bluuebunny/crossref_metadata_2025_split huggingface dataset:
The distribution of cholinesterase in cholinergic neurons demonstrated with the electron microscope
Authors: Lewis P. R. , Shute C. C. D. 
Published: April 2021

Abstract
The thiocholine technique for cholinesterase has been successfully adapted for the demonstration of enzyme distribution with the electron microscope. After fixation in buffered glutaraldehyde, thin slices of tissue were taken through a histochemical procedure designed to minimize diffusion artifacts and cytological damage; appropriate areas were dissected out, fixed with osmium tetroxide and embedded in Araldite.
This technique has been used to study the distribution of enzyme in and around known cholinergic neurons in the rat. In diaphragm muscle the intense staining of the motor end plates is confined to the actual synaptic clefts. The distribution of cytoplasmic staining was similar in all three types of cholinergic neurons studied (ventral horn cells from the cervical cord, cells from the dorsal motor nucleus of the vagus, and cells from the hypoglossal nucleus). There was intense staining of the space contained within the individual bilaminar sheets of the rough endoplasmic reticulum and occasionally in areas of the nuclear envelope. Mitochondria, lysosomes, the smooth endoplasmic reticulum and most of the plasma membrane were unstained.
In cholinergic nerve fibres staining was particularly intense at the axonal membrane and absent from the myelin sheath. In several regions of the brain known to receive an afferent cholinergic innervation many of the identifiable synaptic areas were heavily stained. Staining here was usually present round most of the presynaptic process, spreading over part of the postsynaptic process and often penetrating into the actual synaptic space. The mitochondria, microvesicles and the general cytoplasm of the synaptic processes were all unstained. In some areas, such as the hippocampus, there was intense membrane staining of fine cholinergic neuropil.
The enzyme specificity of the technique is not in doubt and evidence is adduced for the view that diffusion artifacts are small. The close correlation between the electron-microscopic results and evidence from physiological and biochemical investigations is discussed.
Evolution of the nucleoli during oogenesis in Xenopus laevis studied by electron microscopy
Authors: Van Gansen P. , Schram A. 
Published: April 2021

ABSTRACT
Xenopus laevis tadpoles and toads were killed at several ages. The structure of the nuclei of the germinal cells has been observed by light and electron microscopes. We distinguish 11 successive stages in nucleolar structure: (1) a single, essentially granular nucleolus in the oogonium (10 μm diameter), (2) a reticulated nucleolus in the leptotene oocyte, (3) fragmentation of this nucleolus into a few smaller nucleoli, (4) multiple tiny nucleoli appearing in the cap of the pachytene oocyte, (5) enrichment in the fibrillar constituent of these intra-cap nucleoli, (6) grouped spherical nucleoli, with well segregated granular and fibrillar constituents, as the disintegration of the cap is going on (diplotene A oocyte, 30 μm diameter), (7) dispersion of those nucleoli in the nuclear sap (diplotene B oocyte, 50 μm diameter), (8) formation of long, ribboned nucleoli with multiple DNA-rich spots (diplotene C oocyte, 100 μm diameter), (9) fragmentation of the nucleolar ribbons into multiple spherical nucleoli with excentric fibrillar core and granular cortex (diplotene D oocyte, 150 μm diameter), (10) multiple purely fibrillar nucleoli (diplotene E oocyte, between 150 and 400 μm diameter), and (11) multiple classical nucleoli with concentric fibrillar core and granular cortex (diplotene F oocyte, between 400 and 1000 μm diameter).
The multiplication of the nucleoli in Xenopus laevis may occur successively (a) by the fragmentation of the single oogonium nucleolus at the leptotene stage, (b) by de novo formation of nucleolar bodies inside the cap at the pachytene stage, and (c) by the growth of those nucleoli lying free in the nucleolar sap at the early diplotene stage. They evolve into nucleolar ribbons which later on fragment into spherical bodies.
Four successive phases during the growth of an oocyte can be distinguished with respect to the ribosomal system. (I) The first phase is characterized by the nucleolar DNA amplification. (II) During the second phase, the multiplication of the nucleoli is going on. Ribosomes are present in the cytoplasm and the rate of cellular growth is very high. (III) During the third phase, the synthesis of rRNAs seem to be repressed while the synthesis of heterogenous small RNAs is going on. Ribosomes are no longer visible in the cytoplasm. The nucleoli are purely fibrillar. The rate of cell growth is lower than in the preceding phase. (IV) During the fourth (= Duryee lampbrush stages 3—6), or vitellogenic phase, rRNAs are actively synthesized and numerous ribosomes appear in the cytoplasm. The nucleoli have the classical structure and the rate of growth is about the same as during phase III.
Biochemical and structural variations in the flight muscle mitochondria of ageing blowflies, Calliphora erythrocephala
Authors: Tribe M. A. , Ashhurst Doreen E. 
Published: April 2021

ABSTRACT
Biochemical investigations with isolated blowfly flight muscle mitochondria show that uncoupling of oxidation and phosphorylation increases with increasing age of the adult fly. Of the two principal substrates used (i.e. a-glycerophosphate and pyruvate), uncoupling is most marked when α-glycerophosphate is used as substrate.
Although age-related changes in the structure of the thoracic flight muscle are observed by electron-microscope studies, no obvious degenerative changes take place in either the mitochondrial structure or the myofibrils of old flies. Labelling experiments with [3H]leucine indicate that uncoupling is mainly due to the lack of repair and replacement of mitochondrial proteins. These experiments also show that mitochondria] protein synthesis is important in the maturation of young flies, that is, those between o and 4 days old, but is insignificant in the further increase in mitochondrial size observed in older flies, where mitochondrial fusion appears to be more important.
The termination of centrifugal fibres in the glomerular layer of the olfactory bulb
Authors: Pinching A. J. , Powell T. P. S. 
Published: April 2021

ABSTRACT
The termination of the centrifugal fibres running in the lateral olfactory tract to the glomerular layer of the rat olfactory bulb has been determined with the electron microscope; this has been done with material perfused at various times after section of the lateral olfactory tract, as well as after a combination of this lesion with the long-term degeneration of olfactory nerves. The axon terminals are sparse at the glomerular level, but undergo typical degenerative changes; they are distributed solely in the periglomerular region and intermediate zone. The most common post-synaptic profiles are the processes of periglomerular cells, but a few centrifugal fibres terminate on short-axon, tufted and mitral cell dendrites. Evidence is produced to suggest that the anterior olfactory nucleus does not project as far as the glomerular layer. The findings are discussed in relation to previous studies with normal material and silver degeneration methods on similar experimental material; the functional implications of the centrifugal pathways in the bulb are briefly discussed.
The effect of neuraminidase on the aggregation of bhk21 cells and bhk21 cells transformed by polyoma virus
Authors: Vicker M. G. , Edwards J. G. 
Published: April 2021

ABSTRACT
Bacterial neuraminidases increase the adhesiveness in suspension of freshly trypsinized hamster fibroblasts (BHK21 cells). The effect is seen most clearly when the enzymes are added to pre-aggregated suspensions, but can also be observed when cells in monolayer culture are pre-incubated with neuraminidase, suspended, and then aggregated in its absence. BHK21 cells transformed by polyoma virus respond only very slightly to neuraminidase, which therefore increases the difference in adhesiveness between transformed and untransformed cells. Neuraminidase does not eliminate the difference in adhesiveness between sparsely and densely grown BHK 21 cells.
These findings are consistent both with the lyophobic colloid theory of cell adhesion and with proposals that intercellular adhesion depends on complementary molecules on the surface of interacting cells. The low adhesiveness and small response to neuraminidase of transformed cells, however, are more readily explained in terms of the latter.
Mitosis in heterobasidiomycetous yeasts: I. leucosporidium scottii (candida scottii)
Authors: McCULLY E. Kathleen , Robinow C. F. 
Published: April 2021

ABSTRACT
Leucosporidium scottii, for many years considered to be an asporogenous yeast in the genus Candida, is now known to have a heterobasidiomycetous life-cycle. Although morphologically similar to ascomycetous yeasts such as Saccharomyces cerevisiae, budding cells of L. scottii have a strikingly different type of mitosis. In L. scottii, mitosis is not intranuclear as it is in 5. cerevisiae. Neither does the nucleus constrict and separate into daughter nuclei in the neck region between mother cell and bud.
In L. scottii the chromatin-containing portion of the nucleus moves into the bud before division. There is partial breakdown of the nuclear envelope and the chromatin divides along a spindle apparatus formed inside the bud within remnants of nuclear envelope. A portion of the nucleus containing the nucleolus is left behind in the mother cell and disintegrates there when the envelope breaks down. After division, the nuclear envelope reforms around daughter nuclei and one daughter moves back to the mother cell. These events have been established on the basis of 3 types of observation: on living cells with phase-contrast microscopy; on cells stained for chromatin and studied with light microscopy; and on glutaraldehyde-fixed cells studied with electron microscopy.
As in L. scottii, breakdown of nuclear envelope during division has been reported in several mycelial basidiomycetes. The sequence of chromatin movement into the bud of L. scottii, division inside the bud, and return of one daughter nucleus to the mother cell, is closely comparable to the movements of chromatin in and out of clamp connexions known to occur in dikaryotic hyphae of Polystictus versicolor. These mitotic similarities are in accord with the taxonomic relationship of L. scottii to the basidiomycetes.
Observations on a cytoplasmic organelle located outside interphase nuclei of L. scottii have convinced us of its considerable importance during mitosis. This structure consists of 2 globular electron-dense ends joined by a bridge-like middle piece. It accompanies the advancing tips of nuclei which enter the bud. After breakdown of the nuclear envelope, the 2 spherical components of this organelle are seen at opposite poles of the mitotic spindle. Therefore we refer to it as the ‘microtubule organizing centre’ (MTOC). We have also speculated about a possible role for the organelle in the regulation of nuclear envelope growth, breakdown, and reformation.
Differences in adhesion to tissue culture plastic of clonally related transformed and control sublines from an epithelial cell strain
Authors: Steele John G. , Dalton B. Ann , Underwood P. Anne , Smith Garry J. 
Published: April 2021

ABSTRACT
Clonally related sublines of the NAL1A lung epithelial cell strain were used in a comparison of the mechanism of attachment and the morphology of control and transformed epithelial cells. The initial attachment and spreading of the control cells on tissue culture plastic was shown to be dependent upon adsorption of serum vitronectin to the substratum. The alphav subunit of the vitronectin receptor was detected in both the control and transformed cells by immunoprecipitation and immunoblot methods. The spontaneously transformed cells differed from the control cells in that, whereas attachment to tissue culture plastic could occur by binding to adsorbed vitronectin, the transformed cells could also become attached, with time, by a vitronectin-independent mechanism. Attachment by this vitronectin-independent reaction was inhibited by the protein synthesis inhibitor cycloheximide and also by the microtubule-disrupting drugs demicolce-mid and nocodazole. The morphologies of attached control and transformed cells cultured on tissue culture plastic were disrupted by treatment with cytochalasin B, demicolcemid or nocodazole, indicating that the shape of these cultured epithelial cells is dependent upon the microtubule system as well as the actin filaments. These results show one important difference between the control and transformed cells, in that the transformed cells can attach to tissue culture plastic by a vitronectin-independent mechanism that involves new protein synthesis by the cell. Another interesting difference is that this vitronectin-independent attachment of the transformed cells was sensitive to inhibition by microtubule-disrupting agents. On the other hand, the attachment of either transformed or control cells to fibronectin- or vitronectin-coated surfaces was not affected by microtubule-disrupting agents.
Study of vitrified, unstained frozen tissue sections by cryoimmunoelectron microscopy
Authors: Sabanay Ilana , Arad Talmon , Weiner Stephen , Geiger Benjamin 
Published: April 2021

ABSTRACT
We describe the development and application of a novel approach to high-resolution ultrastructural analysis of cells and tissues. It is based on the preparation of ultrathin frozen sections of fixed tissues, rinsing of the sections, followed by their embedding on the grid in a layer of vitrified ice, and direct observation with a cryoelectron microscope. Examination of smooth muscle, kidney and heart tissues showed that although no heavy metal staining was used, high-contrast images are obtained. Fine details of cytoplasmic filaments and organelles, membranes and membrane-associated structures, as well as connective-tissue elements are all visible. The new method is suitable for immunolabeling, including high resolution localization of specific molecules within the cytoplasm.
Lucifer yellow and fluorescein isothiocyanate uptake by cells of Morinda citrifolia in suspension cultures is not confined to the endocytotic pathway
Authors: O’DRISCOLL D. , Wilson G. , Steer M. W. 
Published: April 2021

ABSTRACT
On the basis of previous reports that the uptake of Lucifer Yellow-CH (1YCH) is restricted to the endocytotic pathway in plant cells, it was anticipated that the probe would provide an estimate of endocytotic activity in suspension cultures of Morinda citrifolia. The uptake of LYCH and fluorescein isothiocyanate (FITC) have been examined in whole cell and protoplast forms of M. citrifolia. Rapid staining of the general cytoplasm and nucleus was observed with both fluorochrome treatments, while both markers were excluded from the central vacuole. In addition,treatment of cells with Probenecid, an anion transport inhibitor, prevented LYCH from entering cells. It is suggested that LYCH utilizes an anion transport mechanism to cross the plant cell plasma membrane. Furthermore, LYCH and FITC are excluded from the central vacuole due to the absence of such a mechanism on the tonoplast.
Molecular cloning of the human gene, ccg2, that complements the bhk-derived temperature-sensitive cell cycle mutant tsbn63: Identity of ccg2 with the human x chromosomal scar/rps4x gene
Authors: Watanabe Minoru , Furuno Nobuaki , Goebl Mark , Go Mitiko , Miyauchi Kumi , Sekiguchi Takeshi , Basilico Claudio , Nishimito Takeharu 
Published: April 2021

ABSTRACT
A temperature-sensitive mutant tsBN63 cell line was isolated by the fluorodeoxyuridine method from the BHK21/13 cell Une after mutagenesis with nitrosoguanidine. When cultures of tsBN63 cells growing asynchronously at 33.5 °C were shifted to 39.5 °C, a nonpermissive temperature, the ability for protein synthesis was rapidly reduced and cell proliferation stopped mainly at G1 phase, and partly at G2 phase. Synchronized cultures of tsBN63 cells did not commence DNA synthesis when shifted up in Gt phase. The human gene complementing the tsBN63 mutation was cloned by DNA-mediated gene transfer and its cDNA of 1.1 kb conferring ts+ phenotype on tsBN63 cells was isolated from the cDNA library of Raj (mer+) cells with a frequency of 10−3. On the basis of the determined nucleotide sequence, the isolated human gene turned out to be the X chromosomal RPS4X encoding the ribosomal protein S4. The size of the CCG2 gene was estimated to be about 12 kb by complementation analysis of the tsBN63 mutation with cloned genomic DNA.
Induction of partial mitosis in BHK cells by 2-aminopurine
Authors: Andreassen Paul R. , Margolis Robert L. 
Published: April 2021

ABSTRACT
The protein kinase inhibitor 2-aminopurine (2-AP) inhibits a subset of mitotic events in BHK cells. In the presence of the drug, these cells form a bipolar spindle in mitosis, but chromatin fails to generate functioning chromosomes. Cells in 2-AP progress through a partial mitosis, in which there is no observable metaphase, anaphase or telophase events. After 12 h of exposure to 2-AP the chromatin in mitotic cells fails to condense into discrete chromosomes, and is displaced by the spindle to form ‘binucleate’ cells and cells containing abnormally shaped nuclei in the subsequent interphase. Other mitotic modifications of nuclei, such as nucleolar and nuclear lamina disassembly, occur normally. Centromeres in these nuclei do not become engaged in the spindle, but instead show either no association or a lateral arrangement around the spindle. Cells treated with 2-AP are not arrested in mitosis. Therefore, mitotic exit is not inhibited by the failure of these cells to progress through the latter stages of mitosis. Further, nocodazole-arrested cells quickly exit mitotic arrest when 2-AP is added. We conclude that 2-AP interferes with a specific subset of mitotic events, and that it allows cells to overcome checkpoints that require spindle function for mitotic progression.
Wild type and tailless CD8 display similar interaction with microfilaments during capping
Authors: André Pascale , Gabert Jean , Benoliel Anne Marie , Capo Christian , Boyer Claudec , Schmitt-Verhulst Anne Marie , Malissen Bernard , Bongrand Pierre 
Published: April 2021

ABSTRACT
We examined the influence of the intracytoplasmic region of CD8 a on capping and interaction with microfilaments. We used cell clones obtained by transfecting a CD4+ T-cell hybridoma with (a) T-cell receptor (TCR) α and β chains from a cytolytic clone and (b) CD8a genes that were either native or modified by extensive deletion of the intracytoplasmic region or replacement of the transmembrane and intracytoplasmic domains with those of a class I major histocompatibility complex gene (Letourneur et al. (1990). Proc. natn. Acad. Sci. U.S.A. 87, 2339–2343). Different cell surface structures were cross-linked with anti-T-cell receptor, anti-CD8 or anti-class I monoclonal antibodies and anti-immunoglobulin (Fab’)2. Double labeling and quantitative image analysis were combined to monitor fluorescence anisotropy and correlation between different markers. Microfilaments displayed maximal polarization within two minutes. The correlation between these structures and surface markers was then maximal and started decreasing, whereas the redistribution of surface markers remained stable or continued. Furthermore, wild type and altered CD8□ exhibited similar ability to be capped and to induce co-capping of TCR and MHC (major histocompatibility complex) class I: the fraction of cell surface label redistributed into a localized cap ranged between 40% and 80%. Finally, cytochalasin D dramatically decreased CD8 capping in all tested clones.
It is concluded that the transmembrane and/or intracellular domains of CD8 molecules are able to drive the extensive redistributions of membrane structures and cytoskeletal elements that are triggered by CD8 cross-linking.
The epidermal growth factor-induced migration of rat liver epithelial cells is associated with a transient inhibition of DNA synthesis
Authors: Geimer Pia , Bade Ernesto G. 
Published: April 2021

ABSTRACT
Epidermal growth factor (EGF) is a potent mitogen for most cultured cells and has previously been shown to induce the migration of rat liver epithelial cells. We have now demonstrated that under migration-inducing conditions EGF does not stimulate cell proliferation, but causes instead a transient inhibition of DNA synthesis. Analysis at the singlecell level by [3H]thymidine autoradiography indicated that in 40-50% of the EGF-treated cell population the entry into S phase is delayed. The simultaneous demonstration of migration tracks by laminin immunofluorescence revealed that the transient inhibition of DNA synthesis is not restricted to the migratory cells. The effect is also observed with the stationary subpopulation and appears, therefore, to be independent of the induction of migration. The independence of both processes was further supported by showing that induction of migration by EGF proceeds undisturbed in cells blocked in S phase by aphidicolin.
These results indicated that for rat liver epithelial cells the induction of migration by EGF has priority over cell proliferation. The data also emphasize the need for a time-course analysis when studying factors that stimulate or inhibit DNA synthesis or cell proliferation.
Circadian rhythmicity in the activities of adenylate cyclase and phosphodiesterase in synchronously dividing and stationary-phase cultures of the achlorophyllous ZC mutant of Euglena gracilis
Authors: Tong Jian , Carre Isabelle A. , Edmunds Leland N. 
Published: April 2021

ABSTRACT
Key factors in the adenosine 3’,5-cyclic monophosphate (cyclic AMP) metabolic pathway are two enzymes responsible for its generation and degradation, namely, adenylate cyclase (AC) and phosphodiesterase (PDE). In LD: 12,12 (12 h light, 12 h dark), these enzymes were found to undergo bimodal, circadian variation of activity in both dividing and nondividing cultures of the photosynthesis-deficient, achlorophyllous ZC mutant of Euglena gracilis Klebs (Z). Maximal AC activity occurred 2 h after the onset of the light interval (CT 02) and at the beginning of darkness (CT 12-14); these times corresponded to the acrophase profile for the rhythmic changes in cyclic AMP content that have been previously reported. The activity of PDE also exhibited a daily oscillation, but with an inverse phase pattern. Both the AC and PDE activity rhythms persisted after the cultures were transferred from LD: 12,12 to constant darkness. The activity of AC was activated significantly in vivo by forskolin at the trough phase (CT 20), while that of PDE was inhibited by 3-isobutyl-l-methyl-xanthine (IBMX) at its peak phase. These results indicate that the rhythms of both AC and PDE may be the main factors generating the circadian oscillations of cyclic AMP content in Euglena, which appear to be under control of an endogenous pacemaker.