bluuebunny/crossref_metadata_2025_split huggingface dataset:
Supramolecular structure of the thylakoid membrane of Prochlorothrix hollandica: A chlorophyll b-containing prokaryote
Authors: Miller Kenneth R. , Jacob Jules S. , Burger-Wiersma Tineke , Matthij Hans C. P. 
Published: April 2021

ABSTRACT
Prochlorothrix hollandica is a newly described photosynthetic prokaryote, which contains chlorophylls a and b. In this paper we report the results of freeze fracture and freeze etch studies of the organization of the photosynthetic thylakoid membranes of Prochlorothrix. These membranes exhibit four distinct fracture faces in freeze fractured preparations, two of which are derived from membrane splitting in stacked regions of the thylakoid membrane, and two of which are derived from nonstacked regions. The existence of these four faces confirms that the thylakoid membranes of Prochlorothrix, like those of green plants, display true membrane stacking and have different internal composition in stacked and non-stacked regions, a phenomenon that has been given the name lateral heterogeneity. The general details of these fracture faces are similar to those of green plants, although the intramembrane particles of Prochlorothrix are generally smaller than those of green plants by as much as 30%.
Freeze etched membrane surfaces have also been studied, and the results of these studies confirm freeze fracture observations. The outer surface of the thylakoid membrane displays both small (less than 8·0 nm) and large (greater than 10·0 nm) particles. The inner surface of the thylakoid membrane is covered with tetrameric particles, which are concentrated into stacked membrane regions, a situation that is similar to the inner surfaces of the thylakoid membranes of green plants. These tetramers have never before been reported in a prokaryote. The photosynthetic membranes of Prochlorothrix therefore represent a prokaryotic system that is remarkably similar, in structural terms, to the photosynthetic membranes found in chloroplasts of green plants.
Polarity and differentiation of human rectal adenocarcinoma cells in suspension and collagen gel cultures
Authors: Kirkland Susan C. 
Published: April 2021

ABSTRACT
HRA-19a1.1. cells, derived from a primary human rectal adenocarcinoma, form polarized monolayers when grown on tissue-culture plastic. The apical membrane of the cells is in contact with the culture medium while the basolateral surface is attached to the plastic substratum. Cells cultured on non-tissueculture plastic form floating colonies. Cells within these colonies are orientated so that their apical membrane is in contact with the culture medium while the basolateral membrane faces the centre of the colony. When these colonies are embedded in collagen gel the cells organize to form glandular structures similar to those observed in xenografts of this cell line. In addition a reversal in the orientation of cell polarity is observed with the basolateral membrane now in contact with the collagen gel, while the apical membrane faces lumina within the colony. This interaction is specific to collagen gel, as in a control experiment where colonies are embedded in agarose gel, neither a reversal in polarity nor the formation of glandular structures is observed. These results demonstrate an induction of glandular organization in human rectal adenocarcinoma cells by collagen gel. In addition an increased absorptive cell differentiation and reversal in cell polarity is observed in response to collagen gel.
Modified hydroxyethylmethacrylate hydrogels as a modelling tool for the study of cell-substratum interactions
Authors: Bergethon Peter R. , Trinkaus-Randall Vickery , Franzblau Carl 
Published: April 2021

ABSTRACT
The interactions between cells and their extracellular substratum environment are complex and difficult to study. Defined, synthetic substrata are valuable tools for experimentally determining the role of ionic and receptor-specific interactions between cells and their substrata. Hydrogels have been modified to contain stoichiometrically defined quantities of both positive and negative charge as well as specific proteins. These synthetic surfaces are water-rich matrices that possess hydroxyl groups, positive and negative ionized charges and native proteins, and can be considered as models of extracellular matrices on which an assessment of charge contribution and macromolecular content and specificity can be addressed with respect to cell-matrix interactions. This study shows that simple gels made of polyhydroxyethylmethacrylate do not support the spreading of cells but that the generation of copolymers by the addition of monomers that contain ionizable functional groups, will permit cell spreading. These simple modifications do not lead to cellular proliferation, yet when collagen is entrapped in the hydrogel substratum, proliferation occurs. The proliferative rate of cells grown on collagen-containing surfaces may be modified by altering the stoichiometry of the ionizable polymers used to make the surface. This study describes a synthetic, definable model for the study of cell-substratum interactions and control.
‘Corkscrewing’, as evidence for force generation within a detergent-extracted microtubule translocation system from insect ovaries
Authors: Stebbings H. , Sharma K. K. 
Published: April 2021

ABSTRACT
Microtubule-based translocation channels within the ovaries of the hemipteran insect Notonecta have been isolated by microdissection, and then detergent-extracted to leave a bundle of some 30000 aligned microtubules. On addition of ATP and other hydrolysable nucleotides the microtubule bundle contorts into a helical configuration, a property we have called ‘corkscrewing’, before straightening again. This we believe to be indicative of force generation within the bundle.
Electrophoretic analysis of the bundle of native microtubules reveals many polypeptides apart from the tubulins, and a number of these comigrate with microtubule-associated proteins (MAPs), which copolymerize with tubulins in reassembled microtubules from the same system.
Corkscrewing does not occur if the microtubule bundle is pretreated with salt, a procedure that removes MAPs from microtubules, suggesting that the force is generated by a MAP or MAPs. In addition, certain minor polypeptides comprising the native microtubules are ATP-sensitive, a property expected of a microtubule motor.
Interaction of Drosophila 27000Mr heat-shock protein with the nucleus of heat-shocked and ecdysone-stimulated culture cells
Authors: Beaulieu J.-F. , Arrigo A. P. , Tanguay R. M. 
Published: April 2021

ABSTRACT
The intracellular localization and expression of hsp27 (heat-shock protein 27) were investigated by cellular fractionation and immunofluorescence microscopy in Drosophila S3 cells. In unstressed cells, hsp27 is expressed in only 2 % of the cells, whereas following heat shock, during recovery or after induction by ecdysone, the protein is detected in all cells. Under all these conditions, hsp27 appears to be concentrated in the nuclear region as revealed by immunofluorescence. During heat shock, this hsp is localized primarily in the nucleus with an enrichment in the perinucleolar region. However, the cellular fractionation data indicate that the nature of hsp27 interaction with nuclear components greatly differs depending on whether or not cells were subjected to elevated temperatures. After heat shock, hsp27 is resistant to non-ionic detergent extraction. In cells allowed to recover at normal temperature and in those where its synthesis was induced by the molting hormone, ecdysone, this hsp is readily solubilized by detergent. These data suggest that, following heat shock, hsp27 may become physically associated with some nuclear component(s) that are resistant to detergent extraction.
Methotrexate-induced morphological changes mimic those seen after heat shock
Authors: Jackson Dean A. , Pearson Colin K. , Fraser Douglas C. , Prise Kevin M. , Wong Su Y. 
Published: April 2021

ABSTRACT
The survival of cells cultured in medium containing the chemotherapeutic drug methotrexate (MTX) is related directly to drug concentration. Changes in DNA resulting from a severe imbalance in the cells’ nucleotide pools are thought to account for this cytotoxicity. We have attempted to clarify the gross biochemical changes that might lead to cell death. DNA strand breaks occur in cells treated with high concentrations of MTX but it is not clear that these are sufficient to account for cytotoxicity at lower doses. We observed dramatic changes in cytoskeletal morphology. Gross reorganization of the cytoskeleton is shown by immunolabelling but is highlighted dramatically when cells are lysed to leave ‘nucleoids’. The nature of the changes seen in MTX-treated cells is characteristic of the cells’ general stress response, seen originally following heat shock. This study shows that other factors, such as changes in cytoskeletal function, must be considered together with any contribution from DNA damage, in order to account for the lethal effects of MTX.
Cryotechniques in Biological Electron Microscopy
Authors: Gupta Brij L. 
Published: April 2021

ABSTRACT
Our current knowledge of cell and tissue fine structure is mostly based on methods that, put bluntly, involve ‘poisoning, tanning and drying of living cells’ (Preface, p. xvii). The possibility that gross artefacts may well be generated by the conventional methods of chemical fixation, dehydration, embedding and staining etc. used for light and electron microscopy is implicit in the endless controversies that form a recurrent strand in the history of histology and cytology. The observation that low temperatures preserve living matter in a life-like condition for decades or even centuries must first have been made in the Ice Ages. The earliest attempts to avoid chemical fixation by freeze-drying date back to Altmann (1890, Die Elementarurgamsmen und ihre Beziehungen zu Zellen, Leipzig) and Mann (1902, Physiological Histology, Oxford). However, cells and tissues are up to 90 % water. The frustration of trying to freeze water without the formation of destructive ice crystals is delightfully summarized in this rhyme on the frontispiece from Wilhelm Busch (1832—1908):
The distribution of distinct integrins in focal contacts is determined by the substratum composition
Authors: Fath Karl R. , Edgell Cora-Jean S. , Burridge Keith 
Published: April 2021

ABSTRACT
The distribution of two integrins, the fibronectin receptor and the vitronectin receptor, has been explored in an endothelium-derived cell line plated onto various substrata. On a fibronectin substratum, in the presence of serum, these cells develop focal contacts that contain the fibronectin receptor, whereas the vitronectin receptor is diffusely distributed over the cell surface. Conversely, cells plated onto vitronectin-coated coverslips concentrate only the vitronectin receptor within focal contacts. The accumulation of the vitronectin receptor within focal contacts also occurs when the cells are plated on uncoated coverslips but in the presence of serum. Therefore, we conclude that under normal culture conditions (i.e. in serumcontaining media), the vitronectin receptor is the predominant form of integrin involved in substratum adhesion. This conclusion is supported by experiments in which cells were cultured on fibronectin-coated coverslips in the presence of serum.
Initially these cells developed focal contacts containing only the fibronectin receptor. Within several hours, however, there was a progressive replacement of focal contacts containing the fibronectin receptor by focal contacts expressing the vitronectin receptor. After approximately 12 h in culture, most cells contained focal contacts expressing only the vitronectin receptor.
Focal contacts containing either the fibronectin or vitronectin receptor were both associated with the termini of stress fibres and contained the proteins talin and vinculin. These observations lead us to propose that the cell does not discriminate between these different integrins when assembling the cytoskeletal components at the cytoplasmic face of focal contacts.
In vitro effects of taxol on ciliogenesis in quail oviduct
Authors: Boisvieux-Ulrich Emmanuelle , Laine Marie-Christine , Sandoz Daniel 
Published: April 2021

ABSTRACT
When induced by in vivo oestrogen stimulation, ciliogenesis continues in culture in vitro of quail oviduct implants. Ultrastructure of ciliogenic cells was compared after culture for 24 or 48 h in the presence or absence of 10−5 M-taxol. Taxol, which promotes polymerization and stabilization of microtubules, disturbed ciliogenesis, but formation of basal bodies was unaffected by the drug. Conversely, their migration towards the apical surface seemed to be slowed down or blocked and axonemal doublets polymerized onto the distal end of cytoplasmic basal bodies. They elongated and often constituted a more or less complete axoneme, extending between organelles in various orientations. These axonemes, often abnormal, were not surrounded by a membrane, with the exception of the transitional or neck region between the basal body and axoneme. The formation of membrane in this area resulted from the binding of some vesicles to the anchoring fibres of the basal body. They fused in various numbers, occasionally forming a ring, at the site of the transitional region, and exhibited the characteristics of the ciliary necklace. The association of basal bodies with vesicles or with the plasma membrane appeared to be a necessary signal for in situ polymerization of axonemal doublets.
In addition, taxol induced polymerization of numerous microtubules in the cytoplasm, especially in the apical part of the cell and in the Golgi area. This network of microtubules may prevent basal body migration.
The secretory vesicle in living Paramecium is acidic
Authors: Busch Gerald R. , Satir Birgit H. 
Published: April 2021

ABSTRACT
In Paramecium, secretory proteins are packaged within membrane-bounded vesicles in a condensed form. This form expands when the proteins are released. We have now determined that a proton gradient is present in the secretory vesicles of living Paramecium. Acridine Orange, used as an in vivo indicator of acidic compartments, stained the secretory vesicles in both wild-type and mutant cells. Addition of the two agents that dissipate proton gradients (protonophores), namely, 2,4-dinitrophenol (DNP) and carbonylcyanide m-chlorophenyl-hydrazone (CCCP), eliminated this staining. Washed cells re-established their intravesicular acidity. Effects of sodium azide on vesicular acidity suggest that proton transport in these vesicles involves an ATP-dependent mechanism.
Cell growth kinetics, division asymmetry and volume control at division in the marine dinoflagellate Gonyaulax polyedra: A model of circadian clock control of the cell cycle
Authors: Homma K. , Hastings J. Woodland 
Published: April 2021

ABSTRACT
A new method of determining the dependence of cell growth on the initial cell volume in the absence of cell division is presented. The assumptions are that volume in a certain period of time is either increasing or decreasing, but not both, and is independent of the history of cells. Applying this method to Gonyaulax polyedra in a 12 h light-12 h dark cycle, growth in volume between the 3rd and 12th hours of the light period is found to be more exponential-like than linear. The magnitude of growth in the time period is determined solely by cell volume and environmental conditions, not by cell age. All cells decrease in volume slightly in the dark from the 12th to 23rd hour, and then increase a little from the 23rd to 3rd hour of the following day. Cell division in this species is significantly asymmetric, and the extent of asymmetry is estimated mathematically. Simulations based on the growth patterns and the asymmetric division reveal that cell division must at least partly depend on the volume of cells.
The dependence of conditional cell division probability on cell volume is then experimentally determined. The probability is zero up to a certain cell volume, and then it gradually increases to a plateau level, which is less than unity. Neither the strict size control model nor the transition probability model is fully consistent with the observed shape of the conditional probability function. A hybrid model postulating a ‘sloppy’ critical volume with a constant probability of division above that volume adequately accounts for the conditional probability. With the use of the observed volume growth law, cell division dependence on volume, and the extent of asymmetry in cell division, cell volume distributions are successfully simulated for cells growing in a 12 h light-12 h dark cycle. Another simulation reveals that the true coefficient of variation in generation time is 33%. On the basis of these findings, a model of the cell cycle is presented that incorporates the circadian clock as a cyclic G1 phase. According to this scheme, cells satisfying the minimum cell volume requirement between the 12th and the 18th hour probably exit to the replication/segregation sequence ending in division, and re-enter the cyclic portion after a fixed time interval.
Cell volume and dry weight of cultured Tetrahymena
Authors: Hellung-Larsen Per , Andersen Anders Poul 
Published: April 2021

ABSTRACT
Cultures of Tetrahymena pyriformis, T. hegewishi and T. malaccensis have been studied with regard to control of cell volume and cellular dry weight. Cell volume was measured on cells suspended in 0-9% sodium chloride + 0 ·1% sodium azide using a Multisizer cell counter (Coulter). Tetrahymena were grown at different temperatures and under various up- or downshift conditions. In all cases the changes in cell volume are paralleled by changes in cellular dry weight. The volume and the dry weight of a Tetrahymena cell are determined by the particular medium and the growth temperature. Large cells are seen in concentrated media and at low growth temperatures resulting in cell volumes up to 17000 μm3, whereas starving cells decrease gradually towards 700 μm3 or even smaller sizes. It is proposed that lag phase observed at up- and downshift is to a large extent due to the necessary adjustment of the cell volume to the new conditions.
Three-dimensional arrangements of chromatin and chromosomes: Old concepts and new techniques
Authors: Appels R. 
Published: April 2021

ABSTRACT
The studies of early cytologists, well before the turn of this century, indicated that the positions of mitotic chromosomes in a particular metaphase cell correlated with their respective positions in preceding cell divisions. Observations of this type led to the concept that metaphase chromosomes were not simply aggregations of dispersed chromatin. Furthermore, when it became clear that chromosomes were the carriers of the genetic material many ideas developed relating the arrangement of chromosomes to gene expression in nuclei. A major problem in analysing interphase nuclei was the difficulty in visualizing chromosomes at this stage in the cell cycle. Recent advances in combining the techniques of molecular biology with modifications to the optical microscope and computer image enhancement, analysis and interpretation have revolutionized the capability of studying the very old problem of whether order exists within the eukaryote nucleus.
The effects of tunicamycin, mevinolin and mevalonic acid on hmg-coa reductase activity and nuclear division in the myxomycete Physarum polycephalum
Authors: Engström Wilhelm , Larsson Olle , Sachsenmaier Wilhelm 
Published: April 2021

ABSTRACT
The effects of two inhibitors of 3-hydroxy 3-methyl glutaryl-coenzyme A reductase (tunicamycin and mevinolin) on nuclear division in the myxomycete Physarum polycephalum were examined. Tunicamycin exerted a minor effect on division in synchronized cultures, whereas mevinolin delayed the second, third and fourth nuclear divisions with increasing efficiency. Mevinolin also appeared to be the more potent inhibitor of HMG-CoA reductase, which catalyses the rate-limiting step in the biosynthesis of cholesterol and other isoprene derivatives. These effects of mevinolin could be partially reversed by the addition of mevalonate, suggesting that mevinolin exerts its inhibitory effects on Physarum nuclear division by decreasing the activity of HMG-CoA reductase.
Observations on ultracentrifuging wild-type and mutant (cdc2.33) cells of Schizosaccharomyces pombe
Authors: Khar A. , Mitchison J. M. 
Published: April 2021

ABSTRACT
Ultracentrifuging (400 000 g for 4–6 h at 4 °C) living wild-type cells of the fission yeast Schizosaccharomyces pombe moves the nucleus towards the ends of the cells but scarcely affects their viability. However, in the long cells produced by growing the mutant cdc2.33 for 4–6 h at the restrictive temperature (36–5°C), ultracentrifuging (as above) gives an intense fluorescence with DAPI in about half of the cytoplasm in about 80% of the cells. This is probably nuclear DNA that has moved into the cytoplasm, both because of the DAPI stain and because it is removed by DNase treatment. These cells ultimately divide and are viable, and we suggest that the extended cytoplasmic DNA returns to the nucleus.
Characterization of a heat-resistant strain of Tilapia ovary cells
Authors: Wang H. C. , Chen J. D. , Li G. C. , Yew F. H. 
Published: April 2021

ABSTRACT
Tilapia ovary cells (TO-2) cease to proliferate when moved from normal growth temperature of 31 °C to 37°C, and arrest in G1 and G2 phases of the cell cycle. The ability of the arrested cells to re-enter the cell cycle when restored to 31 °C decreases inversely with time spent at 37°C. A heat-resistant strain, TO-37c, cloned from the surviving fraction of TO-2 after heat treatment, has been found to re-enter the cell cycle with greater facility and to have a higher rate of survival. TO-37c cells have a smaller cell volume than TO-2 and show a distinct morphology at 37°C. Most of the heat-shock proteins (hsps) induced on temperature change were similar, but in TO-37c the decline in the synthesis of a 27×103Afr hsp was faster and a 37°C-specific 60×103Mr hsp was missing. Ultraviolet (u.v.) sensitivity was slightly affected if heat treatment was given after irradiation. However, when cells were preheated and then u.v. irradiated, the u.v. sensitivity increased sharply for TO-2 cells but not for TO-37c.
Expression of nuclear lamins in mammalian somatic cells lacking cytoplasmic intermediate filament proteins
Authors: Paulin-Levasseur M. , Scherbarth A. , Giese G. , Röser K. , Bohn W. , Traub P. 
Published: April 2021

ABSTRACT
Using immunofluorescence and immunoblotting techniques, we have examined the composition of the nuclear lamina in murine plasmacytoma cells, MPC-11, exposed to the phorbol ester TP A as well as in two cell lines devoid of cytoplasmic intermediate filament proteins, the human adrenal cortex carcinoma-derived cells SW-13 and the clone C6;-M-D4 derived from the rat glial cell line C6. Our results show that the inhibition of proliferation and the induction of vimentin synthesis observed in TPA-treated MPC-11 populations are not paralleled by changes in the lamin complement of these cells, which contain lamin B but lack lamins A and C. Furthermore, the analysis performed on SW-13 and C6-M-D4 cell lines clearly demonstrates that mammalian somatic cells display considerable variations in lamin expression and indicates that lamin B may be the only lamin species constitutively expressed in mammalian cells.