UPTAKE OF MAMMALIAN CHROMOSOMES BY MAMMALIAN CELLS

Chromosomes isolated from mouse leukemia L1210 cells were taken up by mouse macrophages, HeLa cells, and rat embryo fibroblasts following simple exposure in vitro. The process, which resembles pinocytosis or phagocytosis, was traced by autoradiography of chromosomes prelabeled with thymidine-H³, and by staining techniques and phase contrast microscopy. During the first six hours, the uptake of chromosomes was restricted to the cytoplasm, but there was some evidence of penetration into the nucleus after 16 and 26 hours of exposure. Treatment of rat fibroblasts with glucose and insulin markedly enhanced the uptake of chromosomes, whereas iodoacetate inhibited their penetration.     

THE FATE OF DNA-CONTAINING PARTICLES PHAGOCYTIZED BY MAMMALIAN CELLS

Particulate DNA protein coacervates were digested immediately after being phagocytized by L strain fibroblasts in suspension culture. Enlargement of the phagocytotic vacuoles occurred simultaneously with a loss of the electron opacity of the phagocytized particles. Cytochemical reactions positive for non-specific esterase, acid phosphatase, and nucleoside phosphatase in the phagocytotic vacuoles provided additional evidence for the probability of complete hydrolysis of the phagocytized nucleoprotein.     

THE OUTWARD TRANSPORT OF CORTISOL BY MAMMALIAN CELLS IN VITRO

It has been determined that cortisol and a few other steroids are transported outward from certain mammalian cells growing in vitro. The extrusion process is temperature dependent, glucose dependent, saturable, and operates for only a few selected steroids. Many, but not all, steroids are able to block the extrusion process but are not themselves transported. The outward transport process for steroids has been found in mouse fibroblasts, mouse lymphoma cells, and functional mouse adrenal gland tumor cells growing in vitro. The transport process is not present in two varieties of cells cultured from human sources—HeLa or diploid fibroblasts, WI-38.     

CELL PENETRATION BY ACIDS : VI. THE CHLOROACETIC ACIDS.

Measurements of the penetration of tissue from Chromodoris zebra are believed to show that a determining factor in penetration involves the establishment of a critical pH (near 3.5) in relation to superficial cell proteins. The rapidity with which this state is produced depends upon acid strength, and upon some property of the acid influencing the speed of absorption; hence it is necessary to compare acids within groups of chemical relationship. The actual speed of penetration observed with any acid is dependent upon two influences: preliminary chemical combination with the outer protoplasm, followed by diffusion. The variation of the temperature coefficient of penetration velocity with the concentration of acid, and the effect of size (age) of individual providing the tissue sample agree in demonstrating the significant part played by diffusion. In comparing different acids, however, their mode of chemical union with the protoplasm determines the general order of penetrating ability.     

AN ELECTRON MICROSCOPIC STUDY OF THE DEVELOPMENT OF THE CLEAVAGE FURROW IN MAMMALIAN CELLS

The process of cytoplasmic cleavage has been studied in thin sections of rat erythroblasts and the cells of mouse leukemia and Walker 256 carcinoma of the rat. The development of the cleavage furrow begins in relation to the mid-body, which, earlier, appears on the equatorial plane in association with the continuous fibers of the spindle. The earliest evidence of a cleavage furrow is the presence of a vesicle or vesicles close to the mid-body. Subsequently, many smaller vesicles are seen in the equatorial plane. The cleavage furrow probably develops by the fusion of these vesicles so that a new plasma membrane is formed between the daughter cells, and extends from the telophase intercellular bridge to the cell margin. During the stage of formation of the vesicles, cisternae, believed to be part of the endoplasmic reticulum, assume an intimate relationship with the cleavage plane, and they may perhaps be involved in the formation of the vesicles.     

哺乳动物细胞去核产物(胞质体及核体)的结构与功能研究

1967年Carter发现细胞松弛素可以诱发组织培养细胞的自发排核之后,Prescott(1972)借助细胞松弛素存在下的离心处理,使这一排核现象普遍化,从而确立了体外细胞去核的标准方法。经过不断改进(croce et al., 1974;Veomett et al., 1976;Lucas etal., 1976;Wigler et al., 1975),现在,这一技术已广泛应用于细胞学研究的各个重要领域(Mc Burney et al., 1979;Goldman et al., 1974;du Bols et al., 1980)。细胞去核技术及其应用的研究在我国已有初步开展(陈瑞铭等,1979;沈鼎武等,1980)。本实验对二种上皮型传代细胞系进行了去核手术,用扫描电镜和透射电镜对所获得的胞质体     

THE RESOLUTION OF MIXTURES OF VIABLE MAMMALIAN CELLS INTO HOMOGENEOUS FRACTIONS BY ZONAL CENTRIFUGATION

Large-scale separation of mixtures of mammalian cells was obtained with the A-1X zonal centrifuge rotor and density gradients consisting of Ficoll dissolved in modified Eagle's MEM suspension-culture medium. The cells remained viable as tested by plating efficiency or by motility observed with time-lapse photography. Rabbit thymocyte and HeLa cell mixtures were separated with 99 and 89 per cent purity, respectively. Mixtures of thymocytes and suspension-cultured, human acute leukemia cells (Roswell Park strain LKID) were separated with 93 and 91% purity, respectively. HeLa cells were isolated 92% pure from a mixture with horse leukocytes. A book of charts giving the sedimentation position and velocity versus time of cells in the A rotor under standard conditions of gradient composition, angular velocity, and temperature was prepared with the use of a computer program based on the differential sedimentation equation. The charts are used to estimate the centrifugation time necessary for maximum separation of cells. The success achieved in separating mixtures of cells points to the future possibility of large-scale fractionation of solid tissues, especially tumor tissues, into preparations cf viable cells of a single type.     

THE PENETRATION OF CATIONS INTO LIVING CELLS

Direct tests of the cell sap of Nitella show that the protoplasm is normally permeable to Li, Cs, and Sr, and that penetration is more rapid in an unbalanced than in a balanced solution.     

CELL PENETRATION BY ACIDS : V. NOTE ON THE ESTIMATION OF PERMEABILITY CHANGES.

The penetration of acid into mantle tissue of Chromodoris zebra is accelerated after local faradic stimulation, and is retarded by brief treatment with anesthetic solutions. The spontaneous outward diffusion of intracellular pigment is an inadequate criterion of "permeability." Outward diffusion of pigment and penetration of acid are both facilitated when the tissue is artificially put under tension.     

THE ELECTRICAL CHARGE OF MAMMALIAN RED BLOOD CELLS

In Vol. 19, No. 4, March 20, 1936, page 603, in the eleventh line from the bottom of the page for "z_j = 2, z_jj = 1", read "z_j = 1, z_jj = 2". On the same page in the fourteenth line from the bottom of the page for "jj(HPO₄-)" read "jj(HPO₄--)".     

THE CATAPHORETIC VELOCITY OF MAMMALIAN RED BLOOD CELLS

1. No significant change with time (to 24 hours) in the cataphoretic velocity of certain mammalian red cells occurs when the cells are suspended in M/15 phosphate buffer at pH = 7.35. Neither successive washings nor standing effect a change. 2. In M/15 phosphate buffer at pH 7.35 ± 0.03 the following order of red cell velocity has been obtained. The numbers in parenthesis are µ per second per volt per centimeter. See PDF for Structure The order, though not the absolute values, was the same in buffered isotonic dextrose. Human and rabbit cells showed similar differences when both were studied simultaneously in the serum of either. Under these conditions, there is no apparent relationship between zoological Order and cataphoretic velocity. 3. Cholesterol and quartz adsorb gelatin from dilute solution in the phosphate buffer. Red cells, on the other hand, even after 24 hours contact with gelatin solution, retain their previous velocity. 4. Pregnant and non-pregnant white female humans have the same red cell cataphoretic velocity. (The cells were not agglutinated.) 5. In a series of severe anemias no significant change in cataphoretic velocity was in general apparent, although marked changes in the morphology of the red cells were present.     

THE KINETICS OF CONTACT INHIBITION IN MAMMALIAN CELLS

To elucidate the process of contact inhibition in mammalian cells, we investigated the kinetics of growth arrest in [³H]thymidine labelled embryonic chinese hamster (Cricetulus griseus L.) cells after the addition of various concentrations of unlabelled cells. It was observed that after the contact inhibition concentration had been reached, the cells grew undisturbed for one more generation. In the following 24 hr the concentration fell back to the level at the beginning of the experiment and stayed there.     

THE CHARACTERIZATIO OF MONOAMINE OXIDASE IN CULTURED MAMMALIAN CELLS

The expression of monoamine oxidase (MAO) in a variety of mammalian cells has been investigated employing tryptamine as substrate. The enzyme present in those cell lines having sufficient activity for detailed analysis exhibited a monophasic response to the inhibitor clorgyline. On this basis the cell lines examined were found to express only A, or only B, type activity. Hypoxanthineguanine phosphoribosyl transferase (HGPRT) deficient derivatives of both MAO type A, or MAOtype B, expressing cells were examined. The HGPRT status of the cells appeared to have little influence on the expression of the enzyme.     

THE PENETRATION OF LUMINOUS BACTERIA BY THE AMMONIUM SALTS OF THE LOWER FATTY ACIDS : PART I. GENERAL OUTLINE OF THE PROBLEM,AND THE EFFECTS OF STRONG ACIDS AND ALKALIES.

It is shown that disappearance of the light of luminous bacteria may be used as a criterion of cell penetration; that luminous bacteria are cytolyzed by water, hypotonic solutions, and by freely penetrating solutions; that luminous bacteria are not injured by hydrogen or hydroxyl ions in the external solutions within the range of pH values employed with the ammonium salts and that therefore disappearance of the light in isotonic solutions of these salts must be due to penetration of the solute; and that there is a characteristic difference between the effects of strong and of weak acids and alkalies on luminous bacteria.     

THE DISSOCIABILITY OF DEOXYRIBONUCLEIC ACID SYNTHESIS FROM THE DEVELOPMENT OF MULTINUCLEARITY OF MUSCLE CELLS IN CULTURE

The effects of a nitrogen mustard on both the morphology and several synthetic capacities of embryonic chick skeletal muscle cells in monolayer culture have been examined. Concentrations of nitrogen mustard which profoundly inhibit deoxyribonucleic acid synthesis specifically do not inhibit the development of multinuclearity in the contractile "ribbons" which form rapidly in culture. Nitrogen mustard affects the nuclear morphology of "fibroblast-like" and multinuclear muscle cells differentially. The mononucleated cells in treated cultures exhibit extreme nuclear enlargement which distinguishes them from the multinuclear cells as well as from both types of cells in control cultures. The nuclei of the multinuclear cells which form after nitrogen mustard treatment, however, do give evidence of having been affected by the treatment. They exhibit somewhat less uniformity of size than similar cells in control cultures. Analogous differences were described by Bodenstein (3) between potentially proliferating cells and postmitotic differentiating cells, marked nuclear enlargement being characteristic of cells in the proliferative zone. The results are more compatible with the hypothesis that multinuclearity arises through successive cell fusion than through amitotic nuclear multiplication, since it is unlikely that any form of nuclear replication could occur in the absence of DNA synthesis.     

THE PENETRATION OF THE MEMBRANE OF BRAIN MITOCHONDRIA BY ANIONS

The permeability of the membrane of rat brain non-synaptosomal mitochondria, towards inorganic and substrate anions, was assessed by measuring the rate of swelling that occurred when mitochondria were suspended in an iso-osmotic solution of a permeant anion, in the presence of a permeant cation such as NH⁺₄ or K⁺ in the presence or absence of valinomycin. In NH⁺₄-phosphate swelling was higher than it was in KCI or K⁺-phosphate, which showed the prevalence of the mechanism of phosphate transport previously demonstrated in liver mitochondria. The entry of succinate and L-malate seemed to require the presence in the inner mitochondrial membrane of specific carriers. as previously postulated for liver mitochondria, but the rate of swelling of brain mitochondria was lower than that of liver organelles. In K⁺-succinate, in the presence of antimycin, added ATP induced swelling and this was attributable to the simultaneous permeation both of the anion and the cation. Fumarate did not penetrate into brain mitochondria. Practically no swelling was recorded in NH⁺₄ or K⁺-citrate, which indicated that this anion penetrated poorly into the isolated brain mitochondria even in the presence of malate. Swelling occurred in NH⁺₄-L-glutamate in the presence of rotenone, and the entry of this anion seemed to follow a gradient of concentration although the presence of a specific translocator in the inner mitochondrial membrane might be concerned. The entry of glutamate was independent of that of phosphate and N-ethylmaleimide appeared to be a specific inhibitor of this entry. Swelling in K⁺-L-glutamate, in the presence of rotenone, was enhanced by the addition of valinomycin or ATP but in the latter case when osmotic equilibrium was reached swelling was not reversed by oligomycin. In conclusion, the lesser extent of swelling of isolated brain mitochondria compared with liver mitochondria could be attributed to the heterogeneity of the populations of these organelles, each population possessing its own characteristics of membrane permeability. Observations of electron micrographs of brain mitochondria incubated in iso-osmotic substrate anions confirmed the heterogeneous rate of swelling of these particles.     

THE NUCLEOLI IN MITOTIC DIVISIONS OF MAMMALIAN CELLS IN VITRO

In a number of mammalian cell strains nucleoli persisted through mitosis. This phenomenon was especially pronounced in several cell lines derived from Chinese hamster tissues. All the methods employed, including radioautography with tritiated uridine, cytochemical stains (methyl green-pyronin and azure B), fluorescent microscopy (coriphosphine O), ribonuclease digestion, and electron microscopy, demonstrated that the bodies identified as persistent nucleoli in the mitotic stages had the same characteristics as did the nucleoli in the interphase. Persistent nucleoli may attach to the chromosomes or may be free in the cytoplasm. In cells where no persistent nucleoli as such were noted, nucleolar material was observed to attach to the chromosomes in shapeless masses which moved with the chromosomes during anaphase. At least a portion of the nucleolar material was included in the daughter nuclei, presumably for immediate use for protein synthesis after cell division.