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.     

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 KINETICS OF OSMOTIC SWELLING IN LIVING CELLS

The rate of swelling of unfertilized sea urchin eggs in hypotonic sea water was investigated. Analysis of curves leads to the following conclusions. 1. The rate of swelling follows the equation, See PDF for Equation where V _eq., V ₀, and V_t stand for volume at equilibrium, at first instant, and at time t, respectively, the other symbols having their usual significance. This equation is found to hold over a wide range of temperatures and osmotic pressures. This relation is the one expected in a diffusion process. 2. The rate of swelling is found to have a high temperature coefficient (Q ₁₀ = 2 to 3, or µ = 13,000 to 19,000). This deviation from the usual effect of temperature on diffusion processes is thought to be associated with changes in cell permeability to water. The possible influence of changes in viscosity is discussed. 3. The lower the osmotic pressure of the solution, the longer it takes for swelling of the cell. Thus at 15° in 80 per cent sea water, the velocity constant has a value of 0.072, in 20 per cent sea water, of 0.006.     

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.     

THE KINETICS OF MULTIPLE ENZYME INHIBITION

The adaptive fermentation of galactose by yeast is inhibited by fluoride and azide. At sufficiently low concentrations, however, it is stimulated. From a mathematical analysis, using the known fact that fluoride inhibits the enzymes enolase and adenosinetriphosphatase, it is possible to infer the existence of such stimulation. Conditions for this effect are derived which relate the sensitivities of the enzymes to the poison with the rate constants of the various reactions in the fermentation chain.     

EXPRESSION OF PRIMARY CILIA IN MAMMALIAN CELLS

Mammalian cellsin vivofrequently express primary cilia. Although some fully differentiated cell types rarely, if ever, express them, most do, indicating that they are regular cell organelles. Their expression can also be exploredin vitro, where conditions—physical and chemical, intrinsic and extrinsic—permit experimental approaches which give far greater control thanin vivo. This ‘state of the art’ paper covers briefly the general biology of primary cilia, highlights the current situation with regard to our understanding of their relevance and importance in cell biology from various facets of our recent research, much of it in collaboration with other laboratories world-wide, and outline future work aimed at answering some basic and applied questions about them, within a context of an increasing awareness that signalling between cells is of the utmost importance in understanding proliferation control and its value in cancer research, the major remit of this unit.     

THE KINETICS OF GRANULOSA CELLS IN DEVELOPING FOLLICLES IN THE MOUSE OVARY

This investigation describes the kinetics of the granulosa cells in medium-sized follicles type 3b, 4 and 5a in ovaries of 28-day-old Bagg mice. the method of labelling with ³H-thymidine followed by high resolution autoradiography is used in the experimental work, which consist of determining percentage labelled mitosis (PLM-) and continuous labelling (CL-) curves. In order to analyse the data by computer two alternative hypotheses A and B are set up. Both include the assumptions of no cell loss, exponential growth and a resting compartment Q. In hypothesis A cells from Q re-enter the mitotic cycle via the normal DNA-synthesis compartment S_p. Hypothesis B includes beside compartment S_p a special DNA-synthesis compartment S_q where only cells from Q are synthesizing DNA, and these cells re-enter the mitotic cycle via the G₂ compartment. the mean transit time in S_q is considered to be longer than the mean transit time in S_q. On the basis of the hypothesis mathematical expressions for the PLM- and CL-curves are obtained, and by means of a computer the theoretical curves are fitted to the experimental values: thereby all relevant cell kinetical parameters are estimated. Hypothesis B seems to give the best fit between the theoretical and experimental curves. the estimated parameters are: mean cycle times, μ_c= (56.1 hr, 56.1 hr and 22.3 hr for type 3b, 4 and 5a respectively), doubling times, T _D= (96.4 hr, 118.6 hr and 59.1 hr) and the proportion of cells in Q, p _Q = (0.60, 0.71 and 0.69).     

CELL POPULATION KINETICS OF THE RECOGNIZABLE ERYTHROID CELLS IN THE RAT

The cell population kinetic parameters defining a simple model of the recognizable part of the erythroid system have been determined. Experimental results using tritiated thymidine and radioactive iron autoradiography have provided estimates of the number of cell divisions, transit times and flow rates for all the recognizable stages of the erythroid system. The accuracy of the estimates and the validity of the model employed are discussed.     

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.     

FURTHER STUDIES ON THE KINETICS OF OSMOSIS IN LIVING CELLS

Using unfertilized eggs of Arbacia punctulata as natural osmometers an attempt has been made to account for the course of swelling and shrinking of these cells in anisotonic solutions by means of the laws governing osmosis and diffusion. The method employed has been to compute permeability of the cell to water, as measured by the rate of volume change per unit of cell surface per unit of osmotic pressure outstanding between the cell and its medium. Permeability to water as here defined and as somewhat differently defined by Northrop is approximately constant during swelling and shrinking, at least for the first several minutes of these processes. Permeability is found to be independent of the osmotic pressure of the solution in which cells are swelling. Water is found to leave cells more readily than it enters, that is, permeability is greater during exosmosis than during endosmosis.     

NUCLEAR MEMBRANES OF CULTURED MAMMALIAN CELLS IN THE PERIOD PRECEDING DNA SYNTHESIS

When kidney cells are cultured directly from the rabbit, the nuclear membranes undergo a change that can be measured as an increase in electrophoretic mobility. The change appears to begin immediately upon culture and is maximal 2 hours later, after which the mobility remains constant at the elevated level. Actinomycin D and p-fluorophenylalanine, but not EDTA or ionizing radiation, suppress the increase in nuclear electrophoretic mobility. With synchronously growing L cells, no change was detected in nuclei from cells taken during various parts of the division cycle.     

PEROXISOMES IN ABSORPTIVE CELLS OF MAMMALIAN SMALL INTESTINE

Huge numbers of peroxisomes are present in guinea pig duodenum, jejunum, and ileum, and in rat duodenum. The peroxisomes have been studied by light and electron microscopy, including visualization by incubation in a newly-developed alkaline 3,3' diaminobenzidine (DAB) medium. Electron micrographs of more than 3700 guinea pig peroxisomes have been studied. The diameter of most peroxisomes ranges from 0.15 µ. to 0.25 µ. They often appear in clusters, surrounded by and continuous, in numerous places, with smooth endoplasmic reticulum (ER). The ER is extremely tortuous in these regions. Serial sectioning is valuable for studying the ER-peroxisome relationships but viewing sections at different angles, tilted with a goniometer stage, is more informative. The intimate relations of the two organelles appear the same in tissue fixed in four different fixatives. The peroxisomes may be interpreted as localized dilatations of smooth ER retaining multiple membranous continuities. This interpretation is discussed in light of the turnover data on peroxisomal proteins of rat hepatocytes reported by Poole and colleagues. The very large numbers of peroxisomes in intestinal epithelium lead to speculations concerning their functional significance. They resemble the small peroxisomes described in many other cell types. Although the distinctive relationship of these peroxisomes to the ER is probably more significant than their small size, for practical purposes we propose the term "microperoxisomes" to distinguish these peroxisomes from the better-known larger peroxisomes of liver and kidney.     

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.     

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.     

MICROTUBULAR CRYSTALS IN MAMMALIAN CELLS

Periwinkle alkaloids in very low concentrations cause an intracytoplasmic sequestration of microtubule protein in the form of symmetrical, microtubular bodies. These crystals, which may measure up to 8 µ in length, appear within 30 min in L-strain fibroblasts in vitro, but they increase in incidence and size with time of exposure to the alkaloids. Similarly, if exposed to these compounds, human leukocytes in vitro contain identical crystalline structures. Neither colchicine nor puromycin prevents the formation of these bodies; the latter compound, however, retards crystal growth.     

THE CELL POPULATION KINETICS OF NEUTROPHILIC CELLS

Autoradiographic data for the entry of tritiated thymidine labelled cells into the post-proliferative neutrophilic cell compartments following a single injection of isotope have been analysed in terms of two cell kinetic models which differ in the assumed relationships between cell maturation and division. Comparisons with the experimental data were made in an attempt to assess the validities of the models, and kinetic parameters for the compartments of recognizable neutrophilic cells were estimated. Control mechanisms which have been proposed for the granulocyte system are discussed in terms of the kinetic models which were chosen in their determination. Although it was not possible to make a clear choice between the proposed models, preference was established for a random model which did not involve cell loss.     

KINETICS OF THE SWELLING OF CELLS AND TISSUES

The rate of swelling of Arbacia eggs in dilute sea water, studied by Lillie and by Lucke and McCutcheon, may be expressed by the formulæ derived for the rate of increase in volume of a solution enclosed in a collodion sac. The rate of swelling of slices of carrot in distilled water, measured by Stiles and Jørgensen, may be expressed by the equation derived previously for the swelling of similarly shaped blocks of gelatin.     

Misonidazole—马蔺子甲素对哺乳动物细胞的辐射增敏作用

Miso(misonidazole)是[活]体内或体外都很有效的一种辐射增散剂.但是,因为它的神经毒性使临床应用受到限制.近年来,许多研究逐渐倾向于或是降低它的神经毒性或者是提高它的敏化效率两个方面.本文中马蔺子甲素是用做乏氧辐射增敏剂和修饰剂以降低Miso的细胞毒性.CHO细胞用0.5mM的Miso和0.05mM马蔺子甲素综合处理,然后在乏氧或有氧条件下进行X射线照射.实验结果表明,由于马蔺子甲素的加入使乏氧细胞的毒性降低而且在上述条件下求得增敏比为1.27.该值接近仅加入1mMMiso时的1.29数值.