bluuebunny/crossref_metadata_2025_split huggingface dataset:
Membrane-cytoskeleton interactions in the flagellum: A 240000 mr surface-exposed glycoprotein is tightly associated with the axoneme in chlamydomonas moewusii
Authors: Reinhart Frederick D. , Bloodgood Robert A. 
Published: April 2021

ABSTRACT
The flagellar surface of Chlamydomonas moewusii is a dynamic structure involved in several adhesive and motile events. In this report, we describe for the first time the flagellar membrane components of vegetative C. moewusii. A glycoprotein (or pair of glycoproteins) with an apparent molecular weight of 240 ×103 is the dominant flagellar protein (other than the tubulins) in this species of Chlamydomonas. Both a rabbit polyclonal antibody (designated P-19) and the lectin concanavalin A recognize this 240K (K= 103Mr) glycoprotein on nitrocellulose transblots of flagellar proteins. Fluorescence microscopic studies using these same two probes suggest that the 240K glycoprotein is exposed at the flagellar surface. Direct evidence that the 240K glycoprotein is exposed at the flagellar surface is provided by vectorial labelling with a N-hydroxysuccinamide-derivitized biotin reagent (NHS-LC-biotin). Nonionic detergent extraction of isolated flagella fails to solubilize most of the 240K glycoprotein, although it completely removes the flagellar membranes as demonstrated by transmission electron microscopy. Furthermore, immunofluorescence microscopy of isolated axonemes demonstrates that both P-19-defined epitopes and surface-biotinylated proteins continue to be associated with the axoneme structure after detergent treatment. These observations demonstrate that the 240K flagellar protein is a glycoprotein that is both exposed at the flagellar surface and tightly coupled to the underlying cytoskeleton (axoneme). Because of its cell surface orientation and axonemal linkage, it is likely that the 240K glycoprotein plays an important role in the adhesive and/or motile phenomena exhibited by the C. moewusii flagellar surface.
Cell biology of the stigma ofBrassica campestrisin relation to Co2 effects on self-pollination
Authors: O’neill Patricia , Singh Mohan B. , Knox R. B. 
Published: April 2021

ABSTRACTThe effect of carbon dioxide in blocking the sporophytic self-incompatibility system in Brassica campestris occurs within the first 2h of pollination at the pollen-stigma interface. Percentage germination of self pollen on the stigma was found to be similar in air and in the presence of 5% CO2. The CO2 effect therefore must occur after pollen germination, modifying the interaction between pollen tubes and stigma cells. Lectin binding studies showed the presence of fucosyl but not galactosyl residues on the stigma surface. Gel electrophoresis of plant extracts showed that stigma esterase activity is marked in comparison to other plant tissue. This activity is shown histo-chemically to be localized on the stigma cell surface and in the nucleus. Carbonic anhydrase has been detected on the stigma surface by two different histochemical methods and its possible relationship to the CO2 effect is discussed.
T-cell-mediated cytolysis: Analysis of killer and target cell deformability and deformation during conjugate formation
Authors: Foa Colette , Mège Jean-Louis , Capo Christian , Benoliel Anne-Marie , Galindo Jean-Rémy , Bongrand Pierre 
Published: April 2021

ABSTRACT
T-cell-mediated cytolysis is initiated by the formation of strong adhesions between killer and target cells. The present work was aimed at determining whether T lymphocytes might exert some mechanical stress on targets during the binding process.
Target S194 myeloma cells were thus conjugated to cytotoxic T lymphocytes (CTLs) raised by mixed lymphocyte culture or a cloned lymphoid line that was no longer cytolytic (TG2OUA2). After incubation periods of various lengths, conjugates were processed for electron microscopy and micrographs were digitized for computerized analysis: the cell surface curvature (at the micrometre level) and rugosity (at the submicrometre level) were quantified in free and adhesion-involved regions. Also, the size of cell interaction areas and the distribution of intermembrane distances were measured. Finally, TG2OUA2 and target cells were aspirated into glass micropipettes with calibrated pressure in order to assay their resistance to deformation by mechanical forces. The following conclusions were suggested.
(1) Formation of extensive contact zones (with a linear size of several micrometres) with tight intermembrane adhesion (more than 30% of the membrane contours in adhesive zones were separated by an apparent distance lower than 500 Å) was essentially completed within less than one minute.
(2) CTLs or TG2OUA2 cells were more villous than their targets, and they seemed to deform in adhesive zones in order to adapt to the target contour, rather than imposing some deformation on the target. This may be a general feature of actively adherent cells.
(3) Some CTLs, but no TG2OUA2 cells, exhibited conspicuous protrusions extending towards the bound target. In this case, the target cell but not the CTL displayed markedly increased roughness in the adhesion area.
(4) TG2OUA2 cells were more resistant to mechanical deformation than S194 target cells, in accordance with previous reports suggesting that the membrane of CTLs was more resistant than that of target tumour cells.
Hence, CTLs might transiently impose mechanical stress on the target membrane during the course of lethal-hit delivery.
A biochemical investigation into the inhibitory effects of glucosamine and N-acetylglucosamine on the aggregation in vitro of embryonic chick muscle cells
Authors: Lloyd C. W. , Kemp R. B. 
Published: April 2021

ABSTRACT
The effect of glucosamine and N-acetylglucosamine on aggregation and energy metabolism was investigated over an 8-h period in cells dissociated by 0·25 % (w/v) trypsin from the skeletal muscle of 9-day-old chick embryos. At 8 h, 0·023 M glucosamine and N-acetylglucosamine inhibited the aggregation of cells suspended in Eagle’s minimal essential medium by 18·9 % and 16·4% respectively, as judged on a basis of aggregate size.
Glucosamine and N-acetylglucosamine reduced the cellular ATP level by a mean of 36 % and 27 % respectively; values reflected in the 32% and 19% loss of total adenine nucleotides caused by these sugars. The adenine nucleotide balance was also changed from a mean control ATP/AMP ratio of I3·7 to 8·75 by N-acetylglucosamine and to 8·0 by glucosamine.
Intracellular lactate/pyruvate ratios were similarly disrupted in cells incubated with 0·023 M hexosamine. Although the hourly values fluctuated, it was seen that the amount of lactic acid relative to pyruvic acid, considered as an average for the 8-h period, was raised from 6:1 in controls to 8:1 in N-acetylglucosamine-treated and to 10:1 in glucosamine-treated cell preparations. Compared to controls at 8 h, glucosamine enhanced the production of lactate into the suspension medium by 99%. The N-acetyl analogue caused cells to produce more lactic acid than did controls for 4–5 h only, for by 8 h 25 % less of this metabolite was assayed in the culture medium.
The incorporation of D-[U-14C]glucose into glycogen paralleled the results of extracellular lactic acid assays. N-acetylglucosamine inhibited the incorporation by 30 % at 4 h, although by 6 h, and for the remainder of the experimental period, there was more 14C-labelled glycogen in these cells than in controls. By contrast, glucosamine inhibited the incorporation of radioactive glucose into glycogen by 42% at 4 h and, unlike N-acetylglucosamine, consistently thereafter.
Glucosamine also enhanced cellular oxygen uptake throughout the experimental period, to the extent of 59 % at 8 h. The oxygen uptake of N-acetylglucosamine-treated cells was similar to controls until about the 5th hour, when there was a subsequent inhibition which had accumulated to 13 % by the end of the experiment. The release of 14COs by cells was inhibited by glucosamine. This hexosamine depressed production by 19% at 12 h whereas N-acetylglucosamine inhibited this evolution by 9 % at this time.
The metabolic effects of these hexosamines on chick muscle cells in vitro are mainly attributed to a central alteration of the adenine nucleotide balance although certain other documented effects of glucosamine are considered to be involved. An inhibition of cell aggregation by glucosamine and N-acetylglucosamine is discussed in terms of a depressed cellular metabolic economy.
Developmental changes occurring in isolated intact etioplasts
Authors: Wellburn Florence A. M. , Wellburn A. R. 
Published: April 2021

ABSTRACT
When dark-grown plants are illuminated, the characteristic morphology of the etioplast changes. The tubules of the paracrystalline prolamellar body disperse as the membranes reorganize and ‘grow out’ as ‘perforated’ thylakoids. Similar changes are expected during the greening of the isolated etioplasts of Avena. Under certain preparative conditions the morphological changes vary from those previously reported for intact tissue.
Following low illumination at a low temperature the process of outgrowth is slowed down, resulting in the outgrowth of regularly spaced tubules from the prolamellar body into the stroma. These tubules appear to develop slowly into normal thylakoids by a process of tubule fusion to form perforated thylakoids. A diagram is included to show how this is believed to take place. The outgrowing tubules have an outer diameter of 25–28 nm with a lumen of 7·0–7·6 nm diameter.
Two types of protein body are observed, the ‘stromacentre ’ which is a regular feature of A vena plastids and a ‘crystallite’ which is only observed under certain conditions. The ‘stromacentre’ is a fibrillar spherulite with fibrils (diameter 9 nm) in bundles up to 200 nm long which in turn are aggregated to form the characteristic spherulite of the stromacentre. The crystallite is composed of fibrils 7·5–8·5 nm in diameter lying parallel to each other with a regular spacing of 12·5 nm. The crystallite appears to develop when the etioplast is damaged and has started to vesiculate.
Particles which are larger than either plastid or cytoplasmic ribosomes have also been observed. These vary in diameter from 18 to 24·5 nm and are arranged in rows adjacent to the thylakoids.
Particles within membranes: a freeze-etch view
Authors: Flower N. E. 
Published: April 2021

ABSTRACT
Particles are commonly present on the membrane faces revealed by freeze-etching. The number, distribution and size of these particles vary considerably both between different membranes and, in many cases, between the 2 fracture faces found in individual membranes. Many of the larger particles appear to be too large to fit totally within smooth-surfaced membranes, so raising the question of how particles, especially the larger ones, are contained within membranes. This could be accomplished by a local reorganization of the membrane’s internal structure such that small particles would be totally enclosed within smooth-surfaced membranes, while large particles would protrude from the membrane surface. Alternatively, all sizes of particles could be contained within membranes by a bulging of the 2 component lamellae such that protuberances, having a larger diameter than the underlying particles, would arise on the membrane surface.
Evidence is presented to show that in the case of specialized particles, which are located in rows around the base of flagella in the mollusc Cominella maculosa, protuberances are present on the membrane surface. However, it is possible that particles could be accommodated within membranes from other tissues by a different mechanism, and only further work will decide whether or not the present findings can be applied to these other membrane surfaces.
Mitosis in the fission yeast Schizosaccharomyces pombe: a comparative study with light and electron microscopy
Authors: McCully E. Kathleen , Robinow C. F. 
Published: April 2021

ABSTRACT
Mitosis in Schisosaccharomyces pombe has been followed in living cells by phase-contrast microscopy and studied in fixed and suitably stained preparations by light microscopy. Successful preservation of nuclear fine structure in this yeast, not previously achieved, has allowed us to confirm and extend the observations made with light microscopy.
Without first arranging themselves on a metaphase plate, mitotic chromosomes become grouped in 2 clusters radiating, finger-like, from 2 points of attachment at opposite poles of an elongating nucleus. At these 2 sites electron microscopy reveals the presence of disk-shaped electron-dense organelles which we have called kinetochore equivalents (KCE). At mitosis the KCEs are connected across the nucleus by a narrow bundle of parallel microtubules which we refer to as the spindle.
Integration of our observations has led us to propose that at mitosis the separation of the KCEs and their attached chromosomes is initiated by a differential expansion of the nuclear envelope restricted to the region between recently divided KCEs and that expansion of the nuclear envelope later becomes general, resulting in a marked elongation of the nucleus. Displacement of the nuclear contents to the ends of the elongated nucleus gives it the shape of a dumbbell.
The elongation of the microtubule bundle keeps in step with the elongation of the nucleus but does not appear to be the cause of it. It may have the function of keeping the separated KCEs rigidly apart.
During mitosis the nucleolus persists and stretches out within the unbroken envelope of the nucleus as it elongates. Towards the end of division equal amounts of nucleolar material are found in the rounded ends of the dumbbell-shaped nucleus.
The break up of the dumbbell shape into daughter nuclei seems to involve the breaking of its tenuous middle part and a pivoting of its 2 ends in opposite directions.
In the course of our work on mitosis we have become aware of features in the cytoplasm of growing S. pombe cells which are described here for the first time. The cells invariably contain several prominent vacuoles containing an extremely electron-dense material which stains metachromatically with toluidine blue and may be polyphosphate. The mitochondria are of special interest for 2 reasons. First, because they have unique mesosome-like membrane invaginations and secondly, because a mitochondrion is regularly associated with the single KCE by the side of the interphase nucleus, as well as with each one of the 2 KCEs that occupy opposite ends of the intranuclear spindle during mitosis.
Longitudinal growth of striated muscle fibres
Authors: Williams Pamela E. , Goldspink G. 
Published: April 2021

ABSTRACT
The direct determination, by counting, of the number of sarcomeres in series along the length of single teased muscle fibres taken from mice of different ages showed that the increase in fibre length during normal growth is accompanied by a large increase in sarcomere number The greatest increase occurs during the 3 weeks after birth. By counting the number of muscle fibre nuclei in single teased fibres it was shown that the number of nuclei per fibre increases with age, and that this increase continues beyond the point at which the fibres have ceased to grow in length. It is suggested that post-natal increase in nuclear number is associated with both increase in length and increase in girth of the muscle fibres.
By injecting tritiated adenosine into young mice, an attempt was made to label newly formed actin filaments and ribosomes and thus to determine the region where new sarcomeres are laid down during increase in fibre length. Using autoradiography and scintillation counting it was shown that the radioactive label was incorporated more into the ends than into the middle regions of the muscles. The implication of these findings is that new sarcomeres are added on serially at the ends of the muscle fibres. An investigation, at the ultrastructural level, of muscle fibres taken from foetal and newborn mice indicates that the end of the fibre is a region of active development. This area is characterized by numerous ribosome formations and by myofilaments which are not organized into myofibrils. Cells which can occasionally be seen fusing with the end regions of young muscle fibres indicate a possible way in which nuclei are added to the growing fibre.
Immobilization experiments have shown that it is possible to alter both the rate and the extent of the post-natal increase in sarcomere number. Immobilization of limb joints, by means of plaster casts, so that the muscle is held in either the extended or the shortened position results in the number of sarcomeres along the fibres falling far short of that in the fibres from control muscles. Removal of the restriction is followed by a rapid increase in the number of sarcomeres in series and a return to the normal level within a period of about 4 weeks. These experiments indicate that for normal growth to occur, it is important for a muscle to be able to contract isotonically.
The nucleoskeleton: Artefact, passive framework or active site?
Authors: Cook P. R. 
Published: April 2021

ABSTRACT
“As seen in the living cell the nucleus most commonly appears as a clear, rounded, sac-like body bounded by a delicate membrane and often showing no visible structure save for the presence within it of one or more smaller rounded bodies, the nucleoli. After coagulation by fixing agents, the nucleus offers a much more complicated appearance containing… a net-like framework….”
“Very often no trace of the framework is seen before coagulation sets in; and this has led to a skeptical attitude concerning it on the part of some observers.”
The nuclear matrix: Structure and composition
Authors: Verheijen Ron , Venrooij Walther Van , Ramaekers Frans 
Published: April 2021

ABSTRACT
The term nuclear matrix was first introduced by Berezney & Coffey (1974) to denote a highly structured residual framework obtained from rat liver nuclei by sequential salt extractions, detergent and nuclease treatments. The isolated three-dimensional structure consisted almost entirely of protein. Subsequent studies showed that when protease inhibitors were included in all isolation steps and ribonuclease (RNase) was omitted, the isolated nuclear matrix contained RNA as the second most abundant component (Herman et a/. 1978; Miller et. al. 1978b ; Shaper et al. 1979; Berezney, 1980; van Eekelen & van Venrooij, 1981; Mariman et al. 1982a; Fey et al. 1986a,b). In this review the term nuclear matrix is defined as the biochemical entity that can be isolated after sequential extraction of cells with non-ionic detergents, nucleases and high-salt buffers (Shaper et al. 1979). With respect to the nucleases, it should be stated here that several authors use only deoxyribonucleases (DNases), while others use DNases in combination with RNases. Nuclear matrices have been isolated from a wide variety of mammalian and non-mammalian cell types (reviewed by Shaper et al. 1979; Barrack & Coffey, 1982).
The initial stages in the action of an insecticidal d-endotoxin of Bacillus thuringiensis var. Israelensis on the epithelial cells of the malpighian tubules of the insect, Rhodnius prolixus
Authors: Maddrell S. H. P. , Lane N. J. , Harrison J. B. , Overton J. A. , Moreton R. B. 
Published: April 2021

ABSTRACT
The effects of the 27×103Mr insecticidal δ-endotoxin from Bacillus thuringiensis var. israelensis have been studied using, as a model system, isolated insect Malpighian tubules. At all concentrations of the toxin higher than 1 μg ml−1 (4×10−8 moll−1) applied to the outer surface of the tubules, fluid secretion failed within about 30 min. Except at very high concentrations, where failure always takes at least 30 s, there was an inverse relationship between the concentration of toxin and the time of failure of toxin-treated tubules. During exposure to toxin, the tubules were initially unaffected for a relatively long period and then rapid failure occurred. If the tubules were removed into toxin-free saline just before failure would have occurred, fluid secretion remained normal for at least 2h, but on return to the original toxin-containing saline failure was almost immediate. The toxin was found not to bind to the basement membrane.
Ultrastructural changes became evident as tubule failure occurred. These initially involvedmodifications to the basal side of the cells, but later also to the luminal microvilli. Intercellular junctions became disassociated and cytoplasmic vacuolization occurred. The population of intra-membranous particles in the basal membranes became reduced with time.
Our findings suggest the following hypothesis for the initial stages in the interaction of the toxin with the tubules. Toxin molecules attach to the accessible cell membranes progressively and irreversibly. They do not readily associate by diffusing laterally in the membrane, so that toxic effects develop only when sufficiently large numbers of them attach close together. The molecules may then associate in some way as a complex, perhaps forming a pore in the membrane. Relatively few such pores lead rapidly to cell failure and death.
Release of lysosomal enzymes in Tetrahymena: A Ca2+-Dependent secretory process
Authors: Tiedtke A. , Rasmussen L. , Florin-Christensen J. , Florin-Christensen M. 
Published: April 2021

ABSTRACT
The ciliate Tetrahymena thermophila releases lysosomal enzymes into nutrient and starvation media. We show here that this process occurs selectively, i.e. without leakage of cytoplasmic components, as indicated by lack of release of isocitrate dehydrogenase, a cytosolic enzyme with high activity in Tetrahymena. The role of intracellular Ca2+ in the process was also investigated. The Ca2+ ionophore A23187 has strong stimulatory effects on this release. Ionophore stimulation is maximal in the presence of extracellular Caz+ but can occur also in its absence. Quin 2 fluorescence measurements indicate that intracellular Ca2+ increases in both cases. Mg2+ completely prevents the stimulatory effects of A23187. lonomycin, another Ca2+ ionophore, also stimulates lysosomal enzyme release with a maximal response in the presence of extracellular Ca2+. Measurements of extracellular isocitrate dehydrogenase showed that ionophore-stimulated lysosomal enzyme release can take place without leakage of cytoplasmic components. The observations that divalent cation ionophores stimulate selective lysosomal enzyme release and that this effect is strongest in the presence of external Caz+ indicate that this cation plays a crucial role in the control of this process in Tetrahymena. Together with other observations they support the view that a subpopulation of Tetrahymena lysosomes has properties like those of secretory vesicles.