Cell and tissue kinetics最新文献

The migration and turnover of epithelial cells was examined in the crypt and villus of the mouse jejunum using 1-micron plastic and 6-microns paraffin sections both with or without [3H]thymidine radioautography. The mean diameter of columnar cells was constant at 13.8 microns throughout the crypt, whereas it gradually increased from 16.8 microns in the lower villus to 25.4 microns in the upper villus. The cell cycle time (Tc) and the duration of DNA synthesis (ts) obtained by plotting labelled mitoses against time after [3H]thymidine injection, were 13.4 and 7.5 hr respectively. The labelling index (LI) at the various cell positions in the crypt, of mean length 27.5 cells, averaged 28.6% with a peak of above 55% in positions 7 to 11. The migration velocity of cells in the villus epithelium was estimated from the leading labelled cells at 2.04 cell/hr. The fraction of epithelial cells present in crypt and villus was 0.44 and 0.56 respectively. The migration velocity in the crypt (expressed as cell positions entered per hour), calculated from a cumulative cell production rate (LI/ts) in each cell position, increased in the lower and middle crypt (that is, in the proliferative zone, cell positions 1-18), but remains constant at a level of 1.0 in the upper crypt in the non-proliferative zone (cell positions 19-28). Therefore the migration velocity increases from 1.05 cell/hr in the upper crypt to 2.04 at the base of villus. Accordingly the velocity (expressed as distance traversed per hour) also shifts from 13.8 microns in the upper crypt to 34.2 microns in the base of villus and further increases to 51.8 microns in the upper villus because of continuous enlargement of the cells. The transit times of epithelial cells through the non-proliferative upper crypt (above ten cell positions) and the villus (67.9 cell positions on the average) are 8.4 and 33.4 hr respectively. The turnover times of crypt, villus, and whole epithelium are estimated at 26.5, 33.4, and 59.6 hr respectively.

Increased cellular polyamine levels are thought to be essential for epidermal keratinocyte proliferation. However, a number of studies report that the induction of keratinocyte proliferation and of ornithine decarboxylase, the rate-limiting enzyme of putrescine, spermidine and spermine biosynthesis, is not concordantly expressed. The relationship between epidermal keratinocyte polyamine synthesis and proliferation was studied in neonatal mouse keratinocyte cultures using specific inhibitors of ODC activity to decrease the intracellular polyamine levels. The ODC inhibitors alpha-methyl ornithine (alpha-Me-Orn), alpha-hydrazino ornithine (alpha-HO) and difluoro-alpha-methylornithine (alpha-DFMO) did not significantly inhibit epidermal keratinocyte proliferation at 5 X 10(-3) to 10(-4) M concentrations. At these doses, only alpha-DFMO was seen to decrease (by 70%) the cellular levels of putrescine, but not of spermidine or spermine. Epidermal keratinocyte growth in the higher dose of 20 mM alpha-DFMO, however, did not decrease the cellular levels of putrescine. Polyamine analyses of the spent medium showed that growth in 10 mM alpha-DFMO decreased the normal epidermal cell transport of putrescine and spermidine into the medium. At 20 mM alpha-DFMO concentration, the keratinocytes actually transported, intracellularly, the putrescine and spermidine that are naturally found in the foetal bovine component of the growth medium. We conclude from these studies that epidermal keratinocyte polyamine levels are determined by both the rate of synthesis, and of the transport of these amines into the extracellular medium. Since epidermal keratinocytes actively maintain specific polyamine levels, it appears that these molecules are essential for epidermal keratinocyte function.

In this paper, we present a procedure for the rapid, quantitative estimation of the G1, S, and G2 + M phase durations and dispersions and the growth fraction for asynchronously growing cell populations. In this procedure, the cell population is pulse-labelled with a radioactive DNA precursor at the beginning of the analysis and then sampled periodically. The samples are dispersed, stained with a DNA specific dye, and processed through a cell sorter where cells from mid-S phase and G1 phase are sorted. The radioactivity per cell (RC) is determined for each sorted sample. In addition, the variation in the rate of incorporation of the radioactive DNA precursor across S phase is determined and the fractions of cells in the G1, S, and G2 + M phase are estimated from DNA distributions measured during sorting. We also describe an automatic computer analysis procedure for estimation of the G1, S, and G2 + M phase durations and dispersions and growth fraction by simultaneous analysis of the variations with time in the radioactivity per cell in G1 (RCG1) and radioactivity per cell in mid-S phase (RCS) curves, the G1, S, and G2 + M phase fractions and the variation in the rate of incorporation of radioactive DNA precursor uptake across S phase. The experimental and analytical aspects of the RC procedure are applied in the cell cycle analysis of Chinese hamster M3-1 cells grown in vitro. The parameters estimated by RC analysis agree well with similar parameters estimated by fraction-of-labelled-mitoses analysis.

Cell cycle parameters measured by the percentage labelled mitoses (PLM) technique have been compared with the results of grain counting and continuous labelling studies in the mouse tumour Carcinoma NT. In [3H]deoxyuridine( [3H]UdR)-labelled tumours a PLM curve showed that the mean length of DNA synthesis (TS) was 7 to 9 hr and the mean cell cycle time (TC) was 16 hr. The turnover time (TT) was between 13 and 17 hr. In contrast, the rate of grain count halving showed that mean TC was 40 hr and TS was at least 19 hr. Cells entered S phase at a rate of 2.3%/hr with continuous labelling, which gave values of 22 hr for TS and 39 to 44 hr for TT. The PLM data therefore gave mean kinetic parameters which were less than half the lengths shown by the other techniques. We conclude that in Carcinoma NT there is a wide range of cell cycle times. The grain count halving and continuous labelling data showed the true mean values of TS and TC or TT, while the PLM data showed only the fastest cycle times. Therefore in this tumour, calculating the cell loss factor from PLM data would give a value too high by at least a factor of two.

The properties were investigated of low molecular weight factors acting on the G1-S transition of baby rat hepatocytes. These factors were produced by incubating adult rat serum with trypsin or a 100,000 g liver microsomal fraction, and isolated by ultrafiltration. Enzyme degradation assays indicated that the active compound was in both cases a glycopeptide sensitive to pronase and papain and to the combination of neuraminidase and beta galactosidase. No loss of hepatocyte G1-S inhibitory activity was observed after heat treatment at pH 7.0. G50 gel filtration showed that both the G1-S inhibitory factors were collected in the last fractions eluted. The elution volume was slightly larger for the trypsin than for the microsomal-induced factor, suggesting a small difference between their molecular weight. These factors are believed to be glycopeptides with a molecular weight around 1400. They might be composed of a 3-sugar polysaccharide chain with a galactose preterminal and a neuraminic acid terminal, linked to a polypeptide chain of 6 to 8 amino acids.

Functional properties of mouse haemopoietic spleen colony-forming cells, enriched 40- to 80-fold, from normal bone marrow were studied. It was found that: (1) the number of partially purified CFU-s (colony forming unit-spleen) required to rescue lethally irradiated mice was similar to the number of normal unfractionated bone marrow CFU-s giving the same level of protection; (2) the homing of partially purified CFU-s was similar to that of CFU-s from unfractionated bone marrow; (3) the regeneration of CFU-s in spleen was similar for enriched and unfractionated cell populations between 4 and 11 days after transplantation. In contrast, the rate of regeneration of CFU-s in femur was slower with enriched progenitor cells than with unfractionated bone marrow. The growth rate in femur, however, could be restored to normal by injecting freshly isolated syngeneic thymocytes with the enriched CFU-s population. The results indicate that the partially purified CFU-s are by themselves functionally normal and show that the rate of CFU-s repopulation in bone marrow can be affected by cell types other than spleen colony-forming cells.

Production of murine haemopoietic progenitor cells, capable of forming colonies on the spleens of irradiated recipients (CFU-s), can be maintained in vitro for up to several months. We have examined the properties of the suspension (SUSP) and adherent (ADH) CFU-s from these long-term marrow cell cultures in the spleen colony assay system. The numbers of colonies formed was linear with the numbers of SUSP or ADH cells injected, although the concentrations were only 20-25% of that found in normal bone marrow (NBM). The seeding efficiencies for SUSP and ADH CFU-s, measured in spleen and femur 24 hr after transplantation, were not significantly different from those for CFU-s from NBM. The results demonstrate that the CFU-s assay can give valid estimates of colony-forming cell numbers in the cultured cell populations. We therefore used the CFU-s assay to study the regeneration of SUSP, ADH and NBM CFU-s in spleen and femur at various times after transplantation. The growth of the cultured cells appeared to be delayed by 36-48 hr compared to the regeneration of CFU-s from NBM. Thereafter, ADH CFU-s grew at the same rate as NBM CFU-s, whereas the rate of SUSP CFU-s regeneration was slightly, but not significantly, slower. This similarity in growth rates indicates that the CFU-s from long-term marrow cultures have similar self-renewal probabilities to normal CFU-s.

Hairless mouse epidermis was treated topically with a single application of undiluted DMSO. Epidermal cell proliferation during the following 72 hr was examined by means of DNA flow cytometry, [3H]TdR autoradiography, and a stathmokinetic method with colcemid. Topical application of DMSO was followed by perturbations in the epidermal cell proliferation that were in general similar to those observed in epidermal regeneration due to sudden cell loss. In contrast to such regenerative reactions, no hyperplasia could be detected after DMSO treatment, in spite of a consistently increased mitotic rate the first 3 days after DMSO treatment. The augmented epidermal cell production following exposure to DMSO therefore appears to be balanced by a correspondingly increased cell loss.

The effects of food consumption on the kinetics of hepatic DNA synthesis after partial hepatectomy (PH) have been studied in rats. Short-term (4-24 hr) fasting before or after PH resulted in depression and/or delay of DNA synthesis on days 1, 2 and 3 of regeneration. This depression was found in hepatocytes and, to a lesser extent, in littoral cells. Re-feeding resulted in an increase of DNA synthesis within 3-8 hr. The results suggest that two different hepatocyte subpopulations exist in regenerating rat liver: one which proceeds to DNA synthesis without apparent exogenous signals, and another one which needs, in addition to the specific mitogenic action of PH, food intake as a secondary permissive signal in order to initiate DNA synthesis. In the latter population food consumption appears to be required at two different stages: (1) in G0 or the early pre-replicative phase (PRP); (2) in the late PRP 3-8 hr before initiation of DNA synthesis. In the latter stage dietary protein is needed, but no so in the former. The dependence on feeding in the late PRP increases relatively with time after PH. No evidence was found to suggest a different distribution of the two cell populations throughout the liver acinus. The findings support the hypothesis that the known effects of the light-dark rhythm on the timing of DNA synthesis after PH are mediated by the natural feeding rhythm of rats fed ad libitum. In addition they offer a means for improving the synchrony of hepatocyte proliferation in regenerating rat liver.