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1.
The response of polycythaemic mice to a standard dose of erythropoietin has been measured at various time intervals after single or repeated injections of hydroxyurea. The results exclude S phase of the cell cycle as the period responsive to erythropoietin. They suggest the existence of feedback mechanisms within the cell cycle, operating at the G1--S boundary and within the G1 phase. Hydroxyurea given to polycythaemic mice at various time intervals after erythropoietin induced characteristic changes in the response. These changes can be explained if both gradual transit of differentiated cells into the DNA synthesis (S phase) and changes in amount of the erythropoietin sensitive cells caused by the feedback mechanisms operating in the cell cycle are considered. 相似文献
2.
A simple stochastic model has been developed to determine the cell cycle kinetics of the isoprenaline stimulated proliferative response in rat acinar cells. The response was measured experimentally, using 3H-TdR labelling of interphase cells and cumulative collections of mitotic cells with vincristine. The rise and fall of the fraction of labelled interphase cells and of metaphase cells is expressed by the product of the proliferative fraction and a difference of probability distributions. The probability statements of the model were formulated and then compared by an iterative fitting procedure to experimental data to obtain estimates of the model parameters. The model when fitted to the combined fraction labelled interphase (FLIW) and fraction metaphase (FMW,) waves gave a mean Gis transit time of 21-2 hr, mean Gis+ S transit time of 270 hr, and mean Gis+ S + G2 transit time of 35-8 hr for a single injection of isoprenaline, where Gis is the initiation to S phase time. When successive injections of isoprenaline were given at intervals of 24 and 28 hr the corresponding values after the third injection were 12-4 hr, 20-8 hr and 25-7 hr respectively. The variance of the Gis phase dropped from 18-1 to 1–3 while the other variances remained unchanged. The estimated proliferative fraction was 0–24 after a single injection of isoprenaline, and 0–31 after three injections of the drug. Independently determined values of the proliferative fraction, obtained from repeated 3H-TdR injections, were 0–21 and 0–36 respectively. 相似文献
3.
The haemopoietic tissue of mice was damaged by different cell-cycle-stage specific and cell-cycle-stage non-specific cytostatic agents. The proliferation rate among the surviving pluripotential stem cells, i.e. those cells forming colonies in spleens of lethally irradiated mice (CFUs), was then investigated. The results suggest that, at least in the CFUs population, the cells which synthesize DNA in the S phase of the cell cycle inhibit the entry of the non-proliferating G0 cells into cell cycle. This evidence was based on the ability of three cytostatic agents, hydroxyurea, cytosine arabinoside and methotrexate, which are toxic specifically to the S phase cells to increase the proliferation in the CFUs population. This increase was quite out of proportion to the small amount of damage they caused to the population. Colchicine, which kills cells in mitosis, and ionizing irradiation, damaging cells in all stages, proved to be much weaker stimulators of proliferation. It has been suggested that a mechanism for the control of cellular proliferation might be based on the negative feedback in the cell cycle. In this feedback control loop the cells which are preparing for cell division in the S phase of the cell cycle inhibit the entry of the non-proliferating G0 cells into cell cycle. 相似文献
4.
REGENERATIVE PROLIFERATION OF MOUSE EPIDERMAL CELLS FOLLOWING ADHESIVE TAPE STRIPPING 总被引:1,自引:0,他引:1
The proliferating cells of mouse epidermis (basal cells) can be separated from the non-proliferating cells (differentiating cells) (Laerum, 1969) and brought into a mono-disperse suspension. This makes it possible to determine the cell cycle distributions (e.g. the relative number of cells in the G^ S and (G2+ M) phases of the cell cycle) of the basal cell population by means of micro-flow fluorometry. To study the regenerative cell proliferation in epidermis in more detail, changes in cell cycle distributions were observed by means of micro-flow fluorometry during the first 48 hr following adhesive tape stripping. 3H-TdR uptake (LI and grain count distribution) and mitotic rate (colcemid method) were also observed. An initial accumulation of G2 cells was observed 2 hr after stripping, followed by a subsequent decrease to less than half the control level. This was followed by an increase of cells entering mitosis from an initial depression to a first peak between 5 and 9 hr which could be satisfactorily explained by the changes in the G2 pool. After an initial depression of the S phase parameters, three peaks with intervals of about 12 hr followed. The cells in these peaks could be followed as cohorts through the G2 phase and mitosis, indicating a partial synchrony of cell cycle passage, with a shortening of the mean generation time of basal cells from 83-3 hr to about 12 hr. The oscillations of the proportion of cells in G2 phase indicated a rapid passage through this cell cycle phase. The S phase duration was within the normal range but showed a moderate decrease and the Gj phase duration was decreased to a minimum. In rapidly proliferating epidermis there was a good correlation between change in the number of labelled cells and cells with S phase DNA content. This shows that micro-flow fluorometry is a rapid method for the study of cell kinetics in a perturbed cell system in vivo. 相似文献
5.
SEPARATION OF NUCLEI REPRESENTING DIFFERENT PHASES OF THE GROWTH CYCLE FROM UNSYNCHRONIZED MAMMALIAN CELL CULTURES 总被引:5,自引:3,他引:2
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Nuclei have been isolated from unsynchronized cultures of Chinese hamster fibroblasts after varying intervals of growth following the incorporation of thymidine -3H for 20 min. These nuclei were fractionated by unit gravity sedimentation in a stabilizing density gradient of sucrose, and fractions were analyzed for the concentration of nuclei, DNA, and radioactivity. A more rapidly sedimenting population of nuclei in the G2 phase of the cell cycle was separated from a group of nuclei in the G1 phase, and nuclei in progressive stages of DNA synthesis (S phase) were distributed between these two regions. The fractionation of intact cells by sedimentation according to their position in the cell cycle was found to be less satisfactory than the corresponding separation of nuclei. This probably results from the continuous accumulation of mass within individual cells throughout the entire cell cycle, whereas most of the mass of a nucleus is replicated during a relatively narrow interval of the total cell cycle. 相似文献
6.
Variation In G1 Transit Time Relative to the Cycloheximide and Actinomycin D Drug Restriction Points
The transit time distribution at various points in the cell cycle of synchronized Chinese hamster ovary cells was determined from the mitotic index, [3H]thymidine labeling index and increase in cell number monitored at regular intervals after mitotic selection. Variation in G1 transit time compared with that for the total cell cycle indicates that variation in cell cycle transit time occurs mainly during G1 phase. the cycloheximide (5.0 μg/ml) and actinomycin D (3.0 μg/ml) restriction points occur 0.2 and 1.7 hr prior to entry into S phase, respectively. the transit time distributions are further characterized by the moments of the distributions. the variance (2nd moment about the mean) of the transit time distribution at the actinomycin D restriction point is similar to the variance of the transit time distribution at the G1/S border, thus variation in cell cycle transit time originates earlier than 1.7 hr prior to entry into S phase (i.e., the first 3/4 of G1). If G1 transit time variability and cell cycle control are related, then the results presented here indicate that the major regulatory events do not occur during late G1 phase. 相似文献
7.
E. Hamilton 《Cell proliferation》1974,7(4):389-398
Cell proliferation, differentiation and migration have been studied in the sebaceous glands of DBA-2 mice in the resting (telogen) phase of hair growth. Cells labelled by a single injection of tritiated thymidine start to leave the glands of adult male mice 5 days later. About 80% of the proliferative cells in the basal layer have a cell cycle time of 40 hr or less. In 18% of the proliferative cells G1 is at least 4 days long and 16% have a G2 phase longer than 17 hr. The S phase is about 7.5 hr long and cells spend at least 21 hr in the basal layer before migrating into the differentiating cell region. The glands of mature female and immature mice are smaller than those of the mature male. They have fewer, smaller cells and a much lower labelling index. 相似文献
8.
The process of continuous resynchronization with excess thymidine provides sufficient cell material for accurate chemical determination of DNA and RNA in HeLa S3 cells at hourly intervals during the cell cycle. Total DNA is constant during the non-S phase portion of the cell cycle but varies widely among cycles of synchronous growth. Total cellular RNA content increases linearly in the G1 phase and accelerates to a higher linear rate of accumulation, which remains constant during most of the S and G2 phases. The ratios of early and late cycle rates of RNA accumulation are not constant among cycles. 相似文献
9.
Erythropoiesis in vitro was studied with practically pure erythroid progenitor cells: CFU-E (colony-forming-units-erythroid). the isolation of CFU-e from spleens of thiamphenicol pretreated anaemic mice with the combined methods of centrifugal elutriation and Percoll density gradient centrifugation was monitored by flow cytometry. the ultimate CFU-e preparation with a density of 1.070 g/ml contained a high percentage of cells in the S phase of the cell cycle (80%). CFU-e occasionally found at a lower density of 1.065 g/ml were predominantly in the G2, + M and G1 phases. When CFU-e were cultured, the number of cells in the distinctive phases of the cell cycle changed periodically, so the cells were partly synchronized. Four periods up to 27 hr were observed by flow cytometrical screening of the cultured cells at hourly intervals. Cell-cycle times between 6 and 7 hr were found for all erythroid cell divisions. This was in agreement with results obtained from colony growth curves. Without the addition of erythropoietin cells start to degenerate after the second cell division. This experimental approach can be used for the cell kinetic modelling of erythropoiesis. 相似文献
10.
HeLa cells were synchronized by a double thymidine block and pulse labeled at different stages of the cell cycle with 3H-choline. The specific activity of phospholipids extracted from the cell, the nucleus and the nuclear membrane showed a progressive increase from S to G1; the incorporation of choline into phospholipids of asynchronous cells showed a specific activity intermediate between the values of S and G1 cells. Similar results were obtained when 32phosphorus was used as a precursor instead of choline. Thin layer chromatographic analysis of phospholipids extracted from cells in S and from cells in G1 failed to show any difference in the distribution of radioactivity among the various phospholipid classes. Choline uptake by HeLa cells in different phases of the cell cycle did not show significant variations. However, during the synchronization process, shortly after the addition of excess thymidine, an increased uptake of choline by cells and an increased incorporation of choline into phospholipids were found. The results indicate that some of the changes occurring in phospholipids synthesis may not be cell cycle dependent, but may be the effect of the synchronizing process. 相似文献
11.
The proliferative response to testosterone in the accessory sex glands (seminal vesicle and coagulating gland) of castrated male Balb/c mice has been examined by pulse and continuous thymidine-labelling experiments, and by the fraction of labelled mitoses technique. Progressive reductions in cellularity followed castration, and by varying the time elapsing between castration and the initiation of testosterone treatment, it was clear that the size of the response depended upon the number of cells in the tissue, relative to the normal complement. Interpretation of FLM data was difficult in periods where proliferative rates changed rapidly. We have attempted to explain the cell kinetic events by postulating a G0 compartment, from which cells are stimulated to enter the proliferative cycle before subsequently returning to an out of cycle state. It was thought unlikely that substantial changes in cell cycle time occurred. In both the accessory sex glands, the overall form of the continuous thymidine labelling curves showed that most proliferative cells entered DNA synthesis in a shorter time after stimulation at 14 days after castration than they did at 3 days after castration. The data were not consistent with cells moving deeper into G0 with time after castration. In the seminal vesicle almost all epithelial cells were potentially proliferative by 3 days after castration. In the coagulating gland only 30% were potentially proliferative at 3 days, increasing to 85% at 14 days after castration. However, such proportional increases represented much smaller changes in terms of absolute numbers of cells, because of a concomitant decline in cellularity from 3 to 14 days after castration. 相似文献
12.
A. B. Rickinson 《Cell proliferation》1970,3(4):335-347
The progress of L-cells through the cell cycle in asynchronous and in synchronous culture has been studied at a concentration of actinomycin D which mediates an apparently‘nucleolar-specific’inhibition of RNA synthesis. Under such conditions, cells may be blocked or seriously delayed in the G1 and G2 phases of the cycle whilst the processes of DNA synthesis and mitosis once initiated, can still occur at control rates. The results show that the sensitivity of a cell to these blocks depends critically upon the position of that cell within the cycle at the time of drug addition. The possible mechanisms of the drug's action are discussed. 相似文献
13.
The effects of irradiation (300, 500 and 1500 rads) on mitosis and DNA synthesis in the estrogen primed vaginal epithelium have been studied. Dose-effect relations and the time sequence of effects on the two processes were investigated. The technique of tritiated thymidine labeling of DNA with autoradiography was used, in conjunction with the mitotic count, to study alterations in the generative cycle. Prior to irradiation, ovariectomized female rats were treated daily with diethylstilbestrol for a period of 2 weeks to create a steady state in the vaginal cell population. It was observed that:
- 1 Within 1 hr following ionizing radiation, mitotic figures disappear from the population and reappear at a time that is dose dependent. Those cells that have begun mitosis at the time of irradiation were able to complete that phase but no cells which were in G2 were able to begin mitosis. Therefore, a G2 block occurs within 1 hr post-irradiation.
- 2 Radiation reduces the rate of DNA synthesis thus prolonging the S phase. There is no evidence of a radiation-induced G1 to S block in this system.
- 1 Cells in G1 at the time of irradiation are relatively insensitive and continue to progress through the generative cycle at a rate primarily determined by the level of estrogen stimulation.
- 2 Radiation may interfere with the estrogen priming mechanism in this hormonedependent system thereby reducing the effective level of estrogen stimulation. This is seen in the behavior of cells which were in G1 at the time of irradiation. The extent of the blockage of estrogen increases with radiation dose and after 1500 rads, estrogen stimulation is essentially at castrate level.
14.
Y. Kowyama T. Kawase H. Yamagata 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(4):297-303
Summary In order to examine changes in survival and mutation rates during a cell cycle in higher plant, fertilized egg cells of rice were irradiated with X-rays at 2 h intervals for the first 36 h after pollination, i.e., at different phases of the first and second cell cycles. The most sensitive phase in lethality was late G1 to early S, followed by late G2 to M, which were more sensitive than the other phases. In both M1 and M2 generations, sterile plants appeared most frequently when fertilized egg cells were irradiated at G2 and M phases. Different kinds of mutated characters gave rise to the respective maximum mutation rates at different phases of a cell cycle: namely, albino and viridis were efficiently induced at early G1, xantha at early S, short-culm mutant at mid G2, heading-date mutant at M to early G1. The present study suggests the possibility that the differential mutation spectrums concerning agronomic traits are obtained by selecting the time of irradiation after pollination. 相似文献
15.
T Hashimoto K Juso M Nakano T Nagano S Kambayashi A Nakashima U Kikkawa S Kamada 《Cell death & disease》2012,3(5):e313
Apoptosis is induced by various stresses generated from the extracellular and intracellular environments. The fidelity of the cell cycle is monitored by surveillance mechanisms that arrest its further progression if any crucial process has not been completed or damages are sustained, and then the cells with problems undergo apoptosis. Although the molecular mechanisms involved in the regulation of the cell cycle and that of apoptosis have been elucidated, the links between them are not clear, especially that between cell cycle and death receptor-mediated apoptosis. By using the HeLa.S-Fucci (fluorescent ubiquitination-based cell cycle indicator) cells, we investigated the relationship between the cell cycle progression and apoptotic execution. To monitor apoptotic execution during cell cycle progression, we observed the cells after induction of apoptosis with time-lapse fluorescent microscopy. About 70% of Fas-mediated apoptotic cells were present at G1 phase and about 20% of cells died immediately after cytokinesis, whereas more than 60% of etoposide-induced apoptotic cells were at S/G2 phases in random culture of the cells. These results were confirmed by using synchronized culture of the cells. Furthermore, mitotic cells showed the resistance to Fas-mediated apoptosis. In conclusion, these findings suggest that apoptotic execution is dependent on cell cycle phase and Fas-mediated apoptosis preferentially occurs at G1 phase. 相似文献
16.
CELL KINETICS OF IRRADIATED EXPERIMENTAL TUMORS: CELL TRANSITION FROM THE NON-PROLIFERATING TO THE PROLIFERATING POOL 总被引:1,自引:0,他引:1
Parenchymal tumor cells of murine mammary carcinomas can be divided into two pools, using nucleoli as morphological ‘markers’. Cells with dense nucleoli traverse the cell cycle and divide, thus constituting the proliferating pool. Cells with trabeculate or ring-shaped nucleoli either proceed slowly through G1 phase or are arrested in it. The role of these non-proliferating, G1 phase-confined cells in tumor regeneration was studied in vivo after a subcurative dose of X-irradiation in two transplantable tumor lines. Tumor-bearing mice were continuously injected with methyl[3H]thymidine before and after irradiation. Finally, the labeling was discontinued, mice injected with vincristine sulfate and cells arrested in metaphase were accumulated over a 10-hr period. Two clearly delineated groups of vincristinearrested mitoses emerged in autoradiograms prepared from tumor tissue at the time of starting tumor regrowth: one group with the silver-grain counts corresponding to the background level, the other with heavily labeled mitoses. As the only source of unlabeled mitoses was unlabeled G1 phase-confined cells persisting in the tumor, this observation indicated cell transition from the non-proliferating to the proliferating pool, which took place in the initial phase of the tumor regrowth. Unlabeled progenitors have apparently remained in G1 phase for at least 5–12 days after irradiation. 相似文献
17.
New techniques for cell cycle analysis are presented. Using HeLa cells, methods are described for the selection of a narrow window or cohort of lightly [3H]-labeled cells located either at the very beginning or the very end of S phase. The cohort cells are tagged by a labeling procedure which entails alternating pulses of high and low levels of [3H]thymidine and are identified autoradiographically. Additional methods are described for following the progress of cohort cells through the cell cycle. Theoretically, with the methods described, it should be possible to follow the ‘early S cohort’ cells as they exit from S phase, as they enter and exit M and as they enter the subsequent S phase. This would allow a determination of S, S + G2, S + G2+ M and T. It should theoretically be possible to follow ‘late S cohort’ cells in a similar manner, allowing a determination of G2, G2+ M and G2+ M + G1. To test these predictions, several experiments are presented in which the progress of the two cohorts is monitored. The best data were obtained from the mitotic curves of cohort cells. For each of the cohorts, values were obtained for the time required for peak concentration of cells in mitosis, the coefficients of variation and of skew. The curve of cohort cells passing through mitosis is shown to fit a log-normal curve better than a normal curve. In addition, the mitotic curves are used to estimate the length of M and to estimate the loss of cohort synchrony. Other uses of these methods are discussed. 相似文献
18.
To better understand how the flow cytometric bromodeoxyuridine (BrdUrd)-pulse-chase method detects perturbed cell kinetics we applied it to measure cell cycle progression delays following exposure to ionizing radiation. Since this method will allow both the use of asynchronous cell populations and the determination of the alterations in cell cycle progression specific to cells irradiated in given cell cycle phases, it has a significant advantage over laborious synchronization methods. Exponentially growing Chinese hamster ovary (CHO) K1 cells were irradiated with graded doses of X-rays and pulse-labelled with BrdUrd immediately thereafter. Cells were subcultured in a BrdUrd-free medium for various time intervals and prepared for flow cytometric analysis. Of five flow cytometric parameters examined, only those that involved cell transit through G2, i.e. the fraction of BrdUrd-negative G2 cells and the fraction of BrdUrd-positive cells that had not divided, showed radiation dose-dependent delays. The magnitude of the effects indicates that the cells irradiated in G2 and in S are equally delayed. S phase transit of cells irradiated in S or in G1 did not appear to be affected. There were apparent changes in flow of cells out of G1, which could be explained by the delayed entry of G2 cells into the compartment because of G2 arrest. Thus, in asynchronous cells the method was able to detect G2 delay in those cells irradiated in S and G2 phases and demonstrate the absence of cell-cycle delays in other phases. 相似文献
19.
REGENERATIVE PROLIFERATION OF MOUSE EPIDERMAL CELLS FOLLOWING APPLICATION OF A SKIN IRRITANT (CANTHARIDIN) 总被引:1,自引:0,他引:1
O. P. F. Clausen 《Cell proliferation》1979,12(2):135-144
The strong skin irritant cantharidin dissolved in benzene was applied to the back of hairless mice. Single cell suspensions of epidermal basal cells were obtained and flow microfluorometric measurements of cellular DNA content were made. Smears were made for autoradiography, and the [3H]TdR labelling index (LI) and mean grain count (MGC) were assessed up to 3 days after cantharidin application. Three successive peaks of cells with S phase DNA content accompanied by three LI peaks were observed. The first two peaks were follwed by peaks of cells in G2 phase, indicating that after the acute cell injury caused by cantharidin the cells traversed the cell cycle in partial synchrony through two subsequent cell cycles, each of 10–12 hr duration. During this phase of rapid proliferation the LI reached the proportion of cells in S phase, contrary to what is observed in untreated mouse epidermis, where the labelled cells contribute to about half the proportion of cells with S phase DNA content. The first two peaks of cells in S phase and LI coincided with an increased MGC, whereas the third peak was accompanied by a MGC significantly below control values. This indicates that this latter peak is due to a longer DNA synthesis time rather than to a partially synchronized and increased cell proliferation. The duration of the G1, S and G2 phases seems to be reduced initially in rapidly proliferating epidermis. 相似文献
20.
The distribution of cellular and nuclear volume in synchronous populations of NHIK 3025 cells, which derive from a cervix carcinoma, have been measured by electronic sizing during the first cell cycle after mitotic selection. Cells given an X-ray dose of 580 rad in G1, were also studied. During the entire cell cycle the volume distribution of both cells and nuclei is an approximately Gaussian peak with a relative width at half maximum of about 30%. About half of this width is due to imperfect synchrony whereas the rest is associated with various time invariant factors. During S the mean volume of the cells grows exponentially whereas the nuclear volume increases faster than for exponential kinetics. Hence, although cellular and nuclear volumes are closely correlated, their ratio does not remain constant during the cell cycle. Volume growth during the first half of G1 is negligible especially for nuclei where the growth appears to be closely associated with DNA-synthesis. For unirradiated cells the growth of cellular and nuclear volume is negligible also during G2+ M. In contrast, the X-irradiated cells continue to grow during the 6 hr mitotic delay with a rate that is constant and about half of that observed in late S. Hence, radiation induced mitotic delay does not appear merely as a lengthening of an otherwise normal G2. During G1 and S the irradiated cells were identical to unirradiated ones with respect to all the parameters measured. 相似文献