The effect of ploidy on chemical mutagenesis in cultured Chinese hamster cells

The frequency of mutations induced by ethyl methane sulfonate was compared in a pseudodiploid Chinese hamster cell strain and in a tetraploid substrain derived from it. The frequency of reverse mutations from glycine auxotrophy to glycine independence was similar in the two strains, as expected for a dominant phenotype. Forward mutation to 6-thioguanine-resistance was 25 fold lower in the tetraploid as compared to the diploid strain. The resistant mutants lack hypoxanthine phosphoribosyl transferase activity and their resistant phenotype is recessive in somatic cell hybrids. A combination of chromosomal segregation and mutation could account for the frequency of these recessive drug-resistant mutants in the tetraploid population.     

Effect of ploidy on spontaneous mutation rate to asparagine non-requirement in cultured cells.

Variations in ploidy do not affect the spontaneous mutation rate to asparagine non-requirement in Jensen rat sarcoma cells cultivated in vitro.     

Long-term cultured human neural stem cells undergo spontaneous transformation to tumor-initiating cells

In this report, we describe the spontaneous malignant transformation of long-term cultured human fetal striatum neural stem cells (hsNSCs, passage 17). After subcutaneous transplantation of long-term cultured hsNSCs into immunodeficient nude mice, 2 out of 15 mice formed xenografts which expressed neuroendocrine tumor markers CgA and NSE. T1 cells, a cell line that we derived from one of the two subcutaneous xenografts, have undergone continuous expansion in vitro. These T1 cells showed stem cell-like features and expressed neural stem cell markers nestin and CD133. The T1 cells were involved in abnormal karyotype, genomic instability and fast proliferation. Importantly, after long-term in vitro culture, the T1 cells did not result in subcutaneous xenografts, but induced intracranial tumor formation, indicating that they adjusted themselves to the intracranial microenvironment. We further found that the T1 cells exhibited an overexpressed level of EGFR, and the CD133 positive T1 cells showed a truncation mutation in the exons 2-7 of the EGFR (EGFRvIII) gene. These results suggest that continuous expansion of neural stem cells in culture may lead to malignant spontaneous transformation. This phenomenon may be functionally related to EGFR by EGFRvIII gene mutation.     

Commitment to ploidy conversion of 3Y1 cells during metaphase arrest by colcemid

Diploid rat 3Y1 fibroblasts proliferate to a saturation density, where they are arrested with a 2N DNA content. After treatment to induce ploidy conversion, the conversion rate can be estimated by determining the fraction of cells with a 4N DNA content in the confluent culture using flow cytometry. Using this method it was found that during mitotic inhibition with colcemid, 3Y1 cells were converted to tetraploids with a high efficiency (above 80%); the optimum colcemid concentration and exposure period were 40 ng/ml and 8 hr, respectively. When metaphase cells were reseeded with 40 ng/ml of colcemid, they delayed anchorage to a dish; 6 hr was required for complete adhesion (in the absence of colcemid only 1 hr was required). When reseeded metaphase cells were exposed to 40 ng/ml of colcemid for 5 hr followed by its removal, a greater fraction of the cells anchored to the substratum were converted to tetraploids, whereas most of the floating cells were not. A greater fraction of the anchored cells had formed nuclei, whereas most of the floating cells preserved condensed metaphase chromosomes. These results indicate that the cells which have formed nuclear structure without chromosome separation during mitotic inhibition are irreversibly committed to ploidy conversion, with restoration of anchorage.     

Inhibition of transport systems in cultured rat hepatoma cells by colcemid and ethanol

The transport of uridine, hypoxanthine, and choline in cultures of Novikoff rat hepatoma cells is competitively inhibited by colcemid with apparent K_i values of 135, 60, and 250 μM respectively, whereas the transport of 2-deoxy-D-glucose is not affected. Ethanol at high concentrations inhibits the transport of all four substrates in an apparent competitive manner.     

The effect of Solcoseryl on in-vitro cultured cells

Explants of peripherical nervous system (PNS), skin and ventriculus cordis from chick embryo were cultivated in Maximow chambers and the effect of Solcoseryl, Fa. Solco Basel AG, on some morphological parameters was tested. 1. The growth of tissue cultures is influenced by Solcoseryl in relation to concentration and time of application. The index of area in cultures of PNS and cor increased within the first days. By long time application up to 6 days in vitro the index of area decreased and the index was the same than in controls. Explants of skin showed no essential stimulation of growth. 2. The number of cells per unit of culture in the outgrowth of PNS, cor and skin was different influenced. The density of cells in cultures of PNS and skin decreased (signif. difference). In explants of heart we could not observe a difference between the inside and outside of the outgrowth. An influence of Solcoseryl on the degree of migration is discussed. 3. The area of cell nuclei from heartcells was observed. The area decreased under the influence of Solcoseryl. The difference is significant. 4. The mitotic index of heart cells increased by application of Solcoseryl within the first 2 and 3 days in vitro. 5. The number of nucleoli per nucleus of heart cells under experimental conditions increased significant. It is discussed, Solcoseryl influenced in vitro metabolic processes in suitable systems; stimulation of cell proliferation and migration and rns-synthesis was observed within the first days of cultivation. In-vitro-systems are important objects and they are suitable for tests of pharmaca in vitro.     

The effect of cytokines on the ploidy of megakaryocytes

The effects of recombinant cytokines on the ploidy of human megakaryocytes derived from megakaryocyte progenitors were studied using serum-free agar cultures. Nonadherent and T cell-depleted marrow cells were cultured for 14 days. Megakaryocyte colonies were identified in situ by the alkaline phosphatase anti-alkaline phosphatase technique, using monoclonal antibody against platelet IIb/IIIa. The ploidy of individual megakaryocytes in colonies was determined by microfluorometry with DAPI (4',6-diamidino-2-phenylindole) staining. Recombinant human interleukin 3 (rhIL-3) and recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) supported megakaryocyte colony formation in a dose-dependent manner. However, both rhIL-3 and rhGM-CSF had no definite ability to increase the ploidy values. Recombinant human erythropoietin (rhEpo) or recombinant human macrophage colony-stimulating factor (rhM-CSF) by itself did not stimulate the growth of megakaryocyte progenitors. rhEpo or rhM-CSF, however, stimulated increases in the number, size and ploidy values of megakaryocyte colonies in the presence of rhIL-3 or rhGM-CSF. Recombinant human interleukin 6 (rhIL-6) showed no capacity to generate or enhance megakaryocyte colony formation when added to the culture alone or in combination with rhIL-3. rhIL-6, however, increased the ploidy values in colonies when added with rhIL-3. These results show that rhEpo, rhM-CSF and rhIL-6 affect endomitosis and that two factors are required for megakaryocyte development.     

Presence of an SAR-like sequence in junction regions between an introduced transgene and genomic DNA of cultured tobacco cells: its effect on transformation frequency

A 12.5-kb DNA fragment with junction regions between the transgene and genomic DNA was cloned from a transgenic tobacco cell line obtained by microprojectile bombardment of plasmid pCaMVNEO. Nucleotide sequence analysis of the fragment (DDBJ accession no. D84238) showed that it carried a 7.7-kb core sequence (concatemer of a complete pCaMVNEO and a partial pCaMVNEO) and two identical 1.3-kb junction sequences that flanked both the 5' and 3' ends of the core sequence and had inverted orientations. These sequences had topoisomerase II (Topo II) cleavage sites and adenine and thimine-rich sequences known to be specific to nuclear scaffold-attachment regions (SARs). An in vitro binding assay showed that a 507-bp fragment (designated TJ1) from the 1.3-kb sequence had the ability to bind to nuclear scaffold preparations of cultured tobacco cells, confirmation that the 1.3-kb sequence is an SAR. Insertion of TJ1 at the 5' and 3' sides of the expression cassette for the npt II gene increased transformant yields 5- to 10-fold and the NPT II enzyme activity per copy of the gene 5-fold. TJ1 enhances the integration or expression of the transgene, or both. Clearly, TJ1 is very useful for producing transgenic plants. This is the first report on an SAR-like sequence that is located in the transgene locus and enhances transformation efficiency in eukaryotic cells. The possible role of TJ1-SAR in the molecular evolution of plant genome is discussed.     

The effect of fibrin on cultured vascular endothelial cells

The normal cobblestone monolayer architecture of cultured vascular endothelium becomes rapidly disorganized after contact of the cell layer with a fibrin clot. The cells of a confluent endothelial monolayer separate into individual migratory cells in 4–6 hr after contact with fibrin. The effect is reversible in that removal of the fibrin clot results in resumption of the normal morphology within about 2 hr. No other cell type tested exhibits the same change in organization when exposed to fibrin. A similar morphological change in endothelium does occur after the cell layer is overlaid with a collagen fibril gel but a gel of methylcellulose has no effect. It is proposed that the change in behavior of endothelial cells in response to contact with fibrin may represent a cellular component of fibrinolysis. The implications of this finding for the pathophysiology of disease states involving intravascular fibrin deposition are discussed.     

High efficiency transformation of cultured tobacco cells

Tobacco calli were transformed at levels up to 50% by cocultivation of tobacco cultured cells with Agrobacterium tumefaciens harboring the binary transfer-DNA vector, pGA472, containing a kanamycin resistance marker. Transformation frequency was dependent on the physiological state of the tobacco cells, the nature of Agrobacterium strain and, less so, on the expression of the vir genes of the tumor-inducing plasmid. Maximum transformation frequency was obtained with exponentially growing plant cells, suggesting that rapid growth of plant cells is an essental factor for efficient transformation of higher plants.     

The effects of transformation and ZnT-1 silencing on zinc homeostasis in cultured cells

We have previously demonstrated that reducing the availability of zinc with the extracellular chelator diethylenetriaminepentaacetic acid (DTPA) promotes efflux of (65)Zn from rat primary hepatocytes and pituitary cells, but increases retention of label in rat hepatoma (H4IIE) and anterior pituitary tumor (GH3) cell lines. To further understand this differential response between primary cells and the corresponding cancer cell lines, we investigated the effects of immortalizing primary cells on their zinc homeostasis. Rat primary hepatocytes were electroporated with the SV40 large T-antigen-coding plasmid pSV3-neo and selected for neomycin resistance. This resulted in cell division of the normally quiescent hepatocytes. When these cells were prelabeled with (65)Zn, DTPA decreased efflux of (65)Zn, similarly to hepatoma cells and differently from primary hepatocytes. This homeostatic change may be required to account for the greater zinc requirements of dividing cells and be mediated by alterations in the activity of zinc transporter ZnT-1, which is responsible for zinc efflux. To further understand the mechanism of DTPA-induced zinc retention, we down-regulated the expression of ZnT-1 in rat hepatoma cells using vector-based short hairpin RNA interference. Expression of ZnT-1 protein was reduced to approximately 50%. Down-regulation of ZnT-1 resulted in greater retention of (65)Zn in control cells. However, DTPA increased rather than decreased efflux of label from knockdown cells, suggesting that functional ZnT-1 is required for the decreased efflux in response to DTPA. We conclude that ZnT-1 expression is crucial for maintaining zinc homeostasis, in particular, for the enhanced retention of zinc in transformed cells when subjected to zinc deprivation.     

Centrioles and microtubules in interphase cells exposed to colcemid. The concentration- and time-dependent effect of the action of the poison

Under the action of colcemid on SPEV cells the network of cytoplasmic microtubules disappears within less than 1 hour; microtubules attached to pericentriolar satellites are retained for 4 hours. The disassembly time of these microtubules does not depend on colcemide concentration. It is therefore assumed that most of the microtubules are not attached to the centrioles, but have two free ends, thus confirming a hypothesis that they are conveyer-assembled. With colcemid concentration equal to 0.5 mcg/ml, the following dynamics of events is observed for the cell centre: after the microtubules attached to the satellites had disappeared, clusters of electron dense material appear around the centrioles (6 hour incubation), then short microtubules occur among clusters (8 hour incubation) to be subsequently retained (up to 40 hour incubation).     

The antimitotic effect of the neem terpenoid azadirachtin on cultured insect cells

When cultured insect cells (Sf9) were grown in the presence of 5 x 10(-6) M azadirachtin, there was a rapid increase in the mitotic index, with the appearance of many aberrant mitotic figures. Flow cytometry established that cells accumulated in the G2/M phase of the cell cycle, and that the effect was concentration-dependent. At 10(-8) M a period of 20 h was necessary to raise the proportion in G2/M to 42% above the control values, but at 5 x 10(-6) M more than 90% of the cells were in this phase. Azadirachtin had the same effect on C6/36 mosquito cells, but failed to affect L929 murine fibroblast cells even at a concentration of 10(-4) M over 72 h. Experiments with colchcine and taxol showed similarities of action between azadirachtin and colchicine, and azadirachtin was apparently able to displace colchicine-fluorescein from binding-sites in living insect cells. Another similarity between azdirachtin and colchicine was that both phytochemicals prevented the polymerisatrion in vitro of mammalian tubulin, although the azadirachtin was much less effective.     

Increased frequency of spontaneous neoplastic transformation in progeny of bystander cells from cultures exposed to densely ionizing radiation

An increased risk of carcinogenesis caused by exposure to space radiation during prolonged space travel is a limiting factor for human space exploration. Typically, astronauts are exposed to low fluences of ionizing particles that target only a few cells in a tissue at any one time. The propagation of stressful effects from irradiated to neighboring bystander cells and their transmission to progeny cells would be of importance in estimates of the health risks of exposure to space radiation. With relevance to the risk of carcinogenesis, we investigated, in model C3H 10T½ mouse embryo fibroblasts (MEFs), modulation of the spontaneous frequency of neoplastic transformation in the progeny of bystander MEFs that had been in co-culture 10 population doublings earlier with MEFs exposed to moderate doses of densely ionizing iron ions (1 GeV/nucleon) or sparsely ionizing protons (1 GeV). An increase (P<0.05) in neoplastic transformation frequency, likely mediated by intercellular communication through gap junctions, was observed in the progeny of bystander cells that had been in co-culture with cells irradiated with iron ions, but not with protons.     

Computational mechanical model studies on the spontaneous emergent morphogenesis of the cultured endothelial cells

To address questions concerning why and how the morphology of endothelial cells (ECs) forms under shear stress loading, a computational fluid dynamics (CFD) three-dimensional (3D) model of ECs simulating cell shape was designed. A full 3D non-linear CFD simulation was conducted to estimate the wall shear stress (WSS) distribution. The model cell was capable of random rotation, deformation, migration, and proliferation. Flow was computed after each update of the cell shape with infinitesimal configuration changes. After a finite interval of the flow computation, only the infinitesimal configuration changes that reduced the WSS were allowed to accumulate. As a result of the very long free-run computation experiment, starting with a sub-confluent pattern of cells, the model cells became confluent and were elongated and aligned, with a shape index (SI) very close to that reported for cells in vivo. The average WSS converged to the lowest value at the same time.     

The effect of environmental pH on collagen synthesis by cultured cells

The synthesis of collagen by cells in culture is markedly affected by environmental pH. In human cells the optimum pH is above pH 7.6, while a mouse fibroblast, L 929, demonstrated a more acid pH optimum. These optima coincide with those for general protein synthesis and growth. The pH optima for some specific steps in collagen synthesis and assembly have also been examined.