bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freeze-fracture study of phagocytosis in Dictyostelium discoideum
Authors: Favard-Séréno Colette , Ludosky Marie-Aline , Ryter Antoinette 
Published: April 2021

ABSTRACT
The plasma membrane and its derivative, the phagosome membrane, were studied during and after ingestion of yeast or latex beads in Dictyostelium discoideum. Freeze-fracture electron microscopy, which provides information on the internal architecture of the membranes, and observation of thin sections of cells treated by cytochemical methods were used in parallel. For visualization of membrane sterols in the replicas, the cells were fixed in the presence of digitonin or the antibiotic filipin.
No lateral phase separation occurred during yeast engulfment: the intramembranous particles (IMPs), phospholipids and sterols remained distributed at random in the forming phagosome membrane. In contrast architectural modifications of the membrane were observed upon phagosome internalization. Compared to the plasma membrane, the phagosome membrane displayed 2–3 times more IMPs, a shift in the IMP size distribution and a higher sterol content. These changes were completed soon after phagosome closure; they were not related either to the nature of the ingested particles (yeast, latex beads) or to the pH in the membrane environment. The membrane changes took place when the phagosomes began to fuse with pre-existing digestive or autophagic vacuoles and lysosomes. Some of the experimental evidence suggests that the restructuring of the membrane may be related to the presence of hydrolases.
Effects of 5-bromo-2′-deoxyuridine on friend erythroleukaemia cells : I. cell ultrastructure and morphometric analysis
Authors: Walter Robert J. 
Published: April 2021

ABSTRACT
The morphology of a subclone of untreated and bromodeoxyuridine (BrdUrd)-treated Friend erythroleukaemia (EL) cells was studied using conventional transmission, high-voltage, and scanning electron microscopy as well as morphometric analysis. Untreated EL cells were generally spherical with a large eccentrically located multilobed nucleus, sparsely scattered endoplasmic reticulum (ER), and moderate numbers of mitochondria that tended to be located at the nuclear hof. In thin sections, the mitochondria appeared to be elliptical or spherical, containing predominantly fingerlike cristae in a somewhat condensed conformation. However, serial-section analysis and reconstruction showed that, in 3 dimensions, the mitochondria were extremely pleomorphic and highly complex. Morphometric analysis of untreated EL cells and their components revealed that, for several days after renewing the growth medium, the volume fractions of cells and nuclei gradually increased (by about 20%) but the mitochondrial volume fraction remained constant. When EL cells were exposed to BrdUrd (20 μg/ml), they continued active growth and division and yet displayed distinct morphological alterations. Cell surface topography changed, ER and mitochondrial profiles were more abundant, and mitochondrial cristae were shelf-like and primarily in orthodox conformations. Morphometric analysis and mitochondrial reconstructions indicated that BrdUrd may have a dual effect on the mitochondrial compartment. During the initial 15 h of treatment with BrdUrd, cell and mitochondrial swelling occurred and a decrease in mitochondrial complexity was seen. This swelling subsided after 72 h but a second component became predominant. The volume fraction of the mitochondrial compartment underwent a 77% increase and the surface densities of inner and outer mitochondrial membranes increased by 60–80%. Thus, in EL cells, BrdUrd may alter the synthesis and/or degradation of mitochondrial constituents and perhaps affect the energy metabolism of these cells.
Immunological delineation in normal and malignant cells of a membrane protein involved in glucose transport : II. Function of the antigen
Authors: Gingrich R. D. , Wouters M. , Bramwell M. E. , Harris H. 
Published: April 2021

ABSTRACT
A review of the literature suggested that the antigen detected by the M/27 antibody described in the preceding paper might be involved in the transport of glucose across the cell membrane. This idea was tested by measuring the amount of M/27 antibody bound to cells under a range of conditions known to influence the rate of glucose uptake. Glucose starvation and the administration of insulin under appropriate conditions are known to increase the Vmax for glucose uptake in certain cells, and high cell density in vitro is known to decrease the Vmax. Glucose starvation was found to increase the amount of M/27 antigen present on the surface of 2 malignant cell lines, but produced no detectable change in 5 different non-malignant cell types. Insulin increased the amount of M/27 antigen on the surface of both malignant and non-malignant cells. At high cell density, the amount of M/27 antigen present on the cell surface decreased. The changes in the Vmax for glucose uptake produced by these manipulations have been shown not to require the synthesis of protein. This was also found to be true for the changes in M/27 antigen concentration. By disrupting cells in detergent, it could be shown that there was an intracellular pool of M/27 antigen. The total amount of M/27 antigen in the cell was found to be about 4 times as large as the amount of the antigen on the cell surface. This figure agrees with the value given in the literature for the size of the intracellular pool of the glucose transport system. The amount of M/27 antigen on the cell surface was found to vary during the cell cycle. A dramatic increase occurred early in S phase.
Laser-light scattering diffusion measurements on brain microtubule protein from dogfish (Squalus acanthus) and beef
Authors: Palmer G. R. , Sattelle D. B. 
Published: April 2021

ABSTRACT
Laser photon correlation spectroscopy and analytical ultracentrifugation were used to compare the equilibrium properties of disassembled, assembly-competent, brain microtubule protein from dogfish (Squalus acanthus) and beef. Analytical ultracentrifugation confirmed that assembly-competent bovine material at 4 °C, purified in the presence of glycerol through 2 cycles of assembly and disassembly, consisted of 6 S (dimer) and 35 S (ring) components, whereas assembly-competent dogfish material prepared in the same way was composed primarily of 6 S protein. By means of photon correlation spectroscopy, z-average diffusion coefficients of 0.55 (±0.04) × 10−11 m2s−1 (beef) and 1.27 (±0.11) × 10−11 m2s-1 (dogfish) were measured at 4 °C for the twice-cycled assembly competent microtubule protein. Although values for dogfish material are significantly higher than those for beef, they depart from the calculated value of 5.0 × 10−11 m* s-1 for a pure 6 S (dimer) solution. Microtubule accessory proteins were not detectable on sodium dodecyl sulphate/polyacrylamide gels of dogfish microtubule protein. By fitting photocount autocorrelation functions to a 2-particle (dimer-ring) model it was estimated that the presence in a solution of assembly-competent dogfish microtubule protein of 1 ring per 250 dimers could_account for the measured z-average diffusion coefficient. The temperature sensitivity of showed that dogfish brain microtubule protein polymerized at lower temperatures than samples prepared by the same methods from beef brain.
Freeze-fracture architecture and polypeptide composition of thylakoid membranes from euploid Ricinus cells
Authors: Timko M. P. , Triemer R. E. , Vasconcelos A. C. 
Published: April 2021

ABSTRACT
The freeze-fracture architecture and polypeptide composition of thylakoid membranes of euploid cells of Ricinus communis L. were examined. Electron microscopic examination of the chloroplasts of 1N, 2N and 4N cells revealed little variation in the size of chloroplasts, lamellar structure and internal organization of plastids, despite increases in plastid numbers per cell observed to accompany the increase in nuclear ploidy. Thylakoid membranes from euploid cells were also similar in their freeze-fracture morphology. Two basic types of intramembranous particles were observed on the fracture faces of thylakoid membranes of euploid cells. The endoplasmic fracture (EF) face of experimentally unstacked thylakoid membranes of 1N, 2N and 4N cells contain 2 size categories of particles (115 –121 Å and 164–166 Å), whereas the protoplasmic fracture (PF) face of these membranes contain a single size category of particles (85–88 Å). The distribution and size of the EF- and PF-face particles were found to be similar among membranes from cells of the 3 ploidy levels. Analysis of the polypeptide composition of thylakoid membranes from 1N, 2N and 4N cells revealed no difference in the relative proportion of the constituent polypeptides of these membranes. The possible factors involved in the regulation of the development of thylakoid structure and composition in the presence of altered nuclear genome size are discussed.
The apparent inducibility of tumour marker glycoproteins in a melanoma cell line selected for growth in low levels of glucose
Authors: Bramwell M. E. , Atkinson M. A. L. 
Published: April 2021

ABSTRACT
It has been reported previously that malignancy in hybrid cells is associated with changes in two glycoproteins of molecular mass 90000 and 100000. In the current paper the characteristics of a clonal derivation of a murine melanoma cell line (PG19G−), selected for growth in low levels of glucose, are described. The cells had considerably reduced amounts of the 90 K and 100 K glycoproteins as judged by lectin affinity-labellipg. When the level of glucose in the medium is raised the two glycoproteins become detectable after a few hours. This inducibility is specific for D-glucose and D-mannose at concentrations in excess of 300 mg/1 and is inhibited by cytochalasin B but not by cytochalasin A.
The 90 K glycoprotein differs from the 100 K in that its level varies with the glucose concentration even in the parent cell line PG19 and in other tumour lines. This is not the case for the 100 K glycoprotein, the synthesis and/or glycosylation of these two glycoproteins are, therefore, governed by separate control mechanisms. The relationship of the glucose-sensitive proteins to the glucose transporter is discussed.
Anatomy of the unpollinated and pollinated watermelon stigma
Authors: Sedgley M. 
Published: April 2021

ABSTRACT
The structure of the watermelon stigma before and after pollination was studied using light and electron microscopy, freeze-fracture and autoradiography.
The wall thickenings of the papilla transfer cells contained callose and their presence prior to pollination was confirmed using EM-autoradiography, freeze-fracture and fixation. No further callose thickenings were produced following pollination.
Pollination resulted in a rapid increase in aqueous stigma secretion and localized disruption of the cuticle, which appeared to remain on the surface of the secretion. Autolysis of the papilla cells, which had commenced prior to pollination, was accelerated and appeared to take place via cup-shaped vacuoles developed from distended endoplasmic reticulum. The reaction was localized to the papilla cells adjacent to the pollen tube only.
Both pollen-grain wall and stigma secretion contained proteins, carbohydrates, acidic polysaccharides, lipids and phenolics.
Extraction of membrane factors that inhibit aggregation in Dictyostelium discoideum
Authors: Laroy Kathy , Weeks Gerald 
Published: April 2021

ABSTRACT
Plasma membrane preparations partially inhibit the reaggregation of dissociated aggregation-competent cells of Dictyostelium discoideum, and membranes from aggregation-competent cells are more inhibitory than membranes from vegetative cells. Inhibitory activity can be extracted from the membranes of aggregation-competent cells with the detergent octyl glucoside or with EDTA, although the inhibition is never more than partial. Extracts of vegetative membranes have relatively little inhibitory activity and the amount of inhibitory activity that can be extracted increases as cells become aggregation-competent. The inhibitory activity is sensitive to Pronase, but relatively stable to heat. Inhibitory activity can also be extracted from intact aggregation-competent cells by 20 mM-EDTA or 0·25% octyl glucoside.
Adhesion and locomotion of l5222 cells on endothelium, collagen and glass
Authors: Kowalczyńska Hanna M. , Nowak Małgorzata , Dowjat Wieslaw K. , Doroszewski Jan 
Published: April 2021

ABSTRACT
Examination was made of the adhesive interaction of L5222 leukaemia cells with endothelial cells, collagen and glass and of cell locomotion on endothelium and collagen.
Leukaemia cells interacted with the substrate under stationary conditions. The fraction of cells adherent to the substrate was defined next, using the given shearing force caused by the medium flowing through the measuring channel. The relative number of adherent cells, A (related to the number of cells after sedimentation), remaining on the given surface despite the detaching action of shearing force, F, was determined. The range of F values applied was 0·1to 30 (× 10 −13) N. It was found that the relation A(F) is a decreasing function for all the substrates examined and takes on values in the relation 1:2:6 for cells adherent to collagen, glass and endothelium, respectively. The critical value of F, at which values of A are maintained at a constant level close to zero, was 0·5, 1 and 3 (× 10 − 12) N, respectively, for cells adherent to these substrates. The function A(F) for L5222 cells adherent to endothelial cells and to glass can be described well by the formula: A = a/√F (where a = constant &gt; 0).
Studies of L5222 cell locomotion on an endothelial cell layer and on collagen revealed that the pattern of locomotion, variations in locomotion velocity and the mean values of cell displacement (5·8 and 5·0 μm, respectively) are similar for both substrates.
Interaction of hyaluronate with the surface of simian virus 40-transformed 3t3 cells: aggregation and binding studies
Authors: Underhill C. B. 
Published: April 2021

ABSTRACT
Previous studies have shown that the divalent-cation independent aggregation of simian virus 40-transformed 3T3 cells (SV-3T3) is mediated by the interaction of endogenous hyaluronate with binding sites on the cell surface. In the present study, the nature of the interaction of hyaluronate with the binding sites was characterized further by examining both the aggregation of SV-3T3 cells and the binding of exogenously added [3H]hyaluronate. The aggregation of SV-3T3 cells was found to be: (1) optimal at pH 7; (2) only slightly affected by variations in temperature between o and 40 °C; (3) more potently inhibited by the addition of high molecular weight preparations of hyaluronate than by lower molecular weight preparations; and (4) enhanced by increasing the ionic strength of the medium. With the exception of the effects of temperature, these characteristics correspond closely to those previously described for binding of [3H]hyaluronate.
The effect of ionic strength on the binding of [3H]hyaluronate by SV-3T3 cells was found to correspond closely to its effect on lowering the viscosity of hyaluronate. Both effects (i.e. binding and reduction in viscosity) had similar dose-response curves for NaCl and MgCI2. This close correspondence between binding and the reduction of viscosity suggested that the effect of ionic strength on binding was due to a change in the structure of hyaluronate. Lowering the temperature (40 to 0°C) also enhanced the binding of [3H]hyaluronate to SV-3T3 cells. However, this effect was blocked if the cells were first fixed with glutaraldehyde, suggesting that temperature mediates its effect through the binding sites. Additional experiments showed that the binding of [3H]hyaluronate by SV-3T3 cells could be prevented by preincubating the cells with several types of lectins.
Stages in the assembly of pleated and smooth septate junctions in developing insect embryos
Authors: Lane Nancy J. , Swales Lesley S. 
Published: April 2021

ABSTRACT
The stages that occur during the assembly of both pleated and smooth septate junctions in developing insect tissues have been examined. The oesophagus and mid-gut of the embryonic moth, and the oesophagus and central nervous system (CNS) of the locust embryo, have been investigated in thin sections and by freeze-fracture during the course of membrane biogenesis. The smooth septate junctions developing between the lateral borders of the mid-gut exhibit, in the early stages, individual intramembranous particles becoming aligned into short ridges. These ultimately migrate over the membrane face and fuse into longer arrays, which become stacked in parallel with other ridges to form the characteristic mature form of the junction just before hatching. Pleated septate junctions occur between the cells both of the oesophagus and of the perineurium, which enβheathes the neurones and the neuroglial cells in the locust CNS; these are also fully formed by the end of embryonic development. The pleated junctions appear to be assembled during the later stages of CNS or gut differentiation, arising first in embryos about two-thirds of the way through development. During their maturation, the initial event seems to be a membrane depression in the P face, which occurs in patches over the presumptive junctional membrane. Into these depressed regions or ‘formation-plaque’ areas, 8–10 nm particles appear to be inserted intramembranouβly in apparently random arrays. These particles are the most common elements but larger particles are also present; the former ultimately become aligned in a row. With time, other intramembranous particles come to lie in rows parallel to the original one. By hatching, the typical undulating stacks of parallel intramembranous particle rows are fully formed. Gap junctions also form between the same perineurial or oesophageal cells, usually before, but in some cases at the same time, or just after, the septate junctions have been assembled. Tricellular associations between cells also appear around the same time in embryonic development. The simultaneous assembly of these different junctions reflects a high degree of organizational capacity at the membrane level.
Discrimination in the uptake of soluble proteins by isolated nuclei
Authors: Cox G. Stanley 
Published: April 2021

ABSTRACT
The uptake of radioactive cytosol proteins has been studied in isolated HeLa cell nuclei. The process is temperature- and pH-dependent, is enhanced by divalent metal ions, and is saturable with respect to the protein concentration of the cytosol. Nuclei prepared by washing in either detergent or sucrose buffers are similar in their abilities to accumulate protein, indicating that the outer nuclear membrane does not affect the process. The uptake is neither inhibited to any great extent by cyanide or 2,4-dinitrophenol nor significantly stimulated by glucose, glucose 6-phosphate, D-lactate, succinate, L-glutamate, NADH, phosphoenolpyruvate, cyclic AMP, or ATP. In fact, ATP is inhibitory, apparently due to its ability to chelate magnesium ions. Fractionation of the cytosol preparations on DEAE-cellulose shows that, as a class, those proteins eluting at higher salt concentrations are taken up better than those eluting at lower salt concentrations. Incubation of nuclei with protein fractions obtained from the chromatography of cytosol extracts on Sephadex G-150 indicates that the uptake of proteins in the molecular weight range from 35000 to 145000 is inversely proportional to molecular weight, but the nuclear accumulation of very small proteins (Mr 15000) was less than would be expected if molecular weight were the only factor determining nuclear uptake. Polyacrylamide gel electrophoresis shows that several protein classes in the cytosol are taken up by the nucleus and that in some cases the amount of protein in the nucleus reflects its relative concentration in the cytosol. Exceptions, however, are the drastic reduction in the nuclei of a class of proteins with approximate molecular weights of 55000 to 70000, and the increase in the nuclei of a protein class in the molecular weight range from 30000 to 40000. Proteins released from the nucleus are taken up by nuclei in vitro more efficiently than are cytosol proteins. In the presence of excess nuclei only 5-10 % of the available protein is taken up. Purified histones are rapidly taken up by nuclei, bovine serum albumin is not accumulated at all, and actin is taken up at an intermediate rate. When nuclei are fractionated following incubation, ribosomal proteins are found associated with the nucleolus to a greater extent than are cytosolic proteins. Thus, the nuclear uptake of soluble proteins in this cell-free system exhibits characteristics and specificity similar to that previously reported for in vivo systems and suggests that isolated nuclei may be useful for studying various aspects of nucleus-cytoplasm interaction.
Events in the cytoplasm during male meiosis in Lilium
Authors: Bird J. , Porter E. K. , Dickinson H. G. 
Published: April 2021

ABSTRACT
An electron microscopic investigation of the events associated with meiosis in Lilium has revealed a number of changes in both the organellar population and the other cytoplasmic components. Ribosome numbers decrease significantly in early prophase and are later replenished in the tetrads, a process most likely involving the newly arising cytoplasmic nucleoloids. The organelles show a cycle of de- and redifferentiation and later in meiosis unusual internal structures can be seen before these organelles enter a division phase resulting in increased numbers. The localization of acid phosphatase during these changes has also been studied using electron microscopic cytochemical methods. In early prophase, considerable amounts of acid phosphatase are found in vesicles scattered through the cytoplasm; activity is also found in association with most membranous surfaces and often markedly associated with condensing mitochondria. Later in prophase the enzyme activity decreases to normal levels. Electron microscopic autoradiography revealed that DNA is synthesized in both plastids and mitochondria during meiotic prophase with activity reaching a peak during zygotene and ceasing by diakinesis and tetrad formation.
These changes point to a certain independence of organelles from nuclear control during meiosis. The events are also evaluated in relation to a cytoplasmic clearing mechanism, which may occur in preparation for the changeover from sporophytic to gametophytic control and the development of gametes.
Visualization of a repeating subunit organization in rat hepatocyte chromatin fixed in situ*
Authors: Derenzini Massimo , Hernandez-Verdun Daniele , Bouteille Michel 
Published: April 2021

ABSTRACT
The chromatin structure of rat hepatocytes fixed in situ was investigated in thin sections selectively stained for DNA with the Feulgen-like osmium-ammine reaction. Visualization of the chromatin structure was facilitated by the dispersal that occurred in the chromatin of regenerating rat hepatocytes at 24 h after partial hepatectomy. Our results show that repeating subunits were present both in the clumps and in the extended fibres of chromatin. These subunit particles appeared to be composed of an electron-translucent core delimited by a strongly electron-opaque DNA ring. Depending on the section plane, they displayed a morphology varying from a flat, oval shape to a rough circle. The mean diameter of the repeating subunits was 11 ± 0·8 nm (S.D.) with a range from 9·5 to 13 nm. The thickness of the DNA ring was about 3nm. Regarding the association of the subunits in the chromatin fibres, two types of fibres were visualized, 11 nm and 20–25 nm thick, respectively. The thinner fibres were composed of a linear array of adjoining subunits. In the thicker fibres the subunit organization did not clearly form discrete superunit structures.