bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction between normal and transformed bovine fibroblasts in culture: II cells transformed by polyoma virus
Authors: Pontén J. , Macintyre Elizabeth H.
Published: April 2021

Bovine fibroblasts transformed by polyoma virus have been cocultivated with syngeneic or allogeneic normal cells. The growth of the transformed cells was inhibited by the presence of normal cells. The strongest depression was obtained when a dense stationary layer of normal fibroblasts was challenged by polyoma cells. The inhibition was least pronounced if normal and transformed cells were simultaneously seeded.

Polyoma-transformed cells were identified by radioautography after incorporation of tritiated thymidine. After 96 h of contact with stationary normal cells the number of grains per nucleus and the number of labelled nuclei had not changed indicating strong depression of DNA synthesis. A deficient attachment or premature detachment of polyoma cells could not account for the observed failure of growth in the normal/polyoma mixed cultures.
The maintenance of kappa during macronuclear reorganization in Paramecium tetraurelia
Authors: Koizumi S. , Kobayashi S.
Published: April 2021

Kappa particles were injected into stock-51 sensitives (KK) of Paramecium tetraurelia to investigate the maintenance of kappa by gene K during macronuclear reorganization. Injection into exconjugants and autogamous cells followed by macronuclear regeneration, induced by microsurgical removal of macronuclear Anlagen, resulted in maintenance of kappa particles by a considerable proportion of the clones descended from the recipient paramecia. Injection into animals that underwent normal reorganization however usually failed to yield particle-maintaining paramecia.
Transfer of human chromosomes via human minisegregant cells into mouse cells and the quantitation of the expression of hypoxanthine phosphoribosyltransferase in the hybrids
Authors: Tourian Ara , Johnson Robert T. , Burg Kornel , Nicolson Susan W. , Sperling Karl
Published: April 2021

The behaviour of human cells arrested in mitosis can be severely perturbed so as to generate numerous small minisegregants containing very few chromosomes. These cells can be separated according to size and DNA content and fused with intact cells. In this paper we describe the production and some properties of proliferating cell hybrids generated by fusion of human minisegregant cells derived from a HeLa strain with mouse Ag cells deficient in hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8). The hybrids were shown to contain up to 10 human chromosomes including a single X. Independently derived hybrid clones were quantitatively chracterized and compared with the parental phenotypes with respect to HPRT. Human isozymes of each of the 3 enzymes HPRT, glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and phosphoglycerate kinase (EC 2.7.2.3) were found. Tests to evaluate both structure and function of HPRT were utilized. The specific activity of HPRT of more than 10 hybrids tested was approximately 10% that of the HeLa parent. Structural characterization of HPRT from hybrid cells as evidenced by heat inactivation and electrophoretic mobility results in a ‘humanlike’ phenotype. Functional characterization of parental HPRT results in kinetic constants for cofactor and substrate which do not permit distinction of human and of human and mouse enzymes; HPRT from the minisegregant hybrids had normal kinetic constants. The reduced specific activity of HPRT in the hybrids is discussed in terms of the inability of the mouse environment to regulate the full expression of the human structural gene.
Ultrastructural localization of calcium in unfertilized sea-urchin eggs
Authors: Cardasis Constance A. , Schuel Herbert , Herman Lawrence
Published: April 2021

The pyroantimonate technique was employed to identify the binding sites for calcium in unfertilized Arbacia punctulata and Strongylocentrotus purpuratus eggs. Since antimony is non-specific and binds with a variety of cations, the identification of calcium was established by specific chelation with ethyleneglycol tetra-acetic acid (EGTA) and X-ray microprobe analysis. Antimony deposits were observed on the egg’s membranes, i.e. plasma, cortical (secretory) granule, pigment granule, smooth-surfaced vesicle, and yolk platelet. Deposits were also observed in the mitochondria, rod-containing vesicles, and the vitelline layer. Two types of yolk platelets were observed: a more numerous electron-opaque platelet which had precipitate along its limiting membrane as well as within the stored-matrix substance, and a less-frequently seen platelet with lower electron opacity which contained precipitate only along its limiting membrane. Deposits were reduced at all sites following exposure of eggs to EGTA either prior to or after osmium-antimonate fixation. Initial fixation in glutaraldehyde followed by postfixation in osmium-antimonate solutions provided better preservation of structure but less precipitation than direct fixation in osmium-antimonate. The organelle sites of calcium binding identified within unfertilized sea-urchin eggs may participate in stimulus-secretion coupling (exocytosis of the cortical granules) and the activation of embryogenesis at fertilization.
Studies of the endoplasmic reticulum and plasma membrane-bound ribosomes in erythropoietic cells
Authors: Grasso Joseph A. , Sullivan Albert L. , Chan Sai-Chung
Published: April 2021

Erythropoietic cells of 5 species, including man, contain endoplasmic reticulum present as individual cistemae or tubules scattered throughout the cytoplasm of all stages except mature RBCs. The endoplasmic reticulum is mainly agranular but occurs frequently as a variant of granular ER which is characterized by an asymmetrical and irregular distribution of ribosomes along one cytoplasmic face. In most cells, the endoplasmic reticulum occurs in close proximity to mitochondria or the plasma membrane, suggesting that the organelle may be involved in functions related to these structures, e.g. haem biosynthesis. Endoplasmic reticulum is more abundant in early than in late erythroid cells. Its exact role in RBC development is unclear.

Since endoplasmic reticulum could account for ‘plasma membrane-bound ribosomes’ reported in lysed reticulocytes, studies were performed which ruled out this possibility and which suggested that such ribosomes were an artifact of the lysing conditions. Hypotonic lysis in less than 20 vol. of magnesium-containing buffers yielded ghosts variably contaminated by ribosomes and other structures. Lysis of reticulocytes in 20—30 vol. of magnesium-free buffer or homogenization of whole cells or crude membrane fractions in hypotonic buffer removed virtually all contaminating ribosomes from the purified membrane fraction.
Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos: iv. biochemical and autoradiographic observations on fucose-, glucose-, and mannose-labelled materials
Authors: Johnson Kurt E.
Published: April 2021

Normal Rana pipiens gastrulae show more incorporation of isotopically labelled fucose, glucose, and mannose into TCA-insoluble materials than blastulae. Interspecific hybrid embryos which undergo developmental arrest at the onset of gastrulation often synthesize reduced amounts of fucose-, glucose- and mannose-labelled materials. These materials are high-molecular weight and are degraded by Pronase into fragments which are included in Sepharose CL-4B but excluded from Sephadex G-50. Labelled materials contain label predominantly in fucose and galactose with little label in glucose or mannose. Labelled materials migrate slowly on cellulose acetate, bind to DEAE-cellulose and elute at low ionic strength and are precipitated by cetyl pyridinium chloride (CPC) without the addition of carrier compounds.

Pulse-chase labelling experiments and light- and electron-microscopic autoradiography were used to examine the site of synthesis, mode of transport, and sites of deposition of fucose-, glucose- and mannose-labelled materials in different developmental stages of normal developing Rana pipiens embryos and interspecific hybrid embryos formed by fertilizing the eggs of R. pipiens with the sperm of R. catesbeiana. In both normal and hybrid embryos, after a 15–30-min pulse, grains are closely associated with juxtanuclear and cytoplasmic collections of membranebound vesicles which resemble the Golgi apparatus. In normal embryos following a 15–30-min pulse and a 60-min chase, grains are largely cleared from the cytoplasmic vesicles and deposited in the extracellular spaces or along cell surfaces. In contrast, arrested hybrid embryos given a 15–30-min pulse and a 6o-min chase show a marked accumulation of grains over cytoplasmic structures such as the Golgi apparatus and vesicular elements in the cell cortex. Certain interesting features of regional variation in synthetic activity in developing normal embryos are also described.
Development of intercellular junctions in the pulmonary epithelium of the foetal lamb
Authors: Schneeberger E. E. , Walters D. V. , Olver R. E.
Published: April 2021

The integrity of epithelial tight junctions in foetal mammalian lungs is essential to maintain the unique ionic composition of lung liquid, and to prevent leakage of serum proteins into peripheral air spaces. In the present study the development of intercellular junctions of the lining epithelium of foetal lamb lungs during gestation was examined by light and electron microscopy. Both thin sections and freeze-fracture replicas were examined by electron microscopy. By 39 days of gestation, epithelial tight junctions consist of a minimum of 3·1 ± 1·6 (S.D.) and a maximum of 5·8 ± 2·0 discontinuous rows of particles and short segments of strands on P face ridges and in complementary E face grooves, while from 58 to 76 days they are composed of a network of 4·3 ± 1·6 to 7·7 ±1·9 focally interrupted P face strands. Complementary replicas show that many of the discontinuities on the P face are due to separation of junctional particles on to the E face during fracturing, and not to an absence of junctional particles. From 76 days to term, epithelial tight junctions (exclusive of upper airway epithelium which was not examined) resemble those of adult lungs, and consist of a continuous network of 4·5 ± 2·0 to 7·5 ± 2·5 P face strands and complementary particle-free grooves. Permeability measurements, published elsewhere, indicate that the epithelium is functionally ‘tight’ from 69 days onwards. Tight junctions in peripheral air-space epithelium, therefore, are structurally continuous and functionally ‘tight’ early in foetal lung development, and form seals at one end of long, narrow intercellular spaces; these features may be important for coupled ion and water transport. When the bounding epithelial cells become flattened, these narrow intercellular spaces remain intact as a result of complex interdigitations of adjacent cell membranes. Desmosomes were present throughout gestation near the abluminal side of the tight junctions and occasionally near the base of the intercellular space. These junctions may serve to connect cells to each other at a time when tight junctions may be mechanically weak. In addition, gap junctions are associated with tight junctions from the glandular through the canalicular stages of lung development. They disappear by 120 days when the epithelial cells are differentiated.
Selecting somatic cell hybrids with hat media and nystatin methyl ester
Authors: Fisher Paul B. , Sisskin Enid E. , Goldstein Neil I.
Published: April 2021

The structurally modified polyene antibiotic nystatin methyl ester (NME) has been utilized as a half-selection agent for isolating interspecific mouse-Syrian hamster hybrids. By using HAT media supplemented with NME we have isolated hybrid clones from polyethylene glycol-fused cultures of biochemically defective mouse (A9 or B82) and genetically normal Syrian hamster (BHK/C13) cells. Unfused parental cells were killed in HAT-NME media as a result of their genetic defect, absence of hypoxanthine guanine-phosphoribosyl transferase-HGPRT”(A9) or thymidine kinase— TK”(B82), or innate sensitivity to NME (BHK/C13). In contrast, hybrid cells proliferated and clones were isolated after 3 weeks growth in HAT-NME media, indicating that genetic complementation had occurred and polyene resistance was expressed as a dominant phenotypic property in the hybrids. The presently described technique is efficient in eliminating unfused parental cells and should prove useful in isolating other types of hybrids formed between genetically defective and normal parental cells.
Fertilization in brown algae: I. sem and other observations on Fucus serratus
Authors: Callow Maureen E. , Evans L. V. , Bolwell G. P. , Callow J. A.
Published: April 2021

The cell wall secreted immediately following sperm entry into an egg can be visualized by the fluorescent dye Calcofluor white. Cell wall secretion precedes nuclear fusion by 10–20 min. SEM observations of the surface of unfertilized and fertilized eggs and sperm attachment to eggs are described. These results are discussed in relation to fertilization in sea urchins and the biochemical phenomena associated with egg-sperm recognition in Fucus.
The packaging unit: a basic structural feature for the condensation of late cricket spermatid nuclei
Authors: Kierszenbaum A. L. , Tres Laura L.
Published: April 2021

The alignment, folding and packaging of cricket chromatin was examined during late spermiogenesis by an electron-microscope study of nuclei dispersed by air–liquid surface tension forces after detergent treatment. Late developing spermatid genomes arrange themselves in multiple packaging units in a stepwise process which includes: (1) a loss of the beaded repeating structure of chromatin as nucleoprotein fibres become smooth and gradually assume a uniform diameter; (2) a side-by-side alignment of structurally modified chromatin fibres; and (3) a regular folding into packaging units. Alignment and folding of chromatin fibres are presumably mediated by intermolecular bonds easily disrupted by spreading forces. In very late spermatids, interfibre binding forces are difficult to override by spreading alone, indicating a stronger cross-linking of increasingly coalescent packaging units. ‘Unit to unit’ coalescence stabilizes the nuclear structure, first limiting and afterwards denying penetration of phosphotungstic acid, as displayed in thin sections of extremely condensed cricket spermatid nuclei. Binding of phosphotungstate by nuclear basic proteins can be facilitated by limited protein solubilization after disulphide reduction of unfixed cricket testes with sodium dodecyl sulphate and dithiothreitol. Results of this study permit the proposal of model experiments useful for clarifying the organization of highly condensed spermatid genomes and for evaluating the structure of genome segments in systems wherein changes of chromatin-associated protein occur.
Membrane changes associated with mucus production by intestinal goblet cells
Authors: Swift J. G. , Mukherjee T. M.
Published: April 2021

Changes in the structural organization of membranes of mucous bodies and the plasma membrane that occur during mucus production in goblet cells of rat rectum have been studied by thin-section and freeze-fracture techniques.

Immature mucous bodies are bounded by a trilaminar membrane and fracture faces of the membrane have randomly distributed intramembrane particles. During maturation, mucous bodies become packed tightly together and changes in the structure of their membranes include (1) fusion of apposing membranes of adjacent bodies to form a pentalaminar structure, (2) a reduction in the density of particles on membrane fracture faces, and (3) exclusion of particles from regions of membrane apposition. Some trilaminar membranes of mucous bodies fuse with the lumenal plasma membrane to form a pentalaminar structure. Sites of apposition between mucous body membranes and the lumenal plasma membrane are seen as particle-cleared bulges on fracture faces of the plasma membrane.

Our results indicate that membrane reorganization associated with mucous production in goblet cells includes a reduction and redistribution of some membrane proteins and that membrane fusion occurs between portions of membranes from which proteins have been displaced.
Mobility of concanavalin a receptors and distribution of cytoplasmic actin in odontogenic epithelial and mesenchymal cells
Authors: Prime S. S. , Toh B. H.
Published: April 2021

The distribution of concanavalin A (Con A) surface receptors and cytoplasmic actin in the same cell was studied in monolayer cultures of 2 odontogenic epithelial cells of different developmental age and in ecto-mesenchymal cells derived from the same tooth germ. Con A receptors were demonstrated by fluorescein-isothiocyanate-labelled Con A (FITC-Con A) and cytoplasmic actin by a specific anti-actin autoantibody (AAA) traced with a rhodamine-labelled goat anti-human globulin (R-AHG). All 3 cell types, incubated with FITC-Con A at 37 °C for increasing time periods, showed progressive changes in staining patterns from clusters, caps to perinuclear globules. Capping was seen in the majority of immature epithelial cells at 120–180 min, in cells of more mature epithelium at 180-240 min and in ecto-mesenchymal cells at 240–360 min. Binding of FITC-Con A to cell surfaces resulted in sequential changes in AAA staining from filamentous to an aggregated or diffuse pattern, co-capping of aggregated or diffusely stained areas with those capped by FITC-Con A, presence of aggregated or diffusely stained areas in sites similar to the perinuclear globules stained by FITC-Con A, to final re-emergence of filamentous staining. Prior treatment of cells with cytochalasin B or colchicine promoted capping in epithelial but not in ecto-mesenchymal cells while presence of cither drug throughout the staining procedure inhibited capping. The results show that Con A receptors are more mobile in epithelial compared to ecto-mesenchymal cells and in immature epithelial cells compared to their more mature counterparts, and that binding and mobility of Con A receptors on the cell surface is associated with redistribution of cytoplasmic actin. The cytochalasin B and colchicine experiments suggest that both microfilaments and microtubules may have synergistic roles in the opposing functions of receptor anchorage and mobility, and that the relative receptor immobility of ectomesenchymal compared to epithelial cells may be attributed to firmer receptor anchorage to the cytoskeleton.
Oxygen uptake during the cell cycle of the fission yeast Schizosaccharomyces pombe
Authors: Creanor James
Published: April 2021

Oxygen uptake was measured in synchronous cultures of the fission yeast Schizosaccharomyces pombe. The rate of oxygen uptake was found to increase in a step-wise manner at the beginning of the cycle and again in the middle of the cycle. The increases in rate were such that overall, oxygen uptake doubled in rate once per cell cycle.

Addition of inhibitors of DNA synthesis or nuclear division to a synchronous culture did not affect the uptake of oxygen. In an induced synchronous culture, in which DNA synthesis, cell division, and nuclear division, but not ‘growth’ were synchronized, oxygen uptake increased continuously in rate and did not show the step-wise rises which were shown in the selection-synchronized culture.

These results were compared with previous measurements of oxygen uptake in yeast and an explanation is suggested for the many different patterns which have been reported.
Interaction of leukocytes with vascular cells in culture
Authors: Beesley Julian E. , Pearson Jeremy D. , Carleton J. Susan , Hutchings Amanda , Gordon John L.
Published: April 2021

The nature, kinetics and cofactor requirements of leukocyte adhesion to cultured vascular cells have been investigated in vitro, using a model system in which leukocyte suspensions are in continuous motion over the cultured cells. Adhesion is assessed by histological examination or by using 51Cr-labelled leukocytes.

Leukocytes adhere preferentially to endothelial cell monolayers rather than to smooth muscle cells, adventitial fibroblasts or serum-coated glass. Arterial and venous endothelium are equally good substrates for leukocyte adhesion, and lymphocytes and granulocytes at the same suspension density adhere to endothelial cells in similar numbers. Adherence is greatest during the first 10 min, and is inversely related to flow rate. Numbers of leukocytes adhering to the cell monolayer are proportional to the initial concentration of leukocytes in suspension, although only 2–10% of the leukocytes adhere. Leukocytes that have adhered to the cell monolayer spread over the cells and then migrate, apparently through intercellular junctions. Adhesion requires Ca2+ or Mg2+ ions, but not plasma protein cofactors. Fewer leukocytes adhere to endothelial cells grown for 48 h in rapidly stirred medium than to cells grown under conventional, static conditions.
Cell differentiation during fruiting body formation in Polysphondylium Pallidum
Authors: O’Day Danton H.
Published: April 2021

The spatial pattern of cellular differentiation was studied during fruiting body formation in Polysphondylium pallidum using 3 different staining methods: Calcofluor fluorescence (cellulose accumulation), neutral red (prestalk cells) and immunofluorescence (prespore cells). Neutral-red staining revealed the existence of a clear prestalk region which becomes evident during aggregation and continues throughout culmination. Immunofluorescent staining demonstrated that cells in the prestalk region gradually lose their presporeness (fluorescence) as they are transformed into differentiated stalk cells. Calcofluor staining revealed that stalk cell differentiation begins during the mid-aggregation phase and that the mode of formation of the main stalk and the side branches differs slightly in morphology. Calcofluor staining also demonstrated the development, during aggregation, of a thick cellulosic girdle with lateral tubular extensions which surround the aggregation streams. The above results are discussed in terms of our present knowledge about differentiation and morphogenesis in cellular slime moulds.
Tumorigenicity of cells transformed by simian virus 40 and of hybrids between such cells and normal diploid cells
Authors: Gee C. J. , Harris H.
Published: April 2021

A number of newly isolated clonal cell lines derived from diploid mouse embryo cells transformed by SV40 were examined in vitro and in vivo. Although these lines showed the properties that define transformation in vitro, they were not tumorigenic for many passages after their initial isolation.

Cells from tumours eventually produced by the SV40-transformed cells were fused with diploid mouse embryo cells. The hybrids formed were initially non-tumorigenic. This indicates that a normal diploid cell can suppress the malignant phenotype of a tumorigenic SV4O-transformed cell. The hybrid cells did, however, express the SV40 T antigen and they had a clearly transformed phenotype in vitro. It thus appears that neither the transformed phenotype nor the expression of the SV40 T antigen are enough to endow a cell with the ability to grow progressively in vivo.

The relationship between the transformed phenotype and tumorigenicity was further studied by fusing malignant mouse melanoma cells with non-tumorigenic SV4o-transformed cells. The hybrids expressed the transformed phenotype in vitro but were unable to form tumours in vivo. The changes that occur in cells after transformation by SV40 do not apparently affect the ability of these cells to suppress the malignant phenotype of tumour cells.
Specificity of the immaturitysubstances in Paramecium
Authors: Miwa Isoji
Published: April 2021

Cytoplasm of Paramecium caudatum syngen 3 in the period of sexual immaturity was effective in inducing immaturity when injected into mating-reactive cells of other syngens of P. caudatum. When immature cytoplasm of P. caudatum was injected into mature cells of P. multimicronucleatum, immaturity was also induced in the latter cells. When cytoplasm of P. bursaria in the immaturity period was injected into mature cells of the same species, the latter became immature. But immature cytoplasm of P. caudatum was ineffective when injected into mature cells of P. bursaria. When immature cytoplasm of P. bursaria was injected into mature cells of P. caudatum, no difference from the control was observed. These results suggest that a difference in specificity of the immaturity substances exists between paramecia of the ‘aurelia’ group and those of the ‘bursaria’ group.
The sorting out of embryonic cells in monolayer, the differential adhesion hypothesis and the non-specificity of cell adhesion
Authors: Nicol A. , Garrod D. R.
Published: April 2021

It has been reported previously that sorting out of chick embryonic liver parenchyma and limb bud mesenchymal cells would take place in monolayer culture. The distribution of cell types obtained (liver formed the internal, discontinuous phase) was interpreted in terms of the differential adhesion hypothesis. It was suggested that, in monolayer, liver cells were more cohesive than limb bud cells. In this paper we set out to extend the previous observations with 2 particular questions in mind: (i) Is sorting out in monolayer a general phenomenon occurring between a wider range of cell types ? (ii) Can evidence be provided for or against the interpretation of results in terms of the differential adhesion hypothesis ?

Sorting-out experiments were conducted on circular hydrophilic islands, on an otherwise hydrophobic substratum. Under these conditions, sorting-out in monolayer was obtained with binary combinations of 4 chick embryonic tissue types: liver parenchyma, limb bud mesenchyme, pigmented epithelium of the eye and corneal epithelium. With every combination but one, the cells of one type surrounded the cells of the other type, generating what we have called a ‘circle-within-a-circle’ configuration. With the remaining combination, liver parenchyma and corneal epithelium, only localized sorting was obtained. The ‘circle-within-a-circle’ configuration is consistent with an interpretation in terms of the differential adhesion hypothesis, according to which the distribution of cells is determined by the relative strengths of cohesions between their lateral surfaces.

In direct support of this is the finding from plating the different cell types at sub-confluent density on hydrophilic substrata that limb bud is the cell type having the weakest lateral cohesion in monolayer. Limb bud surrounded the other 3 tissues on hydrophilic islands. A hierarchy of lateral cohesiveness between the 4 cell types has been constructed. It is unlikely that the results can be explained in terms of specific cohesion. When plated together at subconfluent density, the 3 epithelial cell types aggregate together to form mixed monolayered islands, suggesting that they share common adhesive mechanisms.
Cell surface lipids and adhesion IV. The effects of trypsin on lipid turnover by the plasmalemma
Authors: Curtis A. S. G. , Hill Oya
Published: April 2021

Trypsin treatment of intact cells or isolated plasmalemmae from embryonic chick neural retinae leads to an accumulation of lysophospholipids in the plasmalemmae. Trypsin was used at activities commonly used in cell disaggregation techniques. This accumulation appears to result from the decrease in acyltransferase activity in the plasmalemma produced by enzyme treatment. Plasmalemmal CoA ligase activity is not affected by trypsin treatment. Trypsiniza-tion has little effect on plasmalemmal phospholipase A2 activity. These results are discussed in relation to (a) the effects of trypsinization on cell adhesion, and (b) the theory that cells cannot adhere to lecithins because of their fluidity or surface-free-energy values. We propose that the effects of trypsinization on adhesion may in large part be due to the effects of the enzyme on plasmalemmal enzymes of the lipid turnover system rather than to effects on other plasmalemmal proteins. Similarly the inability of cells to adhere to lecithin substrates is simply explained as being due to the lysolecithin that contacting cells release from these substrates.
Interaction of lectins with proteins of the endoplasmic reticulum and golgi system of rat liver
Authors: Winqvist L. , Eriksson L. C. , Dallner G.
Published: April 2021

The interaction of glycoproteins of rough and smooth microsomal and Golgi membranes with Sepharose-bound lectins has been studied. One of these lectins was a crude preparation from wheat germ lipase which was found to bind primarily to N-acetyl neuraminic acid. Rough microsomes, smooth microsomes and Golgi membranes contain glycoproteins which bind to Concanavalin A (Con A specific for mannose residues) in decreasing amounts in the order indicated (rough, smooth and Golgi) and to wheat germ agglutinin (WGA, glucosaminespecific) and to the crude lipase preparation in increasing amounts in the order indicated. The small amount of binding of rough microsomes and Golgi membranes to Crotalaria (galactosespecific) increases substantially after neuraminidase treatment. Three submicrosomal particle preparations enriched either in AMPase or in NADH- or NADPH-oxidizing electron-transport enzymes contain glycoproteins which bind Con A and wheat germ agglutinin. The latter binding is sensitive to neuraminidase treatment. Two other submicrosomal particle preparations, both enriched in glucose-6-phosphatase activity, bind preferentially to WGA. This binding is, however, not sensitive to neuraminidase. Prolonged incubation with Ervilia lectin (mannose-specific) inhibits NADH-ferricyanide reductase activity, while the electrontransport chain involving cytochrome b5 is also inhibited by Crotalaria, indicating that both the flavoprotein and the cytochrome b5 are glycoproteins whose oligosaccharide chains have terminal mannose or galactose residues.
Rectal papillae in Musca domestica: The cuticle and lateral membranes
Authors: Flower N. E. , Walker G. D.
Published: April 2021

The role of specialized regions of insect rectal papillae in the regulation of water and ion uptake is well documented. Although the apparatus for active uptake of water or ions is located in various cell membranes, the absorbed molecules must first pass through the cuticle which lines the rectal epithelium. Most cuticle (e.g. abdominal) has been shown to be permeable only to molecules soluble in wax, and to be impermeable to water and ions. Obviously if such cuticle lined the rectum, absorption of water and ions would be severely restricted. The present freeze-fracture and lanthanum tracer study was undertaken to investigate in more detail both the morphological features of the rectal papillae cuticle which could be responsible for its anomalous permeability and the various cell membranes involved in this transport.

It has been suggested from permeability studies that the anomalous permeability of rectal papillae cuticle could be due to the lack of a complete wax layer over the surface of the rectal cuticle. The present study strongly supports this suggestion. Thus, the freeze-fracture micrographs have shown that a surface layer of the cuticle reacts during fracturing like a lipid bilayer. However, in rectal papilla cuticle this surface bilayer is interrupted at each epicuticular depression by areas of different fracturing behaviour. These discontinuities in the surface bilayer probably allow the rectal contents to contact directly the true cuticular matrix. They could, therefore, explain the ease with which water and ions penetrate the rectal cuticle and so gain access to the underlying epithelial cells. Although similar discontinuities are present on some of the rectal cuticle surface external to the rectal papillae, they appear to be filled in by plugs of lipid-like material.

The lateral plasma membranes of the rectal papillae cells are generally considered to be the main site of active transport. The present lanthanum tracer and freeze-fracture study has shown that the lateral plasma membranes contain 3 distinct differentiations. Septate junctions are present at the apical and basal surfaces of the epithelial layer; a further membrane differentiation is found adjacent to the septate junctions; and thirdly, an array of short, variable length, non-anastomosing linear structures covers most of the lateral plasma membrane surface. These latter structures, unlike known types of cell junctions do not show equivalent arrays in apposing membranes even when the lateral plasma membranes of adjacent cells are closely apposed. The possible function of these structures is discussed.
Location of radioactively labelled extracellular fluid indicators in nervous tissue by autoradiography
Authors: Brown D. A. , Stumpf W. E. , Roth L. J.
Published: April 2021

The location of three radioactively labelled extracellular-space indicators ([3H]methoxyinulin, [3H]-D-mannitol and sodium [MS]sulphate) in the superior cervical sympathetic and nodose ganglia of cats was studied using an autoradiographic technique. The technique was designed to eliminate movement of soluble, diffusible substances in tissues after excision, and to provide high autoradiographic resolution. Ganglia were rapidly excised after administration of the radioactive compounds in vivo, and frozen in liquid propane. Frozen sections were cut at – 60 °C at a thickness of 0·7–0·8 μ. The frozen sections were freeze-dried, dry-mounted on dried, photographic emulsion-coated microscope slides, and exposed at – 15 °C until development.

The highest densities of silver grains in the autoradiographs were associated with regions of the tissue containing the greatest amounts of connective tissue. Lowest densities occurred beneath neurons and myelinated nerve fibres. The silver grain density beneath neuron peri-karya was between 10% and 15% of that associated with plasma. Attempts were made to determine the source of these subneuronal silver grains. The results suggested that they could not be ascribed to the following: background; chemographs and pressure artefacts; spread of radiation from radioactive material outside the perikarya; and in vitro translocation of radio-active material into the neurons or into the emulsion beneath the neurons. It was concluded that the subneuronal grains reflected a small amount of intraneuronal penetration of the compounds in vivo. There was very little difference between inulin, mannitol and sulphate with regard to the proportion of intracellular activity. Except for this small amount of intracellular radioactivity, the findings accord with the view that inulin, mannitol and sulphate are confined predominantly to the extracellular fluid.
Changes in the cytochemical properties of erythrocyte nuclei reactivated by cell fusion
Authors: Bolund L. , Ringertz N. R. , Harris H.
Published: April 2021

When the nucleus of a chick erythrocyte is introduced into the cytoplasm of a HeLa cell it resumes the synthesis of RNA and DNA. This reactivation of the red cell nucleus is associated with an increase in volume and with changes in nuclear composition. These changes have now been studied by quantitative cytochemical techniques. During the process of reactivation the dry mass of the erythrocyte nucleus shows a marked increase which takes place largely before the replication of the DNA begins. Within 24 h of cell fusion, some erythrocyte nuclei already contain an increased amount of DNA, and 48 h after fusion many of them contain twice the normal diploid amount, thus indicating that they have replicated their DNA completely. The physical properties of the nuclear deoxyribonucleoprotein complex also change. The ability of the nuclear chromatin to bind acridine orange increases 4- to 5-fold well before the synthesis of DNA begins; and changes in the melting profile of the deoxyribonucleoprotein suggest that its structure is loosened. This view is also supported by the observation that the reactivity of the erythrocyte nuclei to the Feulgen stain is altered during the early stages of reactivation.
Preprophase microtubule bands in some abnormal mitotic cells of wheat
Authors: Pickett-Heaps J. D.
Published: April 2021

Caffeine treatment of growing wheat tissues was used to form binucleate or polyploid cells; preprophase microtubules in subsequent division cycles in these and some other abnormal cells were then examined. In root tips, binucleate cells or those with greatly enlarged nuclei usually contained one transverse preprophase band of microtubules; sometimes this was slightly asymmetrical or skew, and less commonly two bands were seen. In coleoptile vascular bundles, there were generally two or more bands in the greatly elongated cells, these sometimes appearing in different planes. During formation of the stomatai complexes, preprophase microtubules were almost invariably found where expected, preceding abnormal development both in untreated and also in caffeine-treated material, regardless of the number, disposition or size of nuclei. This occurred even when wall stumps, formed during a previous abortive division, indicated that that previous division was also asymmetrical. It is concluded that the position(s) of preprophase band(s) of microtubules is not particularly influenced by the nucleus or nuclei, being more susceptible to external morphogenetic influences which can persist for some considerable time. Particularly in the case of stomatai complexes, a cell wall seems necessary to seal off or otherwise fulfil the tendency towards asymmetrical division.
Observations on the collagen and proteinpolysaccharide complex of rabbit corneal stroma
Authors: Smith J. W. , Frame J.
Published: April 2021

The form and interrelationship of the collagen fibrils and proteinpolysaccharide complex of rabbit corneal stroma were studied by electron microscopy. The intact tissue was examined as Araldite sections stained with alkaline lead citrate and uranyl acetate, and the mechanically disintegrated cornea after positive or negative staining with phosphotungstic acid or after treatment with 0·5 % bismuth nitrate in 0·1M nitric acid.

The corneal collagen fibrils vary in cross-sectional area from 4·6 to 9·6 × 104 sq. Å and do not exhibit a regular hexagonal distribution. Like tendon fibrils they consist of longitudinal filaments, but their appearance suggests that they lack some of the interfilament cross-links present in tendon.

In sections of intact cornea and in negatively stained disintegrated cornea, filaments which are considered to be the protein cores of proteinpolysaccharide macromolecules are evident. They are about 40 Å wide and 2000 Å long. They appear to run an angular course, orthogonal to the collagen fibrils, and to be tangentially attached to several fibrils in the region of the a band.

After treatment with bismuth nitrate disintegrated cornea contains coarsely beaded filaments. The filaments are about 2000 Å long and the beads about 70 Å in diameter. It is considered that these are again proteinpolysaccharide macromolecules and that each bead represents one or more polysaccharide chains in coiled configuration.
Effect of isolated plasma membranes on cell cohesion in the cellular slime mould
Authors: Jaffé Alida R. , Garrod David R.
Published: April 2021

The effects of isolated plasma membranes on cohesion of Dictyoslelium discoideumAx-2 cells have been studied. Membranes isolated from cells in the log phase of growth gave complete inhibition of log-phase cell cohesion. This effect was specific for the cohesion of log-phase cells mediated by contact sites B, since the cohesion of aggregation-competent cells which have acquired contact sites A was only partially inhibited by log-phase plasma membranes. Membranes isolated from stationary phase cells gave partial inhibition of log-phase cell cohesion, while membranes from aggregation-competent cells gave complete inhibition of log-phase cell cohesion but at much higher concentration than log membranes. Treatment of log-phase cells with cyclohex imide for 8 h rendered them completely non-cohesive. Membranes from cyclo- heximide-treated cells had no effect on log-phase cell cohesion. Log-phase membranes gave complete inhibition of cohesion of 4 slime mould species. The results are discussed in terms of our liga nd-receptor model of log-phase cell cohesion.
Magnesium ions and the control of the cell cycle in yeast
Authors: Walker Graeme M. , Duffus John H.
Published: April 2021

A study has been made of the role of magnesium ions in cell division cycle control in the fission yeast, Schizosaccharotnyces pornbe, and the budding yeast, Kluyveromyces fragilis. Synchronization of cell division in these organisms can be induced by restoring magnesium to magnesium-exhausted cultures. In S pombe, a correlation exists between the time taken for cells to enter the first synchronous division and the period of magnesium exhaustion. During short-term incubation in magnesium-deficient media, S. pombe cells are observed to continue growth in length, but they fail to make a cell plate and divide ; long-term magnesium deficiency results in the production of aberrant cell forms, and a reduction in viability. Analysis of total cell magnesium in cultures of both S, pombe and K. fragilis, synchronized by various induction and selection procedures, revealed that there is a fairly steady fall in magnesium concentration as cells grow, terminating in a rapid influx of magnesium just before cell division. This leads to the hypothesis that falling magnesium concentration may act as a transducer of cell size, eventually triggering spindle formation and a membrane change which permits rapid uptake of magnesium to a concentration which brings about spindle breakdown. The hypothesis was tested directly using the divalent cation ionophore, A23187, in the absence of calcium ions; the results obtained showed that a short pulse of A23187, very late in the cell cycle, accelerated cells into division and shortened the subsequent cycle. The hypothesis is discussed in relation to current models of cell cycle regulation.
Microtubules and control of macronuclear ‘amitosis’ in Paramecium
Authors: Tucker J. B. , Beisson J. , Roche D. L. J. , Cohen J.
Published: April 2021

The ‘amitotic’ division of the macronucleus during binary fission in P. tetraurelia includes a detailed sequence of shape changes that are temporally coordinated with the adoption of a series of well-defined positions and orientations inside the cell. The deployment of nucleo-plasmic microtubules that is spatially correlated with the shaping ritual is more complex and precise than has been reported previously. Macronuclear division is not amitotic. It is not a simple constriction into two halves.

As a dividing macronucleus starts to elongate it becomes dorsoventrally flattened against the dorsal cortex of the organism and assumes an elliptical shape. Concurrently, an elliptical marginal band of intranuclear microtubules assembles that has the same spatial relationship to nuclear shape as the marginal microtubule bands of certain elliptical vertebrate blood cells have to cell shape. The band breaks down as further elongation occurs and the nucleus adopts the shape of a straight and slender sausage. Most of the intranuclear microtubules assemble as elongation starts and break down shortly after elongation is completed; the majority are oriented parallel to the longitudinal axis of the nucleus throughout elongation. Some of them are attached to nucleoli and are coated with granules which are almost certainly derived from the cortices of nucleoli. The peripheral concentration, interconnexion, orientation, and overlapping arrangement of microtubules, and the reduction in microtubule number per nuclear cross-section as elongation proceeds at a rate of about 40 μm min−1, are all compatible with the provision of a microtubule sliding mechanism as the main skeletal basis for elongation. There are indications that this mechanism is augmented by anchorage and/or active propulsion of nucleoli that may perhaps facilitate fairly equitable segregation of chromosomal material to daughter nuclei.
Inhibition of leukocyte locomotion by hyaluronic acid
Authors: Forrester J. V. , Wilkinson P. C.
Published: April 2021

The effect of hyaluronate on neutrophil motility in vitro was studied by the micropore filter technique and by direct visual analysis of the locomotion of neutrophils on glass. Both directed and random locomotion of neutrophils were inhibited by physiological concentrations (0·5–6·0 mg ml−1) of hyaluronate in adose- and molecular weight-dependent manner. Inhibition of cell movement was more pronounced for high molecular weight chemoattractants such as casein than for small chemotactic peptides such as f-Met-Leu-Phe. Chemotactic factor gradient formation in filter chambers was profoundly retarded by hyaluronate, which may partly explain the inhibitory effects of hyaluronate on directed neutrophil locomotion. In addition, hyaluronate inhibited the binding of chemotactic factor to the neutrophil surface. This effect, together with a reduction in cell-to-substratum adhesion, may provide an additional explanation for hyaluronate-induced inhibition of random neutrophil locomotion. Inhibition of locomotion by hyaluronate was easily reversed by washing the cells free of hyaluronate; thus competition by hyaluronate for cell-surface binding sites is unlikely, and physical effects such as steric exclusion or molecular sieving by the large hyaluronate polymer provide the most probable explanations of its inhibitory effect on cell locomotion.

Since hyaluronate is a major constituent of tissue matrices, these results draw attention to the importance of the extracellular environment in regulating inflammatory cell movement in vivo.
Use of purified endopolygalacturonase for a topochemical study of elongating cell walls at the ultrastructural level
Authors: Roland Jean-Claude , Vian Brigitte
Published: April 2021

Endopolygalacturonase, a fungal enzyme purified by Albersheim and hia group which specifically degrades the galacturonosyl linkages of pectic polysaccharides, was used at the ultrastructural level on intact tissues from differentiated organs. Specimens were taken from the elongating zone of mung bean (Vigna radiata) hypocotyls. Incubation with the enzyme solution was performed en bloc, prior to embedding and to ultrastructural cytochemistry (PATAg test for polysaccharides), or by flotation of ultrathin frozen sections.

From the morphological viewpoint, the images obtained are sharp and reproducible. They support the plywood model for the organization of expanding walls. The ordering of walls appears to be built up very early, at the very beginning of elongation, in the upper part of the hypocotyl (hook). The specificity of the enzyme allows a topochemical study of the wall. Data indicate an uneven distribution of polysaccharides of pectic type across a single wall and among the different cells. Outer and inner wall areas are highly resistant to extraction by endopolygalacturonase. In the middle lamella the insolubility of amorphous components probably indicates a local concentration of highly methyl-esterified carboxyl groups not susceptible to endopolygalacturonase attack; conversely, adjacent parts of the middle lamella are regularly extracted, indicating a high concentration of galacturonans. An intense extraction occurs in the bow-shaped zone, revealing the occurrence of a massive embedding of unesterified pectic polysaccharides around the fibrillar subunits responsible for the twisted patterns. In the inner and recent part of the wall, the ordering of fibrillar subunits seems progressive and possibly related to the pectic embedding. This incrusting material could play a role in the morphogenesis of the ordered wall by means of specific assembly and interconnections of wall subunits.