The kinetics of granulopoiesis in long-term mouse bone marrow culture. Part II

A mathematical model of mouse granulopoiesis in long-term bone marrow culture was constructed, based on established in vivo cell kinetic parameters. We applied the model to the cell kinetic experiment presented in Part I. Comparing model-predicted cell kinetics with the experimental data led to iterative testing of several hypotheses. In the final model, the cell kinetics of intact tissue culture flasks were reconstructed, using the experimental data from 10 days of tube culture. Among other things, our analysis suggests that the parameters of normal in vivo granulopoiesis apply to bone marrow culture.     

The kinetics of granulopoiesis in long-term mouse bone marrow culture. Part I

The spontaneous stratification in long-term bone marrow cultures was illustrated and quantified. The cultures were separated into three hematopoietic layers: nonadherent cells in the supernatant medium, lightly adherent cells on top of the stromal layer, and remaining cells buried within the stromal layer. The cells of each layer were subcultured for 10 days in plastic tubes that inhibit the formation of a stromal layer. Daily samplings with absolute and differential cell counts were obtained. We identified three families of cell disappearance curves and cell types: CFU-s, hemocytoblasts, myeloblasts, and promyelocytes (G1, 2); myelocytes (G3); and postmitotic granulocytes (G4). Also, the numbers of mitotic and necrotic cells were determined. The longest half-time of CFU-s was 2.5 days. Lacking stromal support, CFU-s disappeared faster than other differentiated cells. Generally, these cells maintained their numbers for the first week of subcultures, which was attributable to a temporarily maintained balance of cell death and fresh cell production. After more than 7 days, there was a rapid decline of all differentiated cell types.     

Cell kinetics simulation languages

The use of stochastic simulation languages in cell kinetics research is discussed. Two special purpose simulation languages; CELLSIM and CELLGROW are described and example problems are presented.     

Cell kinetics and radiation biology

The cell cycle, the growth fraction and cell loss influence the response of cells to radiation in many ways. The variation in radiosensitivity around the cell cycle, and the extent of radiation-induced delay in cell cycle progression have both been clearly demonstrated in vitro. This translates into a variable time of expression of radiation injury in different normal tissues, ranging from a few days in intestine to weeks, months or even years in slowly proliferating tissues like lung, kidney, bladder and spinal cord. The radiosensitivity of tumours, to single doses, is dominated by hypoxic cells which arise from the imbalance between tumour cell production and the proliferation and branching of the blood vessels needed to bring oxygen and other nutrients to each cell. The response to fractionated radiation schedules is also influenced by the cell kinetic parameters of the cells comprising each tissue or tumour. This is described in terms of repair, redistribution, reoxygenation and repopulation. Slowly cycling cells show much more curved underlying cell survival curves, leading to more dramatic changes with fractionation, dose rate or l.e.t. Rapidly cycling cells redistribute around the cell cycle when the cells in sensitive phases have been killed, and experience less mitotic delay than slowly proliferating cells. Reoxygenation seems more effective in tumours with rapidly cycling cells and high natural cell loss rates. Compensatory repopulation within a treatment schedule may spare skin and mucosa but does not spare slowly proliferating tissues. Furthermore, tumour cell proliferation during fractionated radiotherapy may be an important factor limiting the overall success of treatment.     

Cell kinetics of a chondrosarcoma.

The cell kinetics of the transplantable DC-II mouse chondrosarcoma have been studied by the pulse labelled mitoses method. The analysis gave the following estimates for the phases of the cell cycle: G1, 10-5 hr; S, 9-5 hr; G2, 4 hr with an intermitotic time of 23-5 hr. Consideration of the overall growth of the tumour indicated that the growth fraction and cell loss factor both had values of about 0-5. The results are compared with cell kinetic data from sarcomas and other cartilage tissues.     

Cell kinetics in a tumour cord

In some tumours, the viable cells grow around blood vessels forming cylindrical structures called tumour cords, which are surrounded by regions of necrosis. In the present paper, we propose a mathematical model for the cell kinetics in a tumour cord at the stationary state. Both proliferating cells and quiescent cells are considered, and the proliferating cell population is structured by age. Cell migration towards cord periphery is accounted for from a continuum viewpoint. The age distribution of proliferating cells, the fraction of cells in S phase, the growth fraction and the velocity along the cord radius are computed. The predictions of the model are compared with literature data obtained from two experimental rat hepatomas. The model was used to compute the profile of the oxygen tension within the cord. Possible modifications and extensions are also presented.     

Cell kinetics of mouse urinary bladder epithelium

A dose of 0.2 ml propylene glycol (1,2 propanediol) was injected subcutaneously into 12 hairless mice three times a week for three months. Four animals were killed at 1, 2 and 3 months and micro-flow fluorometric histograms of the bladder epithelial cells were made. The proportion of cells in diploid S phase was not much altered, but the proportion of tetraploid S-phase cells was significantly reduced and at three months DNA synthesis in tetraploid cells completely disappeared. The proportion of diploid cells increased, the proportion of tetraploids was slightly reduced and almost all octoploid cells disappeared. The changes are qualitatively similar to those seen after the bladder carcinogen dibutylnitrosamine, and after repeated injections of cyclophosphamide, but quantitatively much less pronounced. They can be explained as a result of cell toxicity whereby propylene glycol kills some bladder epithelial cells and disturbs the mechanism of repeated DNA synthesis. Propylene glycol is thus not a completely harmless solvent and when the kinetic effects of bladder carcinogens dissolved in propylene glycol are studied, the effect of the solvent alone must be accounted for.     

Cell migration regulates the kinetics of cytokinesis

Cytokinesis is the final stage of cell division in which the daughter cells separate. Although a growing body of evidence suggests that cell migration-induced traction forces may be required to provide physical assistance for daughter cells to dissociate during abscission, the role of cell migration in cytokinesis has not been directly elucidated. Recently, we have demonstrated that Crk and paxillin, which are pivotal components of the cell migration machinery, localize to the midbody and are essential for the abscission. These findings provided an important link between the cell migration and cytokinesis machineries and prompted us to dissect the role of cell migration in cytokinesis. We show that cell migration controls the kinetics of cleavage furrowing, midbody extension and abscission and coordinates proper subcellular redistribution of Crk and syntaxin-2 to the midbody after ingression.Key words: cell migration, cytokinesis, midbody, abscission, cleavage furrow, Crk, paxillin, syntaxin-2, ExoT     

Cell kinetics of human epithelial ovarian cancers

Tumor cellular proliferative activity was evaluated by 3H-thymidine labeling index (LI) determination in 73 lesions from 62 patients with ovarian cancers. The median LI value for the overall series was 5.8% and places this tumor type in a position of intermediate proliferative activity. In this case series, the relationship between proliferative activity and different morphologic and pathologic characteristics of the disease was analyzed. Similar median LI values were found for ascitic effusions and solid tumors and, among these, between primary tumors and metastases. No significant relation was observed between proliferative activity and histologic type, whereas a definite direct correlation was found between the kinetic variable and prognostic features such as pathologic stage and histologic grading. In fact median LI was higher for stage IV for stage I and for grade 3 than for grade 1 tumors. The strong association between tumor proliferative rate and conventional prognostic factors suggests that also on this tumor type the kinetic variable could play a role as a prognostic indicator and modulator of aggressiveness.     

Cell kinetics of a rat thyroid transplantable tumour

Abstract. Changes in morphology and cell kinetics are described in a rat thyroid transplantable tumour (TTT) during the first few transplant generations. The growth of TTT in animals was possible only with an increased circulation level of the thyroid stimulating hormone (TSH). With serial transplantation subcutaneously in isologous animals, the morphology of TTT changed dramatically from that of a follicular tumour in the 3rd passage to become, by the 9th generation, a poorly differentiated tumour with a trabecular arrangement of cells. This change in tumour morphology was accompanied by an increase in the number of proliferating cells–mitotic index (MI), [³H]thymidine labelling index (LI), growth fraction (GF)–and cell loss factor (O) as well as a decrease in the cell cycle time (T_c) and potential population doubling time (T_PD). TTT belongs to the class of tumours with a low proliferative activity and might be used in a variety of cell kinetic, radiobiological and chemotherapy studies.     

Cell kinetics of gliomas by serial stereotactic biopsy

The potential proliferative activity of glial tumors has been investigate by serial stereotactic biopsies and by "in vitro" 3H-thymidine incorporation procedure (labeling index, LI). The methodology of this combined approach and the preliminary results in 33 patients are reported. Cell kinetic data have been matched with the histological classification (W.H.O.).     

Cell population kinetics of the mouse lens epithelium

The dividing lens epithelium of 8-week-old CF1 mice consists of a monocellular layer of about 31,000 cells and does not include the postmitotic cells of the meridional rows and another postmitotic zone of seven cell positions' width immediately anterior to the rows. The latter two populations contain approximately 3,600 and 9,000 cells, respectively, for a total of 44,000 cells in the entire lens epithelium. Autoradiographic analysis based upon mitotic index and cell cycle times indicates that the epithelium produces 207 new lens fibers a day. Throughout the 20-day period of study, labeled cells appeared almost entirely as pairs following a single dose of ³H-thymidine and clusters of labeled nuclei were not seen. Moreover, the number of labeled cells dropped only slowly with time, as did the grain counts. These observations indicate that logarithmic division “cascade” does not occur in the lens. The dividing cell population consists largely of a slowly cycling stem cell group, dividing once about every 17–20 days, and consisting of some 5,000 cells. A subpopulation may exist which undergoes two rapid consecutive divisions before becoming postmitotic, but this is too small to make a significant contribution to lens fiber production. Four days are required to transit the postmitotic zone, and an additional 43 or so are needed to transit the meridional rows and differentiate into anucleate lens fibers. Data from other laboratories indicate that the entire process, from mitosis to final differentiation, requires about 4 months. Hence, most of this time is spent in migration of nondividing cells.     

Cell kinetics of a rat thyroid transplantable tumour

Changes in morphology and cell kinetics are described in a rat thyroid transplantable tumour (TTT) during the first few transplant generations. The growth of TTT in animals was possible only with an increased circulation level of the thyroid stimulating hormone (TSH). With serial transplantation subcutaneously in isologous animals, the morphology of TTT changed dramatically from that of a follicular tumour in the 3rd passage to become, by the 9th generation, a poorly differentiated tumour with a trabecular arrangement of cells. This change in tumour morphology was accompanied by an increase in the number of proliferating cells--mitotic index (MI), [3H]thymidine labelling index (LI), growth fraction (GF)--and cell loss factor (O) as well as a decrease in the cell cycle time (Tc) and potential population doubling time (TPD). TTT belongs to the class of tumours with a low proliferative activity and might be used in a variety of cell kinetic, radiobiological and chemotherapy studies.