bluuebunny/crossref_metadata_2025 huggingface dataset:
Ability of a cell-surface protein produced by fibroblasts to modify tissue affinity behaviour of cardiac myocytes
Authors: Armstrong Peter B.
Published: April 2021

When fragments of 2 diasimilar embryonic tissues are placed in contact in organ culture, cells of one fragment migrate over the surface of the second to envelop it. Holtfreter proposed that this behaviour was in response to ‘tissue affinities’. He proposed that these also play important roles in the control of morphogenetic cell movement during development. The present study demonstrates that the heart fibroblast, present as a minority cell type in heart ventricle, can modify the affinity behaviour of heart tissue. The fibroblast effect appears to be mediated by a factor that can be extracted from living fibroblast monolayers by 1 M urea. The factor is a cell-surface protein since it is absent in monolayers which had been treated with trypsin prior to extraction.
Timing of nuclear division cycle in Neurospora Crassa
Authors: Martegani E. , Tomè F. , Trezzp F.
Published: April 2021

The timing of the nuclear division cycle in Neurospora crassa was studied by inhibiting DNA synthesis with hydroxyurea added to exponentially growing cultures at concentrations that do not inhibit cytoplasmic growth. After the addition of hydroxyurea only the nuclei that have passed the .S’-phase divide, and therefore by counting the increase in the average number of nuclei per hypha, the stage in the cycle in which completion of S phase occurred was determined in different nutritional conditions of exponential growth. The stage at which DNA replication terminates is different in different conditions of exponential growth; however, when the length of Gt+ M phases is calculated a constancy of these phases is shown. Our data indicate that in N. crassa the coordination between cytoplasmic growth and the nuclear division cycle is achieved mainly through a growth-rate-dependent expansion of the G, phase, according to a sizer-plus-timer model of control of the nuclear division cycle.
Fibroblast adhesion on collagen substrata in the presence and absence of plasma fibronectin
Authors: Grinnell Frederick , Bennett Marylyn Hoy
Published: April 2021

We have used scanning electron microscopy and transmission electron microscopy to compare the initial adhesion of baby hamster kidney (BHK) cells and early passage human skin fibroblasts on glass, dried collagen, and hydrated collagen substrata. On glass or dried collagen substrata, BHK cell spreading required fibronectin and the cells were extensively flattened, with broad lamellipodia. In marked contrast, BHK cell spreading on hydrated collagen substrata did not require fibronectin and the cell bodies tended to be rounded, with one or several large filipodia. These filipodia generally penetrated into collagen lattice where they interwove with the collagen fibrils. Proteolysis of the collagen was not evident. In the presence of fibronectin, the morphology of BHK cell spreading on hydrated collagen substrata was similar, except that there was an increase in the number of cells that spread with lamellipodia that did not penetrate the collagen lattice. Human fibroblasts also demonstrated marked differences in cell spreading on glass or dried collagen compared to hydrated collagen substrata. Spreading was characterized by lamellipodia on glass or dried collagen but by multiple filipodia on hydrated collagen. In the latter case, the filipodia penetrated just beneath the surface of the collagen lattice. Added fibronectin was not required for spreading of human fibroblasts on any of the substrata and the presence of added fibronectin had no effect on cell morphology. Finally, the human fibroblasts were observed to form adhesion plaques in some cases where the fibroblasts made close contacts with individual collagen fibrils. The results are discussed in terms of connective tissue organization.
Recovery of sliding ability in arm depleted flagellar axonemes after recombination with extracted dynein I
Authors: Yano Y. , Miki-Noumura T.
Published: April 2021

We compared sliding velocity between outer doublet tubules in demembranated axonemes of sea-urchin (Pseudocentrotus depressus) sperm flagella with that of arm-depleted axonemes recombined with extracted dynein 1.

The outer arm-depleted axonemes after extraction with 0·5 M NaCl had a velocity of 6·9 ± 1·0 μm/s, while the intact axonemes had a velocity of 14·3 ± 1·5 μm/s in the presence of 1 mM ATP and 2 μg/ml trypsin at 25 °C. The sliding velocity was closely related to the number of remaining outer arms following the NaCl-extraction process. When the outer arm-depleted axonemes were recombined with dynein 1, the sliding velocity increased to 11·3 ± 1·3μm/s. Electron microscopy confirmed the recovery of 94 % of outer arms in the axonemes.

After extraction with Tris-EDTA solution for 10 min, the axonemes lost their sliding ability completely, even in the presence of ATP and trypsin. Such axonemes lacked most of both inner and outer arms, although sometimes the basal segment of the arms appeared to remain. When the exogenous dynein 1 fraction extracted from other axonemes was added, the axonemes could extrude tubules, and both types of arms reappeared clearly and distinctly in the axonemes. The recombined axonemes with one-fold stoichiometric excess of dynein 1 recovered 58 % of the total number of arms and had a velocity of 7·4 ± 1·6 μm/s. Those with 2-fold stoichiometric excess had a velocity of 11·0 ± 1·5 μm/s, up to 82% of the arms in these axonemes being restored.

These results indicated that the exogenous dynein 1 fraction derived from the outer arms restored sliding ability to arm-depleted axonemes, recombining with the outer doublet tubules as inner and outer arms, and that the sliding velocity had a close relationship to the total number of arms in the axonemes, irrespective of their being inner or outer arms.
Effect of vinblastine and cytochalasin B on the cytoskeletal domains in 3T3 cells
Authors: Temmink J. H. M. , Spiele H.
Published: April 2021

Normal 3T3 cells were exposed to vinblastine and cytochalasin B in an atttempt to correlate the morphological changes of the cell surface as seen in the scanning electron microscope with ultrastructural changes of the cytoskeletal elements as seen in critical-point-dried cells in the transmission electron microscope. Special attention was given to the changes in the cytoplasmic domains distinguished in a previous paper. Cytochalasin B primarily affects the ultrastructure of the cytocortical domain by inducing the formation of condensation foci in the cytoplasmic material. Vinblastine not only induces the depolymerization of microtubules and the perinuclear concentration of intermediate filaments, but it also causes the disappearance of stress fibres from the cortical cytoplasm and the widening of the cytocortex at the expense of the endoplasmic domain. These results support the hypothesis that the differentiation in ultrastructural domains is dependent on the spreading of the cells and their adhesion to substrate.

* Present address: Agricultural University, Department of Toxicology, De Dreijen 12, 6703 BC Wageningen, The Netherlands.
Cytology and growth characteristics of human tumour astrocytes transformed by Rous sarcoma virus
Authors: Macintyre E. H. , Grimes R. A. , Vatter A. E.
Published: April 2021

Human tumour astrocytes (118MG) were exposed in vitro to the Engelbreth-Holm strain of Rous sarcoma virus at a multiplicity of infection of one. Morphological transformation of the cells in 60-mm plates was complete in 9-11 weeks after viral exposure. The transformed cells (EH-118MG) grew as a monolayer, upon which nests of rounded cells developed. From these nests, rounded cells shed into the medium and in turn on seeding formed a monolayer and repeated the cycle. The transformed cells contained the viral group-specific antigen in the cytoplasm, and produced Rous sarcomas in chickens. No complete virus was demonstrated in the mammalian cells. Electron micrographs of the parent 118MG and transformed EH-118MG cells gave further details of the structure of cytoplasmic protrusions which were formed in some of the free EH-1 18MG but not in the 118MG cells. Their nature is completely unknown.
Isopropyl N-phenylcarbamate affects spindle microtubule orientation in dividing endosperm cells of Haemanthus katherinae baker
Authors: Hepler P. K. , Jackson W. T.
Published: April 2021

The mitotic inhibitor isopropyl N-phenylcarbamate (IPC) effects changes in the ultrastructure of the dividing endosperm cells of Haemanthus katherinae. In cells treated with 10 p.p.m. IPC for 0·5–2 h the microtubules lose their parallel alignment and become oriented in radial arrays. These radial arrays are interpreted as micropoles of the spindle apparatus and are thought to be the focal points for the chromosomes as they aggregate into micronuclei. Thus, IPC has a markedly different effect on the structure of the spindle apparatus than colchicine, which is observed at concentrations of 50 p.p.m. for 1 h to destroy the microtubules in Haemanthus. The structure of the microtubules appears unaffected by IPC since those from control and treated cells are similar in diameter (22 nm), in degree of staining, and in sensitivity to the fixation. In addition, the chromosomes and cytoplasmic components such as mitochondria, plastids, dictyosomes, elements of the endoplasmic reticulum, and ribosomes are not structurally modified by treatment with IPC.
Regulation of mitosis: II. interaction of isopropyl N-phenyl-carbamate and melatonin
Authors: Jackson W.T.
Published: April 2021

Earlier studies on the effects of the herbicide isopropyl N-phenylcarbamate (IPC) on mitosis revealed blocked metaphases, multinucleate cells, giant nuclei and an increase in number of partly contracted chromosomes. It was assumed that IPC, like colchicine, was causing these effects by disruption of the spindle apparatus by destroying the spindle microtubules. The animal hormone melatonin causes an increase in birefringence of the mitotic spindle in animal cells, presumably by increasing the number of microtubules. We have studied the effects of IPC, melatonin, and combinations of the two on mitosis in dividing endosperm cells of the African blood lily (Haemanthus katherinae Baker) in vivo by phase-contrast and polarization microscopy. Both qualitative and quantitative data are presented. Interpretation of these results has been aided materially by a time-lapse cinemicrographic analysis of dividing cells subjected to 1 and 10 p.p.m. IPC (unpublished) and by an accompanying fine-structural analysis of untreated and IPC-treated cells. Mitosis was disrupted by 0·01–10 p.p.m. IPC, the severity of the effect depending on both concentration and stage of mitosis of the cell at the time of treatment. Concentrations of IPC that caused cessation of chromosome movement also caused loss of birefringence of the mitotic spindle. Melatonin increased birefringence of the mitotic spindle in these plant cells and partly nullified the adverse effects of IPC. The results of this study demonstrate that the herbicide IPC, under our conditions, causes disruption of mitosis and loss of birefringence of the spindle. And it has been established that an animal hormone is capable of increasing the birefringence, and presumably the number of microtubules, of the mitotic spindle in dividing endosperm cells of a higher plant. Although melatonin is capable of partly nullifying the effects of IPC, a competitive antagonism is not postulated.
Differentiation of Dictyostelium discoideum mutant cells in a shaken suspension culture and the effect of cyclic AMP
Authors: Abe K. , Saga Y. , Okada H. , Yanagisawa K.
Published: April 2021

In Dictyostelium discoideum, 16 mutants in which cells differentiate into spores and stalk cells without normal morphogenesis were isolated. AU these mutants are rapidly developing and capable of differentiating in a shaken suspension of phosphate buffer. The developmental kinetics of specific activities of enzymes in one of the mutants, HTY1851, cultured in the suspension was compared with that in the parental strain, X2, developed on a solid surface. Most of the enzyme activities appeared much earlier and the peaks of the activities were lower in HTY1851 than X2, but the order of appearance of the activities was the same in both the strains cultured under the conditions described above. These results suggest that the biochemical steps in the development of the mutant in a shaken suspension are essentially the same as those of the parental strain X2 on a solid surface. It was also found that addition of cyclic AMP (2·5 × 10−5 M to 1 × 10−4 M) to the mutant cell suspension 6–8 h after the initiation of development induced an increase in the number of spores and the specific activities of some enzymes to values twice as high as those of an untreated control.
Contact-induced spreading in cultures of corneal epithelial cells
Authors: Brown R. M. , Middleton C. A.
Published: April 2021

The behaviour of dissociated chick-embryo corneal epithelial cells in primary culture was investigated. These cells colliding in subconfluent culture formed long-lasting adhesions with each other and the cells accumulated into islands and sheets of cells. The contacts that developed between the cells were not necessarily permanent since cells often broke away from islands they had previously joined.

Corneal epithelial cells in islands or sheets were extensively spread on the substratum, lacked blebs and, if marginally positioned, displayed a leading lamella from a part of their margin not in contact with other cells. In contrast, isolated cells, lacking contacts with other cells, exhibited a range of different morphologies. They could either be extensively spread with a well-defined leading lamella, or they could be only poorly spread and bleb vigorously. Alternatively, they could have a morphology intermediate between these two extremes. An individual isolated cell could, at different times, adopt any of these varying morphologies. Within 30 min of making contact with an island of cells, an isolated cell, if poorly or partially spread, changed its morphology to become indistinguishable from the well-spread cells or the island it had joined. Well-spread isolated cells did not show similar changes in response to contact. Measurements of the area of substratum occupied (spread area) by the cells showed that, on average, the individual cells in 2-cell islands had larger spread areas than did isolated cells.

These observations suggest that isolated corneal epithelial cells, when poorly or partially spread, exhibit contact-induced spreading. Since isolated cells may spread extensively, cell contact is not an absolute pre-requisite for spreading, but such contact apparently induces and stabilizes the well-spread morphology more transiently displayed by isolated cells.
Acid phosphatase localization in PAS-bodies ofGonyaulax
Authors: Schmitter Ruth E. , Jurkiewicz Antoni J.
Published: April 2021

Periodic acid-Schiff staining, acid phosphatase localization, and yellow autofluorescence have been correlated with the PAS-body of Gonyaulax polyedra for the first time. PAS- staining and acid phosphatase activity are both correlated with the PAS-body of Gonyaulax tamarensis. These results suggest that the PAS-body of these marine dinoflagellate algae functions in subcellular digestion.
Cytoskeleton-related structures in Tetrahymena thermophila: Microfilaments at the apical and division-furrow rings
Authors: Jerka-Dziadosz Maria
Published: April 2021

A ring consisting of microfilaments was found in the apical region of Tetrahymena thermophila wild-type strain B and janus mutant. This ring, about 0·4 μm wide and 0·2 μm thick, is located at the bases of the anterior, non-ciliated basal bodies of the apical ciliary couplets. The apical ring is made of fine filaments showing a banded pattern, the distance between bands depending on the fixation procedure and ranging from 50–200 nm. The bands are made of small beads fastened to the filaments. The microfilaments of the apical ring are attached to the’ bases of the basal bodies. No connection with the cell membrane was found.

In dividing cells in the incipient furrow region a filamentous band originates from the epiplasmic fibrogranular meshwork. This contractile ring is about 0·4 μm wide and 0·8 μm thick. It is formed by circumferentially aligned microfibrils. During constriction the contractile ring remains associated with the epiplasmic layer, which in turn adheres to the inner alveolar membrane. The microfilaments of both the apical and the division-furrow rings have diameters ranging from about 3·8–7·1 nm.
Freeze-fracture study of phagocytosis in Dictyostelium discoideum
Authors: Favard-Séréno Colette , Ludosky Marie-Aline , Ryter Antoinette
Published: April 2021

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

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

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

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

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

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

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

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

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 > 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

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

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

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

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

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.
Relative daughter cell volume and position of the division furrow in Tetrahymena
Authors: Hjelm K. K.
Published: April 2021

The relative daughter cell volume (RDCV) values for Tetrahymena pyrifomtis were determined at division on live cells. It was found that the anterior cell is generally larger than the posterior cell, and that the RDCV values are distributed in groups 5–6% apart. The RDCV value was found to be independent of predivision cell volume, indicating that the mother cell is divided into proportional volumes. The cells seem, however, not to assess volume directly but rather a parameter related to the cell volume. Furthermore, the RDCV value was found to increase during cell division, so that the final value is not reached until actual separation of daughter cells.

It is suggested that the division furrow is positioned so that the area of the cell surface lying between the old oral apparatus and the posterior pole of the cell is divided into equal parts. It is further suggested that several alternative values of the RDCV are possible, only one of which is expressed in each cell. The early division furrow is placed anteriorly to its final position, and its location is adjusted during cytokinesis.
Participation Of Concanavalin A Binding Sites In The Interaction Between Trypanosoma Cruzi And Macrophages
Authors: Meirelles M. N. L. , Martinez-Palomo A. , Souto-Padron T. , Souza W. De
Published: April 2021

Untreated mouse peritoneal macrophages as well as macrophages treated with concanavalin A (ConA) were incubated in the presence of untreated or ConA-treated epimastigotes and trypo-mastigotes of Trypanosoma cruzi. Treatment of epimastigotes or trypomastigotes with ConA increased or decreased their uptake by macrophages, respectively. Treatment of the macrophages with ConA reduced by 70 % and increased by five times the ingestion of epimastigotes and trypomastigotes, respectively. These results are discussed in relation to previous studies on the mobility of ConA receptors in the membrane of the parasite. Using fluorescein- or ferritin-labelled ConA we observed that ConA binding sites located on the plasma membrane of macrophages are internalized during endocytosis of T. cruzi, and observed in association with the membrane of the endocytic vacuole. Vacuoles without parasites showed a uniform distribution of ConA binding sites, while these sites were distributed in patches in vacuoles containing parasites. These results, in association with others previously reported, suggest the involvement of glycoproteins and/or glycolipids localized on the cell surface of T. cruzi and macrophages during the T. cruzi-macrophage interaction.
Surface Membrane Regeneration In Deciliated Tetrahymena
Authors: Williams Norman E.
Published: April 2021

The induced synthesis of identified surface membrane proteins has been demonstrated in deciliated Tetrahymena. Cells in the process of regenerating cilia were also studied using transmission electron microscopy in order to obtain information on the deployment of new membrane at the cell surface. The results obtained suggest a pattern of membrane flow that includes the ‘pellicular alveoli’, a subsurface membrane system characteristically present in ciliated protozoa. The results of 125I surface-marking experiments were consistent with the notion that new membrane is added initially in non-ciliated regions, then subsequently flows laterally to cover regenerating cilia.
Syncytioskeletons in choriocarcinoma in culture
Authors: Ockleford C. D. , Dearden L. , Badley R. A.
Published: April 2021

Indirect immunofluorescence microscopy using anti-actin serum has been used to investigate the distribution of actin-containing polymers in BeWo cells. This cell line, derived from a human choriocarcinoma, contains tissue that, like its tissue of origin, is partly syncytial. The syncytial nature has been inferred from study of Nomarski optical sections and from transmission electron microscopy.

The multinucleated plaques of tissue possess a syncytioskeleton with a number of actin-containing features characteristic of cultured cells. These include stress fibres, cortical layers and ruffled membranes. Other actin-containing structures are more typical of the related non-pathological syncytiotrophoblast. These include a dense population of microvilli.

The overall organization of the actin syncytioskeletons bears no obvious relationship to the number or position of nuclei in the syncytium.

Indirect immunofluorescence microscopy has also been employed to localize the protein tubulin in BeWo cells. The microtubules do not appear to be spatially organized by a particular nucleus. Rather, there are numerous microtubule-organizing centres (MTOCs) that exist in the cytoplasm and do not have the expected numerical and positional relationship to nuclei.

From these data it appears that polymeric cytoskeletal elements in these syncytia are organized in a manner not immediately subordinate to syncytial nuclei.
Hela cells form focal contacts that are not fibronectin dependent
Authors: Morgan Jean , Garrod David
Published: April 2021

HeLa cells cultured on glass substrata produce numerous prominent focal contacts, which reside at the termini of actin microfilament bundles. However, very few of the cells stain for fibronectin with specific anti-fibronectin antibody. Moreover, the cells form focal contacts in fibronectin-depleted medium, in the presence of high concentrations of anti-fibronectin immunoglobulin G and in the presence of monensin. No fibronectin synthesis can be detected by [35 S]methionine-labelling and immunoprecipitation. The possibility that HeLa cell focal contacts are independent of fibronectin in their formation is discussed in relation to the controversy about the relationship between fibronectin and focal contacts.
Scintillation and autoradiographic studies on 63Nickel uptake inPseudomonas tabaci
Authors: Al-Rabaee R. H. , Sigee D. C.
Published: April 2021

Scintillation studies on the uptake of 63Ni2+ by Pseudomonas tabaci demonstrate an incorporation of approximately 2·5 nmol per 1010 bacterial cells, in medium containing 12 nmol (8·3 μCi) per ml. Over 80% of the incorporated Ni2+ is lost from the cells during washing, fixation and dehydration with ethanol. The remaining insoluble (bound) 63Ni2+ has the highest level in cells fixed in acetic acid/ethanol (O·4 nmol/1010 cells), with smaller amounts in paraformaldehyde- and glutaraldehyde-fixed cells. The radioactive level in aldehyde-fixed cells represents a total Ni2+ uptake of about10−18g or 104 atoms per cell.

Light- and electron-microscope autoradiography corroborated the scintillation studies in demonstrating a higher retention of label by cells fixed in acetic acid/ethanol, possibly reflecting a higher retention of medium Mτ proteins with this type of fixation. High-resolution electron-microscope autoradiography involving gold latenβification with physical development demonstrated a clear localization of silver grains to the central nucleoid region (seen most clearly over the discrete nucleoid of aldehyde-fixed cells) and within this to the chromatin (seen most clearly over the condensed chromatin of acetic acid/ethanol-fixed cells). It is suggested that the incorporated