bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase equilibria of cytoplasmic actin of cultured epithelial (BHK) cells
Authors: Koffer Anna , Gratzer W. B. , Clarke G. D. , Hales Anne 
Published: April 2021

ABSTRACT
The actin in cold lysates of cultured baby hamster kidney cells was predominantly monomeric, as judged by the DNase inhibition assay. Most of the filamentous actin attached to the membranes could be dissociated by washing with low ionic strength buffer, but a minor part was tightly associated in complexes with other proteins and could not be liberated for assay by DNase after exposure to a depolymerizing medium.
The monomeric actin in the cell extract must be sequestered as a complex with a profilin-like protein, since its concentration was greatly in excess of the critical concentration for polymerization. On warming, rapid polymerization ensued, with loss of most of the monomeric actin. A separate cross-linking process could be observed by light-scattering measurements. A gel was formed, that contained besides actin substantial amounts of constituents identified as filamin, myosin, a-actinin, a gelsolin-like protein and other species of apparent subunit molecular weights 58 000 and 300 000, presumed to derive from intermediate filaments. Some low molecular weight protein subunits, including tropomyosin, were also present. The gelation was not accompanied by a significant degree of phosphorylation of any of the actin-associated proteins, with the exception of the minor species of 300000 molecular weight, the phosphorylation of which was cAMP-dependent.
In the presence of concentrations of free calcium in the sub-micromolar range, the gel initially formed contracted and gradually dispersed. At higher concentrations of free calcium a loose turbid gel formed, but the bulk of the actin was found in the supernatant after high-speed centrifugation. Using a fluorescent actin derivative as a tracer, the quantum yield of which increases by nearly two orders of magnitude when it is incorporated into a polymer, it was established that the actin in the supernatant was not monomeric, but rather in the form of very short filaments. It was shown that scission of filaments accompanied the contraction of the cytoplasmic gel at the lower concentrations of calcium. The short filaments were highly effective in nucleating the polymerization of added G-actin and were evidently rapidly dissociated by DNase, since they reacted as monomers in the DNase inhibition assay.
The gel obtained in the absence of calcium was revealed by electron microscopy to consist of clusters of filaments, many of which show a highly regular lateral spacing of about 7·0 nm.
The physical basis for the temperature- and calcium-dependent phase equilibrium observed in this system are analysed in semi-quantitative terms.
Substrata formed by combinations of extracellular matrix components alter neural crest cell motility in vitro
Authors: Erickson C. A. , Turley E. A. 
Published: April 2021

ABSTRACT
Extracellular matrix components such as collagen, fibronectin and sulphated glycosaminoglycans can act as substrata that promote neural crest motility in vitro, in the absence of serum. The cells appear to be less adhesive and move more randomly on collagen or chondroitin sulphate substrata than on fibronectin substrata. Cells do not spread or become motile on plastic dishes to which hyaluronate has been bound, presumably owing to weak adhesion to this surface. Hyaluronate added to the medium alone has little effect on cell motility. When combinations of matrix molecules are used as substrata, however, the presence of fibronectin increases spreading, directional persistence of cell motility and speed of movement above that observed on collagen alone. When added to fibronectin, chondroitin sulphate appears to reduce adhesions slightly, since the cells are more rounded. Hyaluronate added in the medium significantly reduces the extent, speed and directionality of movement on fibronectin substrata. The presence of collagen in combination with fibronectin plus glycosaminoglycans does not have a noticeable effect on cell motile behaviour, beyond that observed with fibronectin alone. The effects of combinations of matrix compounds on neural crest cell motility are thus predictable, and can be explained in terms of the known adhesive properties and reported binding interactions of these molecules. These studies in vitro are compared with neural crest cell motility in vivo.
Studies of nuclear and cytoplasmic behaviour during the five mitotic cycles that precede gastrulation in Drosophila embryogenesis
Authors: Foe Victoria E. , Alberts Bruce M. 
Published: April 2021

ABSTRACT
Using differential interference contrast optics, combined with cinematography, we have studied the morphological changes that the living, syncytial embryo undergoes from stage 10 through 14 of Drosophila embryogenesis, that is just prior to and during formation of the cellular blastoderm. We have supplemented these studies with data collected from fixed, stained, whole embryos. The following information has been obtained.
The average duration of nuclear cycles 10, 11, 12 and 13 is about 9, 10, 12 and 21 min, respectively (25 °C). In these four cycles, the duration of that portion of the mitotic period that lacks a discrete nuclear envelope is 3, 3, 3 and 5 min, respectively. The length of nuclear cycle 14 varies in a positionspecific manner throughout the embryo, the shortest cycles being of 65 min duration.
During nuclear cycles 10 through 13, it is commonly observed in living embryos that the syncytial blastoderm nuclei enter (and leave) mitosis in one of two waves that originate nearly simultaneously from the opposite anterior and posterior poles of the embryo, and terminate in its midregion. From our preparations of quick-frozen embryos, we estimate that these mitotic waves take on average about half a minute to travel over the embryonic surface from pole to equator.
The yolk nuclei, which remain in the core of the embryo when the rest of the nuclei migrate to the periphery, divide in synchrony with the migrating nuclei at nuclear cycles 8 and 9, and just after the now peripherally located nuclei at nuclear cycle 10. After cycle 10, these yolk nuclei cease dividing and become polyploid.
The syncytial embryo has at least three distinct levels of cytoskeletal organization: structured domains of cytoplasm are organized around each blastoderm nucleus; radially directed tracks orient colchicine-sensitive saltatory transport throughout the peripheral cytoplasm; and a long-range organization of the core of the embryo makes possible coherent movements of the large inner yolk mass in concert with each nuclear cycle. This highly organized cytoplasm may be involved in providing positional information for the important process of nuclear determination that is known to occur during these stages.
Reversible disruption of cultured endothelial monolayers by sulphated fucans
Authors: Glabe Charles G. , Yednock Ted , Rosen Steven D. 
Published: April 2021

ABSTRACT
We have examined the effects of a variety of polysaccharides and glycoconjugates on the organization and morphology of cultured AI4CL-I endothelial monolayers. The sulphated fucose-containing polysaccharides, fucoidin and sea-urchin egg jelly fucan, induce a dramatic disruption of the organization of the monolayers, characterized by the retraction of adjacent borders of cells exposing areas of the subendothelial matrix. This effect, which occurs at a fucoidin concentration of 10 μg/rnl, is rapidly reversible after the fucoidin-containing medium is removed. Within 1 h after replacement with fresh medium many cell contacts are re-established; within 20h the fucoidin-treated monolayers closely resemble the untreated controls. The effect of the sulphated fucose-containing polysaccharides is specific. Of a wide variety of sulphated polysaccharides and glycoconjugates tested, only fucoidin and the egg jelly fucan produce a detectable alteration in the morphology of cultured endothelial monolayers. The endothelial monolayer has specific binding sites for fucoidin. The binding of fucoidin is saturable and a maximum of 4·5 × 105 molecules of fucoidin are bound per cell with an apparent affinity of 2·3 × 10−7M. A significant proportion (26%) of the total monolayer-associated fucoidin is apparently internalized by the endothelial cells after incubation with fucoidin for 1 h at 37 °C. The morphological response to fucoidin is probably not due to its internalization, since the effect is observed at 7 °C where little uptake (3’5 %) occurs. Fucoidin appears to bind at two distinct sites on endothelial monolayers. One site is inhibitable by heparin, while the other site seems to be specific for fucoidin. The observation that fucoidin still induces the retraction of the endothelial cells in the presence of a 100-fold excess of heparin, suggests that binding at the fucoidin-specific site is responsible for the morphological effect of fucoidin. In addition, fucoidin has no detectable effect on monolayers of 3T3 and BHK fibroblast-like cells at 1 mg/ml, 100-fold higher than the concentration required to produce an effect on endothelial cells. Among the possible interpretations of these results is that sulphated fucose-containing glycoconjugates may play a role in the adhesive interactions of endothelial cells.
Spontaneous Turning Behaviour By Dictyostelium Discoideum Slugs
Authors: Fisher P. R. , Grant W. N. , Dohrmann U. , Williams K. L. 
Published: April 2021

ABSTRACT
Dictyostelium discoideum slugs migrating in the absence of external stimuli tend to continue migrating in the original randomly ‘chosen’ direction. Spontaneous deviations from the starting direction accumulate with time at a rate that measures the ‘physiological noise’ in the slugs’ steering mechanism. Most of the spontaneous turning signals arise in the transduction chain ‘downstream’ of the convergence of photosensory and thermosensory processing, and the site(s) of action of the mutation pho-355. A significant amount of steering ‘noise’ arises ‘upstream’ of the site(s) of action of fluoride (which has specific effects on phototaxis and thermotaxis).
Macrocyst Development In Dictyostelium Discoideum : III. Cell-Fusion Inducing Factor Secreted By Giant Cells
Authors: Saga Y. , Yanagisawa K. 
Published: April 2021

ABSTRACT
A factor was discovered that markedly enhances the degree of fusion activity between cells of the opposite mating-type strains, HM1 and NC4, in the sexual cycle of Dictyostelium discoideum. This factor, designated cell-fusion inducing factor (CFIF), was detected initially in supernatants taken from 24 h dark-grown mixed cultures of HM1 and NC4 cells, and subsequently shown to be secreted by giant cells - the fusion products of HM1 and NC4 cells. HM1 cells, cultured in the dark at appropriate temperature, normally acquire fusion-competence specific to NC4 cells. The addition of CFIF to such dark-grown HM1 cultures results in a marked increase in their fusion-competence. In addition, when CFIF is added to light-grown HM1 cultures, in which cells normally do not acquire the ability to fuse with NC4 cells, fusion-competence is induced. The fusion-competence of NC4 cells is unaffected by CFIF, being quite high under the culture conditions used here. Experiments, using actinomycin D, daunomycin and cycloheximide showed that the secretion of CFIF from giant cells requires synthesis of RNA and protein. Possibly, cell fusion triggers production of CFIF, which is rapidly released into the external medium.
Regulation of cytoplasmic streaming in Vallisneria mesophyll cells
Authors: TAKAGI SHINGO , NAGAI REIKO 
Published: April 2021

ABSTRACT
Induction and cessation of the rotational cytoplasmic streaming in Vallisneria mesophyll cells could be controlled by external stimuli. In cells that had been kept in darkness the cytoplasm remained quiescent. However, when the cells were treated in the dark with EGTA solution (10 mM or 20 mM buffered with 10mM-Tris-maleate at pH7·0), rotational cytoplasmic streaming was induced. When the cells were transferred again to artificial pond water in the dark, the induced streaming was inhibited; that is, only 50 % of the observed cells exhibited active streaming after 2 h. When the cells were irradiated continuously with far-red light (λmax = 750 nm, 0·4W/m2) in the same external medium, the induced streaming was inhibited almost completely within 2h.
The relative quantum effectiveness of monochromatic light (450—800 nm) in producing cessation of streaming was also investigated. Irradiation with light of 45 0, 550 and 600 nm was almost as effective as darkness. Light of 500 and 650 nm was less effective than dark exposure. Only irradiation at 750 nm stopped streaming in almost all cells. But when calcium was excluded from the external medium, the effect of far-red light decreased to almost the dark control level. Light of 800 nm also inhibited the streaming but the effect was much less than that of far-red light.
Microfilaments in bundles with the long axis parallel to the streaming direction were localized in the vicinity of the cell membrane. Their configuration, localization and distribution were the same in the present experimental system irrespective of whether the cytoplasm was streaming or quiescent.
Intracellular calcium was examined by electron microscopic cytochemistry and X-ray microanalysis. In cells with streaming induced by EGTA, only a small amount of calcium-containing precipitates formed in the cytoplasm in the presence of antimony. A few precipitates were found in the chloroplasts, the middle lamella of the cell wall and at the border between the cytoplasm and the cell wall. On the other hand, in cells treated with EGTA and subsequently irradiated with far-red light in artificial pond water, many precipitates were observed in the cytoplasm, chloroplasts, mitochondria and endoplasmic reticulum. The middle lamella was also heavily stained.
On the basis of these observations, it was concluded that rotational cytoplasmic streaming in Vallisneria cells can be induced when the free calcium concentration in the cytoplasm decreases and that the induced streaming is arrested when the free calcium concentration in the cytoplasm increases. Far-red light accelerates the increase of calcium in the cytoplasm.
Three-dimensional intranuclear dna organization In situ: three states of condensation and their redistribution as a function of nuclear size near the G1-s border in hela S-3 cells
Authors: Belmont A. , Kendall F. M. , Nicolinif C. 
Published: April 2021

ABSTRACT
Characteristic variations in nuclear morphology occurring with variations in the physiological state of the cell have been observed in a number of systems to date. In this paper, we have critically examined the relationship between nuclear morphology and intranuclear DNA organization near the G1–S transition in HeLa S–3 cells, by the study of both the spatial distribution of optical density values and the optical density histograms for individual Feulgen-stained nuclei. Our results demonstrate that the majority of the DNA is located in a narrow shell surrounding the nuclear and nucleolar borders, and present evidence for at least three discrete states of chromatin condensation. Greater than 90% of the genome appears distributed among the two classes with larger density, and a redistribution between these two classes occurs as a function of changing nuclear size. Numerical simulations indicate that the observed distribution does not arise as an artifact related to overlapping but, in fact, actually represents discrete states of condensation. Interestingly, the extrapolated nuclear area at which the fraction of DNA in the state of highest density is reduced to zero, corresponds closely to the nuclear size shown elsewhere as representing the critical size that HeLa S-3 nuclei must exceed in order to initiate S phase.
Video digitizer analysis of birefringence along the lengths of single chromosomal spindle fibres II. Crane-fly spermatocyte chromosomal spindle fibres are not temperature-labile
Authors: Schaap Catherine J. , Forer Arthur 
Published: April 2021

ABSTRACT
Retardations were measured along the lengths of single chromosomal spindle fibres, from metaphase through anaphase, from video-taped images of crane-fly spermatocytes incubated at various temperatures (4–30°C). These measurements were made using a video digitizer interfaced to a microcomputer. Over most of the range of temperatures at which normal anaphase movement occurs the chromosomal spindle fibres are not temperature-labile. The non-specific and continuous fibre birefringence is temperature-labile, however. The data are discussed with respect to the ‘dynamic equilibrium’ model of anaphase chromosome movement. We conclude that, since single chromosomal fibre birefringence is not temperature-labile over most of the range of temperatures at which normal anaphase chromosome movement occurs, these data do not support the dynamic equilibrium model of anaphase chromosome movement.
Activity and stability of centrosomes in chinese hamster ovary cells in nucleation of microtubules in vitro
Authors: Kuriyama Ryoko 
Published: April 2021

ABSTRACT
Mitotic centrosomes were prepared from Chinese hamster ovary cells and their capacity to nucleate microtubules in vitro was demonstrated by incubation with exogenous brain microtubule protein. The number of microtubules polymerized onto centrosomes was directly counted by electron microscopy of whole-mount preparations. This simple and accurate quantitative assay has permitted characterization of the microtubule nucleating activity of centrosomes in vitro.
The number of microtubules polymerized onto centrosomes varied according to the structure of the centrosome. The activity was roughly proportional to the centriole number. The number and length of microtubules nucleated by centrosomes depended both on the concentration of tubulin and the incubation time with tubulin. Under saturating conditions, an average of 200–2 50 microtubules were initiated by single centrosomes. Centrosomal activity is unstable ( = 8h) and could easily be irreversibly disrupted by a medium of high ionic strength. The activity is stabilized by the addition of glycerol. Centrosomes can be stored at —80°C. The optimum pH for microtubule nucleation is 6·8. Activity is sensitive to protease digestion, but neither DNase or RNase affected the nucleating activity of centrosomes. The activity is temperature-sensitive, but addition of phenylmethylsulphonyl fluoride (PMSF) induces thermal stability. At an optimal concentration of 0·5 mg/ml, this drug increased the half-life of the activity ( = 95 h) and made it resistant to salt extraction. Protease inhibitors other than PMSF or dansyl fluoride did not have any stabilizing effect on the activity.
The difference between the centrosomal structure of polymerized microtubules in vivo and in vitro is discussed.
Deficiency in intercellular communication in two established renal epithelial cell lines (LLC-PK1 and MDCK)
Authors: Sepúlveda F. V. , Pearson J. D. 
Published: April 2021

ABSTRACT
We have studied the cell-to-cell passage of uridine nucleotides in two renal epithelial cell lines (LLC-PK1 and MDCK) and in porcine aortic endothelial cells (PAE). All three cell types incorporated tritiated uridine. After a 3 h incubation the radioactivity was predominantly in the form of acid-soluble compounds, mainly UTP. Prelabelled LLC-PK1 or MDCK cells were unable to transfer radioactivity to added adjacent, non-labelled cells, whereas PAE cells readily formed communicating intercellular junctions, as judged by autoradiographic analysis after a 3h co-culture period. Cell-to-cell communication m either of the renal cell lines was not promoted by treatment with dibutyryl cyclic AMP and methylisobutylxanthine. Radioactivity incorporated into the acidinsoluble pool was not available for intercellular transfer, as assessed in experiments in which cells were prelabelled 24 h before co-culture.
Association Of An Integral Membrane Protein With Glucose Transport And With Anion Transport
Authors: Banyard M. R. C. , White M. K. 
Published: April 2021

ABSTRACT
A monoclonal antibody that recognizes a cell-surface glycoprotein associated with glucose transport was reported previously. Additional information about the function and intracellular distribution of the antigen recognized by this antibody is presented. The monoclonal antibody recognizes a cell-surface and a cytoplasmic determinant. The density of the cell-surface determinant is heterogeneous within the cell population. The subpopulation of cells that carry the cell-surface determinant at high density correspond with a subset of cells that incorporate 2-deoxy-D-[3H]glucose more rapidly than the population as a whole. The monoclonal antibody is used, with cell-affinity chromatography, to isolate this subset of cells.
The cytoplasmic determinant, to which the antibody binds, is associated with the cytoplasmic microfilaments but the antibody is not absorbed by actin. The cell-surface and cytoplasmic components are not identical since the apparent affinity of the antibody for each site is different. The portion of the antigen in the membrane behaves as an integral membrane protein while the remainder is tightly associated with the detergent-insoluble cytoskeleton.
The expression of the antigen on the cell surface is modified by covalent attachment of an inhibitor of anion transport, 4,4’-diisothiocyano-2,2’-disulphonic stilbene. The possible interaction of the anion/lactate transporter with the glucose transporter is discussed.
Kinetic Parameters Of Neutral Amino Acid Transport In Hybrids Between Malignant And Non-Malignant Cells
Authors: White Martyn K. 
Published: April 2021

ABSTRACT
The kinetics of neutral amino acid transport were examined in isogeneic matched pairs of hybrid cells, one member of each pair being tumorigenic, the other not. The L system of transport, which is sodium-independent, was measured by the uptake of leucine, and the A system, which is sodium dependent, by the uptake of methylaminoisobutyric acid. Although there was variation from one cell type to another in both Km and Vmax for the transport of these amino acids, no systematic change was found to be associated with tumorigenicity. This is in marked contrast with hexose uptake where tumorigenicity was invariably found to be associated with a reduction in Km. It thus appears that whatever molecular change is responsible for the alteration in the kinetics of hexose transport, it is specific, at least to the extent that it does not affect either sodium-dependent or sodium-independent transport of neutral amino acids.