bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toroidal bands in polytene chromosomes of Drosophila
Authors: Sorsa Veikko 
Published: April 2021

ABSTRACT
Results obtained from the thin-section electron microscopy of salivary gland chromosomes of Drosophila melanogaster mainly support the concept of cable-like organization of polytene chromosomes, with disk-like bands composed of parallel bundles of homologous chromomeres. Outward orientation of loop fibres may generally cause a toroidal bending in the chromomere bundles. Both longitudinal and transverse sections of polytene chromosomes indicate that the bands may contain toroidal subunits. Torus-shaped bands were only found in thin sections of the most distal and most proximal regions, as well as in certain heavy bands at the late-replicating regions of polytenized interphase chromosomes. This suggests that an incomplete duplication of chromomeres may be a reason for torus formation, by preventing the separation of sister chromatids at the earliest phases of the polytenization process. The appearance of more numerous, but smaller, subunits in thin-sectioned faint bands is interpreted as a consequence of more complete segregation of sister chromatids in those bands during polytenization.
Dimethylsulphoxide induction of the murine macrophage-like line p388d1: Change of phagocytic ability and cell surface properties
Authors: Capo Christian , Mishal Zohair , Balloy Vincent , Benoliel Anne-Marie , Bongrand Pierre 
Published: April 2021

ABSTRACT
The murine macrophage-like cell line P388D1 ingests immunoglobulin-coated sheep red cells (IgG-SRC) poorly, but after 3 days incubation in the presence of 1–5% dimethyl sulphoxide (DMSO), it becomes highly phagocytic. We used this model to correlate triggering of phagocytosis with some surface properties of P388D1 cells, possibly involved in recognition or engulfment of particles. The accessibility of Fc receptors on the cell membranes did not seem to be affected by DMSO treatment since the binding of IgG-SRC to cells was the same before and after treatment with DMSO. A technique allowing quantitative determination of the stability of cell-particle binding showed that binding strength was not the only essential factor in triggering ingestion. Hydrophobicity and surface charge were postulated to play a role in phagocytic recognition. No change in hydrophobicity, as assayed by contact-angle measurement, and in net surface charge evaluated by cell electrophoresis, was observed for normal and DMSO-treated P388D1 cells. On the other hand, the fluorescence polarization of a membrane lipophilic probe (1,6-diphenyl-1, 3,5-hexatriene) was significantly (P &lt; 0’01) decreased when P388D1 cells were treated with DMSO. Since the effect of DMSO on P388D1 function was delayed, our results were consistent with the view that enhancement of phagocytosis might be a consequence of some modification of membrane dynamics, due to changes in lipid composition.
Effects of respiratory-burst stimuli on the flow properties of pig blood neutrophils
Authors: Higson F. K. , Kikuchi Y. , Jones O. T. G. , Hughes G. M. 
Published: April 2021

ABSTRACT
Stimulants of the neutrophil respiratory burst, both soluble and crystalline, greatly inhibit the flow of cells through a Nuclepore filter with 5 μm diameter pores. The stimuli appear to reduce cell deformability by a mechanism independent of the activation of respiration, since inhibitors of the respiratory burst (N-phenyl maleimide, quercetin) are without effect on the change. It is suggested that stimuli reduce membrane deformability rather than cause aggregation, since slowing of flow is independent of cell density and is much less when the filter pore size is increased to 8μm. The technique, recently used to study alterations in erythrocyte deformability, may be appropriate for investigating leucocyte flow in some clinical disorders.
Plasma membrane-associated filament systems in cultured cells visualized by dry-cleaving
Authors: Mesland Dick A. M. , Spiele Hermina 
Published: April 2021

ABSTRACT
Substrate-attached critical-point-dried cells cleave along the level of the substrate-adherent membrane if removed by means of adhesive tape. The remaining membrane fragments on grids can be visualized three-dimensionally by means of stereo transmission electron microscopy. Attachment of cells may be achieved by active spreading of the cell, or artificially by poly-L-lysine adherence of prefixed cells. In 11 different cell types a filamentous network appears to remain associated with the cytoplasmic face of the membrane. In one hepatoma cell type virtually no filamentous network could be detected. Two general network morphologies are described: the hepatocytic network and the lymphoid network. Since no correspondence could be found between cytoplasmic structure and the structure of the membrane-associated network, and since cells generally cleave along the level of this network, excluding cell organelles, we conclude that it comprises a distinct structural system, analogous to the membrane skeleton of the red cell membrane.
Prometaphase forces towards opposite spindle poles are not independent: An on/off control system is identified by ultraviolet microbeam irradiations
Authors: Sillers Peggy J. , Wise Dwayne , Forer Arthur 
Published: April 2021

ABSTRACT
Individual spindle fibres in prometaphase spermatocytes of the cricket, Neocurtilla hexadactyla, were irradiated with an ultraviolet microbeam. The stretched heteromorphic bivalent (X2Y) contracted to about 75% of its pre-irradiation length after irradiation of either of its two oppositely directed spindle fibres (i.e., the X2 or Y spindle fibre). The X2Y bivalent also contracted after irradiation of the connection between the kinetochores of the univalent X1 chromosome and the Y chromosome but it did not contract after irradiation of autosomal spindle fibres or of the spindle fibre of the X1 univalent sex chromosome. The spindles sometimes shrank after irradiation, but contraction of the X2Y bivalent was independent of spindle shrinkage.
The data strongly suggest that the oppositely directed forces on a bivalent are not independent. One reason is that the X2Y contractions were asymmetrical: during contraction one kinetochore remained fixed in position while the other kinetochore (facing the opposite pole) moved towards the equator. In 75% of the cases the stationary kinetochore was associated with the irradiated spindle fibre. Thus, we suggest that the irradiation of a spindle fibre produces a state analogous to rigor in the irradiated spindle fibre and, because of effects on the control system, produces relaxation of tension in the oppositely directed non-irradiated spindle fibre, so that the kinetochore associated with the non-irradiated spindle fibre moves towards the equator. These experiments have identified a control system that coordinates force production to opposite poles.
Anchoring filaments of the amphibian epidermal-dermal junction traverse the basal lamina entirely from the plasma membrane of hemidesmosomes to the dermis
Authors: Ellison Janice , Garrod D. R. 
Published: April 2021

ABSTRACT
An electron microscopical study of the epidermal-dermal junction in the axolotl and adult Rana pipiens has been carried out. This shows that filaments of about 12 nm in diameter, known as anchoring filaments, pass from the hemidesmosomes at the base of the epidermal cells across the basal lamina to the dermis. There they may unite to form broader fibres, known as anchoring fibrils, or may simply form bundles.
In the axolotl, particularly, the anchoring fibrils or bundles of anchoring filaments, enmesh with the collagen fibres of the dermis.
Removal of epidermal cells with EDTA results in separation along a plane in the lamina rara of the basal lamina, i.e. between the plasma membrane of the cells and the lamina densa. The anchoring filaments remain inserted into the lamina densa. Hemidesmosomal plaques are no longer visible in regions of the plasma membrane that have been separated from the basal lamina by EDTA, and no evidence was found that plaques are engulfed by the cells.
It is proposed that the hemidesmosome-anchoring filament system provides a structural link between the collagenous filament system of the dermis and the intracellular cytokeratin filament system of the epidermis, which, in turn, is linked between cells by desmosomes.
Pollen-pistil interactions in interspecific crosses of Populus (sections aigeiros and leuce): Pollen adhesion, hydration and callose responses
Authors: Gaget M. , Saï C. , Dumas D, C. , Knox R. B. 
Published: April 2021

ABSTRACT
Intersectional crosses between species of sections Aigeiros (Populus deltoides, P. × euramericana or P. nigra) and Leuce (P. alba or P. tremuloides) are known to be reciprocally incompatible. The site of pollen tube arrest is on the stigma surface in pollinations between pistils of section Leuce and pollen of section Aigeiros; tubes failed to penetrate the stigma surface. In reciprocal matings, pollen of section Leuce germinated and tubes penetrated the stigma and style, where arrest occurred. Rejection may be accompanied by swelling of the tube tips, and callose plug formation. In the cross between P. deltoides and P. alba a callose response was detected in the cell walls of the transmitting tissue, adjacent to the rejected pollen tubes.
Centrioles in the mammary epithelium of the rat
Authors: Dylewski Daniel P. , Keenan Thomas W. 
Published: April 2021

ABSTRACT
Through serial thin-section analysis of rat mammary epithelial cells, the number of centrioles per cell and their intracellular location were determined. In all developmental stages (e.g. virginal, pregnant, lactation, involution), each epithelial cell contained a single centriole that was located in the apical region. Centrioles were 200-220 (ݲ = 210) nm in transverse section, and exhibited the typical 9 × 3 ‘pinwheel’ configuration of microtubules. In longitudinal section, centrioles were 330—380 (ݲ = 360) nm in length. Each centriole was surrounded by a homogeneous pericentriolar matrix. During mitosis in pregnant animals, centrioles were paired at the nuclear poles and oriented at right angles (90°) to each other. At the completion of mitosis a single diploβome (pair of centrioles) was associated with each interphase nucleus. Because all postmitotic cells contained only a single centriole, it was assumed that one of the two diplosomal centrioles had disintegrated. There appeared to be a correlation between centriole location and cell polarity. When centrioles were located near the apical plasma membrane, epithelial cells exhibited polarity. However, when centrioles were associated with the nuclear poles during mitosis, epithelial cells were typically apolar. These observations suggest that centrioles may function as determinants in cell polarity.
Acquisition of a limited lifespan by differentiating cells derived from pc13 embryonal carcinoma cells
Authors: Rayner Michael J. , Pulsford James A. J. 
Published: April 2021

ABSTRACT
Retinoic acid (RA) has previously been shown to induce the differentiation of mouse embryonal carcinoma (EC) cells to endoderm-like cells that have a slower rate of proliferation and are non-tumorigenic. These cells also acquire the ability to respond to a range of exogenous growth factors. Wc have analysed the change in growth phenotype for PC13 EC cells using video recordings and autoradiography. We have shown that the endoderm-like cells have a longer cell cycle time than their undifferentiated counterparts (five cell divisions after exposure to RA the differentiated cells had a median cell cycle time of 1800 min compared to 800 min for control cells). The endoderm-like cells also have a progressively decreasing probability of dividing again and this indicates that the differentiation process is accompanied by the acquisition of a limited life-span. The characteristics of mortal cells are well documented, and the endoderm-like cells demonstrate the properties of such cells.
In addition, we have confirmed the observation that epidermal growth factor (EGF) can stimulate the proliferation of the endoderm-like cells and have shown, using autoradiography, that 92% of these cells express EGF receptors. Using video recordings, we have demonstrated that the effect of EGF is to shorten the cell cycle of the differentiating cells. We have also shown that EGF can enhance the survival of the endoderm-like cells and thereby prolong their life-span. It is known that EGF and other growth factors can prolong the life-span of mortal cells derived from normal tissues, but we have demonstrated that EGF can have this effect on the differentiated derivatives of a tumour cell
The associated reactivation of two x-linked genes the spontaneous and azacytidine-induced re-expression of ornithine transcarbamoylase and glucose-6-phosphate dehydrogenase in a rat hepatoma
Authors: Goss S. J. 
Published: April 2021

ABSTRACT
Two X-linked genes, specifying ornithine transcarbamoylase (OTC) and glucose-6-phosphate dehydrogenase (Glc-6-PD), are reversibly suppressed in certain derivatives of the rat H4-II-E hepatoma. Either gene can become reactivated spontaneously, and it is shown that both can be reactivated by azacytidine treatment. This gene reactivation has been investigated by enzyme assay and by the use of selective growth media (‘ornithine-medium’ to select for OTC, and medium containing diamide to select for Glc-6-PD). There is a clear tendency for both genes to be reactivated together, though either can become active alone. Since OTC is an enzyme of the urea-cycle, and Glc-6-f*D is an enzyme of the hexose monophosphate shunt, and since these two pathways are normally under quite separate control, it would seem that the coupled regulation of the two genes in these hepatomas is abnormal. It is suggested that the suppression of the two genes resembles X-inacti vation: in both cases, azacytidine treatment induces gene reactivation with a high frequency and results in different clones of cells expressing widely varying amounts of enzyme activity. The association between the re-expression of OTC and Glc-6-PD might indicate that some phenomenon like the position-effect is occurring.
Monoclonal antibodies against a nucleolar protein from differentiating chick muscle cells
Authors: Morris G. E. , Man Nguyen Thi , Head L. P. 
Published: April 2021

ABSTRACT
Two monoclonal antibodies, NORM and NORA, bind specifically to a 37 000 molecular weight protein in total protein extracts of chick skeletal muscle cell cultures. They have been used to follow changes in the amount and distribution of this protein during terminal differentiation and the associated cessation of cell division.
Immunofluorescence microscopy shows that the antigen is found almost exclusively in the nucleolus in interphase cells and is dispersed in the cytoplasm during mitosis. Low doses of actinomycin D cause segregation of nucleoli into DNA fibrils and ribonucleoprotein granules, and the antigen is clearly associated with the latter. High doses of actinomycin D cause shrinkage of the nucleolus and the antigen is dispersed within the nucleoplasm, but not released into the cytoplasm. The amount and distribution of antigen is similar in all cell types (myoblasts, myotubes and fibroblasts) and there are no major changes during muscle differentiation.
From known changes in ribosomal RNA metabolism during myogenesis and after actinomycin D treatment, we suggest that the 37 000 Mr protein is involved in some post-transcriptional aspect of ribosome production and that its concentration and distribution may be related to the concentration of ribosomal RNA in the nucleolus.
Isolation and characterization of alkaline phosphatase-containing granules (phosphasomes) from human polymorphonuclear leucocytes
Authors: Smith Gillian P. , Sharp Gaynor , Peters Timothy J. 
Published: April 2021

ABSTRACT
Human polymorphonuclear leucocytes were homogenized in isotonic sucrose and subjected to analytical subcellular fractionation by centrifugation on a discontinuous sucrose density gradient to produce a phosphasome-enriched fraction, contaminated primarily by plasma membrane. Experiments to separate these membrane fractions by centrifugation on gradients of Nycodenz or Percoll, or by toroidal coil counter current chromatography, were unsuccessful.
Fractionation carried out on neutrophils previously suspended in isotonic sucrose containing a low concentration of digitonin resulted in the preparation of a highly purified phosphasome fraction, free of plasma membrane components. Electron-microscope cytochemistry of the purified fraction identified the phosphasomes as regular and irregular-shaped spheres and rods, the alkaline phosphatase being associated with the inner aspect of the vesicle membrane. These granule structures were very similar to phosphasomes observed in intact neutrophils. A proportion of the endoplasmic reticulum and Golgi membrane marker enzymes remained associated with the phosphasomes throughout the separation procedures.
Shape-dependent regulation of cytoskeletal protein synthesis in anchorage-dependent and anchorage-independent cells
Authors: Reiter Theresa , Penman Sheldon , Capco David G. 
Published: April 2021

ABSTRACT
We examine changes in protein synthesis that accompany suspension (i.e, shape alteration) of anchorage-dependent and anchorage-independent cells using a newly developed cell fractionation procedure based on detergent extraction. Using this procedure, a cell can be divided into four distinct and independent fractions: soluble, cytoskeleton, chromatin and nuclear matrix– intermediate filament. This fractionation procedure is used to investigate protein synthetic events associated with the release from anchorage-dependent growth, characteristic of transformed cells. Suspension results in several unexpected events in both anchorage-dependent (3T3) cells and anchorage-independent (SVPy 3T3) cells. Suspension of 3T3 cells results in a reduction of total protein synthesis; however, two proteins are enhanced in their amount of synthesis. Suspension of SVPy 3T3 results in about 20 proteins proceeding through short and long-term alterations in the rate of synthesis. The synthesis of some of these proteins is inhibited, others undergo a transient decrease in synthesis upon suspension and then increase above their rate in the anchored state, while the synthesis of others steadily increases after suspension. Suspension of anchorage-dependent cells results in a fraction specific shift in the rates of protein synthesis. Possible roles for these fraction-specific proteins are considered.
Immunocytochemical identification of cytotrophoblast from other mononuclear cell populations isolated from first-trimester human chorionic villi
Authors: Butterworth Bridget H. , Loke Y. W. 
Published: April 2021

ABSTRACT
Trophoblast biologists are often uncertain as to what cell types they are investigating because the mononuclear cell populations prepared from trypsinization of human first-trimester chorionic villi are morphologically very similar. In the present study, immunocytochemical and phagocytic markers have been used to distinguish cytotrophoblast populations from cell types derived from the mesenchyme of the chorionic villus.
Two anti-trophoblast monoclonal antibodies generated in our own laboratory (18B/A5 and 18A/C4) were found to be very efficient in identifying cytotrophoblast, which made up 35–40% of the cells in a smear. Most cytotrophoblast cells did not stain with a monoclonal anti-HLA-A,B,C antibody but a few cells (5 %) were found to express both trophoblast and HLA-A,B,C antigens by a double-labelling technique.
Endothelial cells from villous capillaries could be identified by a rabbit anti-factor VIII antibody. These cells formed 28 % of the population in a cytospin smear.
Macrophages from the villous mesenchyme were less readily separable as neither specific monoclonal antibodies nor localization of enzymes were found to be effective. However, these cells could be identified by their ability to phagocytose carmine. About 15% of the cells in a smear consisted of macrophages.
The procedure described should prove useful in judging the efficiency of isolation methods from human placental cells.
Unusual structural features and assembly of gap and pleated septate junctions in embryonic cockroach CNS
Authors: Swales Lesley S. , Lane Nancy J. 
Published: April 2021

ABSTRACT
Junctional assembly in the developing CNS in cockroach embryos has been studied during the last half of neurogenesis. Atypical linear tracts of gap junctions are found to develop between attenuated cytoplasmic glial cell processes and their overlying perineurial cells during the last third of development. During both perineurial and glial gap-junctional formation, 13 nm E face (EF) intramembrane particles (IMPs), such as are characteristic of arthropod gap junctions, are seen initially as free IMPs; these then become arranged in 100se irregular clusters or alignments and finally are aggregated in plaques. P face ridges (or EF grooves), typical of tight junctions, are found on the same perineurial membrane face as assembling gap-junctional PF pits (or EF particles). Pleated sepate junctions also develop between adjacent perineurial processes during the last third of embryogenesis; these form by the apparent migration of individual 8 nm PF IMPs into meandering rows, which then become aligned in numerous orderly parallel stacks. Although all these junctions occur on the same perineurial membrane face, the IMPs that form the different junctional types never appear to be confused during junctional assembly. The cues to signal the advent of these precise patterns, however, are unknown.
Pollen–stigma interaction in Brassica. III. hydration of the pollen grains
Authors: Zuberi M. I. , Dickinson H. G. 
Published: April 2021

ABSTRACT
A method is described by which the changes in shape that accompany hydration of Brassica pollen grains may be rapidly measured. Using this technique it has proved possible to chart the small amount of hydration that takes place on anthesis, in addition to the response of pollen to a range of relative humidities in vitro and in vivo. Such measurements, together with pollen transfer experiments, indicate that under normal field conditions self-pollen undergoes a brief period of hydration followed by some loss of water and that, in the course of this hydration, many pollen grains are inhibited from further growth. Raised levels of atmospheric water cause a variety of responses in self-pollen, ranging from tube growth through the pistil to the ovary, to tubes inhibited at the stigmatic surface, accompanied by the formation of callose. Surprisingly, compatible cross-pollen is also affected by high humidity, often developing extended tubes that are incapable of penetrating the stigmatic cuticle. The development of stigmatic callose is also stimulated by these tubes, as also occurs when other members of the Cruciferae are induced to germinate on Brassica stigmas by high levels of atmospheric water. This formation of callose in response to challenge by all types of pollen tube suggests models for the self-incompatibility response in Brassica that involve a direct linkage between S (incompatibility) gene products and the formation of callose may require some re-examination. Close study of the operation of the self-incompatibility system in a number of individuals has revealed all aspects of the response to be heavily dependent on the particular S genes possessed by the plant.