bluuebunny/crossref_metadata_2025 huggingface dataset:
Cell Cycle Kinetics By Brdu‐Hoechst Flow Cytometry: an Alternative to the Differential Metaphase Labelling Technique
Authors: Kubbies M. , Schindler D. , Hoehn H. , Rabinovitch P. S.
Published: May 2008

Abstract. Human lymphocytes cell cycle kinetics was studied in parallel in whole blood and in isolated lymphocyte cultures by differential metaphase labelling and by flow cytometry, employing the principle of quenching of Hoechst fluorescence by BrdU substituted DNA. the BrdU‐Hoechst flow technique yields information on the kinetics of cell recruitment and cell cycle progression superior to the differential metaphase staining, since it provides data from interphase cells, including cycle compartment durations, non‐cycling cell fractions and transition probabilities. the Smith and Martin model, modified to include a fraction of non‐cycling cells, yields excellent correspondence to the experimental data. We show that lymphocytes isolated from Ficoll gradients respond to PHA stimulation with a 4‐6 hr delay compared to whole blood cultures or to cultures with autologous serum supplementation. A detailed study of the effects of such culture supplements on lag phase duration, cell cycle compartment length, non‐cycling cell fractions and transition probabilities illustrates the application and reproducibility of the flow assay. the potential of the method is further documented with two examples showing the dependence of lymphocyte proliferation on donor age and donor genotype.
Proliferative Response of Mouse Submandibular Gland to Androgen But Not to Thyroid Hormone
Authors: Okamoto S. , Ito M. , Kitamura Y. , Matsumoto K.
Published: May 2008

Abstract. Hormone‐induced differentiation and proliferation of cells were investigated in the submandibular gland of castrated female mice, by determining the esteroprotease activity and 3H‐thymidine labelling index, respectively. Injections of 5α‐dihydrotestosterone (4 μg/g body weight/day) or l‐thyroxine (0.5 μg/g body weight/day) induced a significant increase in the activity of esteroprotease, which has been shown to be localized in the convoluted tubule cells of the submandibular gland. Injections of the above‐mentioned dose of 5α‐dihydrotestosterone for 3 days induced a 43‐fold increase in the labelling index of the convoluted tubule cells, but injections of the above‐mentioned dose of l‐thyroxine for any duration did not induce a significant increase in the labelling index. the present result suggests that hormones which induce differentiation of cells in mouse submandibular gland do not necessarily induce cell proliferation.
Effects of the Free Radical Generator Paraquat On Differentiation, Superoxide Dismutase, Glutathione and Inorganic Peroxides In Microplasmodia of Physarum Polycephalum
Authors: Allen R. G. , Newton R. K. , Farmer K. J. , Nations C.
Published: May 2008

Abstract. The herbicide paraquat was used to investigate the effects of oxidative stress on the spherulation of Physarum polycephalum microplasmodia. the responses of a white non‐differentiating strain of Physarum were compared with those of a common yellow strain that readily spherulates in salts‐only starvation medium. the addition of paraquat to the salts medium increased the specific activity of superoxide dismutase in both strains; it also induced an increase in the intracellular inorganic peroxide concentration in both strains. Glutathione concentration was higher in the paraquat‐treated yellow strain than in the controls. Paraquat had no effect on glutathione concentration in white microplasmodia. Paraquat accelerated spherulation in yellow microplasmodia. the white microplasmodia responded to the herbicide by cleaving into structures similar to immature spherules; however, these structures were not viable. the results of this study support the hypothesis that free radicals are involved in cell state transitions.
Some Short‐Term Cell Kinetic Effects of Ionizing Radiation On Mouse Bladder Urothelium
Authors: Reitan J. B. , Tverå K.
Published: May 2008

Abstract. Early morphological changes and the pattern of reactive proliferation of the hairless mouse urinary bladder urothelium after irradiation are reported. Groups of female hairless mice were anaesthetized with sodium pentobarbital and irradiated over the bladder region with 0, 10, 20 and 30 Gy. Control groups were sham‐treated. Short‐term cell kinetic changes were monitored using incorporation of tritiated thymidine and flow cytometry. Only minor radiation‐induced alterations in the cell kinetic pattern were recorded, and no significant histomorphological changes were seen. However, a marked increase in the thymidine incorporation was seen in the control animals on the first day after anaesthesia. Radiation proctitis induced early deaths in the 30 Gy irradiated animals. the present results are in accordance with commonly accepted radiobiological theories, but not in agreement with results previously published by others
Cell Cycle Kinetics of Aerated, Hypoxic and Re‐Aerated Cells In Vitro Using Flow Cytometric Determination of Cellular Dna and Incorporated Bromodeoxyuridine
Authors: Shrieve D. C. , Begg A. C.
Published: May 2008

Abstract. The effects of extreme hypoxia on cell cycle progression were studied by simultaneous determination of DNA and bromodeoxyuridine (BrdU) contents of individual cells. V79‐379A cells were pulse‐labelled with BrdU (1 μM, 20 min, 37°C) and then incubated for up to 12 hr in BrdU‐free medium under either aerated or extremely hypoxic conditions. After the incubation interval (0‐12 hr), the cells were trypsinized and fixed in 50% EtOH. Propidium iodide and a fluorescein‐labelled monoclonal antibody to BrdU were then used to quantify DNA content and incorporated BrdU, respectively. Measurements in individual cells were made by simultaneous detection of green and red fluorescence upon excitation at 488 nm using flow cytometry. Bivariate analysis revealed progression of BrdU‐labelled cells in aerated cultures out of S phase, into G2 and cell division, with halving of mean fluorescence, and back into S phase by approximately 9 hr after the BrdU pulse. Hypoxia immediately arrested cells in all phases of the cell cycle. Both the DNA distribution and the bivariate profile of cells that were fixed from 2 to 12 hr after induction of hypoxia were identical to the 0 hr controls. the percent of cells with green fluorescence in a mid‐S phase window remained 100% and the mean fluorescence of these cells remained at control (0 hr) levels. This indicates that, under hypoxic conditions, cells were moving neither into nor out of S phase. Cultures that had been hypoxic for 12 hr exhibited an increasing rate of BrdU uptake with time after re‐aeration. Re‐aerated cells were able to complete or initiate DNA synthesis, but their rates of progression through the cell cycle were markedly reduced. A large fraction of cells appeared unable to divide up to 12 hr following release from hypoxia.
Establishment and Growth Kinetics of the Mutant Ehrlich‐Lettré Ascites Cell Strain Hd33 In Permanent Suspension Culture1,2
Authors: Granzow Christof , Granzow Viola , Edler Lutz , Sauer Wolfgang
Published: May 2008

Cells of a mutant in vivo subline of the Ehrlich‐Lettré mouse ascites tumour (ELAT) were converted to growth in suspension culture. Kinetic analysis revealed the selective character of the conversion process; without a detectable adaptation period, a fraction of about 2 × 10‐5 of the explanted cells continued to grow in vitro. the resulting, mutant Ehrlich‐Lettré ascites cell strain was designated HD33 and propagated uninterruptedly from 1974 on. the corresponding in vivo ELAT subline HD33 was derived from the HD33 ascites cell strain by intraperitoneal retransplantation.

In HD33 cell suspension cultures, the population doubling time, the average intermitotic interval, as determined by videomonitoring, and the average duration of the cell cycle, as determined from percentage of labelled mitoses (PLM) data, were all measured at 15 hr. Cell loss and quiescent compartments were insignificant. the duration of the G1 phase was effectively zero. Both PLM data and [3H]/[14C] thymidine double‐labetling measurements revealed an S‐phase duration of between 11 and 12 hr. the G2 phase lasted 3–5 hr.

The HD33 strain differs from comparable suspension strains of wild‐type Ehrlich ascites cells in the insignificant role of density‐dependent inhibition in growth, and the striking prolongation of the S phase which is associated with an excessive, cytoplasmic storage of glycogen by the mutant cells.
Mathematical Model For Human Myeloma Relating Growth Kinetics and Drug Resistance
Authors: Hokanson J. A. , Brown B. W. , Thompson J. R. , Jansson B. , Drewinkos B.
Published: May 2008

Abstract. We present a computer‐based mathematical model that can simulate characteristic features of the clinical time course of human myeloma. It asserts that therapy resistance in myeloma cells is an inherited trait associated with the longer inter‐mitotic times of some cells and that the strength of this trait affects tumour growth characteristics. These kinetic differences within the malignant cell clone may also influence therapeutic efficacy. In the model, the same total therapy, administered in different time‐dose fractions, could be ‘curative’ or ‘minimally effective’ depending on kinetic properties. For example, as others have shown, in myeloma pulsed intermittent therapy is often more effective than low dose continuous therapy. According to our model this finding is compatible with a high coefficient of inheritability of resistance from one cell generation to the next. the model also suggests that if there are subclones of varying resistance, a therapy must have some effect on each of them if it is to be employed in a curative fashion. While many aspects of the model are not yet clinically testable, exploration of its concepts might increase knowledge about fundamental neoplastic mechanisms.
Multiple‐Transition Cell Cycle Models That Exhibit Transition Probability Kinetics
Authors: Rigney D. R.
Published: May 2008

Abstract. Cell cycle models that allow multiple random transitions and asymmetric cell division may exhibit a property that has been used to support the transition probability model of the cell cycle: that the absolute value of the difference between sibling cell inter‐mitotic times varies from one sibling pair to another and is described by an exponential statistical distribution. Three models that show this property are described, each of which postulates the existence of objects that are partitioned between daughter cells during cell division and whose number influences the duration of the subsequent cell cycle, e.g., surface receptors for growth factors or transcriptional complexes that are carried by sister chromatids. In the first model, sibling cells receive identical numbers of the objects, which are used to perform multiple random transitions that constitute part of the cell cycle. the second model is like the first, except that the partitioning of objects between the newly‐formed sibling cells is random. the third model is also like the first, except that all of the objects are passed to one of the sibling cells. These results show that the general mechanisms that are responsible for the dispersion of inter‐mitotic times, the correlation between sibling generation times and the apparently exponentially distributed difference between sibling generation times, could be a combination of unequal cell division, multiple random cell cycle transitions and heterogeneity of mitotic cells.
Reparative Growth In the Rat Thyroid: Effect of Tsh Suppression
Authors: Stringer B. M. J. , Wynford‐Thomas D. , Gomez‐Morales M. , Williams E. Dillwyn.
Published: May 2008

Abstract. Previous investigations have shown that thyroid incision leads to a dramatic burst of follicular cell mitotic activity in cells adjacent to the wound edge in both normal rats and rats made hypothyroid by chronic goitrogen administration. Wound‐induced thyroid mitotic activity therefore, is seen in rats with either normal or supranormal levels of circulating thyrotropin (TSH). This study was designed to investigate the thyroid mitotic response to wounding in the absence of detectable levels of circulating TSH. Rats were injected with large doses of L‐thyroxine twice daily to render circulating TSH undetectable. Thyroids were incised and follicular cell mitotic activity, in relation to distance from the incision, determined at 24, 48 and 72 hr after incision. A mitotic response to wounding was maintained in L‐thyroxine treated rats, even though circulating TSH was undetectable. the peak of activity was at 48 hr, but was only 50% of that found in the incised normal rat thyroid. the spatial distribution of the response suggests that there are two components of the wound response in the normal thyroid, one dependent on the presence of circulating TSH, the other TSH‐independent. the results are discussed in relation to current understanding of cellular growth control.
Multi‐Type Galton‐Watson Process As A Model For Proliferating Human Tumour Cell Populations Derived From Stem Cells: Estimation of Stem Cell Self‐Renewal Probabilities In Human Ovarian Carcinomas
Authors: Ciampi A. , Kates L. , Buick R. , Kriukov Y. , Till J. E.
Published: May 2008

Abstract. A mathematical model for proliferation of tumour cell populations is developed. the cell population is assumed to be organized in a hierarchy of decreasing proliferative potential and increasing degree of differentiation. Using some elements of the theory of Multi‐type Galton‐Watson processes, a method is proposed for the estimation of Psr, the probability of self‐renewal of tumour stem cells, from the experimental distribution of clonal unit sizes obtained in cell culture studies. Six data sets from patients with advanced adenocarcinorna of the ovary are used to demonstrate the method. Reasonable estimates are obtained, and the theoretical colony size distributions predicted by the model appear to be in good qualitative agreement with the experimental ones, and lend support to a stem cell model of tumour growth. the possible significance of Psr as a prognostic factor is briefly discussed.
Influence of Growth Hormone and Thyroxine On Cell Kinetics In the Proximal Tibial Growth Plate of Snell Dwarf Mice
Authors: Smeets Ton , van Buul‐Offers Sylvia
Published: May 2008

Abstract. In Snell dwarf mice, the influence of short‐term treatment with human growth hormone (hGH) or thyroxine on the proliferative and sulphation activity of the proximal tibial growth plate was studied. By autoradiographic methods, the [3H]methylthymidine incorporation after a single injection was measured, after 2 hr incorporation time. the labelling index was calculated and the number of labelled mitoses was counted. In addition, the distribution of the labelled nuclei over the proliferating and degenerating zones was determined by continuous labelling for 25 and 73 hr.

In untreated dwarf mice after [3H]‐methylthymidine administration, the number of labelled nuclei in the growth plate is low. Labelling occurs, as expected, mainly in the cells of the proliferative zones. the number of labelled nuclei in control dwarf mice was similar after 25 and 73 hr continuous labelling. This suggests that many cells are in a resting Go or prolonged G1 phase. Both hGH and T4 treatment induce a significant increase of the number of labelled nuclei per growth plate and of the number of mitoses. Since hormonal treatment induces a small number of mitoses after 2 hr incorporation of the label, the minimal G2 phase of the cell cycle is less than 2 hr. In addition, treatment with hGH and T4 stimulates chondrocytes in the zone of proliferative and hypertrophic cells to actively incorporate [35S]‐sulphate.
Do Spermatogonial Stem Cells Have A Circadian Rhythm?
Authors: Oakberg E. F. , Gosslee D. G. , Huckins C. , Cummings C. C.
Published: May 2008

Abstract. Mitotic index was determined in whole mounts of segments of seminiferous tubules of (101 × C3Hf)F1 male mice at 3 hr intervals from 18.00 to 06.00 hours, and at hourly intervals from 08.00 to 16.00 hours. the highest frequency of metaphase‐anaphase figures occurred at 10.00 and 11.00 hours, but was not significantly higher than for other times. Injection of 25 μCi 3H‐TdR per mouse, followed 24 hr later by exposure to 300 rad X‐rays and killing 207 hr after labelling was used to test for circadian rhythm in DNA synthetic activity of the long‐cycling A, spermatogonia. No significant effect of time of day was observed. Likewise, the number of undifferentiated spermatogonia scored 183 hr after 300 rad showed no effect of time of day. the testis therefore appears to have no circadian rhythm in mitotic activity. Stage of the cycle of the seminiferous epithelium, however, showed a significant effect on mitotic index of As spermatogonia and on DNA synthetic activity of undifferentiated spermatogonia. These data are compared with those for other organisms and tissues in respect to which properties of stem cells are general for all organisms and tissues and which are specific for spermatogonia.
Complement Split Product C5a Mediates the Lipopolysaccharide‐Induced Mobilization of Cfu‐S and Haemopoietic Progenitor Cells, But Not the Mobilization Induced By Proteolytic Enzymes
Authors: Molendijk W. J. , van Oudenaren A. , van Dijk H. , Daha M. R. , Benner R.
Published: May 2008

Abstract. Intravenous (i.v.) injection of mice with lipopolysaccharide (LPS), and the proteolytic enzymes trypsin and proteinase, mobilizes pluripotent haemopoietic stem cells (CFU‐s) as well as granulocyte‐macrophage progenitor cells (GM‐CFU) and the early progenitors of the erythroid lineage (E‐BFU) from the haemopoietic tissues into the peripheral blood. We investigated the involvement of the complement (C) system in this process. It appeared that the early mobilization induced by LPS and other activators of the alternative complement pathway, such as Listeria monocytogenes (Lm) and zymosan, but not that induced by the proteolytic enzymes, was absent in C5‐deficient mice. the mobilization by C activators in these mice could be restored by injection of C5‐sufficient serum, suggesting a critical role for C5.

The manner in which C5 was involved in the C activation‐mediated stem cell mobilization was studied using a serum transfer system. C5‐sufficient serum, activated in vitro by incubation with Lm and subsequently liberated from the bacteria, caused mobilization in both C5‐sufficient and C5‐deficient mice. C5‐deficient serum was not able to do so. the resistance of the mobilizing principle to heat treatment (56°C, 30 min) strongly suggests that it is identical with the C5 split product C5a, or an in vivo derivative of C5a. This conclusion was reinforced by the observation that a single injection of purified rat C5a into C5‐deficient mice also induced mobilization of CFU‐s.
Cell Cycle Phase Sensitivity to Cis‐Dichloro‐Bis (Isopropylamine) Trans‐Dihydroxy Platinum (Iv) (Chip)
Authors: Edwards Philippa G. , Nias A. H. W.
Published: May 2008

Abstract. Cis‐dichloro‐bis (isopropylamine) trans‐dihydroxy platinum (IV) (CHIP) is a second generation platinum coordination complex now in Phase II clinical trials. In vitro studies with Chinese Hamster Ovary cell cultures show that CHIP is a phase‐sensitive drug, being most cytotoxic to cells in early G1 phase and least toxic to late S and G1 phase cells. the dose‐modifying factor between the drug sensitivity of cells treated in G1 and in late S phase is 1.6. These findings and their clinical significance are discussed with respect to the phase sensitivity of other cytotoxic agents.
Effect of Cyclophosphamide On the Proliferation of L 1210 Ascites Tumour Cells and of Jejunal Crypt Cells In the Mouse
Authors: Schäfer E. , Maurer‐Schultze B.
Published: May 2008

Abstract. Cyclophosphamide (CY) does not act in a cell‐cycle specific manner. i.e. exclusively on proliferating cells. It also kills non‐proliferating cells, as shown by application of CY to L 1210 ascites tumour‐bearing mice during plateau phase growth of the tumour. Moreover, treatment with CY of L 1210 ascites tumour cells, double‐labelled with [3Hl and [14C]‐thymidine, suggests that CY is not cell cycle phase dependent, but kills cells out of all cycle phases.

There is also an extensive cytocidal effect of CY (300 mg/kg) on the jejunal crypt cells of the mouse, which is even more pronounced than that of cisplatinum (DDP, 13 mg/kg). However, rapid regeneration of crypt cells occurs after treatment with the drugs.
Pluripotent Haemopoietic Stem Cell Entry Into Dna Synthesis In Vitro After Stimulation By Ara‐C Treatment In Vivo
Authors: Izumi H. , Guigon M. , Frindel E.
Published: May 2008

Abstract. Non‐cycling pluripotent bone marrow stem cells (CFU‐S), taken 3 hrs after injection of 20 mg of Ara‐C, have been shown to enter DNA synthesis at 1 to 3 hr after being cultured in α‐medium. This phenomenon was observed when bone marrow was incubated as a plug, but not when incubated as a cell suspension in the present experimental conditions.

These results suggest that a medullary structure is necessary in order to observe this effect and/or that accessory cells are destroyed during the process of single cell preparation.
Some Long‐Term Cell Kinetic Effects of Ionizing Radiation On Mouse Bladder Urothelium
Authors: Reitan J. B.
Published: May 2008

Abstract. The cell kinetics of the mouse bladder urothelium were followed with tritiated thymidine pulse labelling and flow cytometry for one year after irradiation with electrons. No perturbations were registered after 10 Gy. Three to four weeks after 20 Gy an elevation of the labelling index with a subsequent return to normal was seen. Flow cytometry revealed some increase in the proportion of octaploid nuclei at the same time. From about six months after irradiation the normal polyploidization decreased. the urothelium turned into a mainly diploid cell population. the proportion of diploid S phase cells also increased. the data give some support to the model hypothesis of reactive proliferation in a ‘flexible’ tissue, according to Wheldon et al. (1982).
Circadian Variation In Migration Velocity In Small Intestinal Epithelium
Authors: Kaur P. , Potten C. S.
Published: May 2008

Abstract. The variation in migration rates of cells within the small intestinal epithelium was studied over a 24‐hr period at 3‐hr intervals (migration of cells was studied independently for the crypts and the villi using the changing distributions of [3H]TdR labelled cells as an indicator of cell migration).

Clear changes in the rates of cell movement were observed during a 24‐hr period for both crypt and villus epithelium. the rates of cell migration in these two compartments did not correlate well with the exception of samples taken at 18.00 hours. At this time of day there appeared to be no cell movement at all in either crypts or villi. There was not a good correlation between the migration velocity throughout the day and the changes in the number of mitoses.

It is proposed that mitotic rates do not directly govern migration rates but that the converse may be true. Further, the lack of correlation between crypt and villus migration rates at any time of day suggest that the mechanisms controlling all movement in these two regions of small intestinal epithelium may be different.
Cell Migration Velocities In the Crypts of the Small Intestine After Cytotoxic Insult Are Not Dependent On Mitotic Activity
Authors: Kaur P. , Potten C. S.
Published: May 2008

Abstract. The role of mitotic activity in the normal process of intestinal epithelial cell migration was investigated. the movement of [3H]TdR‐labelled cells in the crypt‐villus column was used to study migration both in the crypts and on the villi. Radiation alone or in conjunction with other cytotoxic agents (hydroxyurea, cyclophosphamide and isopropyl‐methane sulphonate) was used to eliminate cell division activity and to decrease crypt cellularity. This was done in order to determine the role of ‘mitotic pressure’ in driving cell migration.

It has been clearly demonstrated in this study that cell migration, both within the crypts and on the villi, can take place in the complete absence of mitotic activity and after a drastic decrease in crypt cellularity. These results add to the continually mounting evidence against the idea that the ‘pressure’ generated by mitoses within the crypt or indeed in other epithelial regions is responsible for propelling epithelial cells. the data also demonstrate that the migration mechanisms are resistant to cytotoxic exposure.
Intestinal Cell Proliferation. I. A Comprehensive Model of Steady‐State Proliferation In the Crypt
Authors: Loeffler M. , Stein R. , Wichmann H.‐E. , Potten C. S. , Kaur P. , Chwalinski S.
Published: May 2008

Abstract. Cell replacement in the crypt of the murine small intestine has been studied and modelled mathematically under steady‐state conditions. A great deal of information is available for this system, e.g. cell cycle times, S phase durations, the rate of daily cell production, the Paneth cell distribution etc. the purpose of the present work was to consider simultaneously as much of these data as possible and to formulate a model based upon the behaviour of individual cells which adequately accounted for them. A simple mathematical representation of the crypt has been developed. This consists of sixteen stem cells per crypt (Tc= 16 hr, Ts= 9 hr), and four subsequent transit cell divisions (Tc= 11 to 12 hr, Ts= 8 hr) before maturation. Experimental data considered to test the modelling were LI and data on the number of vertical runs of similarly labelled cells. All data were obtained from the ileum after 25 μCi [3H]TdR given at 09.00 hours. A number of alternative assumptions have been considered and either accepted or rejected. Two alternative model concepts of cell displacement explain the data equally well. One is dependent upon strong local cell generation age determinance while the other could accommodate any weak local cell displacement process in conjunction with an environmental cut‐off determinant at the middle of the crypt. Both models provide new interpretations of the data, e.g. certain rates of lateral cell exchange between neighbouring columns (250 to 350 per crypt per day out of a total of 420 cell divisions per day) can be concluded from run data, while LI data provide information about the mechanisms involved in maintaining a position‐related age order in the crypt.
Proliferation kinetics of aortic smooth muscle cell populations: comparison of normotensive and spontaneously hypertensive rats
Authors: Tjurmin A. V. , Lacis R. V. , Printseva O. Yu.
Published: May 2008

Abstract. An in vitro autoradiographic study of the proliferation of smooth muscle cells (SMC) from the aorta of normotensive and spontaneously hypertensive rats has been made. It was found, in primary culture, that SMC of spontaneously hypertensive rats entered proliferation at 2‐2.5 days later than those from normotensive animals. As revealed by their very intensive labelling, a subpopulation of SMC with a high turnover rate was found in primary culture. In freshly isolated SMC from normotensive rat aorta, a subpopulation in S phase was detected, but we failed to detect it in aortae from spontaneously hypertensive rats. A difference in proliferative behaviour was also observed in subcultures of SMC from rats of both strains.
Circadian synchronization of hepatocyte proliferation in young rats: the role played by adrenal hormones
Authors: Barbason H. , Herens Ch. , Mormont M.‐C. , Bouzahzah B.
Published: May 2008

Abstract. From the 20th day to the 30th day of life, the mitotic rhythm is progressively induced by a reduction in nocturnal values, while diurnal rhythms remain unchanged. Mitotic peaks emerge at 10.00 hours.

A labelling index wave occurs 8 hr before the corresponding mitotic wave, with a peak at 02.00 hours and a minimum in the evening, coincidental with the acrophase of plasma corticosterone level (activity phase).

Labelled mitoses curves and metaphase accumulation after colchicin injection show that the duration of the S, G2 and M phases remain approximately constant and that the circadian variation is due to a variation in the rate of cells that enter these successive phases. During the synchronization period (from day 20 to 30), the growth fraction decreases progressively. Adrenalectomy at this time is followed by a higher cell proliferation and all rhythms disappear after 2 days.

Corticosterone injected before the triggering of the rhythmic activity in 17‐day‐old rats immediately reduces the labelling index, while the mitotic index is decreased 10 hr later; this delay is equal to the S + G2 duration.

The results are discussed. They favour the hypothesis that the circadian variation of corticosterone is responsible for the induction of a circadian variation in developmental cell proliferation by inhibition of the G1‐S transition when it is higher in the evening.

The circadian rhythm of hepatic cell proliferation in rats appears on the 20th day of life, when the hypothalamo‐adrenal axis is mature enough for circadian activity to occur.
DNA synthesis in Bloom's syndrome fibroblasts
Authors: Fujikawa‐Yamamoto K. , Odashima S. , Kurihara T. , Murakami F.
Published: May 2008

Abstract. The relationship between relative rates of DNA synthesis and DNA content in Bloom's syndrome fibroblasts (BS cells) was investigated by flow cytometry. The cells were pulse labelled with 5‐bromo‐2′‐deoxyuridine (BrdU). The BrdU content and cellular DNA content of individual BS cells were simultaneously measured by flow cytometry in which the cells were double‐stained by a FITC‐conjugated anti BrdU monoclonal antibody (mAb) for the BrdU content (green) and by PI (propidium iodide) (red) for total DNA content. Their red fluorescence histograms were analysed by a microcomputer to evaluate the cell fractions of each S compartment. The BrdU uptake in the early S phase of BS cells was lower than that of normal cells (fibroblasts from skin of a normal human), whereas the uptake in the middle and late S phase was essentially the same as that of normal cells. The early S phase in BS cells accounted for over 50% of the S phase cells. These findings suggest that, in comparison with normal cells, the rate of DNA synthesis in the early S phase of BS cells is lower, but is identical to controls in the middle and late S phases.
Repopulation of spleens of irradiated mice after injection of spleen cell subpopulations
Authors: Girard R. , Metezeau P. , Chaby R.
Published: May 2008

Abstract. Haemopoietic stem cells present in the spleen of adult mice were analysed by grafting X‐irradiated animals with polystyrene‐nonadherent (NABS) and polystyrene‐adherent (ABS) B‐enriched splenocytes from syngeneic donors. The progeny of the haemopoietic stem cells present in NABS and ABS subsets were studied with respect to size, surface markers, and response to mitogens and antigens. Ninety‐six per cent of the precursors of the myeloid cell lineage (CFU‐S) were present in the NABS fraction (50‐fold enrichment). The presence in NABS of progenitors of functional T and B lymphocytes was also demonstrated. Twelve days after grafting with NABS, more than 80% of the recipient splenocytes were large and nonadherent granulocyte‐like cells. These cells had surface similarities with NABS from normal mice, since both populations reacted with peanut agglutinin and with a rabbit anti‐NABS (RAN) serum.
Maintenance of granulopoiesis in long‐term bone marrow cultures from W/Wv mice and effects of lipopolysaccharide on granulopoiesis in culture
Authors: Kirikae T. , Yoshida M. , Sawada H. , Tezuka H. , Kitamura Y. , Mori K. J.
Published: May 2008

Abstract. An attempt was made to establish long‐term cultures of marrow cells from genetically anaemic W/Wv mice. Two batches of horse sera were used. One batch of horse serum (HS‐lot A) supported long‐term maintenance (up to 20 weeks) of granulopoiesis in vitro. The number of suspension cells in W/Wv marrow culture was maintained at the same level as that in the control +/+ culture, but the number of granulocyte‐macrophage progenitor cells (GM‐CFC) and the ratio of immature to mature granulocytes were at a lower level than those in +/+ culture. These data suggest that haemopoietic progenitors in W/Wv cultures maintain a higher level of differentiation, and hence an increased self‐renewal than those in +/+ cultures. Another batch of horse serum (HS‐lot B) was less effective in the maintenance of the cultures, and the cultures deteriorated within 10 weeks. Addition of bacterial lipopolysaccharide (LPS) induced increased granulopoiesis in +/+ cultures, whereas such treatment resulted in the depletion of suspension cells in W/Wv cultures. The results suggest that haemopoietic cells of W/Wv mouse cannot cope with the strong stimulus for differentiation that occurs after the administration of LPS, although the cells can continue a moderately increased self‐renewal and differentiation, as indicated by the results in the culture with HS‐lot A.
The production of factors regulating the proliferation of haemopoietic spleen colony‐forming cells by bone marrow macrophages
Authors: Wright E. G. , Lorimore S. A.
Published: May 2008

Abstract. Media conditioned by normal murine bone marrow cells contain an inhibitor of haemopoietic spleen colony‐forming cell proliferation that is concentrated in a nominal 50‐100K fraction. Media conditioned by regenerating marrow cells contain a proliferation‐stimulatory activity that is concentrated in a nominal 30‐50K fraction. Cell separation experiments demonstrated that the activities are produced by adherent, phagocytic, radioresistant, Thy 1.2‐ Fc+, F4/80+ cells. Cultured macrophages, obtained from long‐term marrow cultures or derived from progenitor cells in methyl cellulose cultures are also capable of producing inhibitory and stimulatory activities. The results are consistent with macrophages being an important source of stem cell proliferation regulators in the bone marrow.
Long duration of mitosis and consequences for the cell cycle concept, as seen in the isthmal cells of the mouse pyloric antrum. II. Duration of mitotic phases and cycle stages, and their relation to one another
Authors: El‐Alfy M. , Leblond C. P.
Published: May 2008

Abstract. The kinetics of isthmal cells in mouse antrum were examined in three ways: (a) the duration of cell cycle and DNA‐synthesizing (S) stage was measured by the ‘fraction of labelled mitoses’ method; (b) the duration of interphase and mitotic phases was determined from how frequently they occurred; and (c) mice were killed at various intervals after an intravenous injection of 3H‐thymidine to time the acquisition of label by the various phases of mitosis.

The duration of the isthmal cell cycle was found to be 13.8 hr and that of the DNA‐synthesizing (S) stage, 5.8 h. Estimates for the duration of the G1 and G2 stages were 6.8 and 1.0 hr, respectively.

From the frequency of mitotic phases, defined as indicated in the preceding article (El‐Alfy & Leblond, 1987) and corrected for the probability of their occurence, it was estimated that prophase lasted 4.8 hr; metaphase, 0.2 hr; anaphase, 0.06 hr and telophase, 3.3 hr, while the interphase lasted 5.4 hr. In accordance with this, the duration of the whole mitotic process was 8.4 hr.

Ten minutes after an intravenous injection of 3H‐thymidine, 38% of labelled isthmal cells were in interphase and 62% in early or mid prophase, while cells in late prophase and other mitotic phases were unlabelled. After 60 min, label was in late prophase, after 120 min, in mid telophase and after 180 min, in late telophase.

We conclude that there is overlap between some mitotic phases and cycle stages. Thus, while nuclei are at interphase during the early third of S, they are in prophase during the late two‐thirds as well as during G2. Also, nuclei are in telophase during the early half of G1 but at interphase during the late half. Differences in nuclear diameter show that subdivision of both S and G1 into early and late periods is practical.
The effect of prolonged stress‐inducing electrical stimulation on cell proliferation in rat palatal epithelium
Authors: Østergaard E. , Fisker A. V. , Karring T.
Published: May 2008

Abstract. This study examines whether blocking of cell division by stress‐inducing electrical stimulation can be maintained for a prolonged period of time and whether this results in the accumulation of a large number of cells ready to divide when the block is released.

A total of 96 rats was subjected to electrical stimulation at intervals of 30 min for periods of 2,4,6 or 12 hr. Groups of animals were killed every second hour during these stimulation periods. After 2, 4 and 6 hr groups of animals were exempted from further stimulation and killed 2 or 4 hr later. After termination of the 12 hr stimulation period, groups of animals were killed every second hour during the succeeding 24 hr. Forty‐eight animals were left undisturbed and served as controls. Two and a half hours prior to death, each of the experimental and control animals was injected intraperitoneally (i.p.) with colchicine. Histological sections of the palatal mucosa were prepared and the numbers of arrested metaphases were counted.

The electrical stimulation for 2, 4, 6 and 12 hr consistently resulted in a reduced number of cells entering mitosis, indicating a blockade at the G2/M transition. However, with an increase in the length of electrical stimulation, an increasing number of cells passed the block, while a decreasing number entered mitosis during the first 4 hr following cessation of the stimulation. The sum of metaphases accumulated during the various stress periods and the following 4 hr was always similar and consistently lower than the number of metaphases accumulated in the control animals within the same time periods. This observation indicates that, during stress‐inducing electrical stimulation and the succeeding 4 hr, only a defined number of cells can enter the mitotic phase. Thus, in addition to the block at the G2/M transition, there appears to be another block of cell division at an earlier stage in the cell cycle.
Combined flow and absorption DNA measurements of [3H]TdR‐labelled tumour cells. I. Studies of MCa‐11 cells grown as tumours in vivo and as exponential cultures in vitro*
Authors: Allison D. C. , Chakerian M. , Ridolpho P. F. , Anderson S. , Curley S. , Wilder M. E. , Robertson J.
Published: May 2008

Abstract. Flow cytometry of cellular DNA content provides rapid estimates of DNA distributions, i.e. the proportions of cells in the different phases of the cell cycle. Measurements of DNA alone, however, yield no kinetic information and can make it difficult to resolve the cell cycle distributions of normal and transformed cells present in tumour biopsy specimens. The use of absorption cytophotometry of the Feulgen DNA content and [3H]TdR labelling of the same nuclei provides objective criteria to distinguish the ranges of DNA content for G0/G1, S, and G2/M cells. We now report on a study in which we combined flow and absorption cytometry to resolve the cell cycle distributions of host and tumour cells present in biopsy specimens of MCa‐11 mouse mammary tumours labelled in vivo for 0.5 hr with [3H]TdR. A similar analysis of exponential monolayer cultures, labelled for 5 min with [3H]TdR under pulse‐chase conditions, revealed a highly synchronous traversal of almost all cells through the different phases of the cell cycle. Combination of the flow and absorption methods also allowed us to detect G2 tumour cells in vivo and a minor tumour stem‐line in vitro, to show that these two techniques are complementary and yield new information when they are combined.
Haemopoietic stem cell proliferation in the bone marrow of Sl/Sld mice
Authors: Wright E. G. , Lorimore S. A.
Published: May 2008

Abstract. In marrow from Sl/Sld mice (but not +/+ mice) day 7 and day 8 CFU‐S proliferate whilst day 10 and day 12 CFU‐S exhibit negligible proliferation. Media conditioned by both +/+ and Sl/Sld marrow contains an inhibitor of CFU‐S proliferation but day 8 CFU‐S in +/+ and Sl/Sld marrow show marked dose‐response differences to this factor. To inhibit the proliferation of Sl/Sld CFU‐S required approximately ten times the concentration of inhibitor that inhibited the proliferation of +/+ CFU‐S. Thus abnormally responsive day 8‐CFU‐S were shown to proliferate in an inhibitory environment.

Abnormalities in Sl/Sld CFU‐S function were also demonstrated in heterotopic transplantation experiments using +/+ and Sl/Sld donors and hosts to obtain ectopic bone marrow with various stromal (donor) and haemopoietic (host) combinations. Day 8 Sl/Sld CFU‐S were seen to proliferate, irrespective of whether the stromal environment was derived from Sl/Sld or +/+ marrow.

Sl/Sld mice are generally regarded as animals in which there is a genetically determined defect in haemopoiesis due to an abnormality in the haemopoietic environment. It is difficult, however, to attribute the abnormal CFU‐S behaviour in these experiments to environmental factors and the results are consistent with mutation at the Sl locus affecting the responses of CFU‐S to regulatory signals, i.e. the genetic defect is not confined to the stromal environment.
Inhibition of hepatocyte proliferation in vivo by a glycopeptide from rat serum
Authors: Nadal C.
Published: May 2008

Abstract. The activity of a glycopeptide prepared from rat serum by treatment with trypsin and ultrafiltration was investigated in several in vivo proliferation systems. In baby rat hepatocytes synchronized by a subcutaneous injection of casein solution it caused a G1‐S block, stopping cells at the end of the G1 phase and sending them back to the G0 phase. The glycopeptide also caused a G1‐S block in young adult rats during the first semi‐synchronized wave of proliferation that followed partial hepatectomy. Inhibition of hepatocyte proliferation by the glycopeptide was suppressed by blood proteins from normal rats but not from acute phase rats. α1‐acid glycoprotein, an acute phase protein, increased this inhibition and reversed the antagonistic effect of normal blood proteins. In normal baby rats a G1‐S block of non‐synchronously proliferating hepatocytes was produced in two situations in which the antagonistic effect of normal blood proteins was eliminated: after treatment of the glycopeptide with leucine‐aminopeptidase, and after mixing it with α1‐acid glycoprotein. The glycopeptide did not inhibit cell proliferation in kidney, submaxillary gland, or tongue epithelium. It seems to be the active component of a system that inhibits the proliferation of hepatocytes, probably by reducing their sensitivity to various mitogenic stimuli.
Cytotoxic effect and induction of sister chromatid exchange in exponentially growing rat 9L gliosarcoma cells after brief exposure to BrdU
Authors: Zhang R. X. , Nagashima T. , Hoshino T.
Published: May 2008

Abstract. The magnitude of DNA modulation in rat 9L gliosarcoma cells after a brief exposure to bromodeoxyuridine (BrdU) was studied by assaying colony‐forming efficiency (CFE) and the number of sister chromatid exchanges (SCEs) per metaphase. The CFE assay showed that a 1‐hr exposure to BrdU, at concentrations ranging from 10 to 1000 μM, produced a maximum cell kill of 5%. After a 2‐hr exposure to 20 μM BrdU, the surviving fraction was 0.99, and even at a BrdU concentration of 1000 μM, 77% of the 9L cells survived. Compared with control cultures, the relative number of SCEs per metaphase in treated cultures was increased after a 1‐hr exposure to BrdU at concentrations of 100 μM or more and after a 2‐hr exposure to concentrations of 20 μM or more; no increase was observed in cells treated for 30 min with BrdU at concentrations up to 1000 μM. When the treated cells were allowed to grow in BrdU‐free growth medium, the number of SCEs per metaphase returned to the control level within 24 hr, even after exposure to BrdU at concentrations as high as 1000 μM. These results demonstrate that exposure to BrdU at concentrations of up to 1000 μM for 30 min, 100 μM for 1 hr, and 20 μM for 2 hr causes little modulation of DNA.
Effect of graft versus host reaction on cell cycle time in neonatal mouse jejunum
Authors: Lund E. K. , Smith M. W.
Published: May 2008

Abstract. The duration of cell cycle parameters in control mouse jejunum has been compared with that found following induction of a graft‐versus‐host reaction (GvHR) during the first 3 weeks of postnatal life.

Values for tc, and tG1 were found to decrease progressively during normal development: estimates for the whole crypt column in 21‐day‐old mice were approximately half to one quarter those found 6 days after birth 12.1 ± 0.5 hr and 24.2 ± 0.3 hr for tc; 2.8 ± 0.3 hr and 12.1 ± 0.3 hr for tG1 respectively; (means ± SE).tS and tG2 were found to remain approximately constant during this period of neonatal development.

Injecting foreign spleen cells into 3‐day‐old mice produced no effect on crypt cell proliferation or cell cycle parameters measured 3 days later. GvHR mice studied 8 days after spleen cell injection, however, showed both an increase in crypt cell proliferation and decreases in the values for tc and tG1, to levels similar to those normally found in 21‐day‐old control animals (tc 12.4 ± 0.4 hr and tG1 5.4 ± 0.4 hr for 11‐day‐old GvHR mice). The possible mechanism leading to these changes is discussed.

The ability of GvHR to stimulate cell proliferation is used in the present work to test the hypothesis that the total number of cell divisions taking place after birth determines the temporal sequence of changes in disaccharidase content produced during neonatal development.
Prediction of X‐ray induced mitotic delay and recovery of G2 cells
Authors: Easton D. M. , Schneiderman M. H.
Published: May 2008

Abstract. A mathematical model is presented that predicts the delay of mitosis caused by X‐irradiation of an asynchronous, exponentially growing cell culture (data of Schneiderman & Schneiderman, 1984). In the model, based on Gompertz kinetics, the driving function to generate the curves is a simple exponential decay expression. For the delayed mitotic progress curves, this function characterizes the distribution of the time required for cells to enter mitosis.
Haemopoietic spleen colony growth: a versatile, parsimonious, predictive model
Authors: Blackett N. M.
Published: May 2008

Abstract. Substantial support has been obtained for the stochastic model for stem cell differentiation first proposed by Till, McCulloch & Siminovitch (1964), over 20 years ago. By adding a cell maturation pathway, it is possible to predict (by computer simulation) the total number of cells and consequently the time at which individual colonies appear and disappear.

Only a few uncontroversial assumptions are required to predict that cells, uniform with respect to self‐renewal, are capable of producing the high proportions of late disappearing and late appearing colonies observed experimentally in the spleens of irradiated mice that have been injected with normal haemopoietic cells. It is shown that differences in stem cell self‐renewal only slightly influence the time of appearance of colonies; whereas changes in the kinetics of the maturing cells, by changing the size of colonies, has a marked effect on the time of appearance and disappearance of colonies and on the average doubling‐time of colony‐forming cells per colony (but not the doubling‐time of individual colonies).

These results (1) seriously question the prevailing view that spleen colonies scored at 8 days measure a separate population (without the capacity for self‐renewal), from those scored at 12 days; (2) argue against the existence of multiple sub‐populations of stem cells with differing self‐renewal and toxicity to cytotoxic agents; (3) help to identify those experiments for which it is obligatory to postulate heterogeneity, and (4) are consistent with self‐renewal being regulated by a feedback control of stem cell differentiation, to which only proliferating stem cells can respond and where the stimulus for differentiation decreases at a time when the bone marrow is known to be depleted.