bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution of desmosomal components in the tissues of vertebrates, studied by fluorescent antibody staining
Authors: Cowin P. , Mattey D. , Garrod D. 
Published: April 2021

ABSTRACT
In previous work we used immunofluorescent staining with specific antibodies to study the distribution of five desmosomal antigens in the epithelia of different vertebrate animals. We showed that all five antigens were present in all epithelia studied in human, bovine, rat, guinea pig, chick and frog (Rana piptens) tissues. It was concluded that desmosomes are highly conserved structures. This paper extends those studies: (a) by including three other species, a lizard (Lacerta viridis), the axolotl (Ambystoma mexicanum) and the trout (Salmo trutta), and (b) by looking at several tissues in more detail.
The principal results are as follows. (1) The epidermis of all species down to the frog stain with equal intensity for all desmosomal antigens. (2) In the epidermis of axolotl and trout, staining for desmosomal plaque constituents is present, but staining for the desmosomal glycoproteins is greatly reduced or absent. (3) Within mammalian species as well as chick, lizard and frog, staining for the 115 × 103 and 100 × 103 molecular weight desmosomal glycoproteins is less intense in non-epidermal tissues than in the epidermis, while staining for desmosomal plaque constituents and for the 150 × 103 molecular weight glycoprotein is undiminished. It is possible, therefore, that slight differences exist between certain glycoproteins of epidermis and non-epidermal epithelia. (4) The hearts of lower vertebrates (lizard, frog, axolotl and trout) stain only for individual desmosomal plaque antigens. (5) The pillar cells of trout gill stain, adjacent to their collagenous columns, for one desmosomal plaque antigen. There is a fibrous cytoplasmic mat in this position but no desmosomes. Thus one of the desmosomal antigens may have a function outside the desmosome.
Arginine synthesis by hepatomas in vitro: II. Isolation and characterization of morris hepatoma variants unable to convert ornithine to arginine, and modulation of urea-cycle enzymes by dexamethasone and cyclic-amp
Authors: Goss S. J. 
Published: April 2021

ABSTRACT
‘77orn’, a derivative of the Morris rat hepatoma 7777, stably expresses high levels of ornithine transcarbamoylase (OTC) and carbamoylphosphate synthetase I (CPS-I), and is able to grow indefinitely in ornithine-medium (medium with ornithine in place of arginine). Variants that have lost this ability are isolated from 77orn by a ‘suicide’ selective technique dependent on the cellular incorporation of [3H]ornithine. These variants, which have reduced levels of CPS-I, or of both CPS-I and OTC, are shown to have developed multiple hormonal requirements; their enzyme deficiencies can be reversed by use of an appropriately supplemented medium. In particular, CPS-I is inducible by dexamethasone and dibutyryl-cyclic-AMP in combination. Cholera toxin can be used instead of cyclic-AMP, but then butyrate is additionally required if the induction is to be maintained in the long term. The use of these agents in excess can depress OTC. Several other hepatomas, and also explanted foetal rat liver cells, have similar requirements for CPS-I expression. It is argued that multiple hormonal requirements for CPS-I production are normal in liver cells in vitro, and that hormone-independent hepatomas should be regarded as abnormal. The implications of this for the somatic cell genetic investigation of differentiation are briefly discussed.
Division of peribacteroid membranes in root nodules of white clover
Authors: Robertson John G. , Lyttleton Pamela 
Published: April 2021

ABSTRACT
Division of peribacteroid membranes in the cytoplasm of root nodules of white clover was found, from a study of serial thin sections prepared for electron microscopy, to accompany division of the bacteroids. It was also observed that the peribacteroid membranes appeared to have adhered to various sites on the surface of the bacteroid envelope outer membranes. Wherever peribacteroid membranes were constricted as though undergoing division in the region of the cleft formed by partial division of the bacteroids, these constrictions could be related to the point of adhesion of the peribacteroid membranes to the surface of the bacteroids within the cleft. It was concluded that adhesion of the peribacteroid membranes to the bacteroid envelope outer membranes is likely to be a critical element in the process of division of the peribacteroid membranes. Differences in the degree of adhesion between peribacteroid membranes and the bacteroid envelope outer membranes may explain variations in the number of bacteroids enclosed by peribacteroid membranes in nodules of different legumes.
Lateral fusion of membranes in bacteroid-containing cells of leguminous root nodules
Authors: Gunning B. E. S. 
Published: April 2021

ABSTRACT
Bacteroid-containing cells of leguminous root nodules (Pisum and Trifolium) provide an environment in which the membrane envelope surrounding each bacteroid can exhibit unusual properties. The bacteroids are crowded, and frequently neighbouring membrane envelopes come into close contact. In such cases the two envelopes can fuse laterally to give a symmetrical tripartite membrane, probably consisting of a composite inner layer sandwiched between the outer leaflets of the two parent membranes. The expanse of fused membrane forks at its periphery, i.e is confluent with both of the envelopes from which it is derived, and seems to be relatively stable.
The effects of irradiation with high energy electrons on the structure and reactivity of native and cross-linked collagen fibres
Authors: Grant R. A. , Cox R. W. , Kent C. M. 
Published: April 2021

ABSTRACT
Native and cross-linked rat tail tendon collagen was irradiated with high energy electrons up to a maximum dose of 100 × 104 J kg − 1 (100 Mrd). Fibres irradiated dry showed greater damage when examined in the electron microscope using negative staining techniques than those irradiated wet. Cross-linking with glutaraldehyde prior to irradiation resulted in the band structure being preserved even at the highest dose but an unequal shrinkage of the bands was noted.
Irradiation altered the reactivity of both native and cross-linked collagen with collagenase and elastase. Wet-but not dry-irradiated native collagen became resistant to collagenase. Both wet- and dry-irradiated specimens were digested with elastase. Cross-linked collagen, normally resistant to both elastase and collagenase, became sensitive after varying doses of radiation; different results were obtained after irradiation in the wet and dry states.
Irradiated collagen reacted abnormally with various histological stains and tended to resemble elastin in tinctorial properties.
No marked changes were noted in the amino acid composition of the collagen after irradiation. Solubility in dilute alkali, acetic acid and hot water was decreased after irradiation of collagen in the wet state and increased after irradiation in the dry state.
The results were consistent with the hypothesis that electron irradiation of collagen in the dry state results in scission of the polypeptide chains and that, in the presence of water, this is accompanied by the formation of intermolecular bonds. It also appears that changes in the configuration of the polypeptide chains accompany both these processes.
Chloramphenicol-related changes in mitochondrial ultrastructure
Authors: Smith Una , Smith D. S. , Yunis Adel A. 
Published: April 2021

ABSTRACT
An electron-microscopic examination of bone marrow mitochondria derived from 10 patients before and after chloramphenicol (CAP) therapy has shown that CAP induces an ultrastructural modification resulting in an increase in the density of the mitochondrial matrix. These changes resemble the condensed mitochondrial configurations which have previously been interpreted in terms of electron transfer and oxidative phosphorylation. However, in the concentrations employed in this study, CAP has no effect on mitochondrial respiration or on oxidative phosphorylation, but is a potent inhibitor of mitochondrial protein synthesis. Evidence relating this effect of the drug to its myelotoxicity has been supported by a comparative study demonstrating lack of effect of a drug such as tetracycline which is not known to be myelotoxic, and the excel lent correlation between the extensiveness of mitochondrial changes in the marrow and the serum level of free CAP. The results were confirmed in a parallel study on insect flight muscle mitochondria, in which the metabolic state under which the drug is administered can be controlled and where the regular disposition of the mitochondrial cristae provides an ideal model for the study of configurational changes.
Improvements in a chemically defined medium for the growth of mouse cells (strain LS) in suspension
Authors: Birch J. R. , Pirt S. J. 
Published: April 2021

ABSTRACT
In the medium used in previous work, both growth rate and maximum cell population density were reduced in protein-free medium. This was due to iron limitation. In a medium supplemented with iron, the average minimum population doubling time was reduced from 78 to 37 h and the average maximum cell population density increased from 1·6×106 to 3·3 × 106/ml.
In the improved medium described, sodium pyruvate, α-ketoglutaric acid, methylcellulose and polyvinylpyrrolidone are no longer required although methylcellulose prevents an initial fall in population which occurs in polymer-free medium. The present study indicates that amino acids now limit maximum cell population density. By increasing the concentration of the relevant amino acids we have obtained maximum cell populations in excess of 5 × 106 cells/ml without medium change.
Finally we describe a method for measuring the growth of the LS cell in the denned medium by an opacity method.
Kinetics of cell spreading in the presence of different concentrations of serum or fibronectin-depleted serum
Authors: Knox Peter 
Published: April 2021

ABSTRACT
A morphometric assay has been used to show that speed of cell spreading is sensitive to the level of serum in the surrounding growth medium. There was an inverse relationship between serum concentration and speed of spreading; as serum concentration was increased from 0·1% to 100% cells took progressively longer to become fully spread. The time taken to achieve complete spreading in serum concentrations of 0·1, l·0, 10 and 100% serum was 45, 60, 105 and 240 min, respectively. At serum concentrations of 3% and above, fibronectin depletion had no effect on rates of spreading. Only at concentrations below 3% was there an effect of fibronectin depletion and although cells became fully spread in the depleted serum they took longer to do so in comparison to native serum. It is suggested that plasma fibronectin plays no role in serum-stimulated spreading at serum concentrations of 3% and above since at these concentrations rates of spreading are identical whether fibronectin is present or not. At concentrations of 3% and above spreading is mediated by the 7OK spreading factor. At serum concentrations below 3% both fibronectin and 70K factor are effective. The reason for the lack of effect of fibronectin at higher serum concentrations is an inhibition by albumin and other plasma proteins. In contrast, 7OK factor is not affected by exogenous protein concentration. The effect of exogenous protein concentration on cell adhesion is discussed in terms of cell migration between compartments that have different extracellular protein concentrations.
Chick embryonic pigmented retina is one of the group of epithelioid tissues that lack cytokeratins and desmosomes and have intermediate filaments composed of vimentin
Authors: Docherty R. J. , Edwards J. G. , Garrod D. R. , Mattey D. L. 
Published: April 2021

ABSTRACT
Using sodium dodecyl sulphate/polyacrylamide gels to analyse detergent-insoluble residues, and indirect immunofluorescence, we have found that the major protein of intermediate filaments in cultures and freshly explanted fragments of chick embryonic retinal pigment epithelium (RPE) is vimentin. Moreover, these cells also fail to stain with antibodies against cytokeratins and most components of true desmosomes (maculae adhaerentes). Staining with anti-vinculin antibody suggests that the principal intercellular junction is the zonula adherens. Thus although RPE is an epithelium according to all other criteria, it belongs to a group of tissues (including vascular endothelium, iris and lens-forming epithelium) that have intermediate filaments composed of vimentin and possess neither cytokeratins nor desmosomes. That a tissue can be fully epithelial by other criteria, whilst lacking these components, is in agreement with other work, which has shown a lack of effect of micro-injection of antibodies to cytokeratin, and of the suppression of desmosome formation, on epithelial organization in culture.
Although our observations were made solely on chick embryonic tissue, we suggest that published ultrastructural studies are consistent with the possibility that RPE of other species, including human, may lack true desmosomes.
The transcriptional activity of individual ribosomal dna gene clusters is modulated by serum concentration*
Authors: De Capoa A. , Marlekaj P. , Baldini A. , Archidiacono N. , Rocchi M. 
Published: April 2021

ABSTRACT
The activity of ribosomal gene clusters has been studied by cytological methods in human cultured cells grown in different amounts of serum under controlled experimental conditions. It has been shown that increasing amounts of serum induce an increase in ribosomal RNA synthesis at the single cell level. Furthermore, the concomitant identification of individual rRNA gene clusters by fluorescent techniques allowed us to demonstrate: (1) that individual gene clusters have differential transcriptional activity and differential frequency of activation; (2) that ribosomal gene activity is closely associated with the amount of silver-positive gene product and; (3) that environmental variations modulate rRNA synthesis by repressing or derepressing specific gene clusters.
The effect of medium changes on the growth and metabolism of the human diploid cell, W1-38
Authors: Griffiths J. B. 
Published: April 2021

ABSTRACT
It has been established that although an inhibitory interaction occurs when a culture of human diploid cells become crowded together (contact inhibition of growth), multiple-layered cell sheets are obtained by using a continuous medium perfusion culture. A similar effect is obtained when the culture medium is changed at frequent intervals, and this paper reports the effects of a medium change on cell growth and metabolism.
A direct relationship was found between cell yield and the number of medium changes given to a culture. This was an unexpected result because normally when a culture is prolonged by additional feeding the cell yield shows a diminishing return. The amino acid and glucose uptakes and growth yields (the ratio of the amount of cell dry weight produced to substrate used) were determined and they also showed that a unit amount of growth occurred per medium change, and that cessation of growth was accompanied by cessation of nutrient uptake and metabolism. Medium changes had a profound affect on cellular metabolism, especially on DNA and protein synthesis. As a culture approached confluency, DNA, RNA and protein synthesis were sequentially inhibited. After a medium change there was a sequential stimulation of DNA, RNA and protein synthesis in the same order as they were inhibited. The inhibitory mechanism that is affected by cell crowding is obviously reversed by a medium change.
The results presented in this paper suggest that contact inhibition of growth primarily affects DNA synthesis and that if the cell is able to take up a sufficient supply of nutrients in a crowded culture then this inhibition can be overcome.
Studies on the formation of ‘floating’ guard cell mother cells in Anemia
Authors: Galatis B. , Apostolakos P. , Palafoutas D. 
Published: April 2021

ABSTRACT
The protodermal cells producing the ‘floating’ guard cell mother cells (GMCs) in three Anemia species undergo an extraordinary polarization and an unexpected shaping. During interphase an intercellular space is initiated at the internal proximal end of the cell, while the polar region bulges outwards. At this stage a microtubule girdle traverses the cortical cytoplasm underneath the rims of the external periclinal wall curvature. In addition, another system of microtubules converges on a cortical site adjoining the wall delimiting the intercellular space and, or, the neighbouring region of the internal periclinal wall (internal polar cortical site, IPCS). Vacuoles are found in all regions of the cell except for that between the centrally located nucleus and the intercellular space.
As the cell approaches mitosis, the growing vacuolar system retreats from the cytoplasmic region below the external periclinal wall curvature. In most cells the polarized cytoplasm forms an inclined truncated cone, the bases of which abut on the external periclinal wall curvature and the wall lining the IPCS. The organization of the cortical microtubule cytoskeleton does not change significantly during preprophase-prophase. A preprophase microtubule band (PMB) is localized in the cortex lining the rims of the external periclinal wall curvature, while some microtubules traverse the IPCS and the cytoplasm adjacent to the neighbouring wall regions. The mitotic spindle axis is diagonal, while the cell plate separating the GMCs exhibits an unusual mode of growth. It gradually encircles the proximal daughter nucleus, becoming funnel-shaped. One of its periclinal edges fuses with the external periclinal wall area lined by the PMB cortical zone and the other with the internal periclinal wall area adjoining the IPCS. The latter region seems to behave like the PMB cortical zone.
The results show that the morphogenetic mechanism underlying the formation of the conical GMCs includes a series of highly integrated processes, initiated or carried out during cell polarization.
Adhesion, growth and morphology of human mesothelial cells on extracellular matrix
Authors: Niedbala M. J. , Crickard K. , Bernacki R. J. 
Published: April 2021

ABSTRACT
Human mesothelial cells (HMC) cover a variety of serosal surfaces and have been shown to rest upon an underlying subcellular basement membrane in vivo. Bovine corneal endothelial cells produce an extracellular matrix (ECM) in vitro that mimics HMC subcellular basement membrane and was found to modulate HMC adhesion, morphology and proliferation in vitro. Our results indicated that within minutes after plating, a high percentage (&gt;80%) of HMC firmly attached to ECM. Active cellular migration and subsequent proliferation were observed leading to the formation of a well-organized closely apposed cell monolayer. However, when cells were plated on plastic, the rate of cell attachment was much lower and the proliferative rate of HMC grown on plastic also was strikingly lower (exponential doubling time 4·3 days) than that of cells grown on ECM (exponential doubling time 2·4 days). Cells upon reaching confluency on plastic were markedly enlarged as compared to confluent cells grown on ECM. These observations corroborated differences in final cell density where it was noted that HMC cultured on ECM demonstrated a 10fold greater final cell density as compared to cells grown on plastic. Results from these studies illustrate the fact that phenotypic expression as well as proliferative responsiveness of HMC can be modulated by adhesive interactions with preformed ECM.
Mutants of Polysphondylium pallidum showing delayed modifications of glycoproteins are altered in a regulatory signal for development
Authors: Toda K. , Francis D. , Gerisch G. 
Published: April 2021

ABSTRACT
Binding of a monoclonal antibody, Ab293, to cell-surface glycoproteins of Polysphondylium pallidum is known to be blocked by L-fucose, and Fab of this antibody has been shown to inhibit intercellular adhesion of aggregation-competent cells. Mutants with delayed expression of the carbohydrate epitope, ep293, recognized by the antibody, have been shown to be retarded and altered in cell aggregation. The present study shows that ep293 is a modification of carbohydrate structure that is subject to regulation not only in mutant but also in wild-type cells; ep293 is expressed at an early stage of exponential growth in wild-type and only after 12 h of starvation in mutant PN6002. Proteins are already glycosylated before the epitope is expressed. The developmental regulation of pallidin, a lectin known to be an unglycosylated protein, was investigated in parallel with ep293 using a monoclonal antibody. Pallidin was expressed at about the same time as the carbohydrate epitope in cells of the wild-type as well as the mutant. These results indicate a regulatory signal to which various events are coupled. Induction of ep293 and expression of pallidin are two of these events, and mutants such as PN6002 are altered in the timing of the signal.
Junctional Complexes of Epithelial Cells
Authors: Skerrow C. J. 
Published: April 2021

ABSTRACT
This book contains the proceedings of a Symposium held in London in February, 1986, and attended by almost all the leading workers in the field of junction research. The first three chapters are concerned with desmosomes: their general molecular organization, the more detailed structure of the plaque, and the effects of calcium on desmosome assembly and stability. Six shorter chapters on gap junctions cover their physical and molecular structure (with both sides of current controversies being represented) and also functional studies on junctional communication in adult and embryonic tissue. A chapter on the role of uvomorulin in tight junction formation is followed by a more general treatment of cell adhesion molecules and rules for their expression during development. The last two chapters deal with factors affecting epithelial cell interactions in vitro and the role of cell junctions in cancer.
Structure and molecular organization of higher plant coated vesicles
Authors: Coleman Julian , Evans David , Hawes Chris , Horsley David , Cole Louise 
Published: April 2021

ABSTRACT
Suspension-cultured cells of carrot contain three populations of coated vesicles, associated with the plasma membrane (84–91 nm diameter), Golgi dictyosomes and the partially coated reticulum (61–73 nm diameter). These were observed by thin sectioning, dry-cleaving and rapid-freeze deep-etching of cells. Dissociation of clathrin coats with Tris, released triskelions that were morphologically identical with those from mammalian tissue. The triskelion arm length of carrot clathrin was greater (61 nm versus 44–50 nm), but packaging results in clathrin cages of pentagons and hexagons of similar size to those from mammalian cells.
SDS—PAGE of Tris-released triskelion preparations revealed a complex of three polypeptides of 190, 60 and 57(× −)Mr. The 190× 103Mr protein is the plant clathrin heavy chain, slightly larger than the mammalian heavy chain. The 60 and 57(× 103) Mr bands showed the same sensitivities to protease treatment as mammalian light chains. Triskelion preparations containing these three proteins reassembled into polyhedral cages.
These results are discussed in relation to the structural organization of coated vesicles and clathrin cages in other systems.