bluuebunny/crossref_metadata_2025_split huggingface dataset:
Circus movements and blebbing locomotion in dissociated embryonic cells of an amphibian, Xenopus laevis
Authors: Johnson Kurt E. 
Published: April 2021

ABSTRACT
Circus movements, which involve the circumferential rotation of a hyaline cytoplasmic protrusion, occur in cells obtained by EDTA dissociation of gastrula-stage Xenopus laevis embryos. Only a few dissociated blastula-stage cells show circus movements, more early gastrula-stage cells show them, and nearly all late gastrula-stage cells show them. Circus movements cease in cells prior to mitosis and begin again in daughter cells after mitosis is completed. In early gastrulae, only 17% of prospective endodermal cells show circus movements while 79% of prospective mesodern, archenteric roof, and posterior neural ectoderm do so. Isolated cells as well as groups of cells in vitro are often propelled by circus movements. There is an obvious antagonism between cell contact and circus movements. The morphogenetic significance of circus movements and biebbing locomotion is discussed.
Cytoplasmic streaming in Chara corallina studied by laser light scattering
Authors: Sattelle D. B. , Buchan P. B. 
Published: April 2021

ABSTRACT
An apparatus is described by means of which the power versus frequency spectrum of the photomultiplier current can be obtained for laser light scattered by streaming cytoplasm in the algal cell Chara corallina. A Doppler peak is noted in the spectrum which is abolished when cytoplasmic streaming is arrested by electrical stimulation. For 5 cells of Chara, this simple laser-Doppler velocimeter gave streaming velocities (46·7 μm s-1, S.D. ±4·8 at 20 °C) similar to those obtained for the same cells using the light microscope (44·3 μm s-1, S.D. ± 5·3 at 20 °C). A narrow distribution of streaming velocities is indicated. The technique described proUdes a rapid, quantitative assay of the in vivo rheological properties of cytoplasm.
The structure of nuclear ribonucleoprotein of amphibian oocytes
Authors: Malcolm David B. , Sommerville John 
Published: April 2021

ABSTRACT
Nuclear RNP from Trituras oocytes is organized as strings of beads which can be converted into 20-nm-diameter monoparticles with mild RNase treatment or into 5-nm-thick linear fibrils with low salt treatment. The protein component comprises a heterogeneous size-range of polypeptides which differ from the polypeptides of the other nucleoproteins of oocytes. The RNA is of high molecular weight, sediments mostly in excess of 50 s, and is capable of assuming considerable secondary structure. Duplex regions in the form of hairpin loops are present and may serve as focal points in the condensation of the RNP transcript fibres to generate the periodic beaded structure. The structure of the beads may be maintained by means of proteinprotein interaction since at salt concentrations between 1 and 2 M NaCl all of the proteins are released in a cooperative manner as various sized aggregates which sediment at 15–30 s. There are no specific proteins obviously peculiar to either the beaded or the fibrillar RNP configuration. The various properties of nuclear RNP are compared with those of chromatin.
Infrared laser damage to ciliary motion in Phragma topoma
Authors: Rikmenspoel Robert , Orris Sandra E. , O’day Peter 
Published: April 2021

ABSTRACT
A glass neodymium laser was modified to make it possible to produce small lesions of 1–2 μm size with a quantitatively known amount of energy. The 1·06-μm radiation of this laser is sufficiently absorbed by water to work without the additions of dyes. Ciliary arrest in Phrag- matopoma gills was produced by an amount of energy, sufficient to cause a rise in temperature of 150 °C in an area of 2 μm3. At these low doses the effect was fully reversible. With higher doses of laser energy the cilia stopped permanently, probably because of structural damage of the irradiated cells.
Nuclear DNA content and chromosome numbers throughout the life cycle of the colonia strain of the myxomycete, Physarum polycephalum
Authors: Mohberg Joyce 
Published: April 2021

ABSTRACT
Nuclear DNA content and ploidy have been determined at different stages of the life cycle of the Colonia strain of the myxomycete Physarum polycephalum. Analyses at the plasmodial stage showed that (a) Burton and Feulgen DNA analyses agreed within 15% with strains which ranged from 0·6 to 3·6 pg of DNA per nucleus; (b) S-phase in Colonia is during the early part of interphase as in the Wisconsin strain; (c) in heterothallic and heterothallic x Colonia crossed strains there are 1·0–1·2 pg of DNA and 70 chromosomes per nucleus and in Colonia 0·6 pg of DNA and 40 chromosomes.
Germinating spores of all strains contained one population of cells with about 0·5 pg of DNA and 40 chromosomes and another of larger cells with up to 2·5 pg of DNA and 200 chromosomes. The polyploid nuclei comprised 2–20 % of the total in heterothallic strains, 2–65 % in heterothallic x Colonia crosses and 25–75 % in Colonia.
A method was devised for making chromosome spreads of amoebae grown on bacterial lawns. Cells were first exposed to dilute formaldehyde at 26 °C for 30 min, then spread on slides with hot lactic acid and stained. Such spreads of CLd (Colonia) and RSD4 (heterothallic) amoebae both contained about 40 chromosomes.
The data are consistent with the view that Colonia is haploid throughout its life cycle and that chromosome number is neither halved during sporulation nor doubled during plasmoidal formation. However, the possibility exists that an alternance of ploidy occurs by way of the few diploid nuclei present in the plasmodium.
The nucleolus and meiosis during microsporogenesis in Endymion Non-Scriptus (L.)
Authors: Luck B. T. , Jordan E. G. 
Published: April 2021

ABSTRACT
Stages of meiosis from the bluebell Endymion non-scriptus (L.) were studied by electron microscopy. The segregated components of the nucleolus at meiotic prophase underwent fragmentation and dissolution at pachytene-diplotene. Nucleoli were absent during both meiotic divisions and reformed on the nucleolus organizer into a fibrillar mass from scattered fibrillar components at the dyad and tetrad stages. It is argued that the fibrillar region shows continuity through nuclear division though undergoing structural transformations in the process. Nucleolar reformation occurs on condensed nucleolus organizers. Processing of the ribosomal precursors and the resumption of RNA synthesis is discussed in relation to the dispersal of the nucleolus organizer into the fibrillar region of the reformed nucleolus.
Pore-like structures in biological membranes
Authors: Orci L. , Perrelet A. , Malaisse-Lagae Francine , Vassalli P. 
Published: April 2021

ABSTRACT
In freeze-fracture replicas, biological membranes appear as smooth surfaces interrupted by random globular protrusions, the intramembrane particles. Smooth areas correspond to the membrane phospholipidic domain, while intramembrane particles are the morphological counterpart of membrane proteins. In the present work, examination of membranes in a variety of cell types reveals that a number of intramembrane particles contain an electron-dense spot. The spot is thought to correspond to a minute pit in the particle, filled by the platinum used in the freeze-fracture procedure. Similar images, described previously in intramembrane particles forming the specific array of the gap junction, were interpreted as hydrophilic channels bridging the interior and the exterior of the plasma membrane. Comparison between the gap junction particles and the non-junctional particles containing a dense spot suggests that these latter may too contain hydrophilic channels. The channels in random intramembrane particles would represent the morphological counterparts of the water-filled pores described in models of membrane permeability.
Differentiated regions of human placental cell surface associated with exchange of materials between maternal and foetal blood: coated vesicles
Authors: Ockleford C.D. , Whyte A. 
Published: April 2021

ABSTRACTCoated vesicles may be an important component of the micropinocytic system of the human placenta. Regions of very dense reaction with glycocalyx stains are restricted to membranes within forming and fully formed coated vesicles. This is interpreted as evidence against permanently grouped specific binding sites having a role in the selective uptake of materials by micropinocytosis, and as support for theories of coated-vesicle formation which take into account the dynamic nature of membrane components. The pyroantimonate precipitation technique which was employed in an attempt to localize cations in placental tissue at term resulted in the deposition of electron-dense material in coated vesicles and basement membrane.Examination of the distribution of coated vesicles in placental tissue expiants at 8– 12 weeks of gestation revealed a restricted distribution of these organelles. Probably more than 89% of coated vesicles lie within the largest vesicles’ diameter from the cell surface.Placental coated vesicles were isolated and examined using negative staining. A polygonally patterned structure was apparent on their surfaces. Analysis of the isolated fraction of coated vesicles using sodium dodecyl sulphate polyacrylamide gel electrophoresis shows the presence of a major protein of molecular weight 180000. This is the same molecular weight that has been given for clathrin, the major protein of the raised polygonally patterned structure on the cytoplasmic surface of coated vesicles from other sources.
Karyotypic analyses of parental and hybrid intraspecific mouse cells, A9/B82, by giemsa- and centromeric-banding
Authors: Russell M. H. , Engel E. , Vaughn W. K. , Mcgee B. J. 
Published: April 2021

ABSTRACT
Hybrids between A9 (HGPRT-) and B82 (TK-), mouse heteroploid fibroblast lines, were obtained through continuous cultivation and clonal selection; such hybrids showed marked segregation and by conventional stains displayed chromosome numbers and distribution similar to that of either parental type.
Detailed analyses by Giemsa (G)- and centromeric-banding of these parental lines, and of 4 of the reduced hybrids, maintained in culture for up to 5 years, revealed the following points: (1) The distribution of the majority of individual chromosomal classes was similar for 3 of the hybrid cell lines. (2) Over two-thirds of the chromosomal arms in both the parental lines and hybrid lines were identical to normal mouse telocentric chromosomes. (3) For 2 of the hybrid lines, segregation was particularly marked with respect to those chromosomal arms whose G-banding patterns were identical to the wild-type genome; this indicated that segregation had occurred at the expense of redundant chromosomal material introduced by cell fusion.
These banded studies demonstrated that segregation chiefly accounted for the sharp reduction in chromosome numbers while recombination accounted for the chromosome heterogeneity of the hybrid cells as compared to the parental genomes.
Differences In Vitro between fibroblast-like cells from cornea, heart, and skin of embryonic chicks
Authors: Conrad Gary W. , Hart Gerald W. , Chen Yeh 
Published: April 2021

ABSTRACT
Populations of fibroblast-like cells of corneal stroma, heart ventricle, and back skin of day-14 embryonic chicks were grown in vitro as primary and secondary cultures and were found to differ from one another by several criteria. Such cells were obtained from tissues either directly (cornea) by dissection or indirectly (heart and skin) by the rapid adhesion of the fibroblast-like cells to glass and plastic substrata. Individual fibroblast-like cells of cornea and heart were distinguishable from one another during their first 24–48 h in vitro. The morphologies of the individual cells of these 2 populations became indistinguishable during logarithmic growth, although each could be distinguished from individual fibroblast-like cells of skin. When the cultures reached saturation, corneal cells formed a monolayer of randomly oriented polygonal cells ; skin cells formed a monolayer of long, narrow, ragged cells in parallel arrays with occasional double-layering; and heart cells formed multilayers of criss-crossed cells whose broad, smooth outlines were in parallel array in each layer. Saturation densities of the 3 fibroblast-like populations were different: heart &gt; skin &gt; cornea. By 3 methods of assay the cells were found to be differentially sensitive to treatment with trypsin and EDTA, and to EDTA alone, heart cells consistently being the least sensitive. Taken together, these data suggest that fibroblast-like cell populations isolated from different tissues of a single organism are different from one another and thus may behave differently from one another during in vitro studies.
In Vitro transcription of rna in nuclei, nucleoli and chromatin from Physarum Polycephalum
Authors: Davies K. E. , Walker I. O. 
Published: April 2021

ABSTRACT
Methods for isolating nuclei, nucleoli and chromatin from Physarum polycephalum which retain high levels of endogenous RNA polymerase activity are described. Under carefully controlled conditions with respect to mono- and divalent cation concentrations RNA synthesis in nuclei displayed linear kinetics for at least 30 min and the RNA products had a similar size distribution to nuclear RNA synthesis observed in vivo. Chromatin showed 60% of the nuclear transcriptional activity but no conditions were found where faithful transcription of the template occurred. Isolated nucleoli were 5-fold more active than nuclei and the endogenous RNA polymerase activity was insensitive to α-amanitin. Under carefully controlled conditions, the nucleoli appeared to support the accurate transcription, re-initiation and processing of rRNA chains in vitro.
5-bromodeoxyuridine-induced formation of virus-like particles in Naegleria Gruberi EGS
Authors: Schuster F. L. , Clemente John S. 
Published: April 2021

ABSTRACT
Exposure of axenic cultures of the amoeboflagellate Naegleria gruberi EG8 to the thymidine analogue 5-bromo-2′-deoxyuridine (BrdU) resulted in the induction of virus-like particles (VLP) and various structures associated with their development and presumed transmission. Previously, VLP induction could be accomplished only by growing amoebae in the presence of living bacteria as a food source. Addition of excess thymidine along with BrdU did not block induction of particles. This account demonstrates that the EG.-VLP system responded to BrdU as do a number of mammalian cell lines harbouring latent viruses, and provides the basis for future work on the infectivity of the VLPs for other amoebae as well as tissue culture cells.
Fine structure and rna synthesis of Tetrahymena during cytochalasin b inhibition of phagocytosis
Authors: Nilsson Jytte R. 
Published: April 2021

ABSTRACT
Cytochalasin B inhibits the formation of normal-sized food vacuoles in Tetrahymena but the cells do not starve. Treated cells differ from starved cells in that they retain a high rate of incorporation of tritiated uridine. Large numbers of smaller vacuoles, about 1 μm in diameter, are formed, presumably by pinocytic activity of the cytopharyngeal membrane. This effect may perhaps be due to interference with the mechanism by which food vacuoles are sealed off at the cytostome, in which microfilaments may participate. Inhibited organisms may form tubes continuous with the cytopharynx instead of separate food vacuoles. It is not clear, however, why the formation of the small vacuoles is resistant to the drug.
Effects of colchicine and vinblastine on the phytohaemagglutinin-induced transformation of lymphocytes
Authors: Thyberg Johan , Moskalewski Stanislaw , Friberg Ulf 
Published: April 2021

ABSTRACT
The effects of 2 microtubular-disruptive drugs, colchicine and vinblastine, on the phytohaemagglutinin (PHA)-induced blast transformation and mitogenic stimulation of human lymphocytes were studied. Both drugs markedly inhibited cell growth and DNA synthesis and lowered the mitotic index. No microtubules were seen with the electron microscope in cells treated with PHA plus colchicine or vinblastine. Moreover, the PHA-induced development of all organelles was partially inhibited by these drugs, especially that of the Golgi complex. As compared to cells treated with PHA alone, the dictyosomes were fewer, not so clearly localized in one area of the cytoplasm, and contained a decreased number of cisternae and an increased number of vacuoles.
These results indicate that cytoplasmic microtubules play an important role in the PHA-induced blast transformation and mitogenic stimulation of lymphocytes. It is suggested that the microtubules function in the structural organization of the cell and particularly the Golgi complex. In the drug-induced absence of microtubules this and other organelle systems do not respond as usual to PHA stimulation, which could largely explain the decreased cell growth. This in turn suggests that lowered mitotic activity is a result of inhibition of cell growth, as a critical amount of G1-associated cell growth is believed to be required for the initiation of DNA synthesis and thus mitosis.
Synthesis of proteoglycans by suspension and monolayer cultures of adult chondrocytes and de novo cartilage nodules-the effect of hyaluronic acid
Authors: Wiebkin Ole W. , Muir Helen 
Published: April 2021

ABSTRACT
Chondrocytes were isolated from adult laryngeal cartilage by an enzymic procedure that included 6 h digestion with collagenase. The level of 35SO42-incorporation into cetylpyridinium chloride-precipitable material by these cells depended upon the subsequent culturing conditions. Suspension cultures incorporated more 35SO42-cell than monolayer cultures. Hyaluronic acid in the medium inhibited 35SO42-incorporation only when the cells were in primary suspension cultures. It had no effect on monolayer cultures, or monolayers organized into nodules, or suspension cultures derived from monolayers. Mild pretreatment with EDTA, however, rendered these susceptible to hyaluronic acid inhibition. In contrast EDTA abolished the inhibitory effect of hyaluronic acid on primary suspension cultures. Oligosaccharides, derived from hyaluronidase digestion of hyaluronic acid that were larger than decasaccharide, had some inhibitory effect on 35SO42-incorporation by monolayer cultures.
The total 35SO42-incorporation was less in primary suspension cultures of chondrocytes isolated after 12 h than after 6 h digestion of cartilage and the inhibition by hyaluronic acid was also less. These differences persisted during 12 days of culture.
It is suggested that the method of isolating chondrocytes and subsequent culture conditions may modify the cell surface and mask or abolish specific binding sites for hyaluronic acid.
Changes in the surface properties of rabbit polymorphonuclear leucocytes, induced by bacteria and bacterial endotoxin
Authors: Thorne Kareen J.I. , Oliver Rhonda C. , Lackie John 
Published: April 2021

ABSTRACT
Rabbit peritoneal polymorphonuclear leucocytes were induced to aggregate by a variety of bacterial species. In the absence of serum, Gram-negative bacteria were more effective at inducing aggregation than Gram-positive. The most effective micro-organism tested, Acinetobacter sp. 199A, was readily phagocytosed and also induced extracellular secretion of the granule enzymes peroxidase and lysozyme. Isolated endotoxin from this bacterial species was highly effective in inducing aggregation and granule enzyme release. Endotoxin-induced aggregation was associated with a large increase in the amount of lactoperoxidase-catalysed iodination of surface protein. Only one iodinatable protein was detected, of molecular weight 150000. It is postulated that phagocytosis of Gram-negative bacteria, followed by granule enzyme release, accelerates the rate of membrane recycling and that this brings new adhesive protein to the surface more rapidly.
Scanning electron microscopy of human lymphocytes during transformation and subsequent treatment with methotrexate
Authors: Hoffmann C. Choo , Moore Kenneth C. , Shih Ching-Yuan , Blakley Raymond L. 
Published: April 2021

ABSTRACT
Preparations of human peripheral blood lymphocytes containing 72–87% T-cells and 10–16% B-cells were shown by scanning electron microscopy to consist almost exclusively of cells bearing numerous microvilli, whereas thymocytes were of mixed surface morphology, with both smooth and encrusted forms numerous. T-lymphocytes purified on long nylon columns were all covered with numerous short villi. Stimulation with phytohaemagglutinin for 2 days produced T-lymphoblasts almost exclusively, and as the T-cells enlarged the microvilli lengthened, the increase in length reaching 5-fold by day 3. Addition of sufficient methotrexate on day 3 to arrest proliferation (50 nv) caused progressive loss of microvilli from the cell surface, with the eventual production of large numbers of smooth cells, the surfaces of which later became pitted, followed by the complete dissolution of the cell. T-lymphocytes were shown to form rosettes with sheep erythrocytes through direct contact of the cell membranes over a significant area, but when, as a result of methotrexate treatment, the lymphocytes had become denuded of microvilli or had reached an advanced state of dissolution, rosettes were no longer formed.
A fluorescence enhancement assay of cell fusion
Authors: Keller Paul Malcolm , Person Stanley , Snipes Wallace 
Published: April 2021

ABSTRACT
Two probes were synthesized which consist of fluorescent molecules conjugated to saturated hydrocarbon chains, 18 carbons long, to ensure their localization into cellular membranes. There is an overlap between the emission spectrum of one probe (donor) and the absorption spectrum of the other probe (acceptor). By the use of appropriate wavelengths it is possible to specifically excite the donor probe and record the fluorescence of the acceptor probe. Two cell populations, each labelled with one of the probes, were infected with a virus that causes cell fusion, mixed in equal proportions, and the fluorescence of the acceptor probe measured as a function of time after infection. An increase in fluorescence was observed beginning at the time of onset of cell fusion indicating a mixing of the fluorescent membrane molecules. An investigation of the distance dependence indicated that the increase in fluorescence was mainly due to resonance energy transfer and not to photon emission and reabsorption. Resonance energy transfer requires that the 2 probes be close together and that there be an overlap of the emission spectrum of the donor probe and the absorption spectrum of the acceptor probe. The possible application of this assay to other types of membrane fusion is noted.
Studies of membrane fusion I. paramyxovirus-induced cell fusion, a scanning electron-microscope study
Authors: Knutton S. , Jackson D. , Ford M. 
Published: April 2021

ABSTRACT
Fusion of erythrocytes and HeLa cells with Sendai and Newcastle disease viruses has been studied by scanning electron microscopy. Most virus particles are spherical but vary in diameter from ∼ 200 to ∼600 nm. At 4 °C virus particles bind randomly to the cell surface and at high cell densities cross-linking of adjacent cells by virus particles results in cell agglutination. Cell-cell fusion takes place when the agglutinated cell suspension is warmed to 37 °C. Fusion is initiated at sites of cell-cell contact and is accompanied in all cases by cell swelling. In the case of suspension HeLa cells, virally mediated cell swelling involves an ‘unfolding’ of cell surface microvilli and results in the formation of smooth-surfaced single or fused cells. With erythrocytes, swelling results in haemolysis. There is a dramatic reduction in the numbers of virus particles bound to cells following fusion.