Wave Of DNA Synthesis Research Articles

Cell cycle characteristics of human solid tumors in vivo.

ABSTRACTThe duration of the DNA synthetic phase of solid tumors in six patients was determined in vivo by local injections of tritiated thymidine into tumor nodules on the skin and serial biopsies of the lesions. Labeled mitosis curves constructed from the data obtained revealed a distinct wave of labeled mitoses but no evidence of a second wave of DNA synthesis in all six patients. The duration of S phase was 24, 22 and 24 hr in the three patients with malignant melanomas and 19, 22 and 24 hr in the three patients with breast cancer. The method is relatively simple and requires much lower doses of tritiated thymidine; reproducible data are obtainable in patients with solid tumors in a much shorter period of time than with previous experiments.

Partial synchronization of hamster embryonic cells in secondary culture

Partial synchronization of hamster embryonic cells in the secondary culture was accomplished by transfer of confluent culture into the medium containing the specific inhibitors of DNA synthesis (excess thymidine or hydroxyurea). A maximum of 60% of cells were in DNA synthesis following removal of the inhibitors, as compared to 20% for asynchronous cells. A sharp mitotic peak and the second wave of DNA synthesis were followed at the predicted time from the cell cycle.

Stimulation of DNA synthesis in cultures of mouse embryo fibroblast-like cells.

AbstractStimulation of the DNA synthesis and mitoses in stationary cultures of mouse embryo fibroblast‐like cells was induced by various agents such as ribonuclease, digitonin, fresh medium and commercial preparations of hyaluronidases. Time sequence of stimulation was similar in experiments with all these agents. Cells were activated to enter S phase from GI phase. The rise of the number of DNA‐synthesizing cells was preceded by a latent period of about 8–12 hours with the maximal number of DNA‐synthesizing cells being observed at 16–24 hours. Mitotic wave was observed after the wave of DNA synthesis. Stimulation of DNA synthesis and mitosis was not preceded by any significant decrease of an average cell density in the culture. The progeny of activated cells had no greater chance than other cells to be activated again when stimulation was repeated.It is concluded that similar proliferative reactions can be induced in stationary cultures by a variety of diverse agents. Possible role of cell surface changes in the induction of these reactions is discussed.

Macrophage-melanocyte heterokaryons. I. Preparation and properties.

High yields of mouse macrophage-melanocyte heterokaryons and macrophage-macrophage homokaryons were obtained through the virus-induced fusion of cells spread on a glass surface. After fusion there was a striking reorganization of cellular architecture by means of a colcemid-sensitive process. Heterokaryons were isolated through the use of differential trypsinization and many underwent division to form melanocyte-like hybrids. The selective uptake of dextran sulfate by macrophages served as a useful cytoplasmic marker in identifying hybrids. Many characteristic macrophage properties were altered in the heterokaryons. Within an hour of fusion macrophage nuclei became swollen, nucleoli were more prominent, and increased nuclear RNA synthesis occurred. 3 hr after fusion, a wave of DNA synthesis took place in the previously dormant macrophage nuclei. The fate of typical macrophage markers was examined in both heterokaryons and homokaryons. Macrophage homokaryons continued to exhibit active phagocytosis of sensitized erythrocytes, whereas this capacity was lost irreversibly in heterokaryons. The loss of phagocytic activity of heterokaryons occurred at an exponential rate and was accelerated by high concentrations of calf serum. Another macrophage surface marker, a divalent cation-dependent adenosine triphosphatase (ATPase), could be demonstrated histochemically on heterokaryons. Shortly after fusion, it was present in discrete regions, but it became more diffuse and disappeared within a day. Acid phosphatase-positive secondary lysosomes and retractile lipid droplets disappeared from heterokaryons but continued to accumulate in macrophage homokaryons. These observations indicate that typical macrophage properties cease to be expressed in heterokaryons, and melanocyte functions presumably predominate in heterokaryons and hybrids.

DNA replication and degradation in mammalian tissue I. Changes in DNA polymerase and nuclease during rat liver regeneration

The incorporation of [ 3H]thymidine into rat liver DNA, DNA polymerase activity, and deoxyribonuclease activity have been compared at various times following partial hepatectomy of the rat. 1. 1. DNA polymerase activity increases when [ 3H]thymidine incorporation in vivo increased and remained elevated for at least 60 h following partial hepatectomy, despite waves of DNA synthesis. Fluctuations in nuclease activity were directly opposite to the peaks of [ 3H]thymidine incorporation at different times during regeneration. It is suggested that deoxyribonuclease plays an important role in the control of DNA synthesis. 2. 2. Rat liver polymerase had a preference for native DNA primer whereas deoxyribonuclease in the same preparation acted preferentially on denatured DNA. It is suggested that the apparent difference in polymerase primer preference is due to nuclease activity associated with the pH 5.0 protein fraction.

Early nucleic acid and protein syntheses and mitoses in the primary root tips of germinating Vicia faba

1. 1. Primary roots of Vicia faba were pulse labeled during early stages of seed germination. DNA, RNA and protein syntheses were studied in homogenates and autoradiographs of 1 mm root tips. 2. 2. Selection of roots of uniform size reduced the great variation in the rates of DNA synthesis found in randomly sampled roots. 3. 3. Very low levels of DNA and RNA synthesis were observed from 15 to 20 h after the beginning of imbibition. A wave of DNA synthesis between 25 and 40 h was followed by a wave of mitoses between 40 and 50 h. 4. 4. It was shown that 96% of the cells which entered the first post-dormancy cell cycle were in G1 (i.e. before DNA synthesis). 5. 5. The curves describing RNA and DNA syntheses were parallel for the first 50 h. Incomplete imbibition was excluded as a factor limiting the onset of synthesis of both nucleic acids, since imbibition by the 1 mm tip was completed by 8 h. 6. 6. 3H-Leucine incorporation increased gradually from a very low level at 14.5 h until 20 h. Several sharp peaks of high precursor incorporation which preceded the first wave of DNA synthesis were observed. Incorporation experiments with different specific activities of 3H-leucine indicated that these bursts of high incorporation represented changes in the level of protein synthesis, instead of abrupt changes in the amino acid precursor pool only. The leucine; precursor pool decreased in size from 20 to 30 h. 7. 7. Protein synthesis between 30 and 50 h paralleled DNA synthesis. The protein synthesis inhibitor cycloheximide was used to demonstrate that meristematic cells synthesize at least some of the protein essential for DNA synthesis throughout their S period. 8. 8. The cycloheximide induced inhibition of protein synthesis could be separated in time from an indirect inhibition of DNA synthesis caused by suppression of protein synthesis essential for DNA synthesis. Cycloheximide had limited usefulness because its inhibitory effect was irreversible.

Synthesis of macromolecules in epithelial cells of the cultured amphibian lens: I. DNA and RNA

1. 1. When bullfrog lenses are introduced into a culture system, the epithelial cells undergo bursts of DNA synthesis and mitosis which reach peaks at 52 and 87 hr post-isolation, respectively. 2. 2. These events are preceded by an augmentation of RNA synthesis which begins within 10 hr of isolation and attains peaks at 36 and 72 hr. 3. 3. If the increment in RNA synthesis is blocked by treatment with 10 −1 μg/ml actinomycin D the waves of DNA synthesis and mitosis are suppressed even though uridine incorporation in “blocked” lenses is still significantly higher than it is in freshly isolated material. 4. 4. It was shown by autoradiographic means that when the actinomycin D was supplied in tritiated form it was incorporated almost exclusively into the nucleus. 5. 5. The foregoing results were discussed with reference to the mechanisms which control proliferation.

Synchronous activation of DNA synthesis in hypophysectomized rat cartilage by growth hormone.

Abstract The influence of growth hormone on cartilage cell multiplication was investigated. Costal cartilage from hypophysectomized rats incorporated much less thymidine- 3 H (THY- 3 H) than did cartilage from normal rats during 4 hours' in vitro incubation (1,481 ± 137 vs. 4,356 ± 435 c.p.m. per milligram cartilage protein). The hypophysectomized rats were injected with 200 μg bovine growth hormone daily. No increase in THY- 3 H uptake in vitro was noted in cartilage removed after 3, 6, and 12 hours. A marked increase in incorporation occurred with a peak at 48 hours when THY- 3 H was 17 to 26 times that of untreated hypophysectomized rats. The degree of stimulation of THY- 3 H uptake was markedly lower at 60 hours (8x) and 72 hours (5x). Insignificant stimulation of THY- 3 H uptake was observed when bovine growth hormone (50 μg per milliliter) was added in vitro during 24 hours' incubations of hypophysectomized rat cartilage. However, a fourfold stimulation of THY- 3 H uptake resulted when normal rat serum was added in vitro. Hypophysectomized rat serum proved slightly inhibitory. It is concluded that bovine growth hormone induces a synchronous wave of DNA synthesis which reaches a peak at 48 hours. The growth hormone does not act directly on cartilage cells but stimulates cell division indirectly by a circulating serum component which may be identical to sulfation factor.

CHROMOSOME DUPLICATION AND THE CELL CYCLE IN LENS EPITHELIUM.

PREVIOUS experiments have shown that a penetrating needle injury to the central area of rabbit lens epithelium in vivo produces a response in which a large number of cells synthesize DNA and divide1. This response begins characteristically at the site of injury and progresses farther and farther away from the wound with time. Experiments have indicated that DNA synthesis is initiated in the cells closest to the wound at about 12–14 h after injury2. Mitosis is first seen at about 24 h after injury. The rate at which the wave of DNA synthesis travels was calculated to be about 17 µ/h. The typical picture obtained at 48 h after injury shows a band of cells which are synthesizing DNA and completely encircle the wound. Another band of mitotic figures is seen encircling the wound and lying between the DNA synthesis band and the injury but close to the DNA synthesis band. Frequently, when the injuries are larger (these can be obtained by using a larger needle) a ‘second wave’ of DNA synthesis and mitosis can be seen.