bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective Extraction With Sarkosyl And Repolymerization In Vitro Of Cytoskeleton Proteins From Giardia
Authors: Crossley Richard , Holberton David V. 
Published: April 2021

ABSTRACT
Sarkosyl has been used to dissociate structures in cytoskeletons isolated from Giardia lambda. Results from sodium dodecyl sulphate/polyacrylamide gel electrophoresis and from electron microscopy of insoluble residues show that the solubilization of components is partly selective. At low concentrations of detergent (&lt;0·3%), microribbons and microtubules of the disc cytoskeleton disappear, but doublet microtubules from axonemes resist extraction. Consequently, the microribbon protein giardin is extracted into solution more completely than tubulin.
Soluble proteins in 0·l % Sarkosyl have been fractionated by gel filtration chromatography in Bio-Gel P300. Giardin elutes in two positions: as a low molecular weight subunit, and in early fractions corresponding to a larger particle size in which subunits might be forming oligomers.
Supernatants prepared in 0·5 % Sarkosyl were diluted with 0·1 M-KC1 or 0· 1 mM-MgCl2 to bring about reaggregation of the cytoskeleton proteins. Reassembled structures seen in negatively stained preparations were polymorphic. Some tubulin ribbons of 5nm protofilaments were identifiable; also there were large fibres and some flat sheets of very thin filaments. Electron micrographs of sheets have been analysed by optical diffraction. The transforms show that the lateral separation of the fine filaments is about 2·5 nm. Axial periodicities from features spaced along filaments were weak. A 3·75 nm layer-line has been detected, corresponding to a similar periodicity found earlier in microribbons.
Determination of patterning in the pollen wall of Lilium henryi
Authors: Sheldon Judith M. , Dickinson H. G. 
Published: April 2021

ABSTRACT
Centrifugation of living pollen mother cells of Lilium henryi has permitted the modification of complex walls developed on the four daughter microspores. This experimental approach has not only provided an insight into the mechanism by which patterning is established, but has also identified the stages in cell development when wall determinants are present. These determinants can be first detected late in the meiotic prophase, but are not necessarily active at the cell surface at this early stage. The fact that treatment during cytokinesis may affect subsequent wall formation, combined with the obvious interference of the colpus with the spore patterning, indicates pattern determination to be a lengthy process, commencing during late prophase and reaching completion in the young tetrad. The study of walls formed on enucleate cell fragments suggests that neither the spindle nor the cytoskeleton is intimately involved in formation of the basic reticulate patterning. It is proposed that material is inserted into the mosaic of the plasma membrane and is reorganized biophysically to form contiguous ‘plates’, which then modify the properties of the membrane in such a way that the cytoplasmic protrusions that constitute the first stages of wall formation only develop in the interstices between them. Changes in the plasma membrane have been detected over this period and it seems that a population of coated vesicles is closely involved in these events. Examination of the cytoskeleton of the young spore suggests that microtubules play a critical rôle in the positioning of the colpus, and reveals ways by which only small changes in this skeleton could give rise to multicolporate grains.
Membrane recycling and the control of secretory activity in pollen tubes
Authors: Picton Jill M. , Steer Martin W. 
Published: April 2021

ABSTRACT
Pollen tubes of Tradescantia growing on media containing 10−3M-Ca2+ and 10−2M-Ca2+ exhibit growth rates of 28 μm min−1 and 7 μm min−1, respectively. The rates of vesicle production by the dictyosomes in these tubes were determined from the rates at which vesicles accumulated in the cytoplasm after treatment with cytochalasin D. Although the vesicle requirements for these two growth rates are considerably different, it was found that vesicle production rates were the same. The results indicate that, in pollen tubes, membrane recycling is occurring and that dictyosome activity is not regulated according to the vesicle requirements for tube growth.
Kinetics of In vitro ageing of mouse embryo fibroblasts
Authors: Karatza Calliopi , Stein Wilfred D. , Shall Sydney 
Published: April 2021

ABSTRACT
The kinetics of ageing of normal mouse embryo fibroblast cells in culture have been determined. The growth pattern during every passage was established. It was observed that the growth pattern was not exponential, but that the growth rate declined progressively both within and with every passage.
We also estimated the cell cycle parameters using the Fraction of Labelled Mitoses method at every passage. We found that the cell cycle duration was constant throughout the lifespan of this cell strain; the median value of the cell cycle duration was found to be 15·5 ± 0·5 h (S.D., n = 8).
From these two sets of observations we infer that the fraction of dividing cells declines smoothly from the beginning of the culture. Our data exclude quite positively any description of ageing of the fibroblast population in terms of a catastrophe or any abrupt change in the population. Our data are also inconsistent with a linear decline in growth fraction. On the contrary, we observed that there was a gradual and smooth decline in the growth rate of the strain, due to a smoothly declining growth fraction. This smooth change in the growth behaviour of this cell strain is accurately described by the mortalization theory of Shall & Stein in which the single parameter γ (gamma), describes the change in reproductive potential over the entire lifespan. The parameter γ describes the rate at which the doubling time of the culture increases. It is the number of generations at which half of the newborn cells are themselves reproductively sterile. Our present data provided an estimate of γ for this cell strain, which was consistent during the entire lifespan of the strain; the best estimate of γ for this cell strain was 20·3 ± 0·6 generations (S.D., n = 19).
Effects of monensin on the processing and intracellular transport of influenza virus haemagglutinin in infected mdck cells
Authors: Edwardson J. M. 
Published: April 2021

ABSTRACT
The role of the Golgi complex in the intracellular transport of influenza virus haemagglutinin in infected MDCK cell monolayers has been investigated using monensin, a carboxylic ionophore known to disrupt the functioning of this organelle in other cell types. In untreated cells metabolically labelled 5 h post-infection with [35S]methionine haemagglutinin was first seen in core glycosylated form, which was sensitive to the enzyme endo-β-N-acctylglucosaminidase H (endo H). After approximately 20 min this form was converted into a terminally glycosylated, endo H-resistant form. In the presence of monensin core glycosylation of haemagglutinin was not affected, but terminal glycosylation was interrupted. Two new forms of haemagglutinin were observed, both of which were smaller than the core glycosylated form. Of these, the larger was endo H-sensitive while the smaller was endo H-resistant. These new (and uncharacterized) forms of haemagglutinin are likely to be intermediates in the normal process of terminal glycosylation, which are revealed as a result of the inhibition by monensin of the transport of haemagglutinin through the stack of Golgi cisternae.
In untreated cells 85 % of the pulse-labelled haemagglutinin had reached the plasma membrane after 90 min of chase, as revealed by its sensitivity to externally applied trypsin. In monensin-treated cells, on the other hand, only 55 % of the haemagglutinin had reached the plasma membrane after 90 min of chase, while 94% had arrived there after 180 min of chase.
At 5 h post-infection the density of envelope proteins detected at the apical surface of the monolayer by immunofluorescence microscopy was greatly reduced by monensin treatment. Budding of virions from the apical surface of the monolayer at 4 and 7 h post-infection was also reduced, and the normal Golgi complexes were replaced by distended vacuoles that appeared to contain poorly preserved virions.
Video digitizer analysis of birefringence along the lengths of single chromosomal spindle fibres: I. Description of the system and general results
Authors: Schaap Catherine J. , Forer Arthur 
Published: April 2021

ABSTRACT
A new system, based on a video digitizer interfaced to a microcomputer, has been developed to quantify birefringence of individual chromosomal spindle fibres from videotaped images of spindles. (The system also can be used for any other purpose that requires the analysis of video intensities.) Retardations along the lengths of single chromosomal spindle fibres have been studied throughout metaphase and anaphase in cells kept at constant temperatures. The instrumental readings are accurate to within less than 0·06 nm retardation, but operationally the retardation values along a single chromosomal spindle fibre can vary by up to 0·15nm, primarily because of variation in operator definition of the spindle fibre. Retardations vary with position along the fibre. During anaphase the retardations along a given chromosomal spindle fibre do not move poleward, but rather change as if the oriented material is disorganized at the kinetochore. The retardation at the kinetochore of a chromosomal spindle fibre does not change during anaphase, except for non-predictable jumps of 20 –30 % that sometimes occur. Thus there is no ‘decay of birefringence’ during anaphase, such as has been described in other species. In this regard our data, that pertain only to single chromosomal spindle fibres, differ from those previously published; we argue that this is because the published data deal with mixtures of chromosomal and continuous spindle fibres, and because changes in birefringence can appear to occur, artef actually, when measurements of birefringence are made at a single spot in a spindle.
Inactivation of mitotic factors by ultraviolet irradiation of hela cells in mitosis
Authors: Adlakha Ramesh C. , Wang Yong C. , Wright David A. , Sahasrabuddhe Chintaman G. , Bigo Helene , Rao Potu N. 
Published: April 2021

ABSTRACT
‘Extracts from mitotic HeLa cells, when injected into fully grownXenopus larois oocytes, exhibit maturation-promoting activity (MPA) indicated by germinal vesicle breakdown (GVBD) and chromosome condensation. Recently, we observed that the MPA of mitotic cell extracts is neutralized by the inhibitors of mitotic factors (IMF) in HeLa cells, which are activated at telophase and remain active throughout the G1 period. The activity of the IMF coincides with the process of chromosome decondensation, which begins at telophase and continues until the beginning of S phase, when chromatin reaches its most decondensed state. The objective of the present study was to investigate whether these two phenomena - chromosome decondensation and the activation of IMF -were related. The activity of IMF was measured in N2O-blocked mitotic HeLa cells, in which chromosome decondensation was induced by exposure to ultraviolet light, and subsequent incuba tion in medium containing inhibitors of DNA synthesis, hydroxyurea and arabinosylcytosine (araC). u.v. irradiation activated IMF in mitotic HeLa cells but not in cell extracts. In contrast, much less activation of IMF was seen even at very high doses of X-irradiarion. The IMF seemed to inactivate the mitotic factors directly by forming a complex that precipitated on heating at 60°C for 15 min. Mg2+ or polyamines (i.e. spermine, spermidine, and putrescine), agents known to promote chromatin condensation partially restored the MPA of the u.v.-irradiated mitotic cell extracts. These results tend to support the conclusion that the IMF play a role in the decondensation of chromosomes.
Activation of potential initiation sites of dna replication and induction of new initiation within the same cycle by puromycin in Drosophila polytene chromosomes
Authors: Mukherjee A. S. , Chatterjee Chandana 
Published: April 2021

ABSTRACT
DNA replication in the polytene chromosomes of larval salivary glands of Drosophila hydei has been examined under normal physiological conditions, with or without puromycin, by an autoradiographic procedure using [3H]thymidine. It has been demonstrated that puromycin induces new labelling patterns that can be identified as initiation patterns. Such initiation patterns were found to have been induced during both the initial (interband labelling patterns) and the terminal (discontinuous) phases. Both induced patterns are sensitive to a-amanitin. These findings lead us to suggest that (a) the puff-interband-labelled patterns are indeed the initial patterns, and (b) the induction of new initiation, which is normally known to be prevented until the completion of the cycle, can be brought about by puromycin. The results also suggest the probable existence of a pool of protein factor(s) for the initiation of a replication cycle already present in the cell system.
Primary cell cultures from human embryonic corneas
Authors: Hyldahl Louise 
Published: April 2021

ABSTRACT
This study shows that primary cell cultures can be established from corneas obtained from 8-week-old human embryos. Such corneas, even though they were obtained at an early stage of the embryonic development, are completely differentiated into three layers as in the adult cornea. Both corneal endothelial cells and stromal cells were found to attach and proliferate in vitro. Furthermore, it was possible to obtain pure uncontaminated cultures of stromal cells after five passages in vitro. It was also possible, using feeder cells as the substratum, to obtain pure endothelial cell cultures from embryonic corneas.
Secreted Glycoproteins Of Human Kidney Tumour Cells Contain Sulphated Complextype Oligosaccharides
Authors: Dennis Michael V. , Watson Cheryl B. , Heifetz Aaron 
Published: April 2021

ABSTRACT
Human kidney tumour cells in culture incorporated [3H]glucosamine and 35SO4 into glycoprotein products, which were secreted into the culture medium. The effects of sodium butyrate, a known differentiation-inducing agent, on the production of these sulphated glycoproteins were studied. Cells were cultured in the absence or presence of butyrate (2 MM) in serum-containing medium, for various times, and the labelled glycoproteins were partially purified by DEAE-cellulose chromatography. Treatment of these cells with butyrate resulted in an increase in the synthesis of secreted [3H]glucosamine- and 35SO4-labelled glycoproteins over several days of culture. This same increase in levels of 35SO4 incorporation was not observed with Bie melanoma cells. Sodium dodecyl sulphate (SDS)/polyacrylamide gel electrophoresis revealed that five major glycoproteins labelled with [3H]glucosamine also were labelled with 35SO4. The major secreted glycoproteins from cells cultured in the absence or presence of butyrate over a 3-day period were similar by SDS/poly-acrylamide gel electrophoresis. Analyses of Pronase-derived glycopeptides indicated that these secreted 3H/35S-labelled glycoproteins contained sulphated oligosaccharides with terminal sialic acid → Gal → GlcNAc residues similar to glycoproteins secreted by vascular endothelial cells.
Brief extraction with detergent induces the appearance of many plasma membrane-associated microtubules in hepatocytic cells
Authors: Mesland D. A. M. , Spiele H. 
Published: April 2021

ABSTRACT
In cultured H35 hepatoma cells membrane-associated cortical networks have a microtrabecular appearance as revealed by dry-cleaving. Filaments having diameters of 15 nm can be readily distinguished within these networks and have not been described previously. Microtubules are seldom observed to be part of this structure. Extraction of cells with 0.1% Saponin in microtubulestabilizing buffer produces holes in the membrane and reorganization of the networks resulting in the loss of microtrabecular structure, the loss of 15 nm filaments and the appearance of abundant membrane-associated microtubules (about 1 ·25 µm per µm2 substrate-adherent membrane). These observations were confirmed by immunolabelling experiments with affinity-purified anti-tubulin immunoglobulin G. By both fluorescence microscopy and electron microscopy it was shown that labelled tubulin in the cortical networks became organized into microtubules upon treatment with detergent. By determination of the microtubule density, expressed as µm microtubule per µm2 membrane, the effects of various conditions on microtubule occurrence were determined. The Saponin-induced appearance of microtubules in the membrane-associated network could be inhibited by: (1) 1 % and 2% glutaraldehyde, (2) O°C, (3) millimolar Ca2+, (4) absence of Mg2* (subsequent reversal of inhibition by addition of Mg24- was shown), and (5) 20µM-nocodazole (but not 20µM-colchicine). In addition to Saponin, extraction with 0·l % Nonidet P-40 or 0·l % Triton X-100 also resulted in microtubule-containing cortical networks. However, 0·1 % Triton N-101 was not effective, although holes were produced in the plasma membrane. These data provide evidence suggesting rapid polymerization of membrane-associated microtubule protein rather than detergent-induced displacement or collapse of existing microtubules. The arguments for this hypothesis and its implications are discussed.
Effect of tumour angiogenesis factors on the membrane of capillary and aortic endothelial cells: An e.s.r. spin-label study
Authors: Dodd N. J. F. , Kumar S. 
Published: April 2021

ABSTRACT
Two distinct factors have been separated from an angiogenic extract of a rat Walker 256 carcinoma, one inducing proliferation and the other migration of capillary endothelial cells in vitro, but having no detectable effect on aortic endothelial cells. The influence of these factors on the order of plasma membranes of these cells was examined by electron spin resonance, using the lipophilic spin label 5-doxyl stearic acid. No detectable effect was observed on treating whole cells or isolated membranes with proliferation factor. In contrast, exposure of capillary endothelial cell membranes to migration factor caused a reduction of membrane order, particularly at temperatures above 30°C. The migration factor had no detectable effect on membrane order of aortic endothelial cells.
The three-dimensional structure of the cell wall glycoprotein of chlorogonium elongatum
Authors: Shaw P. J. , Hills G. J. 
Published: April 2021

ABSTRACT
The green alga Chlorogonium elongatum, a member of the Volvocales, possesses a crystalline cell wall composed of hydroxyproline-rich glycoprotein similar to the primary cell wall glycoproteins of higher plants. Electron microscopy and computer image processing have been used to determine the crystal structure of the Chlorogonium cell wall in three dimensions to a resolution of 2·Onm. The structure is composed of heterologous dimers. Each subunit of the dimer comprises a long, thin spacer domain and a large globular domain, which is the site of the intra- and inter-dimer interactions. There are also sites of intersubunit interactions at the opposite ends of the rod domains. We suggest that the rods are composed predominantly of glycosylated polyproline helix, as has been suggested for higher plant cell wall glycoproteins and has been shown for the cell wall glycoprotein of Chlamydomonas reinhardtii, which is closely related to Chlorogonium.
A role for fibronectin in cell sorting
Authors: Armstrong Peter B. , Armstrong Margaret T. 
Published: April 2021

ABSTRACT
A useful approach to the investigation of embryonic morphogenesis is the study of the factors that control cell movement in cell aggregates in organ culture. Previous studies, in which aggregates of embryonic chick heart ventricle tissue were paired in organ culture, supported the hypothesis that the associative behaviour is dominated by the mesenchymal cell (at the stages used the ventricle is composed of approximately 25% mesenchyme (Mes) and 75% myocyte tissue (My)) by virtue of this cell’s ability to establish a pericellular matrix rich in fibronectin. In aggregate pairs, the aggregate types that develop a fibronectin-rich matrix rapidly are spread over by the aggregate types that are less able to deposit fibronectin in the matrix. In sorting conditions, Mes sorts to the surface of My. This is explained as a consequence of a requirement that Mes have access to a component in the serum fraction of the culture medium for deposition of fibronectin in the matrix. It is proposed that the factor penetrates to a shallow depth in aggregates, limiting the establishment of a fibronectin-rich matrix to superficially located Mes. As fibronectin appears in the matrix, Mes becomes more cohesive than My, allowing it to exclude myocytes and establish itself as a pure tissue that increases in volume as mesenchyme cells migrating within the interior contact the surface zone, becoming immobilized and also activated to secrete fibronectin. The analysis presented includes an experimental investigation of the different elements of this hypothesis and also explores some of the predictions of the hypothesis.
Protein synthesis and its relation to the dna-division cycle in the fission yeast Schizosaccharomyces pombe
Authors: Creanor J. , Mitchison J. M. 
Published: April 2021

ABSTRACT
The rate of protein synthesis has been measured with pulse labels of [3H]tryptophan in synchronous and asynchronous cultures of cdc mutants of Schizosaccharomyces pombe shifted up to the restrictive temperature. The cell cycle related fluctuations in rate that occur in normal synchronous cultures vanish when nuclear division is blocked in synchronous cultures of cdcï and cdc10. But they persist in cdcll where nuclear division continues and cleavage is stopped. We conclude that nuclear division affects the rate of synthesis and that this effect is inhibitory and probably persists for the last 40% of the cycle. When nuclear division has been blocked, the rate of synthesis continues to increase until a plateau is reached where the rate remains constant. Three size mutants of cdc2 reach the plateau at the same average protein content per cell although their initial protein contents vary over a threefold range. Comparison of these results with those from cdc 10 leads to the tentative conclusion that the plateau starts when the cells reach a critical protein/DNA ratio.
Species specificity of an enzyme determined by an erythrocyte nucleus in an interspecific hybrid cell
Authors: Cook P. R. 
Published: April 2021

ABSTRACT
When a chick erythrocyte nucleus is introduced into the cytoplasm of a mutant mouse cell lacking inosinic acid pyrophosphorylase, synthesis of the enzyme is induced. The enzyme induced in this way has the characteristics of chick, not mouse, inosinic acid pyrophosphorylase.
The question of relationship between golgi vesicles and synaptic vesicles inoctopusneurons
Authors: Gray E. G. 
Published: April 2021

ABSTRACTElectron microscopy of the vertical lobe of octopus brain shows that the synaptic knobs of axons with penkarya in the median superior frontal lobe have synaptic vesicles, approximately 28 % of which are dense-cored (or granulated). In contrast, the endings of the amaenne neurons in the vertical lobe and the endings in the retina and optic lobe, both of which are derived from the retinal visual cells, have only agranular synaptic vesicles. The Golgi apparatuses of the median superior frontal penkarya have vesicles, approximately 4·3 % of which are granulated. The amaenne Golgi apparatuses have 1·5 % granulated vesicles. The visual cell Golgi apparatuses have virtually no dense-cored vesicles, only agranular ones. The question of the formation of dense-cored and agranular synaptic vesicles at the Golgi apparatus and their subsequent transport to the terminals are related to these observations.