bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations on the collagen and proteinpolysaccharide complex of rabbit corneal stroma
Authors: Smith J. W. , Frame J. 
Published: April 2021

ABSTRACT
The form and interrelationship of the collagen fibrils and proteinpolysaccharide complex of rabbit corneal stroma were studied by electron microscopy. The intact tissue was examined as Araldite sections stained with alkaline lead citrate and uranyl acetate, and the mechanically disintegrated cornea after positive or negative staining with phosphotungstic acid or after treatment with 0·5 % bismuth nitrate in 0·1M nitric acid.
The corneal collagen fibrils vary in cross-sectional area from 4·6 to 9·6 × 104 sq. Å and do not exhibit a regular hexagonal distribution. Like tendon fibrils they consist of longitudinal filaments, but their appearance suggests that they lack some of the interfilament cross-links present in tendon.
In sections of intact cornea and in negatively stained disintegrated cornea, filaments which are considered to be the protein cores of proteinpolysaccharide macromolecules are evident. They are about 40 Å wide and 2000 Å long. They appear to run an angular course, orthogonal to the collagen fibrils, and to be tangentially attached to several fibrils in the region of the a band.
After treatment with bismuth nitrate disintegrated cornea contains coarsely beaded filaments. The filaments are about 2000 Å long and the beads about 70 Å in diameter. It is considered that these are again proteinpolysaccharide macromolecules and that each bead represents one or more polysaccharide chains in coiled configuration.
Effect of isolated plasma membranes on cell cohesion in the cellular slime mould
Authors: Jaffé Alida R. , Garrod David R. 
Published: April 2021

ABSTRACT
The effects of isolated plasma membranes on cohesion of Dictyoslelium discoideumAx-2 cells have been studied. Membranes isolated from cells in the log phase of growth gave complete inhibition of log-phase cell cohesion. This effect was specific for the cohesion of log-phase cells mediated by contact sites B, since the cohesion of aggregation-competent cells which have acquired contact sites A was only partially inhibited by log-phase plasma membranes. Membranes isolated from stationary phase cells gave partial inhibition of log-phase cell cohesion, while membranes from aggregation-competent cells gave complete inhibition of log-phase cell cohesion but at much higher concentration than log membranes. Treatment of log-phase cells with cyclohex imide for 8 h rendered them completely non-cohesive. Membranes from cyclo- heximide-treated cells had no effect on log-phase cell cohesion. Log-phase membranes gave complete inhibition of cohesion of 4 slime mould species. The results are discussed in terms of our liga nd-receptor model of log-phase cell cohesion.
Magnesium ions and the control of the cell cycle in yeast
Authors: Walker Graeme M. , Duffus John H. 
Published: April 2021

ABSTRACTA study has been made of the role of magnesium ions in cell division cycle control in the fission yeast, Schizosaccharotnyces pornbe, and the budding yeast, Kluyveromyces fragilis. Synchronization of cell division in these organisms can be induced by restoring magnesium to magnesium-exhausted cultures. In S pombe, a correlation exists between the time taken for cells to enter the first synchronous division and the period of magnesium exhaustion. During short-term incubation in magnesium-deficient media, S. pombe cells are observed to continue growth in length, but they fail to make a cell plate and divide ; long-term magnesium deficiency results in the production of aberrant cell forms, and a reduction in viability. Analysis of total cell magnesium in cultures of both S, pombe and K. fragilis, synchronized by various induction and selection procedures, revealed that there is a fairly steady fall in magnesium concentration as cells grow, terminating in a rapid influx of magnesium just before cell division. This leads to the hypothesis that falling magnesium concentration may act as a transducer of cell size, eventually triggering spindle formation and a membrane change which permits rapid uptake of magnesium to a concentration which brings about spindle breakdown. The hypothesis was tested directly using the divalent cation ionophore, A23187, in the absence of calcium ions; the results obtained showed that a short pulse of A23187, very late in the cell cycle, accelerated cells into division and shortened the subsequent cycle. The hypothesis is discussed in relation to current models of cell cycle regulation.
Microtubules and control of macronuclear ‘amitosis’ in Paramecium
Authors: Tucker J. B. , Beisson J. , Roche D. L. J. , Cohen J. 
Published: April 2021

ABSTRACT
The ‘amitotic’ division of the macronucleus during binary fission in P. tetraurelia includes a detailed sequence of shape changes that are temporally coordinated with the adoption of a series of well-defined positions and orientations inside the cell. The deployment of nucleo-plasmic microtubules that is spatially correlated with the shaping ritual is more complex and precise than has been reported previously. Macronuclear division is not amitotic. It is not a simple constriction into two halves.
As a dividing macronucleus starts to elongate it becomes dorsoventrally flattened against the dorsal cortex of the organism and assumes an elliptical shape. Concurrently, an elliptical marginal band of intranuclear microtubules assembles that has the same spatial relationship to nuclear shape as the marginal microtubule bands of certain elliptical vertebrate blood cells have to cell shape. The band breaks down as further elongation occurs and the nucleus adopts the shape of a straight and slender sausage. Most of the intranuclear microtubules assemble as elongation starts and break down shortly after elongation is completed; the majority are oriented parallel to the longitudinal axis of the nucleus throughout elongation. Some of them are attached to nucleoli and are coated with granules which are almost certainly derived from the cortices of nucleoli. The peripheral concentration, interconnexion, orientation, and overlapping arrangement of microtubules, and the reduction in microtubule number per nuclear cross-section as elongation proceeds at a rate of about 40 μm min−1, are all compatible with the provision of a microtubule sliding mechanism as the main skeletal basis for elongation. There are indications that this mechanism is augmented by anchorage and/or active propulsion of nucleoli that may perhaps facilitate fairly equitable segregation of chromosomal material to daughter nuclei.
Inhibition of leukocyte locomotion by hyaluronic acid
Authors: Forrester J. V. , Wilkinson P. C. 
Published: April 2021

ABSTRACT
The effect of hyaluronate on neutrophil motility in vitro was studied by the micropore filter technique and by direct visual analysis of the locomotion of neutrophils on glass. Both directed and random locomotion of neutrophils were inhibited by physiological concentrations (0·5–6·0 mg ml−1) of hyaluronate in adose- and molecular weight-dependent manner. Inhibition of cell movement was more pronounced for high molecular weight chemoattractants such as casein than for small chemotactic peptides such as f-Met-Leu-Phe. Chemotactic factor gradient formation in filter chambers was profoundly retarded by hyaluronate, which may partly explain the inhibitory effects of hyaluronate on directed neutrophil locomotion. In addition, hyaluronate inhibited the binding of chemotactic factor to the neutrophil surface. This effect, together with a reduction in cell-to-substratum adhesion, may provide an additional explanation for hyaluronate-induced inhibition of random neutrophil locomotion. Inhibition of locomotion by hyaluronate was easily reversed by washing the cells free of hyaluronate; thus competition by hyaluronate for cell-surface binding sites is unlikely, and physical effects such as steric exclusion or molecular sieving by the large hyaluronate polymer provide the most probable explanations of its inhibitory effect on cell locomotion.
Since hyaluronate is a major constituent of tissue matrices, these results draw attention to the importance of the extracellular environment in regulating inflammatory cell movement in vivo.
Use of purified endopolygalacturonase for a topochemical study of elongating cell walls at the ultrastructural level
Authors: Roland Jean-Claude , Vian Brigitte 
Published: April 2021

ABSTRACT
Endopolygalacturonase, a fungal enzyme purified by Albersheim and hia group which specifically degrades the galacturonosyl linkages of pectic polysaccharides, was used at the ultrastructural level on intact tissues from differentiated organs. Specimens were taken from the elongating zone of mung bean (Vigna radiata) hypocotyls. Incubation with the enzyme solution was performed en bloc, prior to embedding and to ultrastructural cytochemistry (PATAg test for polysaccharides), or by flotation of ultrathin frozen sections.
From the morphological viewpoint, the images obtained are sharp and reproducible. They support the plywood model for the organization of expanding walls. The ordering of walls appears to be built up very early, at the very beginning of elongation, in the upper part of the hypocotyl (hook). The specificity of the enzyme allows a topochemical study of the wall. Data indicate an uneven distribution of polysaccharides of pectic type across a single wall and among the different cells. Outer and inner wall areas are highly resistant to extraction by endopolygalacturonase. In the middle lamella the insolubility of amorphous components probably indicates a local concentration of highly methyl-esterified carboxyl groups not susceptible to endopolygalacturonase attack; conversely, adjacent parts of the middle lamella are regularly extracted, indicating a high concentration of galacturonans. An intense extraction occurs in the bow-shaped zone, revealing the occurrence of a massive embedding of unesterified pectic polysaccharides around the fibrillar subunits responsible for the twisted patterns. In the inner and recent part of the wall, the ordering of fibrillar subunits seems progressive and possibly related to the pectic embedding. This incrusting material could play a role in the morphogenesis of the ordered wall by means of specific assembly and interconnections of wall subunits.
Inversion in Volvox Tertius: The effects of con a
Authors: Ireland Grenham W. , Hawkins Shirley E. 
Published: April 2021

ABSTRACT
During the development of Volvox tertius spheroids, a single-celled gonidium enlarges and undergoes multiple incomplete cleavages to give an embryo which is ‘inside-out’ with respect to the adult organism. A morphogenetic movement, termed ‘inversion turns this hollow ball of cells ‘inside-out’ through a hole, the phialopore. In V. tertius this phialopore possesses 4 inwardly directed lips.
Normal inversion was studied in vitro in slide chambers and involved cell-shape changes accompanied by the production of pseudopodia and the bending backwards of the phialopore lips.
100 µg/ml Con A specifically and reversibly blocked inversion. Despite the inhibitory effect on cell division, the blocking of inversion was not due to the blocking of the last cell division some 50–100 min prior to inversion. Neither did the first cell-shape change from pear-to spindle-shape appear blocked. A feature of inhibition by Con A was the enhanced production of pseudopodia by embryos blocked at inversion, and the abnormal production of pseudopodia by embryos blocked at earlier stages. Non-inverting embryos showed internal flagella. We suggest that the Con A block to inversion, which may be reversed by α-methyl mannoside, arises from the prevention of backwards-bending of the phialopore lips.
Fluorescein-isothiocyanate-Con A bound to embryo and cell coat, and more strongly to the embryo at pre-inversion. SDS-polyacrylamide gel analysis of proteins isolated from embryos showed 4 glycoprotein bands, but Con A binding to these bands could not be demonstrated.
Differentiation of neurosensory cells in Hydra
Authors: Davis Lowell E. 
Published: April 2021

ABSTRACT
The differentiation of neurosensory cells in Hydra has been studied at the level of the electron microscope. These cells arise from interstitial cells (undifferentiated cells) and not from pre-existing nerve cells. Furthermore, there is no evidence to suggest that neurosensory cells represent a stage in the development of other nerve cells, i.e. ganglionic and neurosecretory cells. Major cytoplasmic changes in fine structure during differentiation include development of a cilium and associated structures (basal body, basal plate, rootlets), development of micro tubules and at least two neurites, increase in Golgi lamellae and formation of dense droplets typical of neurosecretory droplets, structural variations in mitochondria and a decrease in the number of ribosomes. Granular endoplasmic reticulum is characteristically poorly developed in all stages of differentiation, including the mature neurosensory cell. Nuclear and nucleolar changes also occur during differentiation but these are less dramatic than the cytoplasmic events.
The possibility of neurosensory cells being bi- or multiciliated and the presence of inter cellular bridges between these cells are considered. The function of neurosensory cells is dis cussed briefly in relation to the function of the cilium and neurosecretory droplets.
Locomotion ofXenopusepidermis cells in primary culture
Authors: Bereiter-Hahn Jürgen , Strohmeier Renate , Kunzenbacher Inge , Beck Konrad , Vüth Monika 
Published: April 2021

ABSTRACTThe locomotion of single epidermis cells, grown out from Xenopus laevis tadpole tails has been investigated by time-lapse cinemicrography using phase-contrast and reflection-contrast optics. The cells develop a large, mostly 200–250 nm thick, lamella, which adheres homogeneously to the supporting coverglass and exceeds the projection area of the cell body. From the comparison of RIC-pictures taken at high (1.06) and low (0.62) numerical aperture of illumination (I.N.A.) we deduce that at low I.N.A. the embossment of the medium-facing side of the lamella is visualized. By this method microcolliculi are demonstrated, which form at the edge of the lamellipodium and move backward. They resemble ruffles, but are flatter and no membrane flow towards the perinuclear region is observed. Indirect immunofluorescence reveals an enhanced staining for actin and α-actinin in the lamellipodium and in the transition region of cell body and lamella. Tonofilaments do not participate in lamella formation, the relatively few microtubules seem to be oriented in the direction of cytoplasmic flow. Electron micrographs demonstrate the course of fibrils in the cell body and a meshwork of actin filaments and membranous tubules in the lamella. Based on these findings a model for cell locomotion is presented : the motive force is generated by the cell body causing a flow of cytoplasm towards the periphery and extension of the lamella at its edge. The activity of the lamellipodium has to ensure the flat form of the advanced edge; microcolliculi are assumed to represent a small membrane store for the extension of the lamella. The lamellipodium is not involved in the production of motive force. The cell body is anchored to the lamella by radiating fibrils and the fibrillar meshwork is inserted at the ‘dorsal’ membrane of the lamella and the basal filament cortex of the cell body. This anchorage provides the structural basis for the uptake of lamella material into the cell body in the transition region.
Effects of organic solvents on flagellar asymmetry and quiescence in sea urchin sperm
Authors: Gibbons Barbara H. 
Published: April 2021

ABSTRACT
Low concentrations of methanol, 2-propanol and ethylene glycol increase the asymmetry of the flagellar waveforms and the turning rate of both live sperm and potentially symmetrical sperm reactivated with 1 mM-MgATP2−, while at the same time causing a decrease in the beat frequency. Similar effects are observed if the solvents are added to preparations of potentially symmetrical sperm reactivated in the presence of 1 mM free Ca2+, or to potentially asymmetrical sperm reactivated without added Ca2+. A second group of solvents, N,N- dimethylformamide, formamide and p-dioxane, also decrease the flagellar beat frequency, but have the opposite effect on symmetry, reducing the asymmetry of the waveforms and the turning rate of potentially symmetrical sperm reactivated in the presence of 1 mM free Ca2+. These effects of solvents are all reversible within about 5 min after initial exposure to solvent.
Higher concentrations of methanol and 2-propanol (above ∼5 and 0·8 mole %, respectively) induce quiescence in potentially asymmetrical sperm reactivated with concentrations of MgATP2− ranging from 10 μM to 1 mM. The quiescent flagella initially assume a bent form very similar to that seen in Ca2+-induced quiescence, and show a subsequent time-dependent distortion of the initial bent form with eventual disintegration and splitting off of bundles of microtubules.
Dimethylformamide, formamide and dioxane have almost no effect on the intrinsic asymmetry of potentially asymmetrical sperm reactivated in the absence of added Ca2+,butaddition of these solvents to potentially asymmetrical sperm that have been induced to become quiescent by addition of 0·1 mM free Ca2+ causes the sperm to resume swimming with flagellar waveforms that are substantially more symmetrical than those of the starting preparation before the addition of Ca2+.
Mild digestion with trypsin of reactivated sperm that have been induced either to beat asymmetrically or to become quiescent by addition of methanol causes a gradual appearance of symmetrical flagellar beating, as in the case of Ca2+-induced quiescence. The flagellar beat frequency, however, remains low, at about 20 Hz.
The results suggest that the solvents either mimic or block the action of Ca2+ by interaction with a Ca,+-dependent regulatory protein, and may also induce alteration in the rate constants of dynein ATPase.
Age-associated change in macronuclear DNA content in Paramecium Caudatum*
Authors: Takagi Yoshiomi , Kanazawa Naoko 
Published: April 2021

ABSTRACT
Macronuclear DNA content in Paramecium caudatum was found to be almost unchanged with a mean of about 400C during the earlier two-thirds of the life span in terms of the number of fissions and then it dropped rapidly to about one-fifth of the initial content. The age when rapid DNA decline occurred corresponded to that when the characteristics of senescence appeared. This decreasing pattern of macronuclear DNA content contrasted with earlier observations in P. tetraurelia, P. bursaria and Tetrahymena thermophila. The data suggested that in P. caudatum the distribution pattern of macronuclear DNA to daughter cells changed from an almost equal distribution in younger cells to an unequal distribution in older cells, while the relative volume of the macronucleus to the whole cell remained almost constant throughout the life cycle.
Interaction between intracellular vacuoles and the cell surface analysed by finite aperture theory interference reflection microscopy
Authors: Gingell David , Todd Ian , Owens Norman 
Published: April 2021

ABSTRACT
Using finite aperture theory we have shown that localized very dark areas in the interference reflection images of Dictyostelium discoideum amoebae are due to the close intracellular approach of vesicles and tubular elements of the contractile vacuole system to the plasma membrane adjacent to the substratum. Vesicles interacting in this way become locally deformed to the planar contour of the substratum and are separated from the cell surface membrane by a constant ≲ 0·1 μm of cytoplasm. Lamellar processes formed by these cells on very adhesive surfaces have identical dimensions. This minimal thickness may be a mechanical consequence of a contractile mechanism which pulls membranes together.
Cell shape and organization of cytoskeleton and surface fibronectin in non-tumorigenic and tumorigenic rat liver cultures
Authors: Bannikov G. A. , Guelstein V. I. , Montesano R. , Tint I. S. , Tomatis L. , Troyanovsky S. M. , Vasiliev J. M. 
Published: April 2021

ABSTRACT
Morphological changes associated with neoplastic transformation of epithelial cells were studied in a series of IAR cell lines derived from rat liver. The series included three independently obtained, non-tumorigenic lines and five derived, tumorigenic lines.
The morphology of cell surfaces was observed by scanning electron microscopy; the distribution of actin, tubulin and fibronectin was determined by indirect immunofluorescence.
All the non-tumorigenic lines had a typical epithelioid morphology: isolated cells of these lines spread on the substratum had a discoid shape and contained circular, marginal bundles of microfilaments and microtubules. In denser areas, the cells formed monolayered sheets with characteristic marginal bundles of microfilaments near the free edges.
Decreased spreading of isolated cells on the substratum was the characteristic feature that distinguished tumorigenic lines from their non-tumorigenic parent lines. In particular a decrease in the size of the ring-like, peripheral lamella and its disintegration into several discrete lamellar zones were often observed; as a result, the cell shape was altered from discoid to polygonal or elongated. The altered distribution of microfilament bundles and microtubules was characteristic in elongated cells; the pattern of the cytoskeletal elements of these cells resembled that of polarized fibroblasts. Complete disappearance of microfilament bundles was observed in cells of only one tumorigenic line.
Various degrees of disorganization of monolayered cell sheets were observed in tumorigenic cultures, accompanied by an altered distribution of microfilament bundles.
The alterations in the fibronectin-containing structures were more complex: there were often fewer fibronectin ‘spots’ and fibrils at the lower surfaces of cells of tumorigenic cultures as compared with those of non-tumorigenic ones; there were more fibrils in dense cultures of certain lines but fewer in others.
It is concluded that alterations in the ability to spread on the substratum and to form cell–cell contacts are common features of morphologically transformed fibroblastic and epithelial cultures. However, the actual changes in the cytoskeletal structures that accompany these alterations are different in transformed cultures of various tissue types.
The Euglena paraflagellar rod: structure, relationship to other flagellar components and preliminary biochemical characterization
Authors: Hyams Jeremy S. 
Published: April 2021

ABSTRACT
Demembranated flagella from Euglena gracilis consisted of three distinct components: a 9 + 2 axoneme of microtubules, an extensive surface coating of long and short mastigonemes and a lattice-like axial fibre known as the paraflagellar rod. Negatively stained preparations of isolated paraflagellar rods showed the major structural unit to be a 22 nm filament oriented at approximately 45° to the long axis of the rod in a 7-start left-handed helical arrangement. Attachment of the paraflagellar rod to the flagellar axoneme was via a series of goblet-shaped projections, which anchored the rod to a single outer doublet microtubule. Comparisons of axonemes from E. gracilis bearing the paraflagellar rod with those of Chlamydomonas rein-hardtii, in which it is absent, by polyacrylamide gel electrophoresis revealed the presence of two prominent additional peptides with molecular weights of 80000 and 69000. Exposure of Euglena axonemes to trypsin selectively solubilized the paraflagellar rod and also removed both proteins, which were therefore tentatively identified as the major subunit proteins of the rod and designated PFR 1 and 2, respectively. In addition to these details of the structure and composition of the paraflagellar rod, the mode of attachment to the axoneme of both long and short mastigonemes was also identified.