bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organotypic cultures of the avian salt gland: Biosynthesis of membrane proteins
Authors: Mazurkiewicz Joseph E. , Barrnett Russell J. 
Published: April 2021

ABSTRACT
The salt glands of control and salt-stressed ducklings were dissociated with collagenase to produce cell aggregates or ‘minilobules’ which were cultured. The fine-structural organization of freshly isolated and cultured (up to 72 h) aggregates were examined and showed surprisingly intact fine-structural organization with minimal changes from untreated glands. Incorporation of [3H]leucine into total protein, membrane protein and immunoprecipitable Na+ ATPase was determined in cultures at various time points, by pulse or pulse-chase experiments. Incorporation of label was linear for 4 h in protein, but higher in cultures of salt-stressed glands than in controls. Na+ ATPase was synthesized throughout the time of the experiment, the rate being highest during the first 4 h, reaching a plateau by 24 h. Up to 10% of the total label was present in Na+ ATPase. These results are discussed with reference to the use of minilobule culture to analyse further synthesis and assembly during biogenesis and control of these processes.
Megasporogenesis in a heterosporous fern: features of the organelles in meiotic cells and young megaspores
Authors: Bell P. R. 
Published: April 2021

ABSTRACT
Megasporogenesis in the heterosporous fem Marsilea (Hydropterideae) shows features intermediate between sporogenesis in homosporous fems and that in heterosporous seed plants. The plastids in the dyads and young spores were associated with tubules 30–35 nm in diameter, probably a specialized form of endoplasmic reticulum. No consistent differences in size or cytoplasmic components could be found between the megaspores of a tetrad that might account for differential survival. The view that megaspore viability within the tetrad is genetically determined is thereby strengthened.
Hordeum and Secale mitotic genomes: Lie apart in a hybrid
Authors: Finch R. A. , Smith J. B. , Bennett M. D. 
Published: April 2021

ABSTRACT
In both unpretreated root tip metaphases and pretreated mitoses of Hordettm vulgare L. cv. Sultan × Secale africanum Stapf F1 hybrids, Hordeum chromosomes tended to be nearer the centre of the mitosis than Secale chromosomes. This was clear in 4 serially sectioned cells examined in the electron microscope. In Feulgen squashes of 38 of 40 cells studied in the light microscope, the mean distances in each cell from the mean centromere position for the cell was less for Hordeum centromeres than for Secale centromeres.
Such spatial separation of parent genomes might prevent pairing of homoeologues in hybrids.
Substratum wettability and charge influence the spreading of Dictyostelium amoebae and the formation of ultrathin cytoplasmic lamellae
Authors: Gingell David , Vince Sheila 
Published: April 2021

ABSTRACT
Amoebae of Dictyostelium discoideum attach and spread on strongly hydrophobic methylated glass and polystyrene as well as the hydrophilic surfaces of clean glass, polylysine adsorbed on glass and acid-treated polystyrene.
On polylysine-treated glass, spreading is rapid and the edges of the fully spread cells withdraw, forming a wide ∼ 0·1 μm thick lamella, which gives a very dark image in the interference reflection microscope. The optical properties of the lamella have been analysed in detail using finite aperture theory and can be distinguished from dark images generated by a small aqueous cell-substratum separation. The formation of the lamella is discussed in terms of the mechanics of cell movement.
Cell-glass separation depends on salt concentration and valency: Measurements on Dictyostelium amoebae by finite aperture interferometry
Authors: Gingell David , Vince Sheila 
Published: April 2021

ABSTRACT
Using pre-aggregation amoebae of the cellular slime mould Dictyostelium discoideum we have investigated the influence of cation concentration and valency on cell–glass separation. For computing the separation we used interference reflection microscopy and converted measured image irradiance to distance by finite aperture theory.
Alterations in ionic strength caused virtually instantaneous reversible changes in the inter-ference image due to changes in cell membrane–glass separation. In solutions containing monovalent cations, a change in ionic strength from 20 mM to ∼ 0·5 mM increased the separation of the plasmalemma from the glass by 60 nm. Divalent cations were better than monovalent cations at maintaining a small separation. Our results show that both divalent and trivalent cations adsorb to one or both of the interacting surfaces, in addition to acting as electrostatic double-layer counterions. The optical measurements also show that the cell membrane–glass gap is not reduced to zero by counterion screening ; this is apparently due to the presence of a cell surface glycoprotein coat.
Flagellar membrane specializations and their relationship to mastigonemes and microtubules in Euglena gracilis
Authors: Melkonian M. , Robenek H. , Rassat J. 
Published: April 2021

ABSTRACT
The flagellum of Euglena gracilis has been studied comparatively, using the freeze-fracture technique and with thin sections involving a tannic acid staining procedure. The flagellar membrane exhibits specializations in the form of two groups of intramembrane particle rows (IMP rows; mean IMP diameter, 6 nm) and single clusters of larger IMPs (mean IMP diameter, 10 nm) associated with the edge of one of the two groups of IMP rows. The IMP rows are helically arranged. The two groups of IMP rows are separated from each other by two membrane areas (measuring 170 and 300 nm in length) devoid of IMP arrays. The IMP rows are arranged in a four-start helix around the flagellum. A comparative morphometric analysis of IMP arrays and the arrangement of the two types of non-tubular mastigonemes (evaluated from tannic-acid-stained thin sections) reveals that the two groups of IMP rows correspond to the attachment points of the short non-tubular mastigonemes, whereas the cluster of three to seven larger IMPs corresponds to the attachment points of a group of the long non-tubular mastigonemes.
Flagellar membrane specializations also occur with respect to sterols, since filipin-sterol complexes are absent from all plasma membrane regions except the flagellar membrane. On the flagellar membrane filipin-sterol complexes occur predominantly in a membrane area free of IMP-arrays and are probably related in location to a prominent microtubule-membrane linkage. Details of the linkage between axonemal microtubules and the flagellar membrane have been evaluated, individual microtubule doublets have been numbered and the absolute configuration of the Euglena flagellum has been established.
In the reservoir region the flagellar membrane of the emergent flagellum is not covered by mastigonemes, but exhibits IMP arrays in the form of IMP rows and IMP clusters. In contrast to specializations on the free part of the emergent flagellum, in the reservoir region IMP rows are not regularly spaced, are distributed on opposite membrane halves (in the reservoir region on the E-face, in the free flagellum on the P-face) and often not associated closely with the clusters of larger IMPs. An hypothesis is presented explaining how mastigonemes might attach to the flagellar membrane and finally become oriented in their characteristic arrays. It is suggested that the observed IMP specializations in the flagellar membrane are (a) responsible for attachment of mastigonemes to the flagellar membrane, (b) responsible for linkage of mastigonemes to intraflagellar structures associated with axonemal microtubules, and (c) play an important role as a template for the development of the characteristic mastigoneme arrays.
Acquisition of β-glucuronidase activity by deficient fibroblasts during direct contact with lymphoid cells
Authors: Olsen I. , Dean M. F. , Muir H. , Harris G. 
Published: April 2021

ABSTRACT
Fibroblasts deficient in β-glucuronidase acquired high levels of this enzyme when they were co-cultured with concanavalin A-stimulated lymphocytes. Acquired enzyme activity, determined using a single-cell cytochemical assay, was directly proportional to the number of lymphocytes added and persisted for several days in fibroblasts maintained at high density.
Lymphocytes did not secrete significant levels of β-glucuronidase into their culture medium, and did not release other substances able to induce synthesis of the enzyme by the deficient fibroblasts. Nor did β-glucuronidase acquisition result from concanavalin A-mediated uptake of enzyme, since a-methylmannoside did not reduce acquired activity. Moreover, lymphocytes from various sources, whether unstimulated or activated by a different mitogen, bacterial lipopolysaccharide, were equally effective in promoting the appearance of β-glucuronidase.
Deficient fibroblasts did not acquire β-glucuronidase by active endocytosis when co-cultured with lymphocytes, since enzyme extracted from lymphocytes was not itself effective in this respect. Furthermore, mannose 6-phosphate, which did inhibit endocytosis by deficient fibroblasts of exogenous β-glucuronidase prepared from 3T3 cells, had no effect on enzyme acquisition by fibroblasts during their co-culture with lymphocytes. Conversely, inhibitors of protein synthesis and energy metabolism, which did not interfere with endocytosis of exogenous enzyme, abolished the acquisition of βglucuronidase during co-culture.
Deficient fibroblasts did not acquire β-glucuronidase when they were cultured together with lymphocytes but separated from them by Millipore membranes permeable to exogenous enzyme. Thus, although the mechanism of acquisition is still unclear, the present results suggest that β-glucuronidase is transferred from lymphocytes to deficient fibroblasts by a process in which direct cell-to-cell contact is obligatory.
Enzymic dissection of embryonic cell adhesive mechanisms: III. *Immunological identification of a component of the calcium-dependent adhesive system of embryonic chick neural retina cells
Authors: Grunwald Gerald B. , Pratt Rodney S. , Lilien Jack 
Published: April 2021

ABSTRACT
Immunological probes and cell-surface biochemical analysis are combined to identify a cellsurface glycoprotein, which appears to be involved in the formation of calcium-dependent adhesions among embryonic chick neural retina cells. Comparison of radioiodinated cells shows that adhesive-competent cells have at their surface two glycoproteins not present on nonadhesive cells. These two components (with M, 130 × 103, pl 4·8 and Mr 70 × 103, pl 4×8) are immunoprecipitable with adhesion-blocking antisera. A fraction derived from retina-conditioned medium, containing one major immunoprecipitable component, neutralizes the inhibitory activity of aggregation-inhibiting Fab’ fragments and competes in immunoprecipitation for the two glycoprotein components. The evidence suggests that one or both of these components is involved in the formation of calcium-dependent adhesions among embryonic chick neural retina cells.
Polyacrolein microspheres as a new tool in cell biology
Authors: Margel S. , Beitler U. , Ofarim M. 
Published: April 2021

ABSTRACT
Polyacrolein (PA) microspheres in sizes ranging from 0·04 μm to 40 μm were synthesized. Magnetic and fluorescent PA microspheres were formed by carrying out the polymerization process in the presence of appropriate ferrofluidic or fluorochromic compounds, respectively. The microspheres carry reactive aldehyde groups, through which various ligands, containing primary amino groups, were covalently bound at physiological pH values.
The potential use of these microspheres was demonstrated by the specific labelling of fresh human red blood cells (RBC) and by the separation of human RBC from turkey RBC by means of a magnetic field. PA microspheres were also bound covalently to the anti-allergic drug disodium chromoglycate (DSCG) and the conjugate was used for the labelling of rat basophilic leukaemia cells.
High-resolution scanning electron microscopy of human metaphase chromosomes
Authors: Harrison Christine J. , Allen Terence D. , Britch Martin , Harris Rodney 
Published: April 2021

ABSTRACT
Human metaphase chromosomes, prepared for light microscopy, were examined by scanning electron microscopy. Use of an osmium impregnation technique eliminated the need for sputter-coating and allowed high-resolution visualization of uncoated specimens. Chromosomes were of three-dimensional cylindrical profile, with well-defined chromatids and centromeres. Prior to Giemsa-banding a smooth surface morphology was observed. Relaxation of chromosome integrity by Giemsa-banding pretreatment allowed resolution of several orders of chromosome structure not previously demonstrated by scanning electron microscopy. The observed organization of the chromatin fibres allowed parallels to be drawn with the radial loop model of chromosome construction as described by Marsden and Laemmli.
Structure and behaviour of the sperm terminal filament
Authors: Omoto C. K. , Brokaw C. J. 
Published: April 2021

ABSTRACT
Light- and electron-microscopic observations of Ciona and Lytechinus spermatozoa show a thin terminal filament at the distal end. The terminal filament is 5·6 μm long and contains the two central microtubules and a variable number of A-tubule extensions of the peripheral doublet microtubules. The transition from the 9 + 2 region to the terminal filament is tapered more gradually in Lytechinus than in Ciona. Photographs of the movement of beating spermatozoa do not show any obvious discontinuity in curvature at the transition region. Bends are propagated smoothly off the end of the flagellum with no decrease in curvature. However, spermatozoa in which the terminal filament has been removed show a clear * end effect ‘. This end effect involves a rapid unbending of bends that have reached the distal end of the flagellum. Computer simulations of flagellar models lacking a terminal filament show a similar end effect. Addition of a terminal filament to the end of the computer model can eliminate the end effect. Realistic bending behaviour of the model is obtained by using a terminal filament with a tapered elastic bending resistance in the basal portion of the terminal filament and a value of 0·03 × 109 pN nm* in the remainder of the terminal filament. This leads to estimates of 0·01 × 109 pN nm2 for the elastic bending resistance of an individual microtubule, and 0·2 × 109 pN nm2 for the elastic bending resistance of the 9 + 2 region of the flagellum. An improvement in propulsive effectiveness by addition of a terminal filament remains to be demonstrated.
Coated and smooth vesicles in the biogenesis of cell walls, plasma membranes, infection threads and peribacteroid membranes in root hairs and nodules of white clover
Authors: Robertson John G. , Lyttleton Pamela 
Published: April 2021

ABSTRACT
Involvement of coated and smooth vesicles in the infection by rhizobia of root hairs and nodule cells of white clover was examined using electron microscopy of thin sections. Coated vesicles, about 100 nm in diameter including coat, were observed free in the plant cell cytoplasm and associated with root hair plasma membranes, infection thread membranes and peribac-teroid membranes. The number of coated vesicles seen associated with segments of the plasma membrane at the tip of the root hair was about 20-fold greater than the number associated with the plasma membrane towards the base of the root hair. Similarly, the number seen associated with segments of the infection thread membrane near the tip of the thread was about 20-fold greater than the number associated with the membrane towards the base of the thread. The number seen associated with segments of the peribacteroid membranes in recently infected nodule cells was comparable to the number associated with the plasma membrane towards the base of the root hair or with the infection thread membrane towards the base of the thread.
Coated vesicles were observed in the vicinity of and associated with both proximal and distal faces of the Golgi bodies; they often possessed, while still attached to the Golgi cistemae, shorter coats than those observed on coated vesicles free in the cytoplasm. Coated vesicles contained electron-dense material that did not stain positively with Thiéry stain for polysaccharides, and which appeared to have been released into the region of the cell wall or peribacteroid space as a result of fusion of the vesicles with plasma membranes or peribacteroid membranes.
Smooth vesicles were also observed in the vicinity of and associated with Golgi bodies, and in association with root hair plasma membranes, infection thread membranes and peribacteroid membranes. The smooth vesicles commonly contained material of varying electron density, which sometimes occurred in the form of droplets. Similar droplets seen in the region of the cell wall and in the peribacteroid space appeared to have resulted from the fusion of smooth vesicles with these membranes.
It is proposed that both smooth and coated vesicles derived from Golgi bodies are involved in the biogenesis of cell walls, plasma membranes, infection threads and peribacteroid membranes in root hairs and nodules of white clover.
Spindle microtubules in the dividing nuclei of trypanosomes
Authors: Vickerman K. , Preston T. M. 
Published: April 2021

ABSTRACT
Stages in nuclear division have been identified in sections of bloodstream and cultured trypanosomes examined with the electron microscope
In the sleeping sickness trypanosome Trypanosoma rhodesiense at division the nuclear envelope and nucleolus-like endosome persist and become stretched along an axis. An acentric spindle of microtubules encases the elongating endosome As division proceeds the endosomal material fragments In bloodstream forms condensed chromatin (chromosomal material) appears to be associated with the nuclear envelope during the phase of nuclear elongation but to fall away from the envelope late in the phase of nuclear constriction. In culture forms the chromatin is not so abundant The discrete chromosomes envisaged by some light microscopists in stained preparations have not been identified using the electron microscope. The spindle may contain only continuous microtubules. It is suggested that the spindle serves to push the two halves of the nucleus apart, and that the nuclear envelope of each half may act as a vehicle in separation of the daughter genomes.
In culture forms of the elasmobranch parasite T. raiae, the endosome appears to disintegrate as the spindle is formed, and from then onwards it becomes difficult to distinguish endosomal material from what might be chromatin. There is no noticeable association between chromatin-like material and the nuclear envelope. Some of the spindle tubules converge on kinetochore-like plaques and the presence of chromosomal microtubules cannot be ruled out.
These preliminary studies indicate that the nuclear division process of trypanosomes is not closely akin to eukaryote mitosis, though it may bear some resemblance to nuclear division in Euglena. Within the genus Trypanosoma, moreover, the nuclear division process may vary from species to species and, possibly, even from one strain to another within a species.
Effect of microtubules and intermediate filaments on mitochondrial distribution
Authors: Summerhayes Ian C. , Wong David , Chen Lan Bo 
Published: April 2021

ABSTRACT
The laser dye rhodamine 123 specifically stains mitochondria in living cells and facilitates the observation of changes in mitochondrial distribution in single cells under a variety of experimental conditions. Visualization of mitochondria in a number of cell lines followed by processing of these cells to study different cytoskeletal elements by indirect immunofluorescence, revealed good but not absolute correlation between mitochondria and microtubules or intermediate filaments. Mitochondria and microfilament distribution within the same cell did not show such a correlation. On the basis of observations made by various experimental approaches, we suggest that mitochondrial distribution is under the strong influence of the two systems, microtubules and intermediate filaments. Neither plays an absolute role but one seems able to play a more dominant role in the absence of the other.
C value and cell volume: Their significance in the evolution and development of amphibians
Authors: Horner Heather A. , Macgregor Herbert C. 
Published: April 2021

ABSTRACT
Cell volume has been determined in 18 species of amphibian, ranging in C value from 1·4 pg to 62 pg DN A. There is a strong linear relationship between C value and both erythrocyte volume and erythrocyte nuclear volume. We have collected data on the timing of early embryogenesis from fertilization of the egg to the hatching tadpole in some amphibians ranging in C value from 1·4 pg to 83 pg. The species with large genomes take up to 24 times longer to reach a comparable state of development. Polyploid species develop faster than closely related diploid species. These data are discussed in relation to genome expansion and increase in cell cycle time as factors in the evolution of the Amphibia.
Mechanism of enhanced fusion capacity of mouse red cells infected with Plasmodium berghei
Authors: Nakornchai Sunan , Sathitudsahakorn Chiraporn , Chongchirasiri Suntanee , Yuthavong Yongyuth 
Published: April 2021

ABSTRACT
Plasmodium berghei-infected mouse red cells have enhanced fusion capacity as triggered by addition of poly(ethylene glycol) in the presence of Ca2+. The uptake of Ca2+ in P. berghei-infected cells is greater than in normal cells, and the difference in Ca2+ uptake was found to be enhanced in the presence of poly (ethylene glycol). Fusion of normal and P. berghei-infected red cells by poly (ethylene glycol) was significantly inhibited by N-tosyl-L-lysylchloromethyl ketone and phenyl-methylsulphonyl fluoride. In addition, ethyleneglycolbis(aminoethylether) tetra-acetate, N -ethyl-maleimide, iodoacetamide, cystamine and tetrathionate also prevented fusion in both systems. In contrast, N -tosyl-L-phenylalanylchloromethyl ketone and N-tosyl-L-arginine methyl ester did not inhibit cell fusion. The latter enhanced fusion of infected cells but was without effect on normal cells. These results indicate that a Ca2+-activated thiol proteinase may be involved in membrane fusion in malaria-infected as well as in normal red cells. However, differences in the effect of proteinase inhibitors and substrate on fusion and Ca2+ entry show that the processes leading to fusion may not be identical.
Independent expression of type i collagen and fibronectin by normal fibroblast-like cells
Authors: Connor Nigel S. , Aubin Jane E. , Sodek Jaro 
Published: April 2021

ABSTRACT
A double-label immunofluorescence technique was used to determine whether all normal fibroblast-like cells cultured from porcine connective tissues simultaneously express both type I collagen and fibronectin (FN). Cells surrounding Explants in primary cultures from gingival and periodontal ligament (PL) tissue were heterogeneous in the expression of collagen and FN. Mass population cells at first and second subculture after primary explanting of gingival tissue were also heterogeneous in the expression of collagen and FN. When clonal populations were analysed, four distinct phenotypes were observed : Coll+/FN+; C0II+/FN–; Coll–/FN+; Coll–/FN–. Mass populations of PL cells were more homogeneous than gingival fibroblasts and when clones were analysed only two phenotypes were observed. These data suggest that normal fibroblast-like cells in vitro are capable of expressing collagen and FN independently and that FN-negative cells may utilize a FN-independent attachment mechanism in culture.