bluuebunny/crossref_metadata_2025 huggingface dataset:
CELLULAR AND NUCLEAR VOLUME DURING THE CELL CYCLE OF NHIK 3025 CELLS
Authors: Steen H. B. , Lindmo T.
Published: May 2008

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.
DEVELOPMENT OF HAEMATOPOIETIC COLONIES ON THE MACROPHAGE LAYER FORMED IN THE PERITONEAL CAVITY OF S1/S1D MICE
Authors: Miyano Y. , Tamai M. , Kitamura Y.
Published: May 2008

The colony‐forming ability of haematopoietic cells was examined on the macrophage layer formed in the peritoneal cavity of S1/S1d mice. the bone marrow cells of the congenic +/+ mice formed many macroscopic colonies on the macrophage layer of the S1/S1d mice although they did not form macroscopic colonies in the spleens of the same S1/S1d recipients. the size and the differentiation pattern of colonies on the macrophage layer of the S1/S1d mice were comparable to those of the colonies on the macrophage layer of the +/+ mice. There are two possible explanations for these results: (a) the microenvironmental defect of the S1/S1d mice has a more prominent effect on the development of spleen colonies than that of macrophage‐layer colonies because ‘Steel’ locus may not be expressed significantly in the peritoneal macrophages or (b) because the cells that make colonies on the macrophage layer may be more differentiated cells than the multipotential stem cells that make colonies in the spleen.
ABILITY OF THYMIC LYMPHOCYTES TO ALTER CFU KINETICS IN RADIATION CHIMERAS
Authors: Shinpock Sarah Garner , Goodman Joan Wright
Published: May 2008

It is known that the poor colony‐forming ability of B6 bone marrow transplanted into B6D2F1 hybrids can be improved if B6 lymphocytes are given in addition. It was recently reported that the augmenting lymphocytes decrease the doubling time of differentiating hemopoietic cells. to determine whether thymus cells alter the self‐renewal of CFUs in this parent F1 combination, retransplan‐tation and 3H‐thymidine ‘suicide’ were employed as methods to determine the cell‐division rate. We have observed that in the presence of thymocytes, parental bone marrow cells are seeded more efficiently in the spleen, and the lag phase of the CFUs growth curve is shortened. However, thymic lymphocytes do not increase the slope of the exponential growth phase of CFUs.
A New Analytical Method For Determining Duration of Phases, Rate of Dna Synthesis and Degree of Synchronization From Flow‐Cytometric Data On Synchronized Cell Populations
Authors: BECK H.‐P.
Published: May 2008

L‐cells synchronized by mitotic selection were investigated by flow‐cytometry nd the fractions of cells in the various cell cycle compartments were determined as a function of time. A new analytical evaluation procedure was developed, by which the mean transit‐times of cells through various cell cycle phases can be calculated from these data. Three examples for application of the method are presented: (1) determination of the duration of G1, S, G2+ M and of the whole cell cycle; (2) calculation of the rate of DNA synthesis in several subcompartments of the S‐phase; and (3) evaluation of the degree of synchronization at different stages of the cell cycle.
G2 Sub‐Population In Mouse Liver Induced Into Mitosis By Lead Acetate
Authors: Choie D. D. , Richter G. W.
Published: May 2008

A single intracardiac dose of lead acetate (40 μ lead/g body weight) induced a 25‐fold increase in mitosis of mouse hepatocytes 5 hr after injection, as determined by autoradiography. the prompt appearance of a mitotic wave and the relatively large number of mitoses suggest that the mitotic cells were derived from a hepatocyte sub‐population arrested in the G2 phase. the injection of lead also stimulated a small increase in labeled hepatocytes within 6 hr. Analysis of grain counts gave no evidence for unscheduled DNA synthesis. the incremental labeled cells may have originated from a small fraction of the G1 population that was ready to enter the S phase without the usual pre‐synthetic delay.
Growth Fraction and Cycle Duration of Hepatocytes In the Three‐Week‐Old Rat
Authors: Schultze B. , Kellerer A. M. , Grossmann C. , Maurer W.
Published: May 2008

The proliferation of hepatocytes in the liver of 3‐week‐old rats has been investigated by autoradiographic methods. This investigation is a continuation of earlier work on the same topic (Schultze & Maurer, 1972; 1973). 21 days after birth, 102 rats received a single injection of 3H‐TdR. the percentage of labelled mitoses was then determined 1 hr later and at various times throughout the interval up to 12 days after application of 3H‐TdR. In agreement with earlier work, a first peak of labelled mitoses was found 7 hr after 3H‐TdR injection. the area under the peak indicates an S phase duration of 8 hr. In addition a second very broad peak of labelled mitoses was found between 2 and 12 days after pulse labelling. the analysis of the results leads to the conclusion that the hepatocytes of the 3‐week‐old rat have a growth fraction close to 1 and a doubling time of 6–7 days. This is at variance with earlier results of Post, Huang & Hoffman (1963) and Grisham (1969) who had derived a value of 21.5 hr for the duration of the cell cycle and a value of only 0. 1–0.2 for the growth fraction of the hepatocytes.
DEFECT OF ERYTHROPOIESIS IN NON‐LEUKAEMIC AKR MICE
Authors: Legrand E. , Duplan J. F.
Published: May 2008

The kinetics of the CFU population and of erythropoiesis were investigated in the AKR strain mouse prior to the onset of thymic leukaemias: haemopoiesis was compared in syngeneic AKR, semi‐allogenic C3H and (C3H x AKR) F, mice injected with AKR stem cells. These experiments demonstrate that the reduction in the number of spleen colonies previously described by Perkins et al. (1971) in syngeneic hosts, as compared to semi‐allogenic C3H hosts, is actually related to defective erythropoiesis resulting from a dysfunction of the AKR haemopoietic inductive microenvironment (HIM). Erythropoietin secretion is normal in AKR mice. the early haemopoietic events related to the stem cell: lodgement of the CFU (‘f’ factor) and doubling time, are not disturbed, but the onset of CFU proliferation is markedly delayed in the AKR strain. the main expression of the AKR HIM dysfunction is a significant reduction in the number of erythroid (E) colonies and an impaired output of red blood cells per E‐colony in the syngeneic host as compared to the allogenic one. In addition, data indicate that a weakly histo‐incompatible system, such as that in C3H and hybrid hosts, does not interfere with the stages of haemopoiesis except by lengthening the doubling time of the CFU. the results, on the whole, emphasize the prevalent influence of HIM.
ON THE EXISTENCE OF ‘ARRESTED G2 CELLS’ IN MOUSE EPIDERMIS
Authors: Sauerborn R. , Balmain A. , Goerttler K. , Stohr M.
Published: May 2008

It has been postulated that mouse epidermis contains two populations of resting cells, one of which is blocked at the G1‐S boundary and the other between G2 and mitosis. the ‘arrested G2 cells’ were estimated, by the labelled mitosis method, to comprise 510% of the epidermal population and presumed to function as a ‘reserve pool’ which could be activated by wounding. A comprehensive search has now been carried out for arrested G2 cells in mouse epidermis using the direct methods of single cell and flow through cytophotometry. No evidence was obtained which supports the existence of such a cell compartment. Suitable control experiments were carried out to ensure that G2 cells were not lost during the isolation of epidermal nuclei.
LACK of DNA SYNTHESIS INHIBITORY ACTIVITY IN an IMMUNOSUPPRESSOR OBTAINED FROM SPLEEN
Authors: DIATLOFF C. , BENGTSON A. , BILLARDON C. , OELHO A. MACIEIRA‐C
Published: May 2008

A tissue extract derived from bovine spleen which is an immunosuppressor in vivo inhibits the incorporation of the two DNA pyrimidine nucleosides but does not inhibit the incorporation of purine nucleosides. the results indicate that the immunosuppressive action of the spleen extract is not mediated via inhibition of cell division.
BISACK ANALYSIS OF THE PHYTOHAEMAGGLUTININ‐INDUCED PROLIFERATION OF HUMAN PERIPHERAL LYMPHOCYTES
Authors: Tice R. , Thorne P. , Schneider E. L.
Published: May 2008

The rate of stimulation as well as subsequent cell cycle duration was examined in phytohaemagglutinin‐stimulated human peripheral lymphocytes grown in vitro in the presence of non‐inhibitory concentrations of bromodeoxyuridine. After incorporation of this heavy atom analogue of thymidine into replicating cellular DNA, it was possible to identify unequivocally metaphase cells which had replicated for one, two and three or more cell cycles. Utilizing this technique, distribution curves were obtained for the appearance of metaphase cells in successive generations, were analysed by a computer simulation model, and the rate of stimulation (4.5% per hr of the remaining unstimulated population) and cell cycle duration (12·3 hr) were determined. The results were compared with those obtained by autoradiography and the possible relationship to the ‘transition probability’ model for cellular proliferation is discussed.
ORGANIZATION OF HAEMOPOIETIC STEM CELLS: THE GENERATION‐AGE HYPOTHESIS
Authors: Rosendaal M. , Hodgson G. S. , Bradley T. R.
Published: May 2008

This paper proposes that the previous division history of each stem cell is one determinant of the functional organization of the haemopoietic stem cell population. Stem cells from a lineage of stem cells which have generated many stem cells (older stem cells) are used in the animal to form blood before stem cells which have generated few stem cells (younger stem cells). The stem cell generating capacity of a lineage of stem cells is finite. After a given number of generations a stem cell is lost to the stem cell compartment by forming two committed precursors of the cell lines. Its part in blood formation is taken by the next oldest stem cell. We have called this proposal the generation‐age hypothesis.

Experimental evidence in support of the proposal is presented. We stripped away older stem cells from normal bone marrow and 12 day foetal liver with phase‐specific drugs and revealed a younger population of stem cells whose capacity for stem cell generation was three‐ to four‐fold greater than that of the average normal, untreated population. We aged normal stem cells by continuous irradiation and serial retransplantation and found that their stem cell generative capacity had declined eight‐fold. We measured the stem cell generative capacity of stem cells in the bloodstream. It was a half, to a quarter that of normal bone marrow stem cells and we found a subpopulation of circulating stem cells whose capacity for stem cell generation was an eighth to a fortieth that of normal femoral stem cells. This subpopulation was identified by its failure to express the brain‐associated antigen which was present on 75% of normal femoral stem cells but was not found on their progeny, the committed precursors of granulocytes.
DELAY OF CELL CYCLE PROGRESSION AFTER X‐IRRADIATION OF SYNCHRONIZED POPULATIONS OF HUMAN CELLS (NHIK 3025) IN CULTURE
Authors: Lindmo T. , Pettersen E. O.
Published: May 2008

The effect of X‐irradiation on the cell cycle progression of synchronized populations of the human cell line NHIK 3025 has been studied in terms of the radiation‐induced delay of DNA replication and cell division. Results were obtained by flow cytometric measurement of histograms of cellular DNA content and parallel use of conventional methods for cell cycle analysis, such as pulse labelling with [3H]thymidine and counting of cell numbers. The two sets of methods were generally in good agreement, but the advantages of employing two independent techniques are pointed out.

Irradiation was found to have a minor influence on DNA replication. As compared with unirradiated populations, half‐completed DNA replication was 20‐30 min delayed in populations given 580 rad in mid‐G1 or 290 rad in early S.

Cell cycle progression was markedly delayed in G2. The sensitivity induction of this delay was 0·6 min/rad for populations irradiated in mid‐G1, and 1·4 min/rad for populations irradiated in early S.
GROWTH OF MOUSE AND HUMAN BONE MARROW IN DIFFUSION CHAMBERS IN MICE
Authors: Niskanen E. , Cline M. J.
Published: May 2008

Both murine and human bone marrow cells were cultured in plasma clots which were formed inside diffusion chambers implanted into cyclophosphamide‐ and saline‐treated mice. After an initial fall, the number of mouse bone marrow cells and numbers of mouse myeloid stem cells (CFU‐C) and agar cluster‐forming units rose faster in the cyclophosphamide‐treated animals. These hosts also favored formation of myeloid (CFU‐D‐G) and erythroid (CFU‐D‐E) colonies and myeloid clusters in the plasma clot. The number and growth rate of mouse CFU‐D‐G were higher than those of CFU‐C from the same marrow population. These observations suggest the existence of humoral factors stimulating granulocyte progenitor cell replication and differentiation. At its best the increment of CFU‐D‐E number was equivalent to that caused by a single 0·1 unit erythropoietin dose.

Culture of normal human marrow cells resulted in colonies in the plasma clot containing only granulocytes and macrophages. Cyclophosphamide‐treated host animals were essential for human CFU‐D‐G development. Plating efficiency for human marrow myeloid colonies was better in the conventional in vitro agar cultures than in diffusion chambers.
STUDIES WITH MURINE LPC‐1 PLASMACYTOMA USING [6‐14C]ARGININE
Authors: Humphrey R. L. , Trivedi S. M. , Frondoza Carmelita G.
Published: May 2008

[6‐14C]Arginine ([6‐14C]Arg) was used as an in vivo pulse label to study BALB/c murine LPC‐1 plasmacytoma synthesis and secretion of its tumour‐associated M component (IgG2a, k). With this isotope, an eight‐ to ten‐fold enhancement in the labelling of the γ globulin region and ten‐fold reduction in the albumin labelling were observed. Production and secretion of the M component was detected (within 30 min) after cell transfer. Only mice which received tumour cells showed significant labelling in the γ globulin region 24 hr after isotope injection. The labelling behaviour of the tumour M component correlated with the administered cell dose. The peak heights of radioactivity in the γ region increased with increments in cell number. When the percentage radioactivity diverted into M component was plotted as a function of cell dose, a linear relationship was noted. This study demonstrates the feasibility of using [6‐14C]Arg as a tool to follow the newly synthesized tumour‐associated protein, and provides a means of estimating tumour cell number.
DIURNAL VARIATION IN PROLIFERATIVE COMPARTMENTS AND THEIR RELATION TO CRYPTOGENIC CELLS IN THE MOUSE COLON
Authors: Hamilton Elizabeth
Published: May 2008

The depth of the crypts in mouse descending colon varied diurnally, between twenty‐six cells at 24.00 hours and thirty‐eight cells at 12.00 hours. Cell loss from the colon was greatest immediately before the maximum faeces production, at the beginning of the dark period. The labelling index of the colon also changed, from 9% at 20.00 hours to 16% at 12.00 hours. The greatest variation in labelling index occurred at the top of the zone of proliferative cells, between the ninth and eighteenth cell position up the crypt. In this region a synchronized cohort of about forty cells apparently entered S phase once a day. Although the length of the proliferative zone doubled at 12.00 hours, that of the non‐proliferative zone remained fairly constant all day. The number of cryptogenic cells per crypt was estimated by comparing single and split‐dose X‐ray survival curves. This gave a mean value of two cryptogenic cells per crypt. Crypts rarely regenerated from the base after irradiation. The cryptogenic cells probably lay between cell positions Nos 9 and 18 up the crypt and probably did not function as stem cells in the normal crypt.
COLONY‐FORMING UNITS IN DIFFUSION CHAMBERS (CFU‐d) AND COLONY‐FORMING UNITS IN AGAR CULTURE (CFU‐c) OBTAINED FROM NORMAL HUMAN BONE MARROW: A POSSIBLE PARENT–PROGENY RELATIONSHIP
Authors: Jacobsen N. , Broxmeyer H. E. , Grossbard E. , Moore M. A. S.
Published: May 2008

A series of experiments was performed to elucidate the relationship between cells that form granulocytic colonies in fibrin clot diffusion chambers implanted into the peritoneum (i.p.) of irradiated mice (CFU‐d) and day 7 and day 14 CFU‐c which give rise to colonies after 7 and 14 days in agar cultures in vitro, respectively.

Normal human bone marrow cells were cultured in suspension in vitro or in diffusion chambers implanted into irradiated or non‐irradiated mice. During these culture conditions there was an initial decrease in the number of CFU‐c per culture. This was followed by an increase between day 2 and day 7 of culture. No similar increase of neutrophilic CFU‐d was observed. When CFU‐d, day 14 and day 7 CFU‐c in normal marrow were separated by velocity sedimentation and cultured in suspension culture or in diffusion chambers for 7 days, the maximum increase of day 7 and day 14 CFU‐c was observed in slowly sedimenting cell fractions which contained the majority of CFU‐d. After 3 days in suspension culture, the maximum increase of day 14 CFU‐c was found in fractions which also gave rise to maximum numbers of CFU‐c after 7 days. However, day 7 CFU‐c were found in fractions which initially contained the majority of day 14 CFU‐c. No increase in CFU‐d was found in fractions initially containing peak numbers of CFU‐c. Between 53 and 71% of CFU‐c harvested from diffusion chambers in irradiated mice or from suspension cultures were sensitive to pulse incubation with tritiated thymidine, suggesting that the cells were proliferating during these culture conditions. In diffusion chambers implanted into non‐irradiated mice, however, CFU‐c were found to be relatively resistant to this treatment (3–11% sensitive to tritiated thymidine). Thus marked increases in CFU‐c were also observed during experimental conditions, where no significant DNA synthesis was detected. A reproducible time sequence of increase in CFU‐c populations in culture was observed. Day 14 CFU‐c and cells that gave rise to clusters on day 7 in agar increased between day 2 and day 4, whereas day 7 CFU‐c increased between day 4 and day 7.

The results suggested that CFU‐d gave rise to CFU‐c in culture and that day 14 CFU‐c were precursors of day 7 CFU‐c.
CHANGES IN GROWTH KINETICS OF JEJUNAL EPITHELIUM IN MICE MAINTAINED ON AN ELEMENTAL DIET
Authors: Lehnert Shirley
Published: May 2008

Changes in the kinetics of the intestinal epithelium were observed in mice maintained on an elemental diet containing hydrolysed protein and medium chain triglycerides. An increase in the length of the villi seen shortly after commencement of the diet was followed by a reduction in the rate of proliferation in the crypt. After 7 days on the diet, an equilibrium state was reached with the cellularity of the villi being 120% that of control while the number of proliferative cells/crypt was reduced by 35%. The proliferative response of the crypt following irradiation occurrred 16 hr later in diet‐fed mice than in controls. It was postulated that, because of the increased cellularity of the villus compartment in diet‐fed mice, additional time was required to reduce the number of villus cells to a critical level at which a proliferative response is induced in the crypt.
A CELL KINETIC MODEL TO EXPLAIN THE TIME OF APPEARANCE OF SKIN REACTION AFTER X‐RAYS OR ULTRAVIOLET LIGHT IRRADIATION
Authors: Al‐Barwari S. E. , Potten C. S.
Published: May 2008

Skin reactions to various doses of X‐rays (300 and 10 kV) and ultraviolet light (u.v.) have been compared using hairless mice. Two regions of epidermis with widely differing cell kinetics and gross structure have been compared. Little evidence could be found to support the idea that the early phases of the reaction are dependent on cell cycle time. The data can be explained by a model based on the assumption that epidermis contains only a small fraction of clonogenic (stem) cells and this fraction may vary in different epidermal regions. X‐rays appear to exert their greatest destructive action on these clonogenic cells while u.v. is more indiscriminate in its action, killing both clonogenic and non‐clonogenic cells.
THE ENHANCEMENT OF HAEMOPOIETIC STEM CELL RECOVERY IN IRRADIATED MICE BY PRIOR TREATMENT WITH CYCLOPHOSPHAMIDE
Authors: Blackett N. M. , Aguado M.
Published: May 2008

Studies are reported of the enhancement of stem cell recovery following whole body irradiation as a result of prior administration of cyclophosphamide. It is shown that the much larger enhancement of regeneration observed for the hosts own surviving stem cells, compared to the regeneration of injected bone marrow stem cells, is due to the different numbers of stem cells initiating the regeneration in conjunction with the time course of stem cell regeneration.

The results show that the environmental changes produced by cyclophosphamide greatly enhance haemopoietic recovery even though at the dose used this agent is relatively toxic to stem cells. Furthermore it has been shown that the level of stem cell regeneration is nearly independent of the γ‐ray dose in the range 3–8 gray (300–800 rad). If human bone marrow should respond similarly it follows that regeneration produced by cytotoxic drugs administered prior to radiation embodies a considerable safety factor as far as recovery of the haemopoietic system is concerned.
TRANSIT TIMES THROUGH THE CYCLE PHASES OF JEJUNAL CRYPT CELLS OF THE MOUSE ANALYSIS IN TERMS OF THE MEAN VALUES AND THE VARIANCES
Authors: Schultze B. , Kellerer A. M. , Maurer W.
Published: May 2008

Mean transit times as well as variances of the transit times through the individual phases of the cell cycle have been determined for the crypt epithelial cells of the jejunum of the mouse. To achieve this the fraction of labelled mitoses (FLM) technique has been modified by double labelling with [3H] and [14C]thymidine. Mice were given a first injection of [3H]thymidine, and 2 hr later a second injection of [14C]thymidine. This produces a narrow subpopulation of purely 3H‐labelled cells at the beginning of G2‐phase and a corresponding subpopulation of purely 14C‐labelled cells at the beginning of the S‐phase. When these two subpopulations progress through the cell cycle, one obtains FLM waves of purely 3H‐ and purely 14C‐labelled mitoses. These waves have considerably better resolution than the conventional FLM‐curves. From the temporal positions of the observed maxima the mean transit times of the cells through the individual phases of the cycle can be determined. Moreover one obtains from the width of the individual waves the variances of the transit times through the individual phases. It has been found, that the variances of the transit times through successive phases are additive. This indicates that the transit times of cells through successive phases are independently distributed. This statistical independence is an implicit assumption in most of the models applied to the analysis of FLM curves, however there had previously been no experimental support of this assumption. A further result is, that the variance of the transit time through any phase of the cycle is proportional to the mean transit time. This implies that the progress of the crypt epithelial cells is subject to an equal degree of randomness in the various phases of the cycle.
EFFECTS OF INTESTINALLY ABSORBED THYMIDINE ON TRITIATED THYMIDINE UTILIZATION
Authors: Williams R. P. , Cameron I. L. , Adrian E. K.
Published: May 2008

Experimental evidence presented suggests that [3H]TdR can be rapidly and efficiently transported from the intestine to the systemic circulation. This pathway for thymidine transport may be physiologically important since administration of cold thymidine in the drinking water enhances the utilization of a parenterally injected dose of [3H]TdR in several body tissues of the mouse.
THYMUS DERIVED INHIBITOR OF LYMPHOCYTE PROLIFERATION I. ISOLATION AND ASSESSMENT OF TISSUE SPECIFICITY
Authors: Rijke E. O. , Ballieux R. E.
Published: May 2008

Preparations from bovine thymus tissue were analyzed for their inhibitory effects during in vitro lymphocyte proliferation. The results indicate that these preparations strongly inhibit DNA synthesis in stimulated human peripheral lymphocytes, bone marrow cells, thymocytes and lymphoblastoid cells. This inhibition was dose‐dependent and not due to cytotoxicity of the preparations. No inhibition was found of the spontaneous proliferation of HeLa cells and human fibroblasts indicating that the inhibitory effect was specific for proliferating lymphocytes. Control preparations from bovine liver or kidney did not show any suppression in the test systems used.
GROWTH KINETICS OF A RAT MAMMARY TUMOUR TRANSPLANTED INTO IMMUNE‐SUPPRESSED MICE
Authors: Fu Karen K. , Steel G. G.
Published: May 2008

The growth kinetics of a transplanted rat mammary tumour and its xenografts in immune‐suppressed mice were studied using the technique of labelled mitoses. Growth of the tumour in rats was regular and uniform but when transplanted into mice the growth of the implants was irregular and generally slower. The second passage tumours in mice showed rapid and regular growth with a volume doubling time approximately half that for the tumours in the rat. Values for the G1 phase duration, intermitotic time and growth fraction were greater for the tumours in the mouse although the data for the first passage in mice were difficult to interpret. The kinetic changes between the rat and mouse hosts primarily reflect a large and variable amount of cell loss from the first passage xenografts in the mouse, with adaptation by the second passage towards reduced cell loss.
CORRELATION BETWEEN CELL SIZE AND POSITION WITHIN THE DIVISION CYCLE IN SUSPENSION CULTURES OF CHANG LIVER CELLS
Authors: Skog S. , Eliasson E. , Eliasson Eva
Published: May 2008

Chang liver cells from exponentially growing suspension cultures have been separated by sedimentation at unit gravity. Determinations of the protein content per cell showed that the fractionation procedure resulted in good separation of cells of different size. On the other hand, the DNA content of individual cells from the fractions, as determined cytofluorimetrically, indicated considerable heterogeneity in the size of cells from the same stage of the division cycle.

On the basis of earlier results on intermitotic growth and the variation in the length of the cell cycle in homogeneous cell populations, a mathematical model has been constructed and tested using a computer program. The present results on the size distribution of cells from the different stages of the mitotic cycle are consistent with a regeneration of size heterogeneity in each cell generation, as a result of the dispersion of intermitotic times. The variation in cell cycle times may be related to a probabilistic event in the G1 period. In the mathematical model it was necessary to include a mechanism by which the regeneration of abnormally large cells is prevented. The experimental data are compatible with a gradually increasing inhibition of growth in cells larger than a certain size (circa 400 pg protein per cell).
MITOTIC INDEX, INFLUX AND MEAN TRANSIT TIME IN THE HAMSTER CHEEK POUCH EPITHELIUM, A PARTIALLY SYNCHRONIZED CELL SYSTEM*†
Authors: Møller U. , Hartmann N. R. , Faber M.
Published: May 2008

Mitotic activity was followed in the epithelium of the hamster cheek pouch for about 12 hr in two experiments under different conditions of noise and light intensity.

A mathematical model based on a non‐stationary probability density function for the transit time through mitosis was developed, making an analysis of this partially synchronized cell system possible.

The most important result of the two experiments is the indication of a non‐stationary mean transit time for cells in mitosis. In the first experiment (70 db, 103 lux), which produced high mitotic indices (maximum 2.0%), the influx changed from 0 to 0.9%/hr (mean of 7‐hourly determinations: 0.4%/hr), and the mean transit time from 1.9 to 5.5 hr. In the second experiment (70 db, 265 lux), which had a lower level of MI (maximum 1.3%), the influx changed from 0 to 1.8%/hr (mean of 13‐hourly determinations: 0.4%/hr), and the mean transit time from 0.3 to 3.3 hr.

It was difficult to say precisely whether the variation in influx or in mean transit time was the main factor in the increase and decrease of MI. The data could not be simulated with a stationary mean transit time. It is suggested that changes in MI due to different external circumstances are mainly the result of variation in the mean transit time.
IN VITRO INCORPORATION OF [3H]TdR IN HUMAN AND MURINE SOLID TUMOURS
Authors: Chavaudra N. , Malaise E. P.
Published: May 2008

Using in vitro labelling with [3H]TdR, we measured the variation in mean grain count (MGC) with the distance from the periphery of the biopsy in twenty‐nine human solid tumours (seventeen squamous cell carcinomas of the oral cavity, seven mesenchymal sarcomas and five embryonal tumours). We found a decrease for two histological types of tumours (from 32 to 8 grains for squamous cell carcinomas and 19 to 9 grains for embryonal tumours, comparing the outer 0–40 μm zone to the inner 81–120 μm zone). The number of grains per cell was usually sufficient to provide a satisfactory estimation of the labelling index (LI) in the zone which is routinely studied (80 to 100 μm from the periphery). However, for squamous cell carcinomas for instance, we found the maximal LI between 21 and 40 μm (135% of the mean global LI) and only 77% in the region situated between 81 and 100 μm. Therefore, the probability of underestimating the LI in deeper regions should not be neglected (problems of penetration, metabolism or incorporation of [3H]TdR). This is why we have employed more sophisticated labelling methods to try to improve the results.

In a murine mammary tumour (EMT6), we studied the influence of either hyperbaric oxygen (HPO) or 5‐FU or a combination of the two (5‐FU + HPO) on the change with depth in MGC and LI. In this murine tumour, as in the human tumours studied, MGC decreases slowly with increasing depth (MGC is 30 grains in 0–20 μm zone and 13 in 180–200 μm, and LI in the same zones, 29 and 16%). However, in neither case is the LI maximal at the periphery in spite of maximal MGC; this is probably due to local trauma. In two of the treated groups (5‐FU and 5‐FU + HPO), the MGC is significantly higher than controls (mean ratios: treated/control 1.3 and 1.4 respectively), whereas in the presence of hyperbaric oxygen alone no significant difference is observed. However, LI is greater in all three treated groups than in controls (mean ratios in presence of: HPO or 5‐FU or 5‐FU + HPO/conventional method 1.3, 1.3 and 1.2 respectively) and their change with depth follows a similar profile. In spite of the LI decrease with depth, if the area examined is chosen correctly, these improved techniques which preserve tissue integrity should provide a better LI estimation than conventional labelling methods.
QUANTITATION OF [3H]THYMIDINE UPTAKE BY STIMULATED HUMAN LYMPHOCYTES†
Authors: O'Leary J. J. , Mehta C. , Hall D. J. , Rosenberg A.
Published: May 2008

We have investigated the relationship between cell numbers and the amount of tritiated thymidine ([3H]TdR) taken up by stimulated human peripheral lymphocytes, as a function both of labeling time and of the specific activity of the thymidine. Cells responding either to mitogens or to allogenic cells show simple first order kinetics for the uptake of thymidine. Fitting the data to a Michaelis‐Menten type of model, we observe for labeling times of 12 hr and longer, non‐competitive inhibition of thymidine uptake by increased specific activity of tritium label, regardless of the mode of stimulation. However, for an individual responder in MLC at any arbitrary but fixed specific activity, dose of [3H]TdR and labeling interval, we still observe a linear relationship between cell mass and incorporated label. In contrast, if specific responding combinations in mixed lymphocyte culture are compared, the inhibition by specific activity at longer time intervals becomes significant and influences the quantitative interpretation of results. Specific activities of less than 10 Ci/mmole and labeling times of 6 hr or less avoid inhibition and ensure a linear relationship between dividing cell number and CPM (counts per minute recorded) of incorporated label.
EFFECT OF EHRLICH ASCITES CELL CHALONE ON NASCENT DNA SYNTHESIS IN ISOLATED NUCLEI
Authors: Nakai G. S. , Gergely Hella
Published: May 2008

Ehrlich Ascites Tumor (EAT) chalone has been shown to inhibit nascent DNA synthesis by inhibiting DNA polymerase α and β (Nakai, 1976), but one of the problems in studying eurkaryotic DNA replication has been the relative impermeability of the cell membrane to precursors and macromolecules; hence, to circumvent this restriction without sacrificing the integrity of the replication process, a broken cell system utilizing nuclei in aqueous media was investigated. Isolated nuclei appear to continue the process of DNA replication that was proceeding in vivo before their isolation and under optimal conditions are able to initiate new synthesis (Fraser & Huberman, 1977). The effects of partially purified EAT chalone on nascent DNA could be studied directly in this nuclear system, which excluded effects of the cell membrane, nucleotide pools and other cytosol elements. A concentration‐related inhibition of [3H]thymidine triphosphate ([3H]‐dTTP) incorporation was noted over a chalone range of 50–200 μg/ml. It appears that chalone can inhibit DNA polymerase α directly within the nucleus without an intermediate step such as a cell membrane receptor.
PROLIFERATION KINETICS OF THE MOUSE BLADDER AFTER IRRADIATION
Authors: Stewart Fiona A. , Denekamp Juliana , Hirst D. G.
Published: May 2008

The proliferative response of the mouse bladder was investigated, using continuous labelling with tritiated thymidine, at various times after a single dose of radiation. Bladder epithelial and vascular endothelial cells were studied. The cell turnover rate in unirradiated epithelium and endothelium was found to be extremely slow (in excess of 1 year).

Irradiation with a single dose of 25 Gy resulted in compensatory proliferation of the epithelium but the response was not initiated for many months. At 3 months after irradiation there was little difference from the control proliferation rate, but from 6 to 22 months after irradiation (the end of the study) there was a period of sustained rapid proliferation with the cell turnover time reduced to approximately 1 week. The increase in proliferative activity observed at 22 months was found to be dose—dependent.

Endothelial cells in the blood vessels of the submucosa also showed an increased turnover rate after irradiation and the timing of this reponse was found to be similar to that of the epithelium. The onset of compensatory proliferation in both cell types was found to coincide with marked histological and functional changes in the bladder.

In this slowly proliferating tissue, the onset of rapid compensatory proliferation after irradiation is delayed and occurs at the time that functional impairment is observed. This supports the postulate that proliferation is unlikely to contribute much to the sparing effect of prolonged fractionated radiotherapy in slowly dividing tissues.
THE PROLIFERATION KINETICS OF NHIK 1922 CELLS IN VITRO AND IN SOLID TUMOURS IN ATHYMIC MICE
Authors: Rofstad E. K. , Pettersen E. O. , Lindmo T. , Oftebro R.
Published: May 2008

The proliferation kinetics of cells of the line NHIK 1922 grown in vitro and as solid tumours in the athymic mutant nude mouse has been studied. In vitro, growth curves were determined for exponentially growing populations and for populations synchronized by mitotic selection. The phase durations for these populations were determined by flow cytofluorometric measurements of DNA‐histograms and pulsed incorporation of [3H]TdR respectively. The generation time and the phase durations for synchronized populations were found to be about equal to those for exponentially growing populations. The duration of the phases G1, S and G2+ M was found to be 8·5–9·5, 11·0–12·0 and 6·0–6·5 hr respectively, i.e. the generation time was 26·5–27·0 hr. The proliferation kinetics in vivo were studied by flow cytofluorometry and by the technique of percentage labelled mitoses. The median duration of S‐phase and (G2+ M)‐phase in vivo was found to be approximately the same as that observed in vitro, while the median duration of G1‐phase was found to be approximately 5 hr longer in vivo than under the present in vitro growth conditions. The growth fraction in vivo was estimated to be approximately 50%. The non‐proliferative compartment of the tumour cells was found to consist mainly of cells with the DNA‐content of cells in G1‐phase. It is concluded that the reduced rate of proliferation of NHIK 1922 cells in vivo is correlated with alterations in the duration of G1‐phase and, hence, the proportion of cells in G1‐phase.
EVALUATION OF FLOW CYTOMETRIC DATA OF HUMAN TUMOURS
Authors: Beck H.‐P.
Published: May 2008

Background signals and aggregation of cells affect flow cytometric DNA measurements to a great and mostly uncontrolled extent. These artefacts appear mainly in investigations of solid tumours leading to significant distortions in the results. Procedures are described that make possible quantitative corrections both of the background and of the cell aggregations
AN IN VIVO DOUBLE LABELLING STUDY OF THE SUBSEQUENT FATE OF CELLS ARRESTED IN METAPHASE BY VINCRISTINE IN THE JB‐1 MOUSE ASCITES TUMOUR
Authors: Camplejohn R. S. , Schultze B. , Maurer W.
Published: May 2008

The fate of cells arrested by Vincristine (VCR) in metaphase is of interest because of the wide use of this substance in cancer chemotherapy and, particularly, in relation to its use in so‐called ‘synchronization’ therapy. The present study was designed to answer the question of whether cells blocked in metaphase by VCR subsequently proliferate further or whether they become infertile and die. By means of a double labelling technique with [3H] and [14C]thymidine (TdR) it was shown that all VCR‐arrested metaphases in the JB‐1 ascites tumour subsequently became necrotic. These cells did not re‐enter a viable G2 phase following arrest and thus could not take part in a wave of synchronous proliferation. In agreement with earlier studies, VCR was found to lead to arrest in metaphase, not only of cells in or shortly prior to mitosis at the time of VCR administration, but also of the majority of cells which had at this time been in the S and G2 phase.
ARRESTED GROWTH OF CHINESE HAMSTER OVARY (CHO) CELL COLONIES ON AGAR
Authors: Storrie B. , Konrad M. W. , Glaser D. A.
Published: May 2008

Chinese hamster ovary (CHO) cells plated on agar form two classes of colonies; those which increase continuously in diameter and those which become arrested in outward growth. All colonies continue to increase in mass and thickness as demonstrated by computer‐assisted analysis of time sequence photographs of several thousand colonies and by examination of histological sections. Colonies which shift from a monolayer to a mounded morphology at fairly large colony diameter (≳1 mm) continue to increase in diameter. Colonies in which mounding occurs at smaller colony diameter (≲1 mm) cease to increase in diameter but continue to increase in thickness, as demonstrated by histological examination and by computer‐assisted analysis. Rapid cell division occurs at the edge of all colony classes, as shown by the distribution of mitotic figures. In arrested colonies these dividing cells must move toward the colony core to compensate for dying cells.

Necrotic cells are found as a discrete zone at the air‐colony interface in all cases for CHO cell colonies growing on agar. As such, necrosis is probably due to limitations in nutrient diffusion upward from the agar rather than oxygen diffusion downward.
CELL PROLIFERATION IN EMT6 TUMOURS TREATED WITH SINGLE DOSES OF X‐RAYS OR HYDROXYUREA II. COMPUTER SIMULATIONS
Authors: Demeestere Michèle , Rockwell Sara , Valleron A.‐J. , Frindel Emilia , Tubiana M.
Published: May 2008

A computer simulation technique was used to analyse data on the proliferation of clonogenic cells in EMT6 tumours treated with 5 mg/mouse of hydroxyurea (HU) or 3·0 Gy (300 rads) X‐rays. This simulation technique is able to determine the respective roles of selective killing, blocks in cell progression and recruitment of the treated population.

When the technique was applied to tumours treated with HU, it was possible to prove that both a G1/S block and recruitment occurred. These phenomena could not have been demonstrated quantitatively, or even qualitatively, without the use of the simulation. After irradiation, blocks in cell progression and differences in the proliferative patterns of the surviving clonogenic cells and the total tumour cell population were found.
QUANTITATIVE CHANGES IN THE CELLULARITY OF THE RAT SUBEPENDYMAL PLATE AFTER X‐IRRADIATION
Authors: Hubbard Bethan M. , Hopewell J. W.
Published: May 2008

The brains of young adult rats were irradiated with a single dose of 8 Gy (800 rad) of 250 kVp X‐rays. Within 2 weeks of treatment the cell population of the subependymal plate was reduced by 30%. During this period the cell cycle time remained unchanged but the labelling index was reduced. The cell population subsequently returned to normal after 39‐52 weeks. Damage and subsequent recovery of the plate was due mainly to changes in the number of cells with small dark nuclei. Cells with small and large light nuclei were little affected.

A model for the production and differentiation of cells in the subependymal region is proposed on the basis of age‐related changes in the total number and proportions of the various cell types in the subependymal plate of normal rats. This is discussed both in terms of the radiation response of cells in the plate and the manifestation of delayed white matter necrosis after higher doses.
PROTECTION OF CYCLING CFUs AGAINST HYDROXYUREA BY LOW DOSES OF ACTINOMYCIN D
Authors: Fehér I. , Gidali Julia
Published: May 2008

Low dose (80 μg/kg) Actinomycin D (AD) produced a significant but transient inhibition of proliferation of the haemopoietic stem cells (CFUs) in chimaeras or in mice regenerating after sublethal irradiation. The same dose of AD had no effect on the resting CFUs population. During the period of proliferation inhibition, CFUs proved to be insensitive to the killing effect of [3H]thymidine in vitro and hydroxyurea (HU) in vivo. In Ehrlich ascites tumour (EAT) bearing mice enhanced CFUs turnover rate was found. Eighty μg/kg AD produced a selective effect in these mice: it protected the proliferating CFUs population without diminishing the effect of hydroxyurea on the tumour cells.
CELL KINETIC ALTERATIONS IN NORMAL AND NEOPLASTIC CELL POPULATIONS IN VITRO AND IN VIVO FOLLOWING VINCRISTINE*. A REPLY TO DR CAMPLEJOHN'S REVIEW ARTICLE†
Authors: Klein H. O.
Published: May 2008

It is shown that the lethal action of vincristine (VCR) is dose‐dependent and may occur at interphase and mitosis. In general, the VCR dose used to destroy cells must be approximately ten times higher than that used to arrest cells in mitosis at metaphase. There is strong evidence that cells can survive metaphase arrest by a sublethal dose of VCR either completing cytokinesis normally after metabolism of the drug or becoming polyploid because of an impaired mitotic spindle apparatus. These cells are not doomed to die, at least in some cell systems. Furthermore, there is strong evidence in three animal tumour systems (transplantable and autochthonous tumours) that VCR is able to induce in vivo partial synchronization of proliferating tumour cells and/or recruitment of resting cells into the proliferating compartment. Failures to induce partial synchrony in cell populations by VCR may be attributed to resistance to VCR or cytolysis or slow proliferation of cells in badly vascularized tumours. Chemotherapy after synchronization seems to be effective as shown by non‐randomized trials in bad‐risk patients with solid tumours and acute leukaemias. In a randomized co‐operative trial results of the two‐drug synchronization protocol in patients with non‐Hodgkin's lymphoma of high grade malignancy were statistically better than those of a four‐drug protocol (COPP) established empirically. The two‐drug protocol was equally effective as the four‐drug protocol in Hodgkin's disease. Side‐effects were less pronounced with the so‐called synchronization scheme.
VARIATIONS IN GROWTH AND CELL CYCLE TIME OF ARTERIAL SMOOTH MUSCLE CELLS CULTURED AT LOW DENSITY
Authors: Blaes N. , Bourdillon M. C. , Crouzet B. , Boissel J. P.
Published: May 2008

The population kinetics of cultured rat arterial smooth muscle cells replated at various low densities were studied by direct counting and observation of the cells. Population doubling time decreases with increasing initial density of the culture. These variations in population doubling times depend on both the variation in the percentage of quiescent cells and on the variation of the mean cell cycle time of non‐quiescent cells.
THE STATHMOKINETIC METHOD IN VIVO TIME‐RESPONSE WITH SPECIAL REFERENCE TO CIRCADIAN VARIATIONS IN EPIDERMAL CELL PROLIFERATION IN THE HAIRLESS MOUSE
Authors: Thorud E. , Clausen O. P. F. , Bjerknes R. , Aarnæs E.
Published: May 2008

Groups of hairless mice were injected i.p. with a stathmokinetic dose of 0·15 mg colcemid at seven different times of the day and animals killed 0, 15 and 30 min, 1, 2, 3 and 4 hr after the injection. The proportion of cells in metaphase and ana/telophase was determined in histological sections.

The results showed a transient accumulation of metaphases about 30 min after the injection, followed by an increase in metaphases from 1 to 4 hr. Therefore, no value before 1 hr after the colcemid injection should be used in calculations of the mitotic rate.

The presence of circadian rhythms with high mitotic activity in the morning and low activity in the evening was confirmed. It is shown by regression analyses that the accumulation period of 4 hr is sufficiently short to reflect circadian variations in epidermal cell proliferation and that the 4‐hr accumulation value alone is sufficient to estimate the mitotic rate.