in Physarum polycephalum and that nucleolar DNA replication might exhibit amplification during an experimentally prolonged intermitotic period.

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 Correlation between DNA synthesis in the second, third and fourth generations of spermatogonia and the occurrence of apoptosis in both spermatogonia and spermatocytes

Reproduction ◽  
2003 ◽  
pp. 661-668 ◽  
Author(s):  
J Blanco-Rodriguez ◽  
C Martinez-Garcia ◽  
A Porras
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Functional Significance ◽  
Tunel Assay ◽  
Seminiferous Epithelium ◽  
Cell Cycle Checkpoints ◽  
Clear Correlation ◽  
Cellular Events ◽  
Dna Strand

In the seminiferous epithelium, both DNA synthesis and apoptosis occur at equivalent stages in various species, with apoptosis taking place mainly at the same stages as DNA replication in the second, third and fourth spermatogonial generations. As preservation of the cellular associations found at these stages may have some functional significance, it is important to determine whether there is a correlation between these cellular events. In this study, pairs of immunoperoxidase-stained adjacent testis sections from rats, mice, rabbits and cats in which either bromodeoxyuridine incorporated into the newly synthesized DNA strand (BrdU labelling) or DNA 3' end labelling of the apoptotic DNA fragments (TUNEL assay) were detected were compared. In addition, both events were analysed in double-labelled sections. These two methods revealed a clear correlation between the occurrence of DNA replication in the second to fourth generations of spermatogonia and most physiological apoptosis taking place in both spermatogonia and spermatocytes in the three different mammalian orders (Rodentia, Lagomorpha and Carnivora). This correlation may result from the synchronization of mitotic spermatogonial and meiotic spermatocyte cell cycle checkpoints operating at these stages.

Neurotrophic control of the cell cycle during amphibian limb regeneration

Development ◽  
1978 ◽  
Vol 48 (1) ◽  
pp. 169-175
Author(s):  
M. Maden
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Recent Work ◽  
Limb Regeneration ◽  
Trophic Factor ◽  
G1 Phase ◽  
Neurotrophic Control ◽  
G2 Phase ◽  
Number Of Cells

It is shown here that amputated and denervated limbs of larval axolotls dedifferentiate and a proportion of the cells released undergo DNA synthesis and mitosis. When the limb is denervated prior to amputation fewer cells go through the cell cycle, implying the existence of a pool of trophic factor in the limb. Recent work has demonstrated that denervated blastemal cells accumulate in the G1 phase of the cycle. These results strongly argue against the theory that the trophic factor controls the G2 phase. Rather, it is proposed that this factor regulates either the total number of cells cycling or the rate at which they cycle by varying the length of the G1 phase.

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.

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