bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell cycle-dependent changes in non-membranous nuclear ghosts from HeLa cells
Authors: Riley D. E. , Keller J. M. 
Published: April 2021

ABSTRACT
Non-membranous nuclear ghosts are isolated from the nuclei of cultured HeLa cells after successive treatments with detergents and high ionic strength (0·5 M MgCl2) buffers. These ghosts have been shown by Keller & Riley to consist of a network consisting of annuli (90 nm in diameter), rod-like structures and dense bodies interconnected by DNase-sensitive strands. In nuclear ghosts purified from HeLa cells synchronized by a double thymidine block technique, the arrangement of these components exhibits dramatic cell cycle-dependent organizational differences. During G1 the small dense bodies (or aggregates) are widely dispersed and appear to be associated with the surface of the ghost. In S-phase, only a single (large) dense body is present and it is located in the centre of the ghost. The appearance of nuclear ghosts from cells in G2 is intermediate between those observed in G1 and S. These cell cycle-dependent organizational differences in the ultrastructure of nuclear ghosts are paralleled by differences in their susceptibility in suspension to DNase I. The G1 -phase ghost is markedly sensitive, whereas the S-phase ghost has both a sensitive component, the network consisting of annuli and rod-like structures connected by thin strands, and a resistant component, the single (large) dense aggregate. The unique morphology of ghosts at a particular phase of the cell cycle and the similarity of the polypeptide species present in ghosts isolated at these 3 phases of the cell cycle lead us to conclude that the various organizational patterns described are alternative cell cycle-dependent configurations of what is fundamentally the same macromolecular complex. A model is presented in which internal nuclear skeletal components and the non-membranous nuclear envelope are considered to be dynamic interacting components of interphase nuclei. This model provides a physiological rationale for nuclear envelope expansion capability which has been observed under experimental conditions by many investigators.
Characterization of columnar absorptive epithelial cells isolated from rat jejunum
Authors: Towler Christopher M. , Pugh-Humphreys Geoffrey P. , Porteous John W. 
Published: April 2021

ABSTRACT
The origin and yield of cells isolated from rat jejunum have been assessed; 80—90% of the mature columnar absorptive cells but none of the Paneth, endocrine or regenerating crypt cells were recovered by the methods described. The structural integrity of the isolated cells was tested by phase contrast-, Nomarski interference- and fluorescence light-microscopy; and also by transmission electron microscopy; the isolated cells appeared structurally intact by all microscopic criteria applied. The isolated cells were judged to be functionally intact because they satisfied a number of tests designed to answer three logically related questions, namely: was the cell-surface membrane intact; were the cells able to accumulate selected solutes against a concentration gradient from the exterior medium; and were the cells able to perform biochemical functions which depended upon the integrated activities of several subcellular structures? The isolated cells did retain and accumulate selected solutes, respired at a steady rate on endogenous substrates, showed enhanced respiration on exogenous glucose and glutamine, maintained favourable intracellular proportions of adenine nucleotides (ATP: ADP: AMP), and synthesized cell protein from extracellular amino acids in proportion to the time of incubation. The isolated cells accounted for 80% of the lactic acid produced by intact rat jejunum under similar conditions of incubation.
The viability of the anucleate cytoplasm of Amoeba Proteus
Authors: Ord M. J. 
Published: April 2021

ABSTRACT
The viability of Amoeba proteus cytoplasm was tested at 1-to 2-day intervals throughout the 14 days following enucleation. Viability was demonstrated by renucleating the anucleate cytoplasms and observing whether the resultant amoebae could resume normal activities such as moving, feeding and dividing. Four lines of A. proteus were studied, approximately 200 transfers being made on amoebae of each line. The introduction of a nucleus into anucleate cytoplasm initiated a temporary reactivation followed by a period of relative inactivity before either death by cytolysis or permanent reactivation with feeding, growth and division. Though approximately 70 % of anucleate cytoplasms were still viable 6 days after enucleation, temporary reactivation disappeared about this time and the period of relative inactivity which generally followed it increased in duration from a few days to several weeks. Few amoebae which were able to divide failed to form clones. Anucleate cytoplasms of wheat-cultured amoebae remained viable for longer periods than anucleate cytoplasms of tetrahymena-fed amoebae.
Labelling of the cell surface of the collective amoeba Dictyostelium Discoideum with fluorescent antiserum
Authors: Shaffer B. M. 
Published: April 2021

ABSTRACT
The surface of a separate Dictyostelium discoideum cell exposed to fluorescent antiserum is initially uniformly stained. When the cell moves, labelled material is left on the glass over the area occupied by the cell while in the antiserum. The surface of new pseudopods is fluorescent. The bulk of the label soon accumulates on the rear of the cell and is towed along behind it. The rest of the surface may remain faintly fluorescent for long periods, but this residual label is immediately left behind if the cell advances while strongly compressed between agar and glass. This evidence does not clearly decide between the hypotheses of a permanent, advancing, lateral cell surface and a temporary, stationary one. The fact that the lateral surface of an advancing cell does not drag forward viscous medium in contact with it does not favour the former hypothesis.
Problems of electron stereoscopy of biological tissue
Authors: Gray E. G. , Willis R. A. 
Published: April 2021

ABSTRACT
A detailed study of stereoscopy of tissue sections with the transmission electron microscope has been carried out using different tilt angles and staining techniques, aided with models. Pictures with tilt angle difference of 20° or more can be fused to give pairs of micrographs showing stereodepth. Cytoplasmic filaments, glycogen and ribosomal granules give good stereodepth. Oblique membranes, especially when stained with lead or phosphotungstic acid, give good depth in stereo-pairs but membranes running more vertically in the section do not. A theory, based on the ‘transparency factor ‘that is a feature of transmission electron microscopy, is given to account for this discrepancy. A learning process is involved in achieving depth perception when viewing stereo-pairs of electron micrographs of tissue sections. Complex structures often cannot be perceived in depth even after prolonged scrutiny through the stereoscope. Where structures overlap in the thickness of the section, they can be ‘separated out’ with stereoscopy and in this way clarified, for depending on which micrograph of a stereo-pair is presented to which eye, a structure can be made to appear either in the front or the back of a section. In general, problems of depth perception in stereo-pairs of micrographs obtained with transmission electron microscopy arise because with our normal everyday vision using reflected light, we look at things, whereas with the electron microscope using a transmission electron beam we look through things.
Electron microscopic observations on the basal lamina of chick limb buds after trypsin and edta treatment
Authors: Goel S. C. , Jurand A. 
Published: April 2021

ABSTRACT
Chick hind-limb buds were treated first with calcium- and magnesium-free balanced salt solution and then with either trypsin or EDTA. Treatment with these chemicals, and the subsequent separation of the ectodermal covering from the mesoderm, produces two different results as regards the basal lamina. In the case of trypsin, the lamina stays with the ectoderm but shows signs of probable tryptic digestion. After EDTA treatment the lamina stays with the mesoderm and becomes very loose and swollen. This loosening allows the structure of the otherwise compact lamina to be resolved so that banded collagen fibrils are seen participating in its substance. The above observations are discussed in relation to the mode of action of the two chemicals. The physiological role and the origin of the basal lamina, as well as the possible implications of the present findings to the question of limb development and morphogenesis, are also discussed. A note has also been made regarding the various terms used to describe the epitheliomesenchymal junction layers.
Interaction between normal and transformed bovine fibroblasts in culture: II cells transformed by polyoma virus
Authors: Pontén J. , Macintyre Elizabeth H. 
Published: April 2021

ABSTRACT
Bovine fibroblasts transformed by polyoma virus have been cocultivated with syngeneic or allogeneic normal cells. The growth of the transformed cells was inhibited by the presence of normal cells. The strongest depression was obtained when a dense stationary layer of normal fibroblasts was challenged by polyoma cells. The inhibition was least pronounced if normal and transformed cells were simultaneously seeded.
Polyoma-transformed cells were identified by radioautography after incorporation of tritiated thymidine. After 96 h of contact with stationary normal cells the number of grains per nucleus and the number of labelled nuclei had not changed indicating strong depression of DNA synthesis. A deficient attachment or premature detachment of polyoma cells could not account for the observed failure of growth in the normal/polyoma mixed cultures.
The maintenance of kappa during macronuclear reorganization in Paramecium tetraurelia
Authors: Koizumi S. , Kobayashi S. 
Published: April 2021

ABSTRACT
Kappa particles were injected into stock-51 sensitives (KK) of Paramecium tetraurelia to investigate the maintenance of kappa by gene K during macronuclear reorganization. Injection into exconjugants and autogamous cells followed by macronuclear regeneration, induced by microsurgical removal of macronuclear Anlagen, resulted in maintenance of kappa particles by a considerable proportion of the clones descended from the recipient paramecia. Injection into animals that underwent normal reorganization however usually failed to yield particle-maintaining paramecia.
Transfer of human chromosomes via human minisegregant cells into mouse cells and the quantitation of the expression of hypoxanthine phosphoribosyltransferase in the hybrids
Authors: Tourian Ara , Johnson Robert T. , Burg Kornel , Nicolson Susan W. , Sperling Karl 
Published: April 2021

ABSTRACT
The behaviour of human cells arrested in mitosis can be severely perturbed so as to generate numerous small minisegregants containing very few chromosomes. These cells can be separated according to size and DNA content and fused with intact cells. In this paper we describe the production and some properties of proliferating cell hybrids generated by fusion of human minisegregant cells derived from a HeLa strain with mouse Ag cells deficient in hypoxanthine phosphoribosyltransferase (HPRT, EC 2.4.2.8). The hybrids were shown to contain up to 10 human chromosomes including a single X. Independently derived hybrid clones were quantitatively chracterized and compared with the parental phenotypes with respect to HPRT. Human isozymes of each of the 3 enzymes HPRT, glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and phosphoglycerate kinase (EC 2.7.2.3) were found. Tests to evaluate both structure and function of HPRT were utilized. The specific activity of HPRT of more than 10 hybrids tested was approximately 10% that of the HeLa parent. Structural characterization of HPRT from hybrid cells as evidenced by heat inactivation and electrophoretic mobility results in a ‘humanlike’ phenotype. Functional characterization of parental HPRT results in kinetic constants for cofactor and substrate which do not permit distinction of human and of human and mouse enzymes; HPRT from the minisegregant hybrids had normal kinetic constants. The reduced specific activity of HPRT in the hybrids is discussed in terms of the inability of the mouse environment to regulate the full expression of the human structural gene.
Ultrastructural localization of calcium in unfertilized sea-urchin eggs
Authors: Cardasis Constance A. , Schuel Herbert , Herman Lawrence 
Published: April 2021

ABSTRACT
The pyroantimonate technique was employed to identify the binding sites for calcium in unfertilized Arbacia punctulata and Strongylocentrotus purpuratus eggs. Since antimony is non-specific and binds with a variety of cations, the identification of calcium was established by specific chelation with ethyleneglycol tetra-acetic acid (EGTA) and X-ray microprobe analysis. Antimony deposits were observed on the egg’s membranes, i.e. plasma, cortical (secretory) granule, pigment granule, smooth-surfaced vesicle, and yolk platelet. Deposits were also observed in the mitochondria, rod-containing vesicles, and the vitelline layer. Two types of yolk platelets were observed: a more numerous electron-opaque platelet which had precipitate along its limiting membrane as well as within the stored-matrix substance, and a less-frequently seen platelet with lower electron opacity which contained precipitate only along its limiting membrane. Deposits were reduced at all sites following exposure of eggs to EGTA either prior to or after osmium-antimonate fixation. Initial fixation in glutaraldehyde followed by postfixation in osmium-antimonate solutions provided better preservation of structure but less precipitation than direct fixation in osmium-antimonate. The organelle sites of calcium binding identified within unfertilized sea-urchin eggs may participate in stimulus-secretion coupling (exocytosis of the cortical granules) and the activation of embryogenesis at fertilization.
Studies of the endoplasmic reticulum and plasma membrane-bound ribosomes in erythropoietic cells
Authors: Grasso Joseph A. , Sullivan Albert L. , Chan Sai-Chung 
Published: April 2021

ABSTRACT
Erythropoietic cells of 5 species, including man, contain endoplasmic reticulum present as individual cistemae or tubules scattered throughout the cytoplasm of all stages except mature RBCs. The endoplasmic reticulum is mainly agranular but occurs frequently as a variant of granular ER which is characterized by an asymmetrical and irregular distribution of ribosomes along one cytoplasmic face. In most cells, the endoplasmic reticulum occurs in close proximity to mitochondria or the plasma membrane, suggesting that the organelle may be involved in functions related to these structures, e.g. haem biosynthesis. Endoplasmic reticulum is more abundant in early than in late erythroid cells. Its exact role in RBC development is unclear.
Since endoplasmic reticulum could account for ‘plasma membrane-bound ribosomes’ reported in lysed reticulocytes, studies were performed which ruled out this possibility and which suggested that such ribosomes were an artifact of the lysing conditions. Hypotonic lysis in less than 20 vol. of magnesium-containing buffers yielded ghosts variably contaminated by ribosomes and other structures. Lysis of reticulocytes in 20—30 vol. of magnesium-free buffer or homogenization of whole cells or crude membrane fractions in hypotonic buffer removed virtually all contaminating ribosomes from the purified membrane fraction.
Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos: iv. biochemical and autoradiographic observations on fucose-, glucose-, and mannose-labelled materials
Authors: Johnson Kurt E. 
Published: April 2021

ABSTRACT
Normal Rana pipiens gastrulae show more incorporation of isotopically labelled fucose, glucose, and mannose into TCA-insoluble materials than blastulae. Interspecific hybrid embryos which undergo developmental arrest at the onset of gastrulation often synthesize reduced amounts of fucose-, glucose- and mannose-labelled materials. These materials are high-molecular weight and are degraded by Pronase into fragments which are included in Sepharose CL-4B but excluded from Sephadex G-50. Labelled materials contain label predominantly in fucose and galactose with little label in glucose or mannose. Labelled materials migrate slowly on cellulose acetate, bind to DEAE-cellulose and elute at low ionic strength and are precipitated by cetyl pyridinium chloride (CPC) without the addition of carrier compounds.
Pulse-chase labelling experiments and light- and electron-microscopic autoradiography were used to examine the site of synthesis, mode of transport, and sites of deposition of fucose-, glucose- and mannose-labelled materials in different developmental stages of normal developing Rana pipiens embryos and interspecific hybrid embryos formed by fertilizing the eggs of R. pipiens with the sperm of R. catesbeiana. In both normal and hybrid embryos, after a 15–30-min pulse, grains are closely associated with juxtanuclear and cytoplasmic collections of membranebound vesicles which resemble the Golgi apparatus. In normal embryos following a 15–30-min pulse and a 60-min chase, grains are largely cleared from the cytoplasmic vesicles and deposited in the extracellular spaces or along cell surfaces. In contrast, arrested hybrid embryos given a 15–30-min pulse and a 6o-min chase show a marked accumulation of grains over cytoplasmic structures such as the Golgi apparatus and vesicular elements in the cell cortex. Certain interesting features of regional variation in synthetic activity in developing normal embryos are also described.
Development of intercellular junctions in the pulmonary epithelium of the foetal lamb
Authors: Schneeberger E. E. , Walters D. V. , Olver R. E. 
Published: April 2021

ABSTRACT
The integrity of epithelial tight junctions in foetal mammalian lungs is essential to maintain the unique ionic composition of lung liquid, and to prevent leakage of serum proteins into peripheral air spaces. In the present study the development of intercellular junctions of the lining epithelium of foetal lamb lungs during gestation was examined by light and electron microscopy. Both thin sections and freeze-fracture replicas were examined by electron microscopy. By 39 days of gestation, epithelial tight junctions consist of a minimum of 3·1 ± 1·6 (S.D.) and a maximum of 5·8 ± 2·0 discontinuous rows of particles and short segments of strands on P face ridges and in complementary E face grooves, while from 58 to 76 days they are composed of a network of 4·3 ± 1·6 to 7·7 ±1·9 focally interrupted P face strands. Complementary replicas show that many of the discontinuities on the P face are due to separation of junctional particles on to the E face during fracturing, and not to an absence of junctional particles. From 76 days to term, epithelial tight junctions (exclusive of upper airway epithelium which was not examined) resemble those of adult lungs, and consist of a continuous network of 4·5 ± 2·0 to 7·5 ± 2·5 P face strands and complementary particle-free grooves. Permeability measurements, published elsewhere, indicate that the epithelium is functionally ‘tight’ from 69 days onwards. Tight junctions in peripheral air-space epithelium, therefore, are structurally continuous and functionally ‘tight’ early in foetal lung development, and form seals at one end of long, narrow intercellular spaces; these features may be important for coupled ion and water transport. When the bounding epithelial cells become flattened, these narrow intercellular spaces remain intact as a result of complex interdigitations of adjacent cell membranes. Desmosomes were present throughout gestation near the abluminal side of the tight junctions and occasionally near the base of the intercellular space. These junctions may serve to connect cells to each other at a time when tight junctions may be mechanically weak. In addition, gap junctions are associated with tight junctions from the glandular through the canalicular stages of lung development. They disappear by 120 days when the epithelial cells are differentiated.
Selecting somatic cell hybrids with hat media and nystatin methyl ester
Authors: Fisher Paul B. , Sisskin Enid E. , Goldstein Neil I. 
Published: April 2021

ABSTRACT
The structurally modified polyene antibiotic nystatin methyl ester (NME) has been utilized as a half-selection agent for isolating interspecific mouse-Syrian hamster hybrids. By using HAT media supplemented with NME we have isolated hybrid clones from polyethylene glycol-fused cultures of biochemically defective mouse (A9 or B82) and genetically normal Syrian hamster (BHK/C13) cells. Unfused parental cells were killed in HAT-NME media as a result of their genetic defect, absence of hypoxanthine guanine-phosphoribosyl transferase-HGPRT”(A9) or thymidine kinase— TK”(B82), or innate sensitivity to NME (BHK/C13). In contrast, hybrid cells proliferated and clones were isolated after 3 weeks growth in HAT-NME media, indicating that genetic complementation had occurred and polyene resistance was expressed as a dominant phenotypic property in the hybrids. The presently described technique is efficient in eliminating unfused parental cells and should prove useful in isolating other types of hybrids formed between genetically defective and normal parental cells.
Fertilization in brown algae: I. sem and other observations on Fucus serratus
Authors: Callow Maureen E. , Evans L. V. , Bolwell G. P. , Callow J. A. 
Published: April 2021

ABSTRACT
The cell wall secreted immediately following sperm entry into an egg can be visualized by the fluorescent dye Calcofluor white. Cell wall secretion precedes nuclear fusion by 10–20 min. SEM observations of the surface of unfertilized and fertilized eggs and sperm attachment to eggs are described. These results are discussed in relation to fertilization in sea urchins and the biochemical phenomena associated with egg-sperm recognition in Fucus.
The packaging unit: a basic structural feature for the condensation of late cricket spermatid nuclei
Authors: Kierszenbaum A. L. , Tres Laura L. 
Published: April 2021

ABSTRACT
The alignment, folding and packaging of cricket chromatin was examined during late spermiogenesis by an electron-microscope study of nuclei dispersed by air–liquid surface tension forces after detergent treatment. Late developing spermatid genomes arrange themselves in multiple packaging units in a stepwise process which includes: (1) a loss of the beaded repeating structure of chromatin as nucleoprotein fibres become smooth and gradually assume a uniform diameter; (2) a side-by-side alignment of structurally modified chromatin fibres; and (3) a regular folding into packaging units. Alignment and folding of chromatin fibres are presumably mediated by intermolecular bonds easily disrupted by spreading forces. In very late spermatids, interfibre binding forces are difficult to override by spreading alone, indicating a stronger cross-linking of increasingly coalescent packaging units. ‘Unit to unit’ coalescence stabilizes the nuclear structure, first limiting and afterwards denying penetration of phosphotungstic acid, as displayed in thin sections of extremely condensed cricket spermatid nuclei. Binding of phosphotungstate by nuclear basic proteins can be facilitated by limited protein solubilization after disulphide reduction of unfixed cricket testes with sodium dodecyl sulphate and dithiothreitol. Results of this study permit the proposal of model experiments useful for clarifying the organization of highly condensed spermatid genomes and for evaluating the structure of genome segments in systems wherein changes of chromatin-associated protein occur.