bluuebunny/crossref_metadata_2025 huggingface dataset:
An electron-microscope study of the in vitro transformation of human leucocytes: II. transformation to macrophages
Authors: Chapman J. A. , Gough J. , Elves M. W.
Published: April 2021

Macrophages which develop in cultures of human peripheral blood have the typical ultrastructural features of macrophages occurring in other situations, in vivo and in vitro. The cultured cells usually have irregular nuclei and the cytoplasm possesses numerous digestion vacuoles containing debris; the cell outline is irregular with many filopodia. Other cells were laden with membrane-bounded granular bodies containing periodic-structured material of regular outline. Although it is concluded that no evidence about cell ancestry can be adduced from this morphological study, it seems likely from other work that many of these macrophages arise from lymphocytes.
Fine-Structural Studies of the Gametes and Embryo of Fucus Vesiculosus L. (Phaeophyta): II. The Cytoplasm of the Egg and Young Zygote*
Authors: Brawley Susan H. , Wetherbee Richard , Quatrano Ralph S.
Published: April 2021

Following fertilization, there are rapid changes in the appearance of the Fucus egg. Large electron-translucent vesicles (V1) accumulate fibrillar material, and following pronuclear fusion, they are largely electron-opaque. These vesicles (V1) are formed originally in unfertilized eggs by smooth endoplasmic reticulum (SER) after release of the eggs from the oogonium. Golgi complex hypertrophy follows fertilization, and this increased activity continues throughout early embryogenesis. Wall formation begins after penetration of the egg by the sperm. Vesicles (V2) of unknown origin, which have homogeneously fibrillar contents, and Golgi vesicles (V3) merge with SER-derived vesicles (V1) after wall formation begins. Osmiophilic bodies are a prominent feature of the egg and embryo. They are penetrated by SER, and subsequently there is a loss of electron-opaque material. Alternatively, they discharge concentrically whorled material into the cytoplasm. The nuclear surface of the egg is convoluted in the period close to fertilization, and electron-opaque material is segregated in the cytoplasmic matrix lying within the nuclear invaginations.
Cytochalasin b-induced pseudo-cleavage of mouse oocytes in vitro: Asymmetric localization of mitochondria and microvilli associated with a stage-specific response
Authors: Wassarman P. M. , Albertini D. F. , Josefowicz W. J. , Letourneau G. E.
Published: April 2021

Mouse oocytes are induced by cytochalasin B to undergo ‘pseudo-cleavage’ in vitro into 2 equally sized and separable compartments. This response to the drug is dependent upon the meiotic state of the oocytes, as well as upon the presence of an intact zona pellucida. The resulting 2 cellular compartments can be completely separated from one another and cultured in vitro. Each of the compartments possesses characteristic structural features. The most pronounced structural differences include: (i) the presence of a nucleus (germinal vesicle) and nucleolus in one compartment; (ii) the presence of microvilli on the surface of the anucleate, but not the nucleate, compartment; and (iii) the localization (segregation) of mitochondria at the periphery of the anucleate, but not the nucleate, compartment. The results presented suggest that pseudo- cleavage induced by cytochalasin B arises as a consequence of a limited interaction of the drug with the oocyte surface and/or cortex and that it may represent a topographical dissociation of transporting and non-transporting regions of the membrane. These and other features of mouse oocytes treated with cytochalasin B are of interest in view of the involvement of the oocyte zona pellucida and plasma membrane during meiotic maturation, fertilization, and early embryogenesis.
Pollen ultrastructure in anther cultures of Datura innoxia: I. Division of the presumptive vegetative cell
Authors: Dunwell J.M. , Sunderland N.
Published: April 2021

Ultrastructural features of embryogenic pollen, in Datura innoxia are described, just prior to, during, and after completion of the first division of the presumptive vegetative cell. In anther cultures initiated towards the end of the microspore phase and incubated at 28 °C in darkness, the spores divide within 24 h and show features consistent with those of dividing spores in vivo. Cytokinesis is also normal in most of the spores and the gametophytic cell-plate curves round the presumptive generative nucleus in the usual highly ordered way. Further differentiation of the 2 gametophytic cells does not take place and the pollen either switches to embryogenesis or degenerates. After 48–72 h, the remaining viable pollen shows the vegetative cell in division. The cell, which has a large vacuole and thin layer of parietal cytoplasm carried over from the microspore, divides consistently in a plane parallel to the microspore division. The dividing wall follows a less-ordered course than the gametophytic wall and usually traverses the vacuole, small portions of which are incorporated into the daughter cell adjacent to the generative cell. The only structural changes in the vegetative cell associated with the change in programme appear to be an increase in electron density of both plastids and mitochondria and deposition of an electron-dense material (possibly lipid) on the tonoplast. The generative cell is attached to the intine when the vegetative cell divides. Ribosomal density increases in the generative cell and exceeds that in the vegetative cell. A thin electron-dense layer also appears in the generativecell wall.

It is concluded that embryogenesis commences as soon as the 2 gametophytic cells are laid down. Gene activity associated with postmitotic synthesis of RNA and protein in the vegetative cell is switched off. The data are discussed in relation to the first division of the embryogenic vegetative cell in Nicotiana tabacum.
Pollen ultrastructure in anther cultures of Datura innoxia: III. Incomplete microspore division
Authors: Dunwell J. M. , Sunderland N.
Published: April 2021

During the microspore division in Datura innoxia, the mitotic spindle is oriented in planes both perpendicular (PE) and oblique (OB) to the spore wall against which the nucleus is situated. However, irrespective of polarity, the usual type of hemispherical wall is laid down at cytokinesis and isolates the generative cell from the rest of the pollen grain (type A). In PE spores the vegetative nucleus initially occupies a central position in the pollen grain, whereas in OB spores the vegetative nucleus lies at the periphery of the grain close to the generative cell. In anther cultures initiated just before the microspore division is due to take place, no marked change can be observed in either orientation or symmetry of the mitotic spindle when the spores divide. In some, however, cytokinesis is disrupted and deposition of the hemispherical wall arrested. In the absence of a complete wall, differentiation of the generative cell cannot take place and binucleate pollen grains are formed having 2 vegetative-type nuclei (type B). The 2 nuclei in the B pollens are always situated against the pollen-grain wall, suggesting that the disruption phenomenon is related to the OB spores. The incomplete wall always makes contact with the intine on the intine-side of the spindle. Wall material may be represented merely as short stubs projecting out from the intine into the cytoplasm, in which event the 2 nuclei lie close to each other and are separated by only a narrow zone of cytoplasm. In other grains the wall is partially developed between the nuclei and terminates at varying distances from the tonoplast; in these, the nuclei are separated by a wider zone of cytoplasm. The significance of these binucleate grains in pollen embryogenesis is discussed.
Meiotic maturation of mouse oocytes In Vitro: inhibition of maturation at specific stages of nuclear progression
Authors: Wassarman P. M. , Josefowicz W. J. , Letourneau G. E.
Published: April 2021

In vitro studies of meiotic maturation of mouse oocytes have been carried out in the presence of several drugs. The individual steps of nuclear progression, including dissolution of the nuclear (germinal vesicle) membrane, condensation of dictyate chromatin into compact bivalents, formation of the first metaphase spindle, and extrusion of the first polar body, are each susceptible to one or more of these drugs.

Germinal vesicle breakdown, the initial morphological feature characteristic of meiotic maturation, is inhibited by dibutyryl cyclic AMP. However, even in the presence of dibutyryl cyclic AMP, the nuclear membrane becomes extremely convoluted and condensation of chromatin is initiated but aborts at a stage short of compact bivalents. Germinal vesicle breakdown and chromatin condensation take place in an apparently normal manner in the presence of puromycin, Colcemid, or cytochalasin B. Nuclear progression is blocked at the circular bivalent stage when oocytes are cultured continuously in the presence of puromycin or Colcemid, whereas oocytes cultured in the presence of cytochalasin B proceed to the first meiotic metaphase, form an apparently normal spindle, and arrest. Emission of a polar body is inhibited by all of these drugs. The inhibitory effects of these drugs on meiotic maturation are reversible to varying degrees dependent upon the duration of exposure to the drug and upon the nature of the drug.

These studies suggest that dissolution of the mouse oocyte’s germinal vesicle and condensation of chromatin are not dependent upon concomitant protein synthesis or upon microtubules. On the other hand, the complete condensation of chromatin into compact bivalents apparently requires breakdown of the germinal vesicle. Failure of homologous chromosomes to separate after normal alignment on the meiotic spindle in the presence of cytochalasin B suggest that microfilaments may be involved in nuclear progression at this stage of maturation. Cytokinesis, in the form of polar body formation, is blocked when any one of the earlier events of maturation fails to take place.
Circus movements and blebbing locomotion in dissociated embryonic cells of an amphibian, Xenopus laevis
Authors: Johnson Kurt E.
Published: April 2021

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

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

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

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

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

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

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

Coated 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

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

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 > skin > 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

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

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

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

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

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

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

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

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

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.
Suppression of myoblast fusion by concanavalin A: Possible involvement of membrane fluidity
Authors: Sandra Alexander , Leon Myron A. , Przybylski Ronald J.
Published: April 2021

Experimental evidence is presented which is consistent with the involvement of membrane fluidity during myoblast fusion. Treatment of pretrypsinized myoblasts with tetrameric Con A, but not with the dimeric succinyl derívate, inhibits fusion. Inhibition is reversed by treatment with a-methyl-D-mannoside or subsequent trypsinization. No inhibition is observed when the lectin is incubated with cells at 4 °C unless the incubation is followed by treatment with glycogen, a multivalent Con A cross-linking agent. This effect of glycogen is reversed by subsequent treatment with a-amylase. Direct observation of Con A-binding site topography by transmission electron microscopy of membrane replicas of cells labelled with Con A and haemocyanin reveals that inhibition of fusion correlates with a clustered distribution of Con A-binding sites, whereas normal fusion correlates with a dispersed distribution.
Tubular elements-a new structure in blue-green algal cells
Authors: Khan Z. N. Tahmida , Godward M. B. E.
Published: April 2021

New cell inclusions, ‘tubular elements’ are described from the blue-green alga Calothrix marchica. These structures are found in about 20% of all cells observed. They are 18–22 run in diameter, apparently composed of sub-units of which the estimated number, as seen in transverse section, is 8–10.
Transcriptional reactivation of isolated xenopus erythrocyte nuclei: Patterns of rna synthesis
Authors: Gregory S. P. , Hilder V. A. , Maclean N.
Published: April 2021

Nuclei isolated from Xenopus erythrocytes can be transcriptionally reactivated by exposure to certain cytoplasmic proteins. The types of RNA synthesized during this reactivation have been studied and compared with those present in, or synthesized by, isolated nuclei not so reactivated or in entire Xenopus erythrocytes. In all cases, the pattern of transcription indicates the synthesis of a broad range of low molecular weight RNAs. Competitive hybridization demonstrates that the reactivated nuclei synthesize some transcripts not normally produced by the isolated nuclei and we have shown that a proportion of these possess amino acid-accepting activity. The significance of these results is discussed in relation to the control of gene activity in these cells.
Pattern formation in early insect embryogenesis-data calling for modification of a recent model
Authors: Kalthoff Klaus
Published: April 2021

A mathematical model of biological pattern formation based upon lateral inhibition has recently been applied by Meinhardt to insect embryogenesis. This model has stimulated a re-evaluation of previous results, and new experiments designed to test the validity of the model. Split u.v. dose experiments with eggs of the chironomid midge Smittia show that the effective targets for the production of the aberrant pattern ‘double abdomen’ are not subject to the rapid turnover which is required by the model in its currently published version. Certain types of segment pattern, and differences in the length of segments as predicted by the model could not be observed. Other data conflict with the rather unusual type of photoreversal and the particular view of determination associated with the model. The model can be reconciled with part of the conflicting data if the effective targets for double abdomen induction are regarded as morphogen-producing structures, rather than the morphogen itself which specifies the segment pattern (Meinhardt, personal communication). This version of the model, however, is still at variance with some of the data discussed here.

A complementary explanation is proposed taking into account relevant aspects of homoeotic transformations.
Cytoplasmic changes accompanying the female meiosis in Lilium longiflorum thunb
Authors: Dickinson H. G. , Potter Ursula
Published: April 2021

The events that accompany female meiosis in Lilium parallel almost exactly those characteristic of male cells. The megaspore mother-cell is first cut off from investing tissue by a callosic wall, and this isolated cytoplasm undergoes a phase of comprehensive dedifferentiation. Not only does the major part of the ribosome population appear to be removed from both the cytoplasm and plastids, but also the plastids themselves dedifferentiate to such a degree that they represent almost the sole expression of their genome. Following meiotic prophase the cytoplasm redifferentiates. The ribosomes return by means of the disintegration of cytoplasmic nucleoloids derived from material originally produced at the nucleolar organizer in pachytene, and the plastids redifferentiate into amyloplasts. The mitochondria also exhibit a similar, but less extreme, cycle of differentiation during which a proportion of their population appears to be eliminated. As in the male cells, the megaspore mother-cell energy reserves are converted from starch to lipid in early meiosis, and a low level of protein synthesis appears to be maintained within encapsulated regions of cytoplasm, protected by membranous envelopes from the hydrolytic enzymes present.

Since these cycles of differentiation appear common to both sexes of a higher plant, they must be regarded as forming a significant component of the plant life-cycle. Their precise roles have yet to be clarified, but most certainly they must include the elimination of those informationcarrying molecules characteristic of the diploid phase of growth, and the provision of a fresh and efficient cytoplasm for the expression of the new haploid genome.
Development of hydra lacking nerve and interstitial cells
Authors: Marcum Beverly A. , Campbell Richard D.
Published: April 2021

Hydra attenuata were rendered free of interstitial cells (I cells) and interstitial cell derivatives by colchicine treatment. These hydra were then cloned and cultivated for 18 months and their developmental capacities were studied. Some experimental hydra possessed a few (about 1% of the normal numbers) interstitial cells and retained this low level during prolonged culture and active growth without the differentiation of I-cells into specialized cells. Other hydra were completely freed of interstitial cells by the colchicine treatment. Maceration and histological analyses showed that once a hydra is freed of all interstitial cells it does not recover them, nor do its buds contain interstitial cells. I cell-free hydra also lack nerve cells, nematocytes, gametes and endodermal gland cells, and the tissue consists solely of ectodermal and endodermal epithelial cells. Hydra completely lacking interstitial cells grow, bud, exhibit tissue renewal patterns, regenerate and preserve polarity generally typical of normal hydra. I cell-free hypostomal tissue has inductive capacity, as does normal hypostomal tissue, when implanted in I cell-free or normal gastric tissue. Regenerating I cell-free tissue undergoes precocious determination as does normal tissue. Only in some quantitative aspects do I cell-free hydra develop abnormally. We conclude that hydra consisting only of epithelial cells are capable of essentially normal development.
The cellular origin of chemically induced tumours
Authors: Iannaccone P. M. , Gardner R. L. , Harris H.
Published: April 2021

Tumours were induced by chemical carcinogens in chimaeric mice made by the amalgamation of two embryos each producing a different electrophoretic variant of the enzyme glucose phosphate isomerase. Although, in these chimaeras, the smallest samples of normal tissue that could be analysed almost invariably contained both isoenzymes, almost all the tumours contained only one. An analysis of the size of the clones that formed the chimaeric epidermis permitted the conclusion that the epidermal tumours produced could not have risen from more than 8 cells; and the most probable interpretation of the data is that these tumours were clonal growths.
Lectin-binding sites are found in rat liver cell plasma membrane only on its extracellular surface
Authors: Virtanen Ismo , Miettinen Aaro , Wartiovaara Jorma
Published: April 2021

In the present study ultrastructural localization of binding sites for 5 lectins was studied in rat liver cell surface membrane fractions. For this purpose ferritin-coupled Concanavalin A, wheat germ agglutinin, soybean agglutinin, Ricinus communis agglutinin 120 and Lotus tetragonolobus agglutinin I were used as probes for mannose, N-acetyl glucosamine, N-acetyl galactosamine, galactose and fucose moieties in glycoproteins and glycolipids.

Although recent reports suggest presence of glycogroups on the cytoplasmic surface of cellular membranes ultrastructural identification of membrane surfaces in the present study indicated an asymmetric localization of lectin-binding sites exclusively on the extracellular side of the membranes.
Some mitochondrial changes in denervated muscle
Authors: Miledi R. , Slater C. R.
Published: April 2021

An electron-microscopic study was made of the mitochondria in normal and denervated rat diaphragm muscles. Two types of structurally different muscle fibres were found: one type had a well-defined M-line, while the other did not.

The mitochondria in normally innervated muscle are regularly arranged at both sides of the Z-line. The mitochondria are very long and branched, and surround the myofibrils at the level of the Z-line. In transverse sections of the muscle fibres the worm-like mitochondria give a very characteristic picture.

After denervation the mitochondria are smaller and less regularly arranged. In transverse sections of the muscle fibres the mitochondria have small circular profiles. This contrasts sharply with the normal appearance and makes it possible to distinguish normal from denervated fibres.

The mitochondrial changes can be detected less than 24 h after denervation.
Membranes associated with the disintegration of mycetomal micro-organisms in Sitophilus Zea-Mais (Mots.) (Coleoptera)
Authors: Musgrave A. J. , Grinyer I.
Published: April 2021

The mycetomal micro-organisms of Sitophilus zea-mais give evidence in electron micrographs of having two peripheral unit membranes, an intermediate layer, intracytoplasmic membranes and DNA-like material. They appear to disintegrate, at times, with the concomitant formation of membrane masses. It is suggested that these are visible with the phasemicroscope and that they are probably myelin figures.
Autoradiographic evidence for the In Situ synthesis of chloroplast and mitochondrial rna
Authors: Gibbs Sarah P.
Published: April 2021

The rate of appearance of labelled RNA in the chloroplast and mitochondria as compared with the rate in the remaining cytoplasm was studied in the unicellular flagellate, Ochromonas danica, by electron-microscope autoradiography. Greening cells were labelled with uridine-5,6[3H] for a short (30 min) and a long (2 h) interval and the concentration of label, expressed as grains/unit area, determined for each cell component. The data demonstrate that there is the expected lag in the labelling of the cytoplasm proper, but no apparent lag in the labelling of the chloroplast and mitochondria. This observation, combined with the fact that after the short labelling time the chloroplast and mitochondria have a much heavier concentration of labelled RNA than the surrounding cytoplasm, indicates that most, if not all, chloroplast and mitochondrial RNA is synthesized in situ.

The three kinds of ribosomes present in the cell are distinctly different in size. The mitochondrial ribosomes measure 150–170 Å in diameter, the chloroplast ribosomes average 170–200 Å in diameter, whereas the cytoplasmic ribosomes are 210–230 Å in diameter in glutaraldehyde-osmium-fixed cells. During chloroplast development in the light, the number of chloroplast ribosomes increases approximately tenfold.
The fine structural localization of acid phosphatase in the prolactin cell of the eel pituitary
Authors: Hopkins C. R. , Baker Bridget I.
Published: April 2021

In the prolactin cell of the eel adenohypophysis acid phosphatase activity occurs within the majority of the Golgi cisternae and developing secretory granules. Acid phosphatase is also present within larger membrane-bound bodies, most of which are similar to the lytic dense bodies described in other cell types. In discussing the functional significance of this enzyme distribution particular attention is paid to its association with the secretory mechanisms of the prolactin cell.
Nucleolar dna in oocytes of Xenopus Laevis
Authors: Macgregor H. C.
Published: April 2021

The ovaries of newly metamorphosed Xenopus females contain oocytes in all stages of early meiotic prophase. In pachytene nuclei extrachromosomal nucleolar DNA appears in the form of a thin cap covering one side of the nucleus. During pachytene this cap of DNA enlarges to occupy half the nucleus. After pachytene the nucleus grows rapidly and the cap of DNA disperses into numerous tiny granules which become scattered throughout the nucleoplasm. Autoradiographs of cells which have been incubated with [3H]thymidine, and microspectro-photometric measurements of the Feulgen dye contents of nuclei in various stages of meiosis, show that the extrachromosomal nucleolar DNA is synthesized during the pachytene and immediate post-pachytene stages. Microspectrophotometric comparison of the Feulgen dye contents of post-pachytene nuclei in which the DNA cap has dispersed, and similarly prepared mouse liver nuclei, show that the post-pachytene nuclei have about 30 μ μg of extrachromosomal pachytene nucleolar DNA. In [3H]thymidine autoradiographs early pachytene nuclei are less heavily labelled than late pachytene and early diplotene nuclei. Consequently it is proposed that primary replicas of the chromosomal nucleolar organizer undergo a series of post-detachment replications.