bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the significance of a periodic, cell size-controlled doubling in rates of macromolecular synthesis for the control of balanced exponential growth of fission yeast cells
Authors: Barnes A. , Nurse Paul , Fraser R. S. S. 
Published: April 2021

ABSTRACT
Mutant strains of the fission yeast Schizosaccharomyces pombe are available which divide at smaller mean sizes than wild type. Earlier work by the present authors has shown that all these strains double their rates of polyadenylated messenger RNA synthesis as a step once in each cell cycle. The smaller the cell, the later in the cycle is the doubling in rate of synthesis. Strains of all sizes, however, double their synthetic rate when at the same threshold size. We show here that the differences in cell cycle stage of doubling in rate of polyadenylated messenger RNA synthesis are enough to explain the reduced mean steady state polyadenylated messenger RNA contents of the smaller strains. The cell size-related control over doubling in rate of synthesis is also shown to maintain the mean polyadenylated messenger RNA content as a constant proportion of cell mass, irrespective of cell size. This control thus allows cells to maintain balanced exponential growth, even when absolute growth rate per cell is altered by mutation. It is also shown that the concentration of polyadenylated messenger RNA itself could act as a monitor of the threshold size triggering the doubling in rate of synthesis in each cell cycle.
Three-dimensional reconstruction of the chromatin bodies in the nuclei of mature erythrocytes from the newt Triturus Cristatus: the number of nuclear envelope-attachment sites
Authors: Murray A. B. , Davies H. G. 
Published: April 2021

ABSTRACT
The arrangement of the chromatin bodies in the interphase nuclei of 6 erythrocytes has been investigated by means of 3-dimensi0nal reconstruction from electron micrographs of serial sections. When the borders of chromatin bodies are marked on the surface of each model, discrete areas of chromatin in contact with the nuclear envelope are revealed. The number of these areas is approximately equal to the number of chromosomes in the diploid set. The data suggest that each chromatin body corresponds to a condensed interphase chromosome and that each chromosome is attached to one discrete site on the nuclear envelope. The data are insufficient to show whether or not the condensed chromosomes are arranged in any orderly pattern in these nuclei.
A cinematographical study of the development of vitally stained Dictyostelium discoideum
Authors: Durston A. J. , York Frida 
Published: April 2021

ABSTRACT
We report observations from time-lapse films of the development of Dictyostelium discoideum (Dd) stained with the vital dye neutral red. We have used this dye to enable us to track individual cells, as they move through multicellular tissues in later Dd stages. Our observations lead us to new conclusions about the control of cell movement and cell contact during Dd development, including the tentative conclusion that the aggregation control competences regulate cell behaviour throughout the whole of Dd. development. We are led to specific hypotheses for the mechanisms of later morphogenetic movements and pattern formation.
Quantitative immunoelectron-microscopic analyses of the distribution of cytochrome p-450 molecules on rat liver microsomes
Authors: Matsuura Shiro , Fujii-Kuriyama Yoshiaki , Tashiro Yutaka 
Published: April 2021

ABSTRACT
Specific antibodies to phenobarbital-induced cytochrome P-450 were prepared by affinity chromatography and coupled to ferritin with glutaraldehyde. The ferritin antibody conjugates with molecular ratio of approximately one were isolated by gel filtration and were used for immunochemical and immunoelectron-microscopic analyses of the distribution of cytochrome P-450 on microsomes from untreated, phenobarbital- and methylcholanthrene-treated rats.
Binding assay showed that at the saturation level of the antibodies, microsomes from untreated, phenobarbital- and methylcholanthrene-treated rats bind 0·25, 0·41 and 0·14 mol of the antibody per mol of cytochrome P-450, respectively. From these data, the maximum number of the ferritin particles which can bind with microsomes was calculated. This number was in good agreement with the average number of ferritin particles bound per microsome which was determined by electron-microscopic observations of the microsomes incubated with the antibody conjugates at saturation level. Electron-microscopic observations also indicated that smooth microsomes can bind more conjugates than rough microsomes and this finding was consistent with the biochemical data that, on the protein basis, smooth microsomes contain more cytochrome P-450 than rough microsomes, even after correction for ribosomal proteins. The number of ferritin particles bound per smooth microsome was proportional to the diameter and non-random distribution of the ferritin particles on the microsomal vesicles, which was deduced simply by inspection in the previous paper from this laboratory, was confirmed by statistical analyses of electron micrographs of the labelled microsomes.
Capping of surface immunoglobulin on ‘hairy cells’ is independent of energy production
Authors: Splinter TH. A. W. , Collard J. G. , De Wildt Anke , Temmink J. H. M. , Décary Francine 
Published: April 2021

ABSTRACT
Capping, independent of metabolic energy, of surface immunoglobulin (S-Ig) on ‘Hairy cells’ from patients with Hairy cell leukaemia (HCL) is described. As controls leukaemic cells from a patient with a prolymphocytic leukaemia (PLL) and blood lymphocytes from healthy individuals were used. The specificity of the energy-independent capping of the HCL-cells as compared to the controls was tested by incubation of the cells at 4 °C in the presence of 01 M· sodium azide with different FITC-labelled ligands.
In order to find an explanation for this phenomenon, the influence of cytochalasin B, colchicine and the combination of both drugs on capping of S-Ig and concanavalin (Con A)-receptors at 37 °C was investigated. Furthermore the effect of Con A on S-Ig capping and vice versa was studied. The results show that only S-Ig on HCL cells could form caps at 4 °C in the presence of sodium-azide. Cytochalasin B alone induced a strong inhibition of Con A capping on all 3 cell types, whereas S-Ig capping was unaffected. Colchicine alone had practically no effect. Anti-Ig inhibited subsequent patch and cap formation with Con A on both HCL cells and PLL cells, whereas Con A caps and patches were redistributed by anti-Ig on PLL cells, but not on HCL cells. Conversely, Con A could link S-Ig to other receptors, leading to inhibition of S-Ig capping at 4 °C on HCL cells and to co-capping of S-Ig at 37 °C on both cell types. In addition Con A induced redistribution of S-Ig caps. The combination of cocapping of S-Ig by Con A, followed by redistribution of the caps by FITC-anti-Ig simulated inhibition of S-Ig capping by Con A on PLL cells.
The major conclusions are: in some cases inhibition of capping may actually be caused by redistribution of caps; the energy-independent capping cannot be explained by free diffusion of S-Ig in the membrane through lack of any connexion with receptor-mobility regulating systems. It is proposed that the energy requirement of capping is needed to inactivate a specific mechanism, which restrains receptor mobility and which is non-operative in HCL cells.
Analysis of the time of utilization of proteins for the initiation and completion of division in synchronized Tetrahymena Pyriformis
Authors: Wheatley D. N. , Rasmussen L. , Zeuthen E. 
Published: April 2021

ABSTRACT
We exposed division-synchronized Tetrahymena pyriformis to pulse treatments with the structural amino acid analogue p-fluorophenylalanine. We related the timing of the treatments to the delays in onset or completion of division, or both. The results enable us to distinguish between early and late phases in cell division in which the cells bring into action proteins which contribute to initiate and complete division, respectively. Normally, these events are separated by 25–30 min.
An experimental analysis of bivalent interlocking in spermatocytes of the newt Triturus Vulgaris
Authors: Callan H. G. , Pearce S. M. 
Published: April 2021

ABSTRACT
Interlocked bivalents at 1st meiotic metaphase are relatively uncommon in spermatocytes of the newt Trituras vulgaris, but their frequency of occurrence can be significantly increased by subjecting newts to a 24-h heat shock. Newt spermatocytes are sensitive to a heat shock at any stage between the end of premeiotic S and mid to late pachytene. The heat shock does not cause evident desynapsis, nor does it significantly affect chiasma frequency; therefore the interlocked condition induced in spermatocytes which were subjected to a heat shock when they were in zygotene or pachytene is unlikely to be a consequence of synaptic trapping. By way of explanation it is suggested that a heat shock may cause telomeres to detach from the nuclear membrane, or from the synaptonemal complex where the latter is attached to the membrane, thus allowing non-homologous chromonemata to become intertwined before chiasmata have formed. If this explanation is valid, it is then further suggested that the recombination process which results in chiasma formation probably takes place in chromosomal regions lying outside the synaptonemal complex, rather than inside, between its 2 lateral elements.
Antibody staining of 10-nm (100-Å) filaments in cultured smooth, cardiac and skeletal muscle cells
Authors: campbell Gordon r. , chamley-campbell Julie , gröschel-stewart Ute , Small J. V. , Anderson Paul 
Published: April 2021

ABSTRACT
Antibodies were prepared against the SDS-denatured 10-nm filament protein ‘skeletin’ extracted from chicken gizzard. The specificity of the antibody to the 10-nm filament protein was shown by immunodiffusion before and after purification of the protein on SDS gels by the enzyme-linked immunoabsorbent assay (ELISA) and by its specific absorption with purified skeletin. In immunofluorescence (where preimmune sera and antigen-absorbed antisera gave negative results), cultured cardiac, skeletal and smooth muscle cells and endothelial cells stained intensely. No staining was observed in fibroblasts present in these cultures, nor was there staining in glial cells or nerve cell bodies and fibres from sympathetic ganglion and Auerbach’s plexus cultures. Smooth muscle cells (regardless of their source and phenotypic state) and endothelial cells stained intensely in the perinuclear region and in a fine filamentous network that existed throughout the cytoplasm. In both chick and rat skeletal and cardiac muscle (cultures and frozen sections) filamentous network staining was observed, while in rat muscle the antibody was additionally localized in a regular pattern in the region of the Z-disk, and in the case of cardiac muscle associated with the intercalated disk. The addition of 10−6M colchicine to the culture medium of smooth and striated muscle and endothelial cells resulted in an aggregation of the filaments in the nuclear region.
Cultured smooth and striated muscle and endothelial cells and freshly isolated smooth muscle cells extracted of actomyosin and tubulin by high and low ionic strength solutions gave a staining pattern similar to non-extracted cells and in the electron microscope, exhibited filaments of predominantly 10 nm diameter.
Fine structure of meiotic prophase chromosomes and modified synaptonemal complexes in diploid and triploid Rhoeo Spathacea
Authors: Lin Yue J. 
Published: April 2021

ABSTRACT
The synaptonemal complex (SC) in the diploid Rhoeo consists of 2 amorphous lateral elements, each about 46.0 nm thick, and one amorphous central element about 30.0 nm thick. The central region is about 115.0 nm wide. SC in the triploid have essentially the same dimensions as those of the diploid; both lateral (46.0 nm) and central (30.0 nm) elements are amorphous, and the central region is about 117.5 nm wide. The coil, observed in both diploid and triploid, is a modified short segment of SC with several twists at the end of a synapsed bivalent that is attached to the nuclear membrane. Serial sections in a diploid cell reveal that a coil extends inwards about 3.5 μm from the nuclear membrane and makes a complete turn at a distance of every 0.5 μm. There is a correlation between the modified ends of SC and terminal chiasmata in Rhoeo. The coils might have a positive role in the process of crossing over, or alternatively might be involved in ring formation by holding chromosome ends together while chiasmata are not involved. SC are present in chromocentres of both diploid and triploid. Chromocentres in diploid and triploid are indistinguishable, and appear to be formed from the aggregation of pericentromeric heterochromatin as a result of translocations which occurred close to the centromeres. 3-dimensional hypothetical pachytene configuration of the diploid is presented.
Ammonia plus another factor are necessary for differentiation in submerged clumps of Dictyostelium
Authors: Sternfeld John , David Charles N. 
Published: April 2021

ABSTRACT
Differentiation of Dictyostelium amoebae can occur in submerged clumps of cells; under an oxygen atmosphere mature stalk cells and spores form, as has been shown in previous work. This report shows that at least 2 factors are released by the cells under these conditions, and that both, together, are required for differentiation of stalk cells and spores. One of the factors is ammonia (NH3 + NH4+). The other factor(s) is heat stable and dialysable but has not yet been further characterized. The factors can be collected in conditioned medium and, when added to cells, stimulate differentiation. Conditioned medium loses its biological activity upon the removal of the NH3 + NH4+. When NH3 + NH4+ is added back, activity is restored. Because NH3 + NH4+, alone, has no activity, a second factor(s) in the conditioned medium must be required for differentiation. It is also shown that calcium inhibits differentiation in submerged clumps and that in calcium-free medium the timing of differentiation is essentially the same as under aerial conditions.
A lectin which binds specifically to β-D-galactoside groups is present at the earliest stages of chick embryo development
Authors: Cook G. M. W. , Zalik S. E. , Milos N. , Scott V. 
Published: April 2021

ABSTRACT
Extracts obtained from chick embryos at the pre-gastrula and gastrula stages are able to agglutinate trypsinized rabbit erythrocytes fixed with glutaraldehyde. Agglutination is inhibited by saccharides sharing a β -D-galactopyranoside configuration. Agglutinin activity is also inhibited by desialysed fetuin which bears terminal galactose residues but not by native fetuin, desialysed agalacto-fetuin, bovine submaxillary mucin and desialysed bovine submaxillary mucin. Lectin activity is present in extracts obtained from the embryonic area of the blastoderms as well as in extracts from extra-embryonic endoderm and ectoderm. In extracts subjected to gel filtration on ECD Sepharose, lectin activity eluted between ovalbumin (mol. wt 45000) and chymotrypsinogen (mol. wt 25000). Under some experimental conditions, thiodigalactoside, the most potent inhibitor of lectin activity, inhibited the aggregation of cells of the extra-embryonic endoderm of the primitive chick embryo.
Combined microspectrophotometry and automated quantitative autoradiography applied to the analysis of the plant cell cycle
Authors: Gould Alan R. 
Published: April 2021

ABSTRACT
Two methods, which relate grain number to cell cycle phase in Feulgen-stained autoradiographic preparations, have been developed and compared. Both methods automate grain number estimations, one by taking integrated absorbance measurements at different wavelengths, the other by measuring absorption at a single wavelength before and after chemical removal of silver grains. With tritium-labelled tobacco mosaic virus as a probe, a quantitative analysis has been made of the binding of virus particles to plant protoplasts in different compartments of the DNA replication and partition cycle. The preliminary results indicate that the quantity of virus bound by protoplasts is related to their cell cycle phase. Whilst in this case, the methods have been used with plant cells, both techniques are equally applicable to animal cells.
Electron-microscopy of intact nuclear dna from human cells
Authors: McCready S. J. , Akrigg A. , Cook P. R. 
Published: April 2021

ABSTRACT
Structures retaining many of the morphological features of nuclei may be released by lysing human cells in a non-ionic detergent and 2 M NaCl. Such nucleoids contain all the nuclear DNA packaged within a flexible cage of RNA and protein. HeLa nucleoids have been spread at an air-water interface and viewed in the electron microscope. A tangled network of superhelical fibres surrounds the collapsed cage. Irradiation with γ-rays abolishes supercoiling and treatment with the untwisting enzyme or a low concentration of ethidium reduces it. A high concentration of ethidium induces supertwisting. The nuclear DNA of higher cells can be isolated naked, supercoiled and intact.
Wall substructure of microtubules polymerized in vitro from tubulin of crayfish nerve cord and fixed with tannic acid
Authors: Pierson George B. , Burton Paul R. , Himes Richard H. 
Published: April 2021

ABSTRACT
Microtubules of axons of crayfish nerve cord normally have 1 2 wall protofilaments and microtubules of surrounding glial cells have 13 protofilaments. Tubulin was isolated from such nerve cords and polymerized in vitro; tannic acid staining of sedimented microtubules showed that microtubules with 12 and 13 wall protofilaments were present, suggesting that the ability to form a microtubule with a given number of protofilaments is inherent in the tubulin or its associated proteins. The temperature of polymerization was found to influence the number of protofilaments in resultant microtubules. With assembly at 20 °C, for example, most of the complete microtubules had 13 protofilaments, while at 40 °C most showed 10 protofilaments. It is suggested that the temperature of in vitro polymerization, among other factors, can influence the angle of binding between adjacent protofilaments and thus alter the number of protofilaments required to complete the circumference of the tubule.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: II. effect of sucrose on cellular fine structure
Authors: Glauert Audrey M. , Fell Honor B. , Dingle J. T. 
Published: April 2021

ABSTRACT
A study of the fine structure of embryonic chick limb-bone rudiments in organ culture has shown that exposure to 0·08 M sucrose causes intense cytoplasmic vacuolation of the peripheral cells, while the structure of the cytoplasmic organelles is apparently unaltered. The lamellae and vesicles of the Golgi apparatus are more abundant than in the controls and the vesicles are no longer confined to the Golgi zone. The first vacuoles appear in the articular chondrocytes after exposure to sucrose and are autophagic vacuoles or clear vacuoles, probably containing sucrose. After 24 h or more the vacuoles are more heterogeneous and contain a great variety of membranous, granular and fibrous material. These vacuoles appear to be formed by fusion between endocytotic coated vesicles, autophagic vacuoles, multivesicular bodies, clear vacuoles and vesicles derived from the Golgi zone. After 2 days some vacuoles contain fibrils identical in appearance to those in the surrounding cartilage matrix. The development of vacuoles in the chondrocytes in the inner regions of the epiphyses is much slower and autophagic vacuoles are only seen after 6 days’ exposure to sucrose.
Similar changes are observed in the fine structure of the perichondrial and periosteal fibroblasts, and after 2 days in the presence of sucrose many fibroblasts have cytoplasmic vacuoles containing banded fibres similar to the extracellular collagen fibres. In shafts of 11-day embryonic chicks exposed to sucrose for 8 days the cytoplasmic vacuoles in the osteoblasts contain banded fibres and dense crystallites resembling those of the bone matrix.
When rudiments are transferred to normal medium after 2 days’ exposure to sucrose the vacuoles are gradually lost; some of the vacuoles appear to move to the periphery of the cell and then fuse with the plasma membrane, thus releasing their contents. Throughout this process the fine structure of the cytoplasmic organelles is unaltered.
It is suggested that exposure to sucrose stimulates an increased production of lysosomal enzymes which are transported in small vesicles from the enlarged Golgi region to the clear vacuoles and to the autophagic vacuoles. It seems possible that during this process enzymes are released into the surrounding matrix and modify the ground substance sufficiently to enable some of the connective tissue cells to become actively phagocytic and to ingest collagen fibres and bone crystallites.
Development and dispersal of p-protein in the phloem of Coleus blumei benth
Authors: Steer M. W. , Newcomb E. H. 
Published: April 2021

ABSTRACT
The development of P-protein (slime) in the phloem of Coleus stem apices has been studied electron microscopically using material fixed in glutaraldehyde followed by osmium tetroxide. In phloem parenchyma cells the earliest-appearing groups of tubular P-protein commonly are seen in close association with clusters of ‘spiny’ vesicles similar to those reported in Phaseolus phloem (Newcomb, 1967). The vesicles break down as the P-protein masses enlarge, and are assumed to contribute to P-protein formation. Subsequently the groups of tubules are consolidated into a single spindle-shaped body aligned longitudinally in each phloem parenchyma cell or sieve element. The microtubules observed frequently in the vicinity of the young P-protein body may play a role in its consolidation or in the longitudinal alignment of its constituent tubules. Some P-protein bodies acquire a highly organized structure in which the tubules are arranged hexagonally around lightly staining centres.
Disaggregation of the P-protein body occurs during disintegration of the cytoplasm and nucleus, and results initially in the presence of swirls of packed fibrils. During disaggregation, the tubules of the mature P-protein body, which are about 200 Å in diameter, are converted to fibrils about 70 Å in diameter in a process apparently with several intermediate stages. In longitudinal view the fibrils exhibit alternate electron transparent and dense bands that impart a striated appearance to the mass. During maturation of the sieve element the swirls of fibrillar masses separate into individual fibrils which become dispersed through the cell lumen.