bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytoplasmic accumulation of cyclin B1 in human cells: Association with a detergent-resistant compartment and with the centrosome
Authors: Bailly Eric , Pines Jonathon , Hunter Tony , Bornens Michel 
Published: April 2021

ABSTRACT
Mitotic cyclins are thought to function as key regulatory subunits of the universal M-phase-promoting p34cdc2 protein kinase. Previous immunolocalization studies have demonstrated that a fraction of p34cdc2 undergoes cell cycle-dependent accumulation at the centrosome during G2/M. In order to identify the mitotic cyclins with which this p34cdc2 fraction interacts, we carefully examined the subcellular distribution of both cyclin A and Bl in HeLa cells. We show here that part of cyclin Bl is associated with duplicating centrosomes throughout its accumulation in the cytoplasm and up to metaphase. In contrast cyclin A does not exhibit centrosomal association except at the onset of mitosis, from preprophase up to metaphase. We also present cytological and biochemical evidence that cyclin Bl is preferentially accumulated as a detergent-insoluble protein independently of the state of microtubule assembly and under experimental conditions where most of p34cdc2 is soluble. Interestingly, the electrophoretic pattern of the minor insoluble p34cdc2 fraction was previously shown to be particularly enriched in slow-migrating and presumably hyperphosphorylated isoforms, known to interact specifically with cyclin Bl during interphase. From these results we propose that the interaction of cyclin Bl with the centrosomes and with the cytoplasmic structures is a constitutive feature of the mechanism whereby a fraction of p34cdc2 is recruited and subsequently targeted to the cyclin B-dependent activation pathway.
Protein kinase C isotypes in human erythroleukemia cell proliferation and differentiation
Authors: Hocevar Barbara A. , Morrow Dwight M. , Tykocinski Mark L. , Helds Alan P. 
Published: April 2021

ABSTRACT
The human erythroleukemia (K562) cell line is induced to differentiate into megakaryocytic cells by treatment with the tumor promoter phorbol myristate acetate (PMA). PMA-induced differentiation is characterized by (1) almost complete cessation of cellular proliferation, (2) expression of the megakaryocytic cell surface marker glycoprotein Ilb/IIIa (gpHIa), (3) increased secretion of granulocyte/macrophage-colony stimulating factor (GM-CSF) and (4) increased secretion of interleukin-6 (IL-6). PMA-induced differentiation is dose-dependent with maximal activity seen at 10 nM PMA. In contrast, bryostatin (bryo), a structurally distinct protein kinase C (PKC) activator, fails to induce megakaryocytic differentiation or growth arrest at the concentrations tested (0.01-100 nM). Rather, bryo inhibits PMA-induced growth arrest and megakaryocytic differentiation in a dose-dependent fashion (full inhibition at 100 nM). The divergent biological effects of PMA and bryo correspond to the differential activation and translocation of PKC isotypes in K562 cells. PKC isotype analysis demonstrates that undifferentiated cells express both α and βII PKC but no detectable β I, γ or ∈ PKC.
Treatment of cells with either PMA or bryo leads to rapid translocation of both α and βII PKC from the cytosol to the non-nuclear particulate fraction. However, bryo also induces selective translocation of βII PKC to the nuclear membrane. Nuclear βII PKC is functionally active as evidenced by the time-dependent phosphorylation of lamin B, a previously identified nuclear PKC substrate. These data indicate that the divergent effects of PMA and bryo on erythroleukemia cell proliferation and differentiation correspond to differential activation of βII PKC at the nuclear membrane. Nuclear activation of βII PKC by bryo appears to generate a dominant, proliferative signal that overrides the PMA-induced differentiation signal. Therefore, the α and βII PKC isotypes exhibit distinct translocation and activation profiles during megakaryocytic differentiation and proliferation, indicating that they play distinct roles in these cellular processes.
Effects of cytochalasins on the initial aggregation in vitro of embryonic chick cells
Authors: Appleton J. C. , Kemp R. B. 
Published: April 2021

ABSTRACT
The initial aggregation of trypsin-dissociated cells from the skeletal muscle tissue of 9-day-old chick embryos in the presence of cytochalasins A and B was studied in order to discover the effects of these agents on contact and adhesion.
Cytochalasin B (3 μg/ml) had a negligible effect on the rate of aggregation of cells over an 8-h period, but cytochalasin A at concentrations between 3 and 20 μg/ml markedly inhibited aggregation. Both agents altered the shape and size of aggregates and caused cells at their periphery to appear more spherical.
The oxygen uptake of the treated cells was not noticeably different from that of the controls, despite the severe inhibition of isotopic carbon dioxide evolution. The effect of cytochalasin B on cell aggregation was reversible and although the cytochalasin A effect could not be abolished on return to medium free of A, the unaltered oxygen consumption was taken as an indication that permanent cellular injury did not occur.
The effect of the cytochalasins on aggregate structure was interpreted on the basis of arrested cellular motility, but the singular inhibition by cytochalasin A of the rate of aggregation must await final confirmation of its site of action.
Fine-structural changes in a lepidopteran nervous system during metamorphosis
Authors: McLaughlin Barbara J. 
Published: April 2021

ABSTRACTThe fine structure of the metamorphosing abdominal nerve cord of Manduca sexta has been studied. In fifth instar larvae, the connectives are ensheathed by a complex, thickened neural lamella. The underlying perineurium at this stage consists of 2 layers. The outer layer consists of interdigitating type I cells which are attached to the overlying neural lamella by hemi-desmosomes, and to each other by occasional gap and tight junctions which persist throughout development. They are attached by desmosomes to a thin underlying type II cell layer, which is joined by gap and tight junctions and which has desmosomal attachments with the underlying glial membranes. The larval axons are surrounded by multiple glial wrappings containing bundles of microtubules. During the first week after larval-pupal ecdysis, the neural lamella degenerates and is phagocytosed by invading haemocytes. The underlying perineurial I cells gradually become hypertrophied and vacuolated. At the same time the type II layer, which does not increase in size, appears to be composed of either one or two cells which form a continuous ‘bracelet’ around each connective. The cellular bracelet is joined at one or two places by extensive gap, tight and septate junctions, and gap junctions are also seen along its perineurial I and glial borders. The underlying axons are embedded in vast amounts of glial cytoplasm containing relatively few microtubules. During the second week after larval-pupal ecdysis, the neural lamella is reformed and the perineurium flattens again. Type I and II cell junctions remain as described in earlier stages. Before adult emergence, the axons are again wrapped by glial cells rich in microtubules.
Variation in rdna redundancy level and nucleolar organizer length in normal and variant lines of the mexican axolotl
Authors: Sinclair J. H. , Carroll Carole R. , Humphrey R. R. 
Published: April 2021

ABSTRACT
The level of redundancy of ribosomal genes, and the relationship of this level to nucleolar formation at different stages of embryonic development, have been examined in the Mexican axolotl, Ambystoma mexicanum. Individuals from 4 inbred stocks were examined, as well as descendants from 2 nucleolar variants which, in the heterozygous condition, are distinguished by exceptionally small nucleoli. Ribosomal RNA-DNA hybridization assays show that one of the 4 wild type lines has only about one-third as much ribosomal DNA (rDNA) as the other three. One of the nucleolar variants has the same level of rDNA as the larger wild-type level; the other variant has the same amount as the smaller ribosomal genome line. Both original nucleolar variants arose as F1, progeny of crosses between a large rDNA genome line and the small genome line. Cytological examination of pregastrula stage embryos from wild type and nucleolar variant lines show that the lengths of the nucleolar organizer regions (NOR) and the sizes of nucleoli formed, are directly correlated with the amount of rDNA present at the nucleolar locus. During gastrulation of the nucleolar variants, however, a transition appears to take place and the amount of rDNA ceases to be the determining factor in nucleolar size. After late gastrula, heterozygous progeny resulting from crosses of either large rDNA genome or small rDNA genome wild type individuals with either nucleolar variant line, have a small and a large nucleolus. The factor or factors associated with this apparent lack of competitive ability of the variant NOR, when opposed to a normal NOR, are unknown. It might be suggested that since the chromosomal alterations which produced the nucleolar variants in both cases eliminated the gene determining the dark colour pattern, they could at the same time have eliminated other genetic material.
The properties and subcellular localization of acid phosphatases in the colourless alga, Polytomella caeca
Authors: Cooper Rosemary A. , Bowen I. D. , Lloyd D. 
Published: April 2021

ABSTRACT
The acid p-nitrophenyl phosphatase of homogenates of Polytomella caeca is a latent acid hydrolase, which is partially inhibited by NaF. Its distribution profile in density gradients (which is similar to that of naphthyl AS-TR phosphatase) suggests that this enzyme is partially lysosomal in location. Cytochemical evidence for the localization of acid phosphatases in fine subcellular structures is presented. Naphthyl AS-TR phosphatase is localized in vacuoles, points of focal degradation, Golgi bodies and dispersed throughout the cytosol. β-Glycero- phosphatase is confined to large vacuoles and the cytosol. The nature of acid phosphatase- containing organelles in P. caeca is discussed in view of the inability to detect eleven other latent acid hydrolases in cell-free homogenates.
An electron-microscope study of the intranucleolar chromatin in root meristematic cells ofAllium cepa
Authors: Chouinard L. A. 
Published: April 2021

ABSTRACTThe various states of condensation and configuration of the chromatin material, contained inside the lacunar regions of the interphase nucleolus in Allium cepa, have been investigated by means of conventional electron-microscope techniques. The observations reveal that in a number of lacunar profiles, the chromatin material in question appears in an extended state only; in other lacunar profiles of the same or different nucleoli, the chromatin material is present both in an extended and a condensed condition. Moreover, in some lacunar profiles, a single mass of chromatin in a condensed state is observed; in others, several discrete and often seemingly interconnected masses of condensed chromatin are visualized.An attempt is made to interpret these morphological findings in the light of current knowledge concerning the structural relationship of the nucleolar organizing segment of the nucleolar chromosome with the interphase nucleolus in plant cells. The relevant observational evidence would be consistent with the view that the chromatin-containing lacunar regions of the interphase nucleolus in Allium cepa correspond, in fact, to cross or oblique sections of a meandering channel through which the nucleolar organizing segment of the nucleolar chromosome passes. Assuming the applicability to intranucleolar chromatin of the general concept of condensed-inactive versus extended-active chromatin, it is hypothesized that the various states of condensation of intralacunar chromatin merely reflect variations in the functional activity of the nucleolar organizing segment during the interphase cell cycle in the species investigated. With regard to variations in the configurational state of the intralacunar condensed chromatin, it is postulated that they are the cytological expression of the gradual process of coiling or folding upon itself of the nucleolar organizing segment during late interphase and in preparation for the next mitosis.
Modification of sporulation in yeast strains with two-spored asci (Saccharomyces, ascomycetes)
Authors: Moens P. B. 
Published: April 2021

ABSTRACT
Electron-microscope observations indicate that the single nuclear division of sporulating yeasts which form 2-spored asci resembles, in several aspects, the nuclear behaviour during sporulation of the more common 4-spored yeasts. Specifically the parental nucleolus remains behind in the ascus cytoplasm, a characteristic nucleolus-associatcd spherical structure is formed, and the nucleus divides by budding rather than by elongation and medial constriction.
Quantitative evaluation of cell orientation in culture
Authors: Margolis L. B. , Samoilov V. I. , Vasiliev Ju. M. , Gelfand I. M. 
Published: April 2021

ABSTRACT
A quantitative method to assess mutual orientation of cells in cultures on a substrate includes the following operations: (1) the cellular groups to be evaluated are chosen; (2) position of the long axis for each nucleus of the group is determined ; (3) the axis OX is arbitrary chosen for every group and the angles αi between the long axis of every nucleus i and the axis OX are measured. Every nucleus i corresponds to a vector of unit length ei with the angle 2α.
D, the mean of the vectors ei for every cell group is calculated. This value of D is compared with a set of values of D computed according to a model of mutual orientation studied in a simulation experiment. In this model the group of n vectors consists of a fraction of Kn parallel vectors (o &lt; K &lt; 1) and of (1 —K)n randomly oriented vectors. K corresponding to the computed D which is equal to the experimental value of D is considered as an index of orientation for the group. Contact orientation with respect to the relief of the substrate may be evaluated as a root mean square deviation σ0 of the angles between the long axes of cell nuclei and the direction of relief. Examples of the measurements of K and σ0 in cell cultures are given.
Reversion in expression of hypoxanthine-guanine phosphoribosyl transferase following cell hybridization
Authors: Bakay B. , Nyhan W. L. , Croce C. M. , Koprowski H. 
Published: April 2021

ABSTRACT
Hybridization of mutant cell lines deficient in hypoxanthine-guanine phosphoribosyl transferase (HGPRT; E.C.: 2.4.2.8) from a variety of established rodent sources with HGPRT+ human cells yielded progeny cells which grew in selective medium containing hypoxanthine, aminopterin and thymidine (HAT). The same result was obtained when the human cell used was an HGPRT- transformed line derived from a patient with the Lesch-Nyhan syndrome. Electrophoretic analysis indicated that all HAT-resistant progeny clones contained an active HGPRT enzyme which was indistinguishable from the wild type enzyme of the corresponding normal rodent cells. In contrast, no HAT-resistant cells have been obtained when the same HGPRT- rodent cells were subjected to fusion processes in the absence of human cells or when they were fused with similarly derived HGPRT- mutant cells of other rodents. Reversion in expression of the rodent gene for HGPRT was detected in clones which retained one or more human chromosomes and in clones which contained no detectable human chromosomal material. The observed re-expression of rodent HGPRT in HAT-resistant clones suggests that HGPRT+ as well as HGPRT- human cells contributed a factor which determined the expression of respective rodent structural genes for HGPRT. In contrast, HGPRT- rodent cells were unable to induce the synthesis of normal HGPRT in the cells derived from the patient with the Lesch-Nyhan syndrome.
Ultrastructural changes in chloroplasts resulting from fluctuations in nacl concentration: freeze-fracture of thylakoid membranes in Dunaliella salina
Authors: Pfeifhofer A. O. , Belton J. C. 
Published: April 2021

ABSTRACT
The structure of chloroplasts isolated from Dunaliella salina has been studied with respect to changing concentrations of sodium chloride in the culture medium. Freeze-fracture replicas and thin sections of intact chloroplasts do not exhibit any noticeable changes in structure at concentrations ranging between 3·5 and 25 % NaCl. Chloroplasts isolated from algal cells that have been acclimatized to the higher salt concentration show a change in the thylakoid membranes. The thylakoid membranes appear compressed over a major portion of the membrane surface, with only the end of the thylakoid membranes unappressed. The number of particles per unit area on the B face is also altered by the salt concentration. The chloroplasts acclimatized to 25 % NaCl have about 3 times the number of particles per unit area on a B face of endmembranes as on a comparable face of thylakoid membranes acclimatized to low (3·5 % NaCl) salt concentration. These morphological changes can be reversed if the chloroplasts acclimatized to high or low salt concentrations are returned to a medium of different salt concentration prior to freeze-fracturing.
Characterization of an sv40-transformed 3t3 cell line expressing an unusual phenotype
Authors: Thompson J. E. , Elligsen J. D. , Frey H. E. 
Published: April 2021

ABSTRACT
A transformed variant derived as a clone from normal 3T3 cells infected with simian virus 40 (SV40) has been found to possess a phenotype intermediate between that of normal cells and that characteristic of the transformed state, yet cells of the variant still test positively for the SV40-specific nuclear T-antigen. The variant exercises growth control, although not as stringently as do normal cells. Its cell size more closely resembles that of normal cells than of transformed cells. The variant also exhibits levels of spontaneous agglutination that are in line with those characteristic of the normal cells from which it was derived, and far higher than corresponding values for cells exhibiting the fully transformed phenotype. Plasma membranes of variant cells more closely resemble those of transformed cells than of normal cells as estimated by polyacrylamide gel electrophoresis. Perhaps the most distinguishing characteristic of the transformed variant is its complete immunity to agglutination by concanavalin A (Con A), even at concentrations of the lectin as high as 500 μg/ml. Moreover, trypsinization does not render variant cells as agglutinable in the presence of Con A as are untreated fully transformed cells. By contrast the variant displays a low tolerance to Con A toxicity, as monitored by ability to grow after treatment with the lectin, and on this count resembles transformed cells. Moreover a survey of several normal cell lines has revealed that even they do not consistently show resistance to Con A toxicity. These observations indicate that Con A-mediated agglutination and inability to grow after treatment with Con A are quite independent and do not bear a cause and effect relationship.
Mode of action of amphotericin b on chick embryo fibroblasts and on mouse ehrlich tumour cells: a cytological and cytochemical analysis
Authors: Paermentier F. De , Bassleer R. , Lepoint A. , Desaive Cl. , Goessens G. , Lhoest-Gauthier M. -P. 
Published: April 2021

ABSTRACT
Chick embryo fibroblasts cultivated in vitro and Ehrlich ascites tumour cells (in vivo or in vitro) have been treated with amphotericin B. Cell multiplication is strongly inhibited. Large clear zones appear in the fibroblast nucleoli (phase-contrast and electron-microscope observations). Many treated fibroblasts and tumour cells have a high DNA content (pre-mitotic or polyploid level; measurements by cytophotometry). However, the RNA content (cytophotometry) and the total protein content (cytophotometry and micro-interferometry) are relatively low in the tumour cells. As shown by autoradiography, DNA synthesis is active but RNA synthesis and, in some cases, protein synthesis are inhibited. Due to this unbalanced growth, the cells cannot divide.
Electron-microscope observations of mitosis and cytokinesis in multinucleate protoplasts of soybean
Authors: Fowke L. C. , Bech-Hansen C. W. , Gamborg O. L. , Constabel F. 
Published: April 2021

ABSTRACT
Multinucleate soybean protoplasts produced by spontaneous fusion during enzyme digestion of the cell wall initiated cell division after approximately 40 h in culture. The structure of these protoplasts during mitosis and cytokinesis was studied with both light and electron microscopes. Most nuclei did not fuse but divided synchronously. Interphase nuclei were commonly connected by short narrow nuclear bridges. At prophase and metaphase the nuclei appeared typical of those in most higher plants; technical difficulties prevented an adequate examination of protoplasts at anaphase. Telophase was characterized by cytokinesis involving phragmoplast and cell plate formation; however, complete partitioning of the cytoplasm by cell plates was not observed. Numerous coated vesicles were present near to or continuous with the cell plate and plasmalemma. The presence of a few dividing protoplasts with at least double the normal chromosome number suggests that some nuclear fusion occurred prior to mitosis. Very little cell wall material was detected at the margin of the dividing protoplasts.
A new occludens-like junction linking endothelial cells of small capillaries (probably venules) of rat jejunum
Authors: Staehelin L. A. 
Published: April 2021

ABSTRACT
Freeze-cleave replicas of small capillaries of rat jejunum have revealed the presence of a new type of junction linking endothelial cells. This new junction resembles tight junctions (zonulae occludentes) in that the adjacent plasma membranes are held closely together along lines of attachment organized in the form of a loose, but frequently discontinuous network. In contrast to tight junctions, the A-face ridges possess a very low profile, and only at low shadowing angles can a repeating, particulate substructure occasionally be resolved. The shallow B-face furrows lack any particulate components. Images of cross-fractured focal points of attachment suggest that the external leaflets of adjacent membranes are closely apposed but not actually fused, as is the case with zonulae occludentes. It appears that this new type of endothelial junction is characteristic of small venules. Thus we propose that it be termed small venule endothelial junction.