Flow cytometry and cell proliferation kinetics

Potassium bisperoxo (1,10-phenanthroline) oxovanadate suppresses proliferation of hippocampal neuronal cell lines by increasing DNA methyltransferases

Bisperoxo (1,10-phenanthroline) oxovanadate (BpV) can reportedly block the cell cycle. The present study examined whether BpV alters gene expression by affecting DNA methyltransferases (DNMTs), which would impact the cell cycle. Immortalized mouse hippocampal neuronal precursor cells (HT22) were treated with 0.3 or 3 μM BpV. Proliferation, morphology, and viability of HT22 cells were detected with an IncuCyte real-time video imaging system or inverted microscope and 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2H-tetrazolium, respectively. mRNA and protein expression of DNMTs and p21 in HT22 cells was detected by real-time polymerase chain reaction and immunoblotting, respectively. In addition, DNMT activity was measured with an enzyme-linked immunosorbent assay. Effects of BpV on the cell cycle were analyzed using flow cytometry. Results demonstrated that treatment with 0.3 μM BpV did not affect cell proliferation, morphology, or viability; however, treatment with 3 μM BpV decreased cell viability, increased expression of both DNMT3B mRNA and protein, and inhibited the proliferation of HT22 cells; and 3 μM BpV also blocked the cell cycle and increased expression of the regulatory factor p21 by increasing DNMT expression in mouse hippocampal neurons.

Balance of cell proliferation and death among dynamic populations: a mathematical model

Developmental changes in cell numbers represent the dynamic balance between cell proliferation and death. One obstacle to assessing this balance is an inability to quantify the total amount of cell death, i.e., with a positive indicator such as terminal dUTP nick end labeling (TUNEL) or caspase activity. A novel mathematical model is described wherein data on daily cell growth (the change in cell number) and cell cycle kinetics can be used to determine the total amount of cell death. Two sets of data from previously published studies were tested in this model; primary cultured cortical neurons and B104 neuroblastoma cells. These two preparations have contrasting features: neuronal cultures are heterogeneous and have relatively few cells that are actively cycling (i.e., the growth fraction for these cells is low), whereas B104 cells are relatively homogeneous cultures in which the growth fraction is high. In primary cortical cultures, there was a balance in cell production and death. Treatment with a potent anti-mitogen, ethanol (400 mg/dl), affected this balance principally by reducing cell production, although the rate of cell death was also increased. In untreated B104 cells, there was eight-fold more cell production than cell death. Growth factors such as platelet-derived growth factor BB doubled cell production. Ethanol reduced cell production by >60%, and it eliminated growth factor-mediated cell production. All of these changes occurred in the absence of an effect on the amount of cell death. Thus, the model is ideal for predicting the effects of an epigenetic factor (e.g., a growth factor, toxin, or pharmacological agent) on cell development and can be useful in determining the consequences of a genetic manipulation as well.

Loosening of cell cycle controls of human lymphocytes under the action of tumour promoter TPA

The effect of tumour promoter TPA (12-O-tetradecanoylphorbol-13-acetate) on the cell cycle of human peripheral blood lymphocytes stimulated by phytohaemagglutinin (PHA) in vitro was studied and it was found that TPA caused cells to accumulate in all the cell cycle phases. This accumulation took place preferentially at later culture passages, when lymphocytes stimulated by PHA alone stopped mainly in G0/G1 phases. Other effects of TPA were cell induction to enter higher DNA ploidy and to survive and even synthesize DNA under colchicine block of mitosis or under cytochalasin block of cytokinesis. In addition, in experiments in which a transitory block through the G1 phase of cell cycle was applied with use of aminopterin, we could show that a fraction of TPA-treated cells still entered the active phase of DNA synthesis. These findings suggest that TPA causes cell cycle controls to become loose, thereby enhancing adaptability of human lymphocytes to various hindrances in the course of cell cycle and eventually causing them to acquire characteristics known to be common for tumour cells.

X-ray-induced G2 arrest in ataxia telangiectasia lymphoblastoid cells

Sensitivity to X-ray-induced G2 arrest was compared between ataxia telangiectasia (AT) lymphoblastoid cells and normal human cells. Flow cytometrical analysis of cells following X-ray irradiation revealed that the fraction of cells with 4n DNA content was greater in AT cells than in normal cells as previously reported by other investigators. However, the other parameters for cell-cycle progression kinetics including mitotic indices, cumulative mitotic indices and cumulative labelled mitotic indices indicated that X-ray-induced G2 arrest as a function of dose in AT cells was indistinguishable from that in normal cells. Moreover, no significant difference in cell viability was noted between AT and normal cells until 48 h following X-irradiation up to 2.6 Gy, although X-irradiated AT cells, compared to normal cells, showed a significantly decreased survival in terms of cell multiplication in growth medium and colony formation in soft agar. These data collectively suggest that the greater accumulation of AT cells with 4n DNA content in flow cytometry cannot be attributed to more stringent irreversible blockage of cell-cycle progression at the G2 phase and eventual cell death there. The possible reasons for this greater accumulation are discussed.

Computerized extraction of the time dimension in histopathological sections

Most tissues in the organism renew their cells continuously. A renewing tissue consists of a progenitor compartment P and a functional compartment Q. Cells are first formed in P and only thcn enter Q. Such an arrangement is known as a two-compartment cell renewal system. The cells advance along a trajectory which is called tissue radius. The P compartment occupies the inner radius portion, while the Q compartment covers its outer part. Cell displacement on the radius depends solely on cell production by P cells. Following each mitosis one of the daughter cells replaces its parent, while the other is placed more distally. Concomitantly all distal cells advance by one position. A cell thus starts its existence at radius origin, and when reaching the periphery, it is eliminated. This motion is part of a stream including all tissue cells. Since cells advance along the radius in a single outward direction, they are ordered by their ages: the further a cell from radius origin, the older it is. Age of a cell is thus proportional to its distance from origin, and may be derived by measuring distance. The radius also summarizes the history of the entire system. Generally a cell at location J + 1 represents the future state of a cell at locationj, and its proximal neighbor at location j - 1 represents its past state. Thus, to extract the time dimension of a tissue, it has to be sampled along its radius. This approach is implemented in the software of our tissue analyzer, which sampled Feulgen-stained hepatocytes and determined their optical densities. The optical density of the hepatocyte increases with its age. Since it is generally accepted that the Feulgen stain binds to the DNA stoichiometrically, our experiments indicate that hepatocyte DNA content increases with its age.

Methylisobutylxanthine, a potent inhibitor of cAMP phosphodiesterase, enhances the sensitivity of Chinese hamster ovary cells to mitomycin C

The effect of 1-methyl-3-isobutylxanthine (MIX) on the sensitivity of CHO cells to mitomycin C (MC) was examined. Treatment of cells with MIX before MC-exposure greatly enhanced the cellular sensitivity to MC, with no effect on plating efficiency. Treatment with MIX after MC-exposure had only a slight effect. The sensitivity to MC was enhanced, biphasically, with increases in the period of pretreatment with MIX. The sensitivity of cells to MC fluctuated through the cell cycle, in that they were most sensitive to MC in G1 and resistant in the G2/M phase. Flow cytometric studies revealed a partial accumulation of cells in G1 (12% increase) at 16 h after MIX treatment. This means that the enhanced sensitivity with MIX pretreatment may partly depend on the accumulation of the cells in G1 and which are sensitive to MC. However, other cellular processes may also be involved, since the accumulation in G1 cannot explain all of the sensitization.

A modified harlequin stain for cell kinetics

Lymphocytes cultured with 4 X 10(-4) M bromodeoxyuridine (BrdU) and stained by the harlequin procedure show wide variations in the colour and texture of their interphase nuclei. We demonstrate that we are able, by inspection, to identify four sets of nuclei: small dark nuclei (D) in cells that have not transformed in response to mitogenic stimulation; red nuclei (R) in transformed cells that have not synthesized DNA in culture; speckled nuclei (S)--red speckles on a bluish background--in cells that are synthesizing DNA for the first time in culture; blue nuclei (B) in cells that have completed one or more cycles of DNA synthesis. By using this modified harlequin stain to score the fraction of proliferating cells, and using the modified or conventional harlequin stain to determine the relative frequencies of mitotic cells in the first, second, or later divisions, we are able to estimate the fraction of lymphocytes in the original blood sample that can divide in culture. In addition, we show that the technique lends itself to automation. For this we have digitized black and white video images of the cells and extracted features based on the distribution of optical densities in the nuclei. Discriminant analysis carried out on these descriptors resulted in the correct classification of the three major groups R, S and B with an accuracy of 80.3%, 58.5% and 85.1%, respectively.

Rapid flow cytometric analysis of the cell cycle in intact plant tissues

Mechanical chopping of plant tissues in the presence of mithramycin released intact nuclei representative of the cells within the tissues. The amount of nuclear DNA in the homogenates of monocotyledonous and dicotyledonous plants was accurately and rapidly determined by flow microfluorometry, and the distribution of nuclei involved in the cell cycle was charted for tissues selected from different physical locations or developmental stages.