bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemotactic reorientation of granulocytes stimulated with micropipettes containing fmet-leu-phe
Authors: Gerisch G. , Keller H. U. 
Published: April 2021

ABSTRACT
Human granulocytes were stimulated by means of a micropipette, with an orifice of about 0.2 μm in diameter, which contained fMet-Leu-Phe at a concentration of 10−5 M. The cells were reorientated by extending lamellipodia towards the source of the attractant, often within less than 10 s. Any part of the granulocyte, from the front to the tip of the tail, could be stimulated to produce new lamellipodia. Usually, but not always, this response occurred at the side of the cell nearest to the micropipette.
Cells stimulated from behind responded in one of the following ways : Cells that maintained their polarity extended new lamellipodia at one side of the leading front and reorientated by moving in a U-tum towards the micropipette. Occasionally, the leading front was split because one part of the front tried to make a left-hand and the other a right-hand turn.Formation of lamellipodia at the leading front was arrested and new lamellipodia were formed at the tail instead, indicating reversal of polarity. The result was an immediate change in the direction of locomotion by about 180°.A combination of the first 2 forms of behaviour was observed occasionally. Transiently, lamellipodia were extended from cell surface areas both close to and distant from the micropipette. These observations show that parts of a cell can respond independently to chemotactic gradients by extending lamellipodia towards the source of the attractant. The phenomenon can easily be explained by assuming that a temporal change of attractant concentration is recognized.
Development of the cell wall inTetraselmis:role of the golgi apparatus and extracellular wall assembly
Authors: Domozych David S. , Stewart Kenneth D. , Mattox Karl R. 
Published: April 2021

ABSTRACTThe green algal flagellate, Tetrasehnis, is a key transition organism in the phylogeny of green algae. It has been proposed that the cell wall of Tetraselmis arose evolutionarily from the fusion of scales and that this event secondarily caused the alteration of some cytoplasmic processes such as mitotic and cytokinetic mechanisms. Ultrastructural and developmental studies of the cell wall were performed with several strains of Tetraselmis. Two major wall types are reported. The wall of type 1 cells consists of a thick inner region covered by a layer of regularly repeating subunits of 26 nm, comparable to the subunits found in the median W2-W6 layer of Chlamy-domonas. The more elaborate type 2 cell wall consists of a thick median wall layer, homologous to the type 1 inner wall, with additional inner and outer strata of hairs, grains and scales. Development of the cell wall begins in the endomembrane system, particularly the Golgi apparatus, where fibrillar tufts and electron-dense droplets are synthesized, modified and transported to the outside. Here, the tufts and droplets are displaced around the protoplast and assemble in several steps to yield the intact wall. Edge-growth assembly of the wall occurs here synchronously with cytoplasmic developments to yield the characteristic anterior flagellar pit. Models explaining various aspects of this development are discussed. When released from the cell, the wall subunits are not completely comparable to stellate scales, but appear to correspond to developmental stages of scales in green flagellates possessing body scales.
Rapid cellular translocation is related to close contacts formed between various cultured cells and their substrata
Authors: Kolega John , Shure Michael S. , Chen Wen-Tien , Young Nevin D. 
Published: April 2021

ABSTRACT
Interference-reflection microscopy combined with time-lapse cinemicrography was used to examine the relationship between cell-to-substratum contact patterns and the speeds of translocation for a variety of cell types. Rapid translocation of amphibian leukocytes (average speed = 9·0 μm/min), amphibian epidermal cells (7μm/min) and teleost epidermal cells (7 μm/min) was found to correlate with patterns of broad grey close contacts. Similar contact patterns were found under freshly seeded (2 h) chick heart fibroblasts (moving 1–3 μm/min), the rapidly advancing (1–5 μm/min) margin of spreading human WI-38 fibroblasts, and isolated MDCK canine epithelial cells (0·5–1·0 μm/min). Conversely, numerous dark streaks of focal contact were found associated with the slow rate of translocation displayed by older cultures (72 h) of chick fibroblasts (&lt; 0·1 μm/min), well-spread WI-38 cells (≤ 0·3 μm/min) and confluent MDCK cells (&lt; 0·01 μm/min). It is concluded that close contacts, but not focal contacts, are associated with rapid cellular translocation, and that the build-up of focal contacts is associated with reduced cellular translocation and maintenance of the spread cell shape.
Ultrastructure of nucleomorph division in species of cryptophyceae and its evolutionary implications
Authors: Morrall Susan , Greenwood A. D. 
Published: April 2021

ABSTRACT
An ultrastructural study of nucleomorphs in species of Cryptophyceae revealed aspects of division not previously reported, including the formation of a structured fibrous system, which accompanies the ordered alignment, duplication and separation into two groups of the densely staining particles typically characteristic of each nucleomorph. Despite reports indicating the presence of nucleic acids in the nucleomorph, the division process appears to be unlike any known form of nuclear division. However, the possibility exists that the nucleomorph represents the nucleus of a primitive ancestral red algal endosymbiont displaying a form so antique that its nuclear division bears no resemblance to any other known form of mitotic division.
Sensory behaviour in Dictyostelium Discoideum slugs: Phototaxis and thermotaxis are not mediated by a change in slug speed
Authors: Smith Elizabeth , Fisher Paul R. , Grant Warwick N. , Williams Keith L. 
Published: April 2021

ABSTRACT
The speed of sustained migration of Dictyostelium discoideum slugs was similar in a temperature gradient and at different light intensities, including a light intensity sufficient to cause significant disorientation of slugs. No change was observed in slug speed in the presence of high levels of Slug Turning Factor (STF), a low molecular weight compound through which phototaxis and thermotaxis are mediated. Thus orientation of D. discoideum slugs is not mediated by a sustained changed in slug speed and we propose that slug movement is not directly coupled to tactic responses. Slug speed depended on the size, age and genotype of slugs as well as the nature of the substratum (charcoal-containing water agar versus water agar).
Protein and glycoprotein synthesis by friend erythroleukaemic cells during erythroid differentiation
Authors: Marshall Linda M. , Hunt Richard C. 
Published: April 2021

ABSTRACT
The proteins synthesized by Friend erythroleukemic cells (line 707B) have been studied by high-resolution polyacrylamide gel electrophoresis at various stages after the induction of erythroid differentiation by addition of dimethyl sulphoxide to the medium. After 24 h of differentiation, the rate of synthesis of most of the more abundant proteins is reduced, correlating with the reduction in the proliferation rate of the cells. However, the qualitative composition of the major proteins synthesized by control and differentiating cells remains very similar until at least 96 h after the induction of differentiation. Proteins characteristic of the mature erythrocyte membrane are an exception to the reduction in synthesis in line with the proliferation rate, for they continue to be synthesized at similar rates to those found in control cells. Only two major proteins (an as yet unidentified cytoplasmic protein and globin) are reproducibly induced, while the synthesis of a few proteins is almost completely abolished. In contrast to the similarity of the synthesis of the major proteins in the control and differentiating cells, the synthesis of glycoproteins that bind to Concanavalin A is markedly changed. The synthesis of many Concanavalin A-binding glycoproteins is abolished and they disappear from differentiating cells. The synthesis of a major glycoprotein is, however, induced early in differentiation. This protein, which has an apparent molecular weight of 100000, becomes the most abundant Concanavalin A-binding glycoprotein in the cell.
Electrophoretic movement of fertilized sea-urchin eggs
Authors: Oshima Noriko 
Published: April 2021

ABSTRACT
The eccentric shift of the sea-urchin egg within the fertilization membrane under an electric field was analysed by measuring the electrophoretic mobility of the isolated fertilization membrane and that of the egg deprived of the fertilization membrane. In addition, the migration speed of the egg proper was measured within the fertilization membrane under the conditions that: either (1) the movement of the whole egg was arrested, or (2) protamine sulphate was adsorbed on the fertilization membrane to reduce its mobility.
The results led to conclusions that: (1) both the fertilization membrane and the egg cell with the hyaline layer are negatively charged; (2) movement of the normal fertilized eggs is due mainly to the surface charge of the fertilization membrane; and (3) the eccentric position of the egg within the fertilization membrane is due to migration of the egg proper, which is independent of the movement of the whole egg.
Purified tumour angiogenesis factor enhances proliferation of capillary, but not aortic, endothelial cells in vitro
Authors: Keegan A. , Hill C. , Kumar S. , Phillips P. , Schor A. , Weiss J. 
Published: April 2021

ABSTRACT
Purified tumour angiogenesis factor (TAF) obtained from rat Walker 256 carcinoma and found to induce neovascularization in vivo was examined for its effect on endothelial cell cultures of capillary (CBEC), cow aorta (CAEC) and pig aorta (PAEC) in vitro. Treatment with TAF increased the growth of capillary but not aortic endothelial cells, and then only when the cells were growing on a native collagen substratum. These data show an important growth difference between endothelial cells in that the ability to proliferate in response to TAF depends not only on the substratum used but also on the vascular origin of the cells.
Concanavalin-a-mediated thymocyte agglutination: a model for a quantitative study of cell adhesion
Authors: Capo Christian , Garrouste FranÇoise , Benoliel Anne-Marie , Bongrand Pierre , Ryter Antoinette , Bell George I. 
Published: April 2021

ABSTRACT
This report describes a quantitative study of the agglutination of rat thymocytes with concanavalin A (ConA).
The probability that two ConA-coated cells remain bound after centrifugation was determined over a wide range of lectin concentrations. The minimal force required to separate agglutinated cells and the number of ConA molecules bound per cell were measured in similar experimental conditions. Agglutinated cells were examined by electron microscopy to estimate the area of membrane involved in adhesion. The dependence of agglutination on cell metabolism was studied: cold (4 °C), sodium azide (15 mM) and cytochalasin B (10μg/ml) inhibited thymocyte adhesion. The importance of lateral movements of ConA molecules was assayed by measuring the adhesion of ConA-coated glutaraldehyde-fixed thymocytes to untreated cells: substantial binding occurred, but at a reduced level relative to untreated cells.
A mathematical analysis of experimental data allowed the following conclusions. At least 103 ConA bonds were involved in cross-linking two bound cells, which required the lectin molecules to be concentrated in the binding area, at least when low ConA concentrations (0·5 μg/ml or less) were used.The dependence of the binding probability on lectin concentration was fairly linear when the latter was small, which implied that the limiting step in cell-cell adhesion was the formation of a bond between a single ConA molecule and a ligand on the other cell.The mean intercellular-contact time for the formation of this first bond was about 10 s for high concentrations of ligand (8 μg/ml).
It was possible to fit the above data into a physically consistent quantitative model of cell adhesion.
Mechanism of entry and development of Trypanosoma dionisii in non-phagocytic cells
Authors: Glauert Audrey M. , Baker J. R. , Selden Linda F. 
Published: April 2021

ABSTRACT
Cultures of ‘buffalo’ (bison) lung (BL) cells were infected with epimastigotes or trypo-mastigotes of Trypanosoma (Schizotrypanum) dionisii derived from cultures in vitro, fixed after various periods of incubation at 37 °C and examined by light or electron microscopy. Few if any epimastigotes entered the BL cells, but many trypomastigotes did so; they adhered to the cell surface within 2 h and then appeared to sink into furrows on the cell surface until engulfed in parasitophorous vacuoles. Cytochalasin D (5–10 μg ml−1) completely, but reversibly, inhibited entry of trypomastigotes without affecting parasite motility. It was concluded that entry depended on the interaction of stage-specific components on the trypomastigote’s surface with receptors on the BL cells, and that this interaction induced active uptake of the protozoa by a phagocytic process not involving pseudopod formation.
Soon after entry of the trypomastigotes into BL cells, the membranes of the parasitophorous vacuoles disintegrated and the parasites, which were now lying free in the cytoplasm of the host cell, transformed into amastigotes (micromastigotes) during the next 24–48 h. Replication then occurred, followed by transformation, beginning after 3 days, through a transitional promastigote phase to small intracellular trypomastigotes at 7 days. The promastigotes had a characteristic curved protrusion extending from the lip of the flagellar pocket (or reservoir) into the host cell’s cytoplasm. Trypomastigotes, released into the supernatant medium by rupture of the plasma membranes of the BL cells after 8 days, could re-invade other cells.
Mosaic structure in the plasma membrane: spiral arrays of subunits in the cytoplasmic tubules of lamprey chloride cells
Authors: Hatae Tanenori , Benedetti E. Lucio 
Published: April 2021

ABSTRACT
The membrane architecture of the cytoplasmic tubules in lamprey chloride cells has been studied by electron microscopy using thin-section and freeze-fracture techniques.
The chloride cell of lampreys (Lampetra japónica, Petromyzon marinus) is largely occupied with a continuous network of cytoplasmic tubules, which are derived from the invagination of the basolateral plasma membrane The lumenal surface of this tubular network is covered with spirally wound parallel rows of electron-dense material, which consist of linear aggregates of particles. Freeze-fracture of the membrane of the tubules also shows spiral arrangements of particles (∽ 9 nm in diameter) on the P-face and complementary shallow grooves on the Eface. These arrangements of particles are about 17 nm apart and wound at a pitch of about 45°.
These complex organizations of the membrane of the tubules are probably the sites of transport of ion and water, which is essential for the maintenance of ionic homeostasis in both low- and high-salinity environments.
Fine structure of the longitudinal flagellum in Ceratium tripos, a marine dinoflagellate
Authors: Maruyama Tadashi 
Published: April 2021

ABSTRACT
The fine structure of the longitudinal flagellum in Ceratium tripos, which performs not only undulations but also retractions, has been examined in both the retracted and relaxed states. Although conventional fixation always triggered retraction, the flagellum was found to remain relaxed when it was washed briefly with Ca2+-free medium prior to fixation. Previous light-microscopic investigation showed that it contained two fibres, the axoneme and the R-fibre. The present study by transmission electron microscopy has revealed that the axoneme that appeared to be a single fibre under the light microscope is a bundle of four fibres; the 9 + 2 microtubular axoneme, the packing material, the striated fibre, and the paraxial fibre. The first two are common in the longitudinal flagella of dinoflagellates, and the axoneme presumably generates the undulation. The last two are new and unique to the longitudinal flagellum of Ceratittm. The R-fibre, which probably contracts to fold the flagellum during retraction, consists of fine filaments, which pursue a loosely spiral course in the contracted state, but align longitudinally in the relaxed state. Periodic striations appear only on the extended R-fibre. The R-fibre shortens to approximately one third of its extended length and pursues a left-handed helix. The packing material, which sticks to the microtubular axoneme on one side, is connected with the R-fibre on the other side at intervals of approximately 5–8 μm. The retraction seems to be regulated by the Ca2+ concentration in the flagellum.
Observations on the molecular components stabilizing the microtubular system of the marginal band in the newt erythrocyte
Authors: Monaco Gianni , Salustrp Antonietta , Bertolini Bruno 
Published: April 2021

ABSTRACT
Microtubules have been classified as either stable or labile, according to their resistance towards depolymerizing agents. The highest stability belongs to those organized in composite structures, in which many other proteins are associated with the tubulin. Among these micro-tubular systems, the marginal band of amphibian erythrocytes is unusually stable. This system can be readily isolated from Triturus red blood cells, and therefore lends itself very readily to ultrastructural and biochemical analyses.
Immunofluorescence and electrophoretic analyses of the isolated bands reveal 14 components, among which tubulin, actin, myosin and a 90K glycoprotein were identified.
Tannic acid-glutaraldehyde fixation reveals a conspicuous opaque material surrounding the microtubules. Cationized ferritin binding suggests the presence of anionic sites. Moreover, neuraminidase causes the disorganization of the microtubule-associated opaque material.
The 90K glycoprotein is presumed to be related to the unusual stability of the microtubular system forming the marginal band.
Gene expression in Acetabularia. II. Analysis of in vitro translation products
Authors: Shoeman Robert L. , Schweiger Hans-Georg 
Published: April 2021

ABSTRACT
The translation products induced by poly(A)+ RNA from Acetabularia mediterránea, A. cliftonii and A. ryukyuensis in a modified, highly efficient wheat germ cell-free in vitro system were separated by two-dimensional gel electrophoresis. A comparison of the translation products on the basis of their molecular weight and their isoelectric point revealed only a limited similarity between the patterns of the three species. The pronounced species specificity will permit the study of the in vivo translation of heterologous poly(A)+ RNA in Acetabularia cytoplasm.
Infections of Paramecium bursaria with bacteria and yeasts
Authors: Görtz Hans-Dieter 
Published: April 2021

ABSTRACT
Infections of Paramecium bursaria with bacteria and yeasts are reported. Bacteria and yeasts multiply in the algae-free ciliate and are transmitted at various conditions as are symbiotic chlorellae. Like chlorellae, the bacteria and the yeast cells are situated in perisymbiont vacuoles. Both bacteria and yeasts maintain their capability for independent existence and can be grown on standard nutrient agar.
Infection experiments show that aposymbiotic P. bursaria can be infected with Chlorella, bacteria and yeast. CAZore/Za-bearing P. bursaria cannot be infected with bacteria or yeast. Bacteria-bearing paramecia can be infected with Chlorella but not with yeast. Yeast-bearing paramecia can be infected with Chlorella but not with bacteria. Following infections with Chlorella the paramecia lose their bacteria or yeast symbionts. The bacteria found in P. bursaria probably belong to the genus Pseudomonas; the yeast has been identified as Rodutorula rubra.
Redistribution of material labelled with [3H]mannose in amoebae induced to undergo pinocytosis
Authors: Flickinger Charles J. 
Published: April 2021

ABSTRACTThe synthesis, transport, and disposition of material labelled with [3H]mannose were studied by electron microscopic radioautography in normal amoebae and in cells that had internalized cell surface as a result of being induced to undergo pinocytosis. Control amoebae were injected with the precursor and placed in normal medium. The Golgi apparatus and rough endoplasmic reticulum were heavily labelled at the earliest intervals, while radioactivity of the cell surface peaked 12 h after injection of precursor. The experimental cells were injected, placed in bovine serum albumin solution from 15 to 60 min after injection, and then removed to normal medium until fixation. Incorporation of the precursor into the rough endoplasmic reticulum was near normal, but the proportions of grains associated with the Golgi apparatus and the cell surface were greatly reduced. The percentage of grains overlying vacuoles increased 12 h after injection, notably in the case of polymorphous vacuoles and dense vacuoles, both of which were identified as lysosomes with the acid phosphatase reaction. The results suggest that addition to the surface of components labelled with [*H]mannose was diminished following induction of pinocytosis. Incorporation of the precursor appeared to be shifted from cell surface material to lysosomal contents, possibly lysosomal enzymes. It is thought that this shift occurred in response to the need for the cell to digest unusually large amounts of endocytosed protein. Recycling of cell surface under these conditions is considered possible.
Migration of human neutrophils in hydrated collagen lattices
Authors: Grinnell Frederick 
Published: April 2021

ABSTRACT
The migration of human neutrophilic granulocytes in hydrated collagen lattices was studied by a combination of cinemicroscopy, and scanning and transmission electron microscopy. The basic pattern of cell migration in collagen was similar to that observed previously for these cells on inert material surfaces; i.e., a cycle of cell extension and cytoplasmic flow into the leading extension. In general, however, neutrophils in collagen were less spread than on glass or plastic surfaces. Thin lamellipodia were absent and the leading extension of the cells was often an elaborately folded pseudopodium. In addition, neutrophils migrating in collagen were never observed to have retraction fibres at the tail end of the cells, although a uropod was usually seen. In the region of the uropod, extensive blebbing of the cells often occurred, and when this happened, forward movement of the cells ceased. At the ultrastructural level, both the leading pseudopodium and the blebs at the tail of the cell were found to contain a dense cytoskeletal network from which cell organelles were excluded. Finally, the cells were found to be coated with an extensive glycocalyx, and individual collagen fibres were sometimes observed within the glycocalyx.