bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fibulin-1 suppression of fibronectin-regulated cell adhesion and motility
Authors: Twal Waleed O. , Czirok Andras , Hegedus Balazs , Knaak Christian , Chintalapudi Mastan R. , Okagawa Hiroto , Sugi Yukiko , Argraves W. Scott 
Published: April 2021

Fibulin-1 is an extracellular matrix protein often associated with fibronectin (FN) in vivo. In this study, the ability of fibulin-1 to modulate adhesion, spreading and motility-promoting activities of FN was investigated. Fibulin-1 was found to have pronounced inhibitory effects on the cell attachment and spreading promoted by FN. Fibulin-1 was also found to inhibit the motility of a variety of cell types on FN substrata. For example, the FN-dependent haptotactic motility of breast carcinoma (MDA MB231) cells, epidermal carcinoma (A431), melanoma (A375 SM), rat pulmonary aortic smooth muscle cells (PAC1) and Chinese hamster ovary (CHO) cells was inhibited by the presence of fibulin-1 bound to FN-coated Boyden chamber membranes. Cells transfected to overproduce fibulin-1 displayed reduced velocity, distance of movement and persistence time on FN substrata. Similarly, the incorporation of fibulin-1 into FN-containing type I collagen gels inhibited the invasion of endocardial cushion mesenchymal cells migrating from cultured embryonic heart explants. By contrast, incorporation of fibulin-1 into collagen gels lacking FN had no effect on the migration of endocardial cushion cells.These results suggest that the motility-suppressive effects of fibulin-1 might be FN specific. Furthermore, such effects are cell-type specific, in that the migration of gingival fibroblasts and endothelial cells on FN substrata is not responsive to fibulin-1. Additional studies found that the mechanism for the motility-suppressive effects of fibulin-1 does not involve perturbations of interactions between α5β1 or α4 integrins, or heparan sulfate proteoglycans with FN. However, fibulin-1 was found to inhibit extracellular signal regulated kinase (ERK) activation and to suppress phosphorylation of myosin heavy chain. This ability to influence signal transduction cascades that modulate the actin-myosin motor complex might be the basis for the effects of fibulin-1 on adhesion and motility.
Changes in some enzymes involved in dna biosynthesis following induction of division in cultured plant cells
Authors: Harland Jennifer , Jackson J. F. , Yeoman M. M. 
Published: April 2021

ABSTRACT
The biosynthetic enzymes DNA polymerase, thymidine kinase (TdR kinase) and thymidine monophosphate kinase (dTMP kinase) show characteristic patterns of activity associated with cell division in synchronously dividing tissue cultures of the Jerusalem artichoke. In each case the first major increase in enzyme activity is coincident with and dependent upon DNA replication. In addition the increased activities of all 3 enzymes are not due to the activation of pre-existing enzyme or to the removal of inhibitors. A theory is advanced to account for the close correlation between DNA synthesis and the major rise in activity of the 3 enzymes.
Visna virus infection of sheep and human cells in vitro-an ultrastructural study
Authors: Macintyre E. H. , Wintersgill C. J. , Vatter A. E. 
Published: April 2021

ABSTRACT
Comparison of human astrocytes (1181N1 line) and sheep choroid plexus cells (SCP) infected with visna virus (V-1181N1 and V-SCP) shows that the mode of virus assembly and the morphology and size of the free virions are identical in the 2 systems. V-SCP cells usually cytolyse soon after infection; V-1181N1 cells do not. This is considered to be due to inter ference with membrane assembly in the former. Syncytial giant cells from both V-1181N1 and V-SCP cultures have a much looser attachment to the growth surface than their un infected parents. This is shown to be associated with a loss of certain microfibrillar arrays close to the plasmalemma. Uninfected SCP cultures have cilia and desmosomes and retain these after infection till cytolysis; 1181N1 cells do not have these structures, but have a well developed microtubular system, which the SCP cells lack.
Histochemical and biochemical demonstration of sialic acid and sulphate in vesicles and membranes isolated from nerve endings of rat brain
Authors: Marx Ruth , Graf Elke , Wesemann W. 
Published: April 2021

ABSTRACT
The reaction of colloidal iron hydroxide (CIH) with acidic groups was applied for an ultra structural study of the distribution of sulphuric acid monoesters and sialic acid in synaptic vesicles and external nerve ending membranes isolated from rat brain. At pH 1·7 CIH was precipitated as electron-dense granules with a uniform size of 6—7 nm specifically labelling the carboxyl group of sialic acid and the sulphate group of monoesters of sulphuric acid. The differentiation of these 2 groups was achieved by treatment with neuraminidase and methylation followed by saponification. After preincubation with neuraminidase, which released 90—100 % of the sialic acid from the membranes of the synaptic vesicles and the nerve endings, the electron-dense deposits marked the reaction sites of sulphate with CIH. The sulphate groups which were present at a concentration of 2·3 and 2·2 μmol/mg protein for the synaptic vesicle and nerve ending membrane preparations, respectively, were rendered soluble as methyl monosulphate by trans-esterification with acid/methanol and quantitatively removed from the structures. By this treatment membrane-bound sialic acid was blocked as sialic acid methyl ester and partly split off by acid hydrolysis. About 55 % of the sialic acid found in the nerve ending membranes remained attached to the structure as compared with about 35 % of the sialic acid of the vesicles. The acid-resistant proportion of the sialic acid could be localized with CIH after saponification of the esterified preparations. The method described allows the electron-microscopical demonstration of acid-resistant, neuraminidase-sensitive sialic acid in synaptic structures and the discrimination from sulphated mucopolysaccharides.
Structural and functional modifications of the nucleus during oogenesis in the mosquito Aedes aegypti
Authors: Fiil Annelise 
Published: April 2021

ABSTRACT
The observations are based on reconstructions from electron micrographs of complete serial sections of some 20 oocytes at different stages of development. At eclosion the Aedes aegypti egg chambers each contain 8 interconnected cells, one oocyte and 7 nurse cells. During the next few days the egg chambers develop up to a previtellogenic resting stage. The most advanced oocytes are now in the diplotene stage of meiosis. Following the first blood meal vitellogenesis commences and lasts for 3−4 days. During this time the oocyte increases from a sphere with a diameter of 30μm to an elongate spheroid of the dimensions 190 × 600μm. The nucleus expands with the oocyte, first branching then forming a cup-shaped structure, and finally elongating to a large sheet-like, cylindrical form. The chromosomes, condensed into a karyosphere, remain at the anterior pole close to the nurse cells. Towards the end of vitellogenesis meiosis is resumed, and shortly thereafter the envelope of the large nucleus disintegrates. For a short period the chromosomes, which are in first meiotic metaphase, are without an enveloping membrane, then several layers of vesiculate membrane reassemble around them, trapping some of the cytoplasm in the process. At this stage the oocyte may be ovulated or it may rest unchanged for some time. Thirty minutes after oviposition meiosis is complete, and the masses of membranes assemble in a few regions which later degenerate with the polar bodies.
Applications of a theory of biological pattern formation based on lateral inhibition
Authors: Meinhardt H. , Gierer A. 
Published: April 2021

ABSTRACT
Model calculations are presented for various problems of development on the basis of a theory of primary pattern formation which we previously proposed. The theory involves shortrange autocatalytic activation and longer-range inhibition (lateral inhibition). When a certain criterion is satisfied, self-regulating patterns are generated.
The autocatalytic features of the theory are demonstrated by simulations of the determination of polarity in the Xenopus retina. General conditions for marginal and internal activation, and corresponding effects of symmetry are discussed. Special molecular mechanisms of pattern formation are proposed in which activator is chemically converted into inhibitor, or an activator precursor is depleted by conversion into activator.
The (slow) effects of primary patterns on differentiation can be included into the formalism in a straightforward manner. In conjunction with growth, this can lead to asymmetric steady states of cell types, cell differentiation and proliferation as found, for instance, in growing and budding hydra. In 2 dimensions, 2 different types of patterns can be obtained. Under some assumptions, a single pattern-forming system produces a ‘bristle’ type pattern of peaks of activity with rather regular spacings on a surface. Budding of hydra is treated on this basis. If, however, gradients’ develop under the influence of a weak external or marginal asymmetry, a monotonic gradient can be formed across the entire field, and 2 such gradient-forming systems can specify ‘positional information’ in 2 dimensions.
If inhibitor equilibrates slowly, a spatial pattern may oscillate, as observed with regard to the intracellular activation of cellular slime moulds.
The applications are intended to demonstrate the ability of the proposed theory to explain properties frequently encountered in developing systems.
Sulphur in different types of keratohyalin granules: a quantitative assay by x-ray microanalysis
Authors: Jessen H. , Peters P. D. , Hall T. A. 
Published: April 2021

ABSTRACT
The elemental composition of keratohyalin granules from the interpapillary and papillary lingual epithelium and the oesophageal epithelium of the rat were studied by X-ray microanalysis in an EMMA-4 analytical electton microscope, equipped with an energy dispersive detector. A quantitative assay of the sulphur concentration in keratohyalin granules was performed, using a suitable sulphur standard. The results demonstrate that different types of keratohyalin granule have different compositions. Single granules - a type of keratohyalin granule present in both nuclei and cytoplasm of the epithelial cells - are rich in sulphur, having a content of 3·6-3·8%. Another type of keratohyalin granule - composite granules - contains a sulphur-rich component and a sulphur-poor component. The sulphur-poor component contains 0··8-1·4% sulphur. It is suggested that the sulphur-rich keratohyalin granules are involved in the deposition of the peripheral envelope protein of cornified cells.
Cytochalasin b: aspects of phagocytosis in nutrient uptake in tetrahymena
Authors: Hoffmann Else K. , Rasmussen L. , Zeuthen E. 
Published: April 2021

ABSTRACT
Cytochalasin B (37 μg per ml) reduces the rate of food vacuole formation, i.e. the rate of phagocytosis, in Tetrahymena pyriformis. Cytochalasin B in this concentration suppresses multiplication rates in a nutrient medium consisting of 2 % proteose peptone, but multiplication is unaffected if this medium is supplemented with glucose and high concentrations of nucleosides. Thus nutrients in high concentrations circumvent the necessity for phagocytosis in Tetrahymena.
Contractile filopodia and in vivo cell movement in the tunic of the ascidian, Botryllus schlosseri
Authors: Izzard C. S. 
Published: April 2021

ABSTRACT
The in vivo movement of one class of cells in the tunic of the ascidian Botryllus schlosseri has been analysed using differential interference optics and time-lapse cinematography. Long (up to 200 μm), thin (0·35–0·5 pm diameter) filopodia radiate from the cell-body into the matrix of the tunic. Movement of the cell-body consists of a series of short, jerky displacements with frequent changes in direction between successive displacements. The net displacement of the cell may be extremely small when the displacements are short and frequently change direction, or considerable when successive displacements show a persistence of direction (up to 114 μm in 60 min). Deformation of the elastic cuticle covering the tunic at points of attachment of the filopodia has been used to record qualitatively changes in tension in the filopodia. Correlation of the changes in tension with changes in length of the filopodia and movement of the cell-body have permitted the following conclusions. Active contractions of filopodia (i.e. increase in tension during shortening) stretch and move the cell-body. These movements exert a force on trailing or opposing filopodia. Relaxations of filopodia (i.e. decrease in tension during lengthening) result in small movements of the cell-body due to the recoil of tension in the cell-body and opposing filopodia. The position of the cell-body in space at any one instant in time is therefore the resultant of the forces developed in all the filopodia. Movement results from unilateral modulation of the tension developed in the filopodia. Active contractions play a more significant role in movement than relaxations.
The control of karyogamy in somatic cells of Ustilago violacea
Authors: Day A. W. , Day Lynne L. 
Published: April 2021

ABSTRACT
The rate of nuclear fusion (karyogamy) in the haploid smut fungus, Ustilago violacea, designated D, can be determined accurately from the frequency of diploid formation. The spontaneous value of D depends mainly on the age of the cells and the temperature, varying from 10−5 to 10−2. Ultraviolet light (u.v., 254 nm) induces high rates of fusion, up to too % of the survivors being diploid after very high doses. That this increase is caused by induction and not by selection is shown by the absolute increase in the number of diploids obtained under some conditions. The high value of D after a u.v. treatment is reduced by conditions which favour photoreactivation or dark repair. Acriflavine, an inhibitor of dark repair, maintains high values of D, while caffeine which also inhibits dark repair abolishes the u.v. induction entirely.
Ultraviolet-sensitive mutants located at 4 loci were tested for their effect on spontaneous and u.v.-induced karyogamy. One mutant (uvs4) showed complete absence of somatic karyogamy even after high doses of ultraviolet. Mutant uvs2 had no effect on the value of D, while mutants uvs1 and uvs3 showed low spontaneous karyogamy, but could be induced by low doses of u.v. to yield large numbers of diploids.
It is suggested that an inhibitor of karyogamy is formed in somatic cells and destroyed prior to premeiotic karyogamy. The accuracy of the transcription of this inhibitor seems to be impaired by ultraviolet, but can be restored following DNA repair. The absence of somatic karyogamy in uvs4 mutants may indicate that these strains contain an altered organelle involved in the control of karyogamy, e.g. the spindle pole body situated on the nuclear membrane, and known to contain DNA. Alteration of such an organelle could produce pleiotropic effects including u.v. sensitivity and inhibitor production or action.
The localization of calcium and phosphorus in human platelets
Authors: Skaer R. J. , Peters P. D. , Emmines J. P. 
Published: April 2021

ABSTRACTLarge amounts of calcium and phosphorus have been found by electron-microprobe analysis in the dense bodies of frozen-dried, human platelets. The calcium and phosphorus occurred in a fixed ratio that was similar to that in dicalcium ATP. No other elements were detectable except chlorine. Minute, electron-dense disks were found in the surface membranes of glutaraldehyde-fixed platelets, and are very variable in number in any population of normal platelets. Both dense bodies and membrane granules are absent if platelets are fixed in the absence of calcium, and are also absent from aggregated platelets.
Decrease in section thickness on exposure to the electron beam; the use of tilted sections in estimating the amount of shrinkage
Authors: Bennett Pauline M. 
Published: April 2021

ABSTRACT
Tilting experiments on sections of embedded light meromyosin paracrystals of known periodic structure indicate that the section thickness decreases during examination in the electron microscope. The material remaining in the section after irradiation collapses uniformly to about one half the initial thickness. This must be taken into account when measurements are made on tilted sections.
Visualization of charged groups on the surface of rat liver nuclei
Authors: Virtanen Ismo , Wartiovaara Jorma 
Published: April 2021

ABSTRACT
Anionic groups on the outer surfaces of isolated rat liver nuclei were rendered visible in the electron microscope by staining with colloidal iron hydroxide at different pH values. At pH 1·8 the nuclei did not adsorb particles of stain, although plasma membranes left in the same preparation showed heavy labelling. After pretreatment with neuraminidase at pH 6 the plasma membranes were no longer stained. At pH 3·0 the nuclear surfaces also stained intensely. The staining pattern acquired at this pH did not appear to be changed by neuraminidase pretreatment.
With the staining method used, rat liver nuclear surfaces seemed to have no exposed sialic acid under isolation conditions which preserve the nuclear membranes and leave the ribosomes attached to the nuclear surface. However, at higher pH values other anionic groups seem to become dissociated and are stained with colloidal iron hydroxide.
Observations on the male nucleus during fertilization in the fern Pteridium aquilinum
Authors: Bell P. R. 
Published: April 2021

ABSTRACT
Fertilization of eggs of Pteridium under controlled conditions has revealed that archegonia containing viable eggs require more than 30 min flooding before opening. Syngamy appears to take place by an engulfing action, and no evidence was found of a ‘membrane-fusion’ kind of conjugation.
Although the gametic nucleus lacks a recognizable envelope, as soon as it comes into contact with the female cytoplasm an envelope is reconstituted from an opaque layer at the surface of its chromatin. This membrane also undergoes growth, the outer layer extending into the cytoplasm and surrounding spermatozoid mitochondria. The male envelope remains distinct from the female, and lacks evaginations and well defined pores.
The male nucleus lies in irregular loops within a funnel, filled with egg cytoplasm, formed by the microtubular ribbon of the gamete. The mouth of the funnel is bordered by the multilayered structure. Karyogamy is initiated at the anterior end of the male nucleus, the orifice connecting the 2 nuclei widening from about 0·7 to 2 μm in diameter during fusion. The contents of the male nucleus flow through the mouth of the funnel into the female, the chromatin relaxing locally, but retaining a rod-like form. The envelope of the male nucleus is probably resorbed at the site of junction. There is no evidence that it contributes significantly to the envelope of the zygotic nucleus.
A light- and electron-microscope study of the oocyte nucleus during development of the antral follicle in the prepubertal mouse
Authors: Chouinard L. A. 
Published: April 2021

ABSTRACT
The ordered changes which occur in the structural organization of the mouse oocyte nucleus during the preparatory, the maturative and the preovulatory stages of antral follicle development, have been studied under both light and electron microscopy. All observations have been made on those antral follicles whose development is initiated on postnatal day 14 and completed by postnatal day 28 in prepubertal animals of the ICR albino mouse strain. The formed entities that can be recognized within the oocyte nucleus during that period are the condensing bivalents, the heterochromatic knobs, the nucleolus and the extranucleolar bodies. At the onset of antral follicle development, the highly unravelled dictyate bivalents are seen to take on a lampbrush-type configuration. Subsequent condensation of these lampbrush bivalents appears to be a very gradual and lengthy process that extends over almost the entire period of antral follicle development. The shortening and thickening of the lampbrush bivalents are best interpreted as resulting from the withdrawal of their lateral loop-like projections into the chromosome axes and from the focal aggregation of these axes into compact chromatin masses. Electron-opaque granules, which appear within the oocyte nucleus during the preparatory and maturative follicle stages, are seen to be intimately associated with these condensing bivalents. A number of Feulgen-positive heterochromatic knobs make their appearance in contact with certain bivalents during the preparatory follicle stage. These knobs are not reincorporated as such into the condensing chromatin masses and undergo disintegration and dissolution during the preovulatory follicle stage. The size, shape and ultrastructural features of the nucleolus remain unchanged throughout the period of antral follicle development. Breakdown and dissolution of the nucleolar mass is a swift process that takes place only in the fully mature preovulatory follicle and more or less concomitantly with the dismantling of the nuclear envelope. The extranucleolar bodies increase noticeably in size during the preparatory and the maturative follicle stages; they shrink in size and undergo dissolution during the preovulatory stage of antral follicle development.
An attempt is made to interpret these morphological changes in the light of current knowledge concerning the architectural and functional organization of the oocyte nucleus in general during meiotic prophase. The relevant observational evidence would be consistent with the view that, during antral follicle development, the mouse oocyte nucleus is not, as too often assumed, in a period of arrested evolution; its formed components undergo structural, maturational and functional changes which are of significance not only for the resumption of the first meiotic prophase but also for the early development of the embryo.