摘要:

AbstractA clonal strain of mammalian cells with increased resistance to acute heat shock at 46° was compared with the heat‐sensitive parental line from which it was derived for possible differences that might account for this acquired resistance. Studies on synchronized populations of the two cell strains did not reveal any differential heat sensitivities in the various parts of the cell cycle (G1, S, G2) within either the sensitive or resistant populations. During thermal stress both cell types exhibited marked inhibition of ability to incorporate isotopically labeled precursors into macromolecular RNA, DNA, and protein.However, significant differences were observed between the sensitive and resistant cells in the amount of leakage of materials from the two cell types during heat stress and in their relative rates of recovery after stress. Sensitive cells pre‐labeled with3H‐uridine released considerably more acid‐soluble (cold, 5% TCA) label‐containing materials during heat stress than did pre‐labeled resistant cells. This differential release of uridine‐containing materials was not paralleled by a generalized differential leakiness to other compounds. In addition, the resistant cells were found to regain the capacity to synthesize vital macromolecules sooner, and at initially faster rates, than the sensitive cells after stress.These results suggest that permeability changes causing decreased leakage of uridine‐containing materials during heat stress combined with accelerated rates of recovery of synthesis of essential macromolecules after stress may be important cellular mechanisms in resistan

ISSN:0021-9541    

DOI:10.1002/jcp.1040790202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractRegulation of haematopoiesis was investigated by studying the response of haematopoietic tissues of mice to a perturbation of the steady state by vinblastine (VLB). Progenitor cells were quantified ly limiting dilution analysis of diffusion chamber cultures of haematopoietic cells and by the spleen colony technique. The diffusion chamber technique appears to assay granulocyte progenitor cells and those multipotent progenitor cells that become committed to granulopoiesis during chamber culture. The spleen colony technique probably assays multipotent progenitor cells.Decaying oscillatory responses to VLB were observed for progenitor cells as well as for differentiating cells in bone marrow. The period lengths of the diffusion chamber progenitor cell oscillations might indicate that these were induced by humoral feedback signal(s) from nonproliferative granulocytes. The oscillations of the multipotent progenitor cells of bone marrow were less pronounced and were earlier damped than those of the granulocyte progenitor cells. This may support the hypotesis that multipotent progenitor cells are regulated by more efficient mechanisms, which may depend on short range cell‐cell interactions rather than long range humoral regulator

ISSN:0021-9541    

DOI:10.1002/jcp.1040790203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractUptake of3H‐thymidine into suspension cultures of mouse marrow cells was stimulated by the addition of serum‐free conditioned medium harvested from cultures of mouse L‐cells. Characterization of the “conditioning factor activity” (CFA) by gel filtration, ion exchange chromatography, velocity sedimentation, polyacrylamide gel electrophoresis and susceptibility to trypsin digestion indicated that the CFA detected by stimulation of3H‐thymidine uptake is the same as the CFA detected previously by its ability to stimulate colony formation by marrow cellsin vitro. The3H‐thymidine uptake assay was used to investigate the kinetics of disappearance of CFA as a function of time in the presence of mouse marrow cells. The CFA recoverable from the cultures decreased rapidly during the first day, and approached background levels by the fifth day. There was no evidence of inhibitory substances in the depleted media. Even if the cultures continued to receive fresh conditioned medium at daily intervals,3H‐thymidine uptake decreased sharply after the fifth day, indicating that the marrow cells had lost their capacity to

ISSN:0021-9541    

DOI:10.1002/jcp.1040790204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe term “contact inhibition of cell division” was borrowed from “contact inhibition of cell movement.” We prefer the term “postconfluence inhibition of cell division” as being more operational and less mechanistically biased; it is operationally defined as a pronounced depression of the mitotic rate in a postconfluent culture which displays a stationary density despite periodic nutrient renewal, the inhibition being locally reversibly by removal of the adjacent cells.The mechanism of postconfluence inhibition is of considerable interest because of the inverse correlation between postconfluence inhibition and the tumorigenicity of a number of cell lines. Several hypotheses, involving direct cell‐to‐cell contacts or locally restricted diffusion gradiens, could explain postconfluence inhibition.With the goal of discriminating among these hypotheses, time‐lapse films were taken of carefully regulated, perfused cultures of 3T3 mouse cells, in which the transition from rapid growth to the stationary phase was recorded. Measurements of cell‐to‐cell contact, local cell density, and generation times were made on an individual cell level and analyzed with the aid of a computer.We observed that all‐around cell‐cell contact or a high local cell density present throughout G1 often did not produce immediate inhibition of cell division. We conclude that either (i) simple visible cell‐cell contacts or a high local cell density are not the direct cause of postconfluence inhibition of cell division, or (ii) their effects often do not inhibit cell division until after a delay of about one cell generation time. Such a delay may be partly responsible for the 50% overshoot past the stationary density that

ISSN:0021-9541    

DOI:10.1002/jcp.1040790205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractA study of aldolases in rat hepatoma clones and subclones has revealed that they synthesize all three forms of aldolase monomers: A (the ubiquitous glycolytic isozyme), B (the form characteristic of the liver) and C, and thatin vitro–in vivopassage results in a reversible modulation in aldolase A activity.Three kinds of somatic hybrids, between rat hepatoma cells and either mouse fibroblasts or rat epithelial cells, have been studied. In each case, aldolase B, found only in the hepatoma parent, was absent in the hybrid cells. The absence of aldolase B in the somatic hybrids seems not to be due to trivial factors (species differences, inactivation of all hepatoma aldolase genes, increase in ploidy or loss of chromosomes); it is concluded that extinction of this differentiated function of the hepatoma parent reflects a genetic regulatory phenomeno

ISSN:0021-9541    

DOI:10.1002/jcp.1040790206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe electrophoretic mobilities (E.P.M.) and pH‐mobility relationships of chick blastoderm cells at successive developmental stages were determined. Mobilities in 0.145MNaCl, pH 7.2, showed a wide spread and decreased from a mean value of 1.63 μ/sec/V/cm in the prestreak blastoderm, to 1.49 in the intermediate streak and 1.34 in the head process stages. Cell surface charge density changes as detected by E.P.M. were observed in all regions of the embryo.pH‐mobility relationship studies showed that two cell populations differing in their approximate isoelectric point appeared at the intermediate streak and head process stages. Neuraminidase treatment indicated that the contribution of sialic acid residues to the negatively charged groups at the cell surfaces is very small at the stages stu

ISSN:0021-9541    

DOI:10.1002/jcp.1040790207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe surfaces of cells from the early embryo of the chick were examined with the electron microscope using histochemical techniques in order to determine the distribution of cell surface material. The use of lanthanum nitrate as a stain for protein‐polysaccharide showed that in whole embryos the surface layer was present in areas of close membrane apposition, but relatively sparse where the membranes bounded large intercellular spaces. On cells freshly dissociated with EDTA, this technique demonstrated a very uniform layer over the surface, possibly indicating some redistribution. Close examination of the lanthanum stained material in whole embryos revealed the presence of periodicities about 180 Å in diameter.In correlation with a progressive reduction of electrophoretic mobility, demonstrated previously, from embryonic stage 1 to stage 5, some decrease in the affinity of the surface for lanthanum and colloidal iron was observ

ISSN:0021-9541    

DOI:10.1002/jcp.1040790208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractAntisera have been prepared to clonal cultured rat astrocytic cells (C6cells) and clonal human astrocytic cells (CHB4cells). When cultured glial cells are grown in the presence of neuraminidase the serological activity of the cell membrane with homologous antiserum is increased extensively. A similar activation of serological activity can be effected by incubating washed harvested cells with this enzyme. Membrane bound N‐acetyl‐neuraminic acid is extensively reduced by either incubation. The activity responsible for promoting the enhanced serological activity co‐chromatographs and co‐electrophoreses with neuraminidase. Proteolytic digestion, unlike neuraminidase treatment, was unable to enhance the serological activity of cultured glia

ISSN:0021-9541    

DOI:10.1002/jcp.1040790209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractUpon addition of bleomycin (BLM) to suspension cultures of Chinese hamster cells (line CHO), cells closer to prophase than 56 minutes continue dividing at the normal rate, whereas cells at earlier positions in the cell cycle either fail to reach mitosis altogether (at 200 μg/ml) or enter mitosis and divide at a reduced rate at lower drug concentrations. At 100 μg/ml of BLM (the rate of cell division slowed to a doubling time of 167 hours), initiation and termination of DNA synthesis occur at normal rates, resulting in an accumulation of cells with a G2DNA content in the first 130 minutes of G2. Bleomycin effects are not readily reversible. The rates of incorporation of leucine, uridine, or thymidine into cells treated for six hours with 100 μg/ml of BLM were 90, 85, and 80%, respectively, of the values obtained in control cultures, suggesting that the effects of BLM on cell‐cycle traverse cannot be correlated with gross inhibition of macromolecular synth

ISSN:0021-9541    

DOI:10.1002/jcp.1040790210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractBlood leukocytes incubatedin vitrowith rabbit‐marrow cells induced a several‐fold increase in basophilic erythroblasts and smaller increases in acidophils and reticulocytes. The main effect was nearly complete in one hour at 37°. Erythropoietin augmented the leukocyte effect; anti‐erythropoietin inhibited it with or without erythropoietin. The erythroblast increase came entirely from the marrow cells; the precursor cell class has not been identified, except that division of pre‐existing basophils appears to be excluded. Autologous and homologous leukocytes were about equally effective.A method is described of measuring on stained smears changes in relative concentrations of different classes of cells induced experimentally. A method of preparing highly concentrated peripheral blood leukocytes is d

ISSN:0021-9541    

DOI:10.1002/jcp.1040790211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY