Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Effect of light quality on movement of Pterostichus melanarius (Coleoptera: Carabidae)
    Allema, A.B. - \ 2014
    insects - movement activity - movement behavior - movement speed - red light sensitivity - resting behavior - arable land - insect pests - natural enemies - predatory insects - predators - pterostichus melanarius - dispersal - movement - animal behavior - quantitative analysis - motility - modeling - methodology
    The aim of this project was to study the effect of red light on night time behaviour of Pterostichus melanarius (Coleoptera: Carabidae). An experiment was conducted in experimental arenas in the autumn of 2008. Beetles were recorded 20 min per hour during a period of 8 hours under red light, near infrared radiation and white light.
    The effect of fibers on coagulation of casein-based enteral nutrition in an artificial gastric digestion model
    Luttikhold, J. ; Norren, K. van; Minor, M. ; Buijs, N. ; Braak, C.C.M. van den; Ludwig, T. ; Abrahamse, E. ; Rijna, H. ; Leeuwen, P.A.M. - \ 2014
    Food & Function 5 (2014). - ISSN 2042-6496 - p. 1866 - 1871.
    critically-ill patients - thermodynamic incompatibility - intestinal-obstruction - in-vitro - motility - proteins - absorption - guidelines - mixtures - feedings
    A serious complication seen in critically ill patients is the solidification of enteral nutrition causing gastrointestinal obstruction. It has been suggested that enteral nutrition enriched with insoluble fibers may increase the risk of this complication. Therefore, we investigate the effect of soluble and insoluble dietary fibers on the coagulation of a casein-based enteral nutrition in an artificial gastric digestion model. A 100% casein-based enteral nutrition was enriched with increasing concentrations of soluble fibers (acacia fiber, oligofructose and inulin) and insoluble fibers (soy polysaccharide, resistant starch and alpha cellulose). After digestion in an artificial gastric model, the chyme was poured over sequentially placed sieves, separating the coagulate into size fractions of larger than 2 mm, between 1 and 2 mm, and between 0.25 and 1 mm. Of these fractions we measured wet weight, dry weight and protein content. A significant effect on the fraction larger than 2 mm was considered to be clinically relevant. Addition of high concentrations soy polysaccharide and resistant starch to a casein-based enteral nutrition, did not alter the wet weight, whereas dry weight and protein content of the coagulate was significantly reduced. When high concentrations of soy polysaccharide and resistant starch are added to a 100% casein-based enteral nutrition, the coagulate consist of more water and less proteins, which may lead to an increased protein digestion and absorption in a clinical setting. The suggestion that insoluble fibers increase the risk of gastrointestinal obstruction in critically ill patients is not supported by these data.
    Quantifying and simulating movement of the predator carabid beetle Pterostichus melanarius in arable land
    Allema, A.B. - \ 2014
    Wageningen University. Promotor(en): Joop van Lenteren, co-promotor(en): Walter Rossing; Wopke van der Werf. - Wageningen : Wageningen University - ISBN 9789461739100 - 133
    bouwland - insectenplagen - natuurlijke vijanden - roofinsecten - predatoren - pterostichus melanarius - verspreiding - beweging - diergedrag - kwantitatieve analyse - motiliteit - modelleren - methodologie - arable land - insect pests - natural enemies - predatory insects - predators - pterostichus melanarius - dispersal - movement - animal behaviour - quantitative analysis - motility - modeling - methodology

    Keywords: landscape entomology, movement ecology, quantifying movement, population spread, habitat heterogeneity, motility, edge-behaviour, diffusion model, model selection, inverse modelling, Pterostichus melanarius, Carabidae, entomophagous arthropod

    Biological control provided by entomophagous arthropods is an ecosystem service with the potential to reduce pesticide use in agriculture. The distribution of entomophagous arthropods and the associated ecosystem service over crop fields is affected by their dispersal capacity and landscape heterogeneity. Current knowledge on entomophagous arthropod distribution and movement patterns, in particular for soil dwelling predators, is insufficient to provide advice on how a production landscape should be re-arranged to maximally benefit from biological pest control. Movement has mainly been measured in single habitats rather than in habitat mosaics and as a consequence little information is available on behaviour at habitat interfaces, i.e. the border between two habitats.

    This study contributes to insight into movement patterns of the entomophagous arthropod Pterostichus melanarius (Illiger) in an agricultural landscape as a knowledge basis for redesign of landscapes for natural pest control. Movement patterns were studied with video equipment in experimental arenas of 5 m2 and with mark-recapture at much larger scales in the field. Interpretation of the results was supported by diffusion models that accounted for habitat specific motility µ (L2 T−1), a measure for diffusion of a population in space and time, and preference behaviour at habitat interfaces.

    Movement of carabids has mostly been quantified as movement rate, which cannot be used for scaling-up. Available information on movement rate of carabids was made available for scaling-up by calculating motility from published data and looking for patterns through meta-analysis of data from thirteen studies, including 55 records on twelve species. Beetles had on average a three times higher motility in arable land than in forest/hedgerow habitat. The meta-analysis did not identify consistent differences in motility at the individual species level, and a grouping of species according to gender or size did not demonstrate a significant gender or size effect.

    A methodology to directly estimate motility from data using inverse modelling was evaluated on data of a mass mark-recapture field experiment in a single field of winter triticale (x Triticosecale Wittmack.). Inverse modelling yielded the same result as motility calculated from squared displacement distances. In the first case, motility was calculated as an average over motility of individuals, in the second case motility was estimated from a population density distribution fitted to the recapture data. The similarity in motility between these two very different approaches strengthens the confidence in motility as a suitable concept for quantifying dispersal rate of carabid beetles, and in inverse modelling as a method to retrieve movement parameters from observed patterns.

    The effect of habitat heterogeneity on movement behaviour was studied for P. melanarius across adjacent fields of oilseed radish (Raphanus sativus) and rye (Secale cereale) in a mark-recapture experiment. The field study was complemented by observations on movement behaviour in the experimental arena. Motility was neither significantly different between the crop species in the field nor in the arena. Overall movement in the field was significantly affected by behaviour at the interface between the crops. Beetles moved more frequently from rye to oilseed radish than in the opposite direction. The arena data indicated greater frequency of habitat entry into oilseed radish as compared to rye. Analysis of video tracking data from the arena resulted in estimates of motility that, when scaled up were close to those obtained in the field. Thus, the studies at the smaller and larger scales gave qualitatively and quantitatively similar results.

    The effect of habitat heterogeneity on within-season dispersal behaviour was further explored in an agricultural landscape mosaic comprising perennial strips and different crop species with distinct tillage management. Semi-natural grass margins were functionally different from the crop habitats. Motility was lower in margins than in crop habitats, and at the crop-margin interface more beetles moved towards the crop than to the margin. Margins thus effectively acted as barriers for dispersal. In the crop habitats motility differed between fields but no consistent relations were found with crop type, food availability or tillage. Based on the motility in crop habitats P. melanarius was predicted to disperse over a distance of about 100 – 160 m during a growing season in a landscape without semi-natural elements. Given this range little redistribution of beetles is expected between fields within a growing season, even more when fields are surrounded by grass margins or hedgerows, meaning that the success of biological control by this species is more dependent on field management affecting local population dynamics than on habitat heterogeneity.

    This thesis has resulted in a methodological approach to quantify dispersal behaviour of ground-dwelling insects from mark-recapture data in heterogeneous environments using inverse modelling. The combination of models and data proved to be powerful for studying movement and contributes to the development of predictive dynamic models for population spread of entomophagous arthropods. These models for population spread may be used as part of multi-objective assessment of alternative landscape configurations to find spatial arrangements of land use that maximize the ecosystem service of biological control as part of a wider set of landscape functions.

    Explaining Bacterial Dispersion on Leaf Surfaces with an Individual-Based Model (PHYLLOSIM)
    Wal, A. van der; Tecon, R. ; Kreft, J.U. ; Mooij, W.M. ; Leveau, J.H.J. - \ 2013
    PLoS ONE 8 (2013)10. - ISSN 1932-6203
    plant-microbe interactions - pseudomonas-syringae - biofilm formation - water availability - growth - detachment - diffusion - motility - colonization - wettability
    We developed the individual-based model PHYLLOSIM to explain observed variation in the size of bacterial clusters on plant leaf surfaces (the phyllosphere). Specifically, we tested how different 'waterscapes' impacted the diffusion of nutrients from the leaf interior to the surface and the growth of individual bacteria on these nutrients. In the 'null' model or more complex 'patchy' models, the surface was covered with a continuous water film or with water drops of equal or different volumes, respectively. While these models predicted the growth of individual bacterial immigrants into clusters of variable sizes, they were unable to reproduce experimentally derived, previously published patterns of dispersion which were characterized by a much larger variation in cluster sizes and a disproportionate occurrence of clusters consisting of only one or two bacteria. The fit of model predictions to experimental data was about equally poor (
    Diversity assessment of Listeria monocytogenes biofilm formation: Impact of growth condition, serotype and strain origin
    Kadam, S.R. ; Besten, H.M.W. den; Veen, S. van der; Zwietering, M.H. ; Moezelaar, R. ; Abee, T. - \ 2013
    International Journal of Food Microbiology 165 (2013)3. - ISSN 0168-1605 - p. 259 - 264.
    4b strains - temperature - motility - surfaces - chloride - 1/2a
    The foodborne pathogen Listeria monocytogenes has the ability to produce biofilms in food-processing environments and then contaminate food products, which is a major concern for food safety. The biofilm forming behavior of 143 L. monocytogenes strains was determined in four different media that were rich, moderate or poor in nutrients at 12°C, 20°C, 30°C and 37°C. The biofilm formation was mostly influenced by temperature, resulting in decreased biofilm formation with decreasing temperature. Biofilm formation was enhanced in nutrient-poor medium rather than in nutrient-rich medium, and especially in nutrient-poor medium significantly enhanced biofilm production was observed early in biofilm maturation underlining the effect of medium on biofilm formation rate. Also serotype had a significant effect on biofilm formation and was influenced by medium used because strains from both serotype 1/2b and 1/2a formed more biofilm than serotype 4b strains in nutrient-rich medium at 20°C, 30°C and 37°C, whereas in nutrient-poor medium the biofilm production levels of serotype 1/2a and 4b strains were rather similar and lower than serotype 1/2b strains. The strains used originated from various origins, including dairy, meat, industrial environment, human and animal, and the level of biofilm formation was not significantly affected by the origin of isolation, irrespective of medium used and temperature tested. A linear model was used to correlate crystal violet staining of biofilm production to the number of viable cells within the biofilm. This showed that crystal violet staining was poorly correlated to the number of viable cells in nutrient-poor medium, and LIVE/DEAD staining and DNase I treatment revealed that this could be attributed to the presence of non-viable cells and extracellular DNA in the biofilm matrix. The significant impact of intrinsic and extrinsic factors on biofilm production of L. monocytogenes underlined that niche-specific features determine the levels of biofilm produced, and insights in biofilm formation characteristics will allow us to further optimize strategies to control the biofilm formation of L. monocytogenes
    Ex vivo transcriptional profiling reveals a common set of genes important for the adaptation of Pseudomonas aeruginosa to chronically infected host sites
    Bielecki, P. ; Komor, U. ; Bielecka, A. ; Müsken, M. ; Puchalka, J. ; Pletz, M.W. ; Ballmann, M. ; Martins Dos Santos, V.A.P. ; Weiss, S. ; Häussler, S. - \ 2013
    Environmental Microbiology 15 (2013)2. - ISSN 1462-2912 - p. 570 - 587.
    burn wound infections - biofilm formation - cystic-fibrosis - therapeutic strategies - expression - motility - mutants - protein - system - identification
    The opportunistic bacterium Pseudomonas aeruginosa is a major nosocomial pathogen causing both devastating acute and chronic persistent infections. During the course of an infection, P.¿ aeruginosa rapidly adapts to the specific conditions within the host. In the present study, we aimed at the identification of genes that are highly expressed during biofilm infections such as in chronically infected lungs of patients with cystic fibrosis (CF), burn wounds and subcutaneous mouse tumours. We found a common subset of differentially regulated genes in all three in vivo habitats and evaluated whether their inactivation impacts on the bacterial capability to form biofilms in vitro and to establish biofilm-associated infections in a murine model. Additive effects on biofilm formation and host colonization were discovered by the combined inactivation of several highly expressed genes. However, even combined inactivation was not sufficient to abolish the establishment of an infection completely. These findings can be interpreted as evidence that either redundant traits encode functions that are essential for in vivo survival and chronic biofilm infections and/or bacterial adaptation is considerably achieved independently of transcription levels. Supplemental screens, will have to be applied in order to identify the minimal set of key genes essential for the establishment of chronic infectious diseases
    Inflammatory Chemokines Direct and Restrict Leukocyte Migration within Live Tissues as Glycan-Bound Gradients
    Sarris, M. ; Masson, J.B. ; Maurin, D. ; Aa, L.M. van der; Boudinot, P. ; Lortat-Jacob, H. ; Herbomel, P. - \ 2012
    Current Biology 22 (2012)24. - ISSN 0960-9822 - p. 2375 - 2382.
    cd8(+) t-cells - heparan-sulfate - neutrophil migration - dendritic cells - in-vivo - zebrafish - chemotaxis - motility - trafficking - attraction
    Chemokines are essential in many cell migration processes, including the recruitment of leukocytes to sites of infection [1-3]. In the latter context, chemokines promote leukocyte extravasation into the relevant tissue through a well-studied cascade of events [4-9]. It is widely believed that chemokines further guide leukocytes within tissues via chemotaxis, the directed migration along gradients of soluble ligands. However, the basic mechanism of chemokine action within tissues has yet to be formally addressed in vivo. We identified a chemokine (zCxcl8) that recruits zebrafish neutrophils to infection loci and analyzed its function directly within interstitial tissues of living larvae. Using noninvasive imaging and a controlled cellular source of zCxcl8, we found that zCxcl8 guides neutrophils in a 2-fold manner: by biasing cell speed according to direction (orthotaxis) and by restricting cell motility near the source. We further show that zCxcl8 establishes tissue-bound gradients in vivo by binding to heparan sulfate proteoglycans (HSPGs). Inhibition of this interaction compromised both directional guidance and restriction of neutrophil motility. Thus, by interacting with extracellular HSPGs, chemokines establish robust surface-bound (haptotactic) gradients that mediate both recruitment and retention of leukocytes at sites of infection.
    Partial and total fish meal replacement by agricultural products in the diets improve sperm quality in African catfish (Clarias gariepinus)
    Nyina-wamwiza, L. ; Milla, S. ; Pierrard, M.A. ; Rurangwa, E. ; Mandiki, S.N.M. ; Look, K.J.W. van; Kestemont, P. - \ 2012
    Theriogenology 77 (2012)1. - ISSN 0093-691X - p. 184 - 194.
    trout oncorhynchus-mykiss - rainbow-trout - reproductive-performance - dicentrarchus-labrax - cottonseed meal - hormone levels - by-products - sea bass - growth - motility
    This study investigated the long-term effects of total and partial replacement of dietary fish meal (FM) by a mixture of agricultural products on sperm quality of African catfish Clarias gariepinus. Four isonitrogenous and isoenergetic diets were formulated containing graded levels of either 50% FM and maize meal (diet 1); 25% FM mixed with crude sunflower oil cake (SFOC) and bean meal (BM) (diet 2); 12.5% FM mixed with sunflower oil cake, BM and ground nut oil cake (GOC) (diet 3) and 0% FM mixed with de-hulled sunflower oil cake (SFOCD), BM and ground nut oil cake (diet 4). Gonadosomatic index (GSI), sperm quality, plasma sex steroids (11-keto testosterone [11-KT]; testosterone [T]; estradiol-17beta [E2]) were evaluated on 10 to 24 fish fed on each diet. Sperm quality was assessed using computer-assisted sperm analysis (CASA). Total replacement of fish meal by plant products markedly increased sperm volume, spermatocrit, spermatozoa integrity, and sperm motility. Fish fed diet 3 (12.5% fish meal) provided intermediate results on sperm quality whereas the lowest values were obtained in fish fed diets 1 and 2. In fish fed 0% fish meal (diet 4), androgen levels were higher and estrogen levels were lower than in fish fed fish meal diets. Based on dietary lipid and fatty acid analyses, these results suggest a positive impact of short chain n-6 fatty acids on androgen synthesis and sperm quality. In conclusion, a combination of ground nut oil cake, bean meal and sunflower oil cake (preferably when the sunflower is dehulled) in African catfish diet improves the sperm quality.
    Optical tweezers for the micromanipulation of plant cytoplasm and organelles
    Hawes, C. ; Osterrieder, A. ; Sparkes, I.A. ; Ketelaar, T. - \ 2010
    Current Opinion in Plant Biology 13 (2010)6. - ISSN 1369-5266 - p. 731 - 735.
    root hair-cells - endoplasmic-reticulum - actin cytoskeleton - f-actin - transvacuolar strands - golgi stacks - myosin - arabidopsis - organization - motility
    Laser tweezers, often known as optical tweezers or optical traps, permit the capturing and micromanipulation of microscopic particles along X, Y and Z axes using the radiation pressure generated by a focused laser beam, normally in the infrared region of the spectrum. For trapping to be successful, the object to be captured must have a higher refractive index than that of its surrounding medium and forces generated by individual traps must be in the piconewton range [1]. Single optical traps are generally used to capture particles in the micron range, although multiple traps have been developed that can be utilized to move larger objects. Optical traps are commonly used in single-molecule techniques where, for example, they can be used to measure forces exerted on polymer beads coated with motor proteins. Thus, for instance, the mechanism of kinesin walking on microtubules or myosin on actin can be probed [[2] and [3]]. At the other end of the spectrum the optical traps are often used for the mechanical stimulation of cells [4] or manipulation of whole cells such as germinating fungal conidia [5]. What is, however, very apparent is that the full potential for using optical tweezers to manipulate organelles within living cells has yet to be fully exploited, with the majority of reports working at the whole-cell or single-molecule levels. Ashkin and Dziedzic [6•] were perhaps the first to show that cytoplasmic particles can be manipulated in vivo, when they demonstrated the pulling cytoplasm strands across vacuoles of onion epidermal cells and displacement of Spirogyra chloroplasts. Redirection of the growth of fungal hyphae by manipulation of the Spitzenkörper has been elegantly demonstrated through lateral displacement of this tip organelle [7]. Recently, and often in combination with confocal microscopy, it has been demonstrated that optical traps can be a very powerful tool in unravelling cytoplasmic dynamics. Here we discuss some of the few applications that have revealed new physical aspects of cytoplasmic and organelle dynamics in plant cells.
    Reconstitution of an Actin Cortex Inside a Liposome
    Pontani, L.L. ; Gucht, J. van der; Heuvingh, J. ; Salbreux, G. ; Joanny, J.F. ; Sykes, C. - \ 2009
    Biophysical Journal 96 (2009)1. - ISSN 0006-3495 - p. 192 - 198.
    proteins - complex - motility - vesicles - gel
    The composite and versatile structure of the cytoskeleton confers complex mechanical properties on cells. Actin filaments sustain the cell membrane and their dynamics insure cell shape changes. For example, the lamellipodium moves by actin polymerization, a mechanism that has been studied using simplified experimental systems. Much less is known about the actin cortex, a shell-like structure underneath the membrane that contracts for cell movement. We have designed an experimental system that mimicks the cell cortex by allowing actin polymerization to nucleate and assemble at the inner membrane of a liposome. Actin shell growth can be triggered inside the liposome, which offers a useful system for a controlled study. The observed actin shell thickness and estimated mesh size of the actin structure are in good agreement with cellular data. Such a system paves the way for a thorough characterization of cortical dynamics and mechanics
    Inherited complex I deficiency is associated with faster protein diffusion in the matrix of moving mitochondria
    Koopman, W.J.H. ; Distelmaier, F. ; Hink, M.A. ; Verkaart, S. ; Wijers, M. ; Fransen, J. ; Smeitink, J.A.M. ; Willems, P.H.G.M. - \ 2008
    American Journal of Physiology: Cell Physiology 294 (2008)5. - ISSN 0363-6143 - p. C1124 - C1132.
    fluorescence correlation spectroscopy - ubiquinone oxidoreductase deficiency - leigh-syndrome - human nadh - oxidative-phosphorylation - correlation microscopy - skin fibroblasts - steady-state - mutations - motility
    Mitochondria continuously change shape, position, and matrix configuration for optimal metabolite exchange. It is well established that changes in mitochondrial metabolism influence mitochondrial shape and matrix configuration. We demonstrated previously that inhibition of mitochondrial complex I (CI or NADH: ubiquinone oxidoreductase) by rotenone accelerated matrix protein diffusion and decreased the fraction and velocity of moving mitochondria. In the present study, we investigated the relationship between inherited CI deficiency, mitochondrial shape, mobility, and matrix protein diffusion. To this end, we analyzed fibroblasts of two children that represented opposite extremes in a cohort of 16 patients, with respect to their residual CI activity and mitochondrial shape. Fluorescence correlation spectroscopy (FCS) revealed no relationship between residual CI activity, mitochondrial shape, the fraction of moving mitochondria, their velocity, and the rate of matrix-targeted enhanced yellow fluorescent protein (mitoEYFP) diffusion. However, mitochondrial velocity and matrix protein diffusion in moving mitochondria were two to three times higher in patient cells than in control cells. Nocodazole inhibited mitochondrial movement without altering matrix EYFP diffusion, suggesting that both activities are mutually independent. Unexpectedly, electron microscopy analysis revealed no differences in mitochondrial ultrastructure between control and patient cells. It is discussed that the matrix of a moving mitochondrion in the CI-deficient state becomes less dense, allowing faster metabolite diffusion, and that fibroblasts of CI-deficient patients become more glycolytic, allowing a higher mitochondrial velocity.
    Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells
    Ingham, C.J. ; Jacob, E. Ben - \ 2008
    BMC Microbiology 8 (2008). - ISSN 1471-2180 - 16 p.
    expanding bacterial colonies - adaptive self-organization - myxococcus-xanthus - bacillus-subtilis - proteus-mirabilis - growth - communication - motility - model - evolution
    Background: Swarming motility allows microorganisms to move rapidly over surfaces. The Grampositive bacterium Paenibacillus vortex exhibits advanced cooperative motility on agar plates resulting in intricate colonial patterns with geometries that are highly sensitive to the environment. The cellular mechanisms that underpin the complex multicellular organization of such a simple organism are not well understood. Results: Swarming by P. vortex was studied by real- time light microscopy, by in situ scanning electron microscopy and by tracking the spread of antibiotic- resistant cells within antibioticsensitive colonies. When swarming, P. vortex was found to be peritrichously flagellated. Swarming by the curved cells of P. vortex occurred on an extremely wide range of media and agar concentrations (0.3 to 2.2% w/ v). At high agar concentrations (> 1% w/ v) rotating colonies formed that could be detached from the main mass of cells by withdrawal of cells into the latter. On lower percentage agars, cells moved in an extended network composed of interconnected snakes with short-term collision avoidance and sensitivity to extracts from swarming cells. P. vortex formed single Petri dish-wide supercolonies with a colony-wide exchange of motile cells. Swarming cells were coupled by rapidly forming, reversible and non-rigid connections to form a loose raft, apparently connected via flagella. Inhibitors of swarming ( p-Nitrophenylglycerol and Congo Red) were identified. Mitomycin C was used to trigger filamentation without inhibiting growth or swarming; this facilitated dissection of the detail of swarming. Mitomycin C treatment resulted in malcoordinated swarming and abortive side branch formation and a strong tendency by a subpopulation of the cells to form minimal rotating aggregates of only a few cells. Conclusion: P. vortex creates complex macroscopic colonies within which there is considerable reflux and movement and interaction of cells. Cell shape, flagellation, the aversion of cell masses to fuse and temporary connections between proximate cells to form rafts were all features of the swarming and rotation of cell aggregates. Vigorous vortex formation was social, i. e. required > 1 cell. This is the first detailed examination of the swarming behaviour of this bacterium at the cellular level.
    Non-Gaussian curvature distribution of actin-propelled biomimetric colloid trajectories
    Schmidt, S. ; Gucht, J. van der; Biesheuvel, P.M. ; Weinkamer, R. ; Helfer, E. ; Fery, A. - \ 2008
    European Biophysics Journal 37 (2008)8. - ISSN 0175-7571 - p. 1361 - 1366.
    comet tails - lipid vesicles - motility - polymerization - listeria - forces - filaments - mechanism - movement - driven
    We analyze the motion of colloids propelled by a comet-like tail of polymerizing actin filaments. The curvature of the particle trajectories deviates strongly from a Gaussian distribution, implying that the underlying microscopic processes are fluctuating in a non-independent manner. Trajectories for beads of different size all showed the same non-Gaussian behavior, while the mean curvature decreased weakly with size. A stochastic simulation that includes nucleation, force-dependent dissociation, growth, and capping of filaments, shows that the non-Gaussian curvature distribution can be explained by a positive feedback mechanism in which attached chains under higher tension are more likely to snap
    Hydrodynamic Flow-Mediated Protein Sorting on the Cell Surface of Trypanosomes
    Engstler, M. ; Pfohl, T. ; Herminghaus, S. ; Boshart, M. ; Wiegertjes, G.F. ; Heddergott, N. ; Overath, P. - \ 2007
    Cell 131 (2007). - ISSN 0092-8674 - p. 505 - 515.
    blood-stream forms - antigenic variation - dna-molecules - brucei - glycoprotein - endocytosis - membrane - movement - motility - antibody
    The unicellular parasite Trypanosoma brucei rapidly removes host-derived immunoglobulin (Ig) from its cell surface, which is dominated by a single type of glycosylphosphatidylinositol-anchored variant surface glycoprotein (VSG). We have determined the mechanism of antibody clearance and found that Ig-VSG immune complexes are passively sorted to the posterior cell pole, where they are endocytosed. The backward movement of immune complexes requires forward cellular motility but is independent of endocytosis and of actin function. We suggest that the hydrodynamic flow acting on swimming trypanosomes causes directional movement of Ig-VSG immune complexes in the plane of the plasma membrane, that is, immunoglobulins attached to VSG function as molecular sails. Protein sorting by hydrodynamic forces helps to protect trypanosomes against complement-mediated immune destruction in culture and possibly in infected mammals but likewise may be of functional significance at the surface of other cell types such as epithelial cells lining blood vessels.
    RasGEF-containing proteins GbpC and GbpD have different effects on cell polarity and chemotaxis in Dictyostelium
    Bosgraaf, L. ; Waijer, A. ; Engel, R. ; Visser, A.J.W.G. ; Wessels, D. ; Soll, D. ; Haastert, P.J.M. van - \ 2005
    Journal of Cell Science 118 (2005)9. - ISSN 0021-9533 - p. 1899 - 1910.
    myosin heavy-chain - actin polymerization - rear retraction - cross-linking - ii dynamics - in-vivo - motility - phosphorylation - discoideum - rap1
    The regulation of cell polarity plays an important role in chemotaxis. Previously, two proteins termed GbpC and GbpD were identified in Dictyostelium, which contain RasGEF and cyclic nucleotide binding domains. Here we show that gbpC-null cells display strongly reduced chemotaxis, because they are unable to polarise effectively in a chemotactic gradient. However, gbpD-null mutants exhibit the opposite phenotype: cells display improved chemotaxis and appear hyperpolar, because cells make very few lateral pseudopodia, whereas the leading edge is continuously remodelled. Overexpression of GbpD protein results in severely reduced chemotaxis. Cells extend many bifurcated and lateral pseudopodia, resulting in the absence of a leading edge. Furthermore, cells are flat and adhesive owing to an increased number of substrate-attached pseudopodia. This GbpD phenotype is not dependent on intracellular cGMP or cAMP, like its mammalian homolog PDZ-GEF. Previously we showed that GbpC is a high-affinity cGMP-binding protein that acts via myosin II. We conclude that cGMP activates GbpC, mediating the chemoattractant-induced establishment of cell polarity through myosin. GbpD induces the formation of substrate-attached pseudopodia, resulting in increased attachment and suppression of polarity.
    Cryopreservation of boar semen: equilibrium freezing in the cryomicroscope and in straws
    Woelders, H. ; Matthijs, A. ; Zuidberg, C.A. ; Chaveiro, A. - \ 2005
    Theriogenology 63 (2005)2. - ISSN 0093-691X - p. 383 - 395.
    0.5 ml straws - acrosomal integrity - spermatozoa frozen - cooling rate - injury - cells - hypothesis - trehalose - viability - motility
    Supercooling causes very abrupt temperature and osmotic changes and can thus lead to freezing damage. Supercooling can be prevented by seeding, using a sample volume and geometry that allows rapid spreading of the ice throughout the sample. In a split-sample comparison of such samples on the cooling stage of a cryomicroscope and seeded at ¿5 and ¿15 °C, respectively, the percentages of membrane-intact sperm and sperm with acrosomes with a `normal apical ridge¿ (NAR) were 72.5 ± 3.8 and 75.8 ± 2.0 versus 46.3 ± 4.8 and 36.0 ± 3.7 (means ± S.E.M., n = 4). In ejaculates of 15 unselected AI boars, after seeding at ¿5 °C, the post-thaw % live and % NAR were 66.3 ± 10.4 and 74.8 ± 7.5, respectively. Our present research is aimed at translating these findings to freezing in straws and at a high sperm concentration. We have designed a novel type of freezing apparatus for controlled-rate freezing of straws, in which supercooling can be effectively prevented in the entire straw. In a split-sample comparison of semen frozen in straws at a sperm concentration of 1.5 × 109 cells/ml with nine ejaculates from eight unselected AI boars, we found 54.8 ± 1.9% versus 40.7 ± 1.7% (means ± S.E.M.) membrane-intact sperm for the new apparatus and a conventional freezing apparatus, respectively. With bull semen (eight ejaculates from six bulls), we obtained 67.3 ± 3.0% versus 59.3 ± 2.9% (means ± S.E.M.) membrane-intact sperm for the new apparatus and conventional freezing, respectively. Additionally, the temperature curve after ice nucleation is of great importance. We have developed a model that allows us to predict that optimal cryopreservation requires a non-linear cooling curve in which the cooling rate varies as a function of subzero temperature
    Determination of bull sperm membrane permeability to water and cryoprotectants using a concentration-dependent self-quenching fluorophore
    Chaveiro, A. ; Liu, J. ; Mullen, S. ; Woelders, H. ; Critser, J.K. - \ 2004
    Cryobiology 48 (2004). - ISSN 0011-2240 - p. 72 - 80.
    human-spermatozoa - entrapped fluorophore - osmotic tolerance - cryopreservation - osmolality - motility - boar
    The objective of this study was to determine the membrane permeability characteristics of bovine spermatozoa. These included the hydraulic conductivity (L-p), the permeability coefficients (P-s) of four common cryoprotective agents (CPAs) and the associated reflection coefficients (sigma). Stopped-flow fluorometry was applied in order to capture rapid cell volume changes under anisosmotic conditions in the absence or presence of permeant solutes (CPAs). This technique utilizes a concentration-dependent self-quenching entrapped fluorophore. The resulting cell volume changes were used in three-parameter fitting calculations to compute L-p in the absence of permeant solutes and P-s and L-p in the presence of permeating solutes (CPAs) at 22degreesC. The hydraulic conductivity in the absence of permeating solutes was estimated to be 0.69+/-0.05 mum/min/atm (mean+/-SEM). Hydraulic conductivity (L-p) in the presence of CPAs was 0.91+/-0.27 (mean+/-SEM), 0.29+/-0.04, 0.42+/-0.05, and 0.39+/-0.03 mum/min/atm in the presence of dimethylsulfoxide (Me2SO), glycerol, propylene glycol (PG), and ethylene glycol (EG), respectively. The values for P-s were estimated to be 1.72+/-0.36 1.75+/-0.03, 2.47+/-0.24, and 1.49+/-0.3x10(-3) cm/min for Me2SO, glycerol, PG, and EG, respectively. The data were used to simulate volume excursions during addition and removal of CPA, to predict the different effects of the four CPAs. (C) 2004 Elsevier Inc. All rights reserved.
    Left displacement of the abomasum in dairy cattle: recent developments in epidemiological and etiological aspects
    Winden, S.C.L. van; Kuiper, R. - \ 2003
    Veterinary Research 34 (2003)1. - ISSN 0928-4249 - p. 47 - 56.
    test day milk - risk-factors - holstein cows - postpartum disorders - genetic-parameters - health disorders - bovine abomasum - energy-balance - motility - herds
    The research with respect to displacement of the abomasum (DA) in dairy cattle is reviewed. Evaluated articles describe epidemiological and experimental studies. The occurrence is elevated with regard to breed, gender, age, concurrent diseases, environmental aspects and production levels as contributing factors and emphasis is placed on the effects of nutrition and metabolism. Reviewing the experimental work, distinction is made between the research into gas production in the abomasum and hypomotility of the abomasum, since both represent presumed pathways in the development of DA. Although the different fields of research have positive contributions to the understanding of the pathogenesis of DA, contradictions in the different studies are present. This is partly due to extrapolation of results from sheep to cows, or because of a low number of cows in the experiments. Finally, general suggestions are made for further research in the field of the pathogenesis of DA.
    Properties of 70S and 80S ribosomes from tobacco leaves
    Brouwer, D. - \ 1970
    Wageningen University. Promotor(en): J.P.H. van der Want; L. Bosch. - Wageningen : Veenman - 101
    nicotiana - tabak - motiliteit - cellen - trilharen - flagellen - nucleïnezuren - plantkunde - nicotiana - tobacco - motility - cells - cilia - flagella - nucleic acids - botany
    1. The interaction of exogenous messengers with 70 S chloroplast and 80 S cytoplasmic tobacco ribosomes in vitro was studied. The isolation of an amino acid incorporating system from tobacco leaves should enable us to study some aspects of viral protein synthesis. Tobacco 70 S and 80 S ribosomes were chosen for the following reasons: Little is known about the interaction of messenger RNA with 80 S ribosomes. In general, plant viral RNAs did not yield meaningful results in the E. coli system. The interaction of 70 S and 80 S ribosomes with messengers could be compared in a homologous tobacco leave system.

    2. The amino acid incorporating system as isolated initially could be characterized by its dependence on an energy source and GTP, on the concentration of ribosomes, on the magnesium and potassium ion concentration, and on the incubation time, but not on tRNA and soluble enzymes or on unlabeled amino acids.

    3. The lack of an effect of tRNA or soluble enzymes was not due to the amino acid activation reaction, but to the presence of these factors in the ribosome preparations.

    4. The ribosomes could be purified by sucrose gradient centrifugation, centrifugation through 0.5 M NH 4 Cl, and by chromatography on a Sephadex G200 column. Then amino acid incorporation became dependent on the addition of tRNA and soluble enzymes but not of 12C-amino acids. It was calculated that even after purification about 0.0012 μmoles 12C-amino acids were still present in the ribosome preparation.

    5. Highly purified ribosomes were active for a longer period than nonpurified ribosomes, but nevertheless the incorporation rate decreased during incubation. The conclusion was drawn that both degradation and read out of the messenger were responsible for this decrease.

    6. Some of the physical properties of 70 S and 80 S ribosomes were determined. Methods were developed to separate 70 S and 80 S ribosomes and polyribosomes from each other. The polyribosomes appeared to consist of 80 S ribosomes. About 5-10 times as much 80 S ribosomes could be isolated from leaves as 70 S ribosomes.

    7. The 70 S ribosomes were not stable at elevated salt concentrations. At low Mg 2+concentrations they dissociated reversibly into 50 S and 35 S subunits; 80 S ribosomes could not dissociate, but unfolded at low Mg 2+concentrations. During this process 60 S particles first appeared, followed by 50 S and 40 S particles. When the Mg 2+concentration was raised again, 80 S particles reformed from 60 S particles but hardly from 50 S and 40 S particles.

    8. Both 70 S and 80 S ribosomes contained two different RNA molecules, i.e., the 70 S ribosomes had 17 S and 23 S RNA, and the 80 S ribosomes 17 Sand 25 S RNA.

    9. The amino acid incorporating activity of the 70 S and the 80 S ribosomes as compared to that of the polyribosomes was not essentially different, but the 70 S ribosomes were about 2.5 times as active as the 80 S ribosomes at their optimal Mg 2+concentrations. The optimal concentration for the 80 S ribosomes was 5 mM and for the 70 S ribosomes 17 mM.

    10. In contrast to the 80 S ribosomes, the 70 S ribosomes had a constant incorporation rate for about 40 minutes, which then decreased abruptly to almost zero. It was concluded that no messenger degradation took place during incubation, but that the messengers had been read out after 40 minutes. The 80 S ribosomes behaved similarly as mentioned for the mixture of ribo somes.

    11. Incubation temperature and pH had a clear effect on both 70 S and 80 S ribosomes. This effect, however, was variable and depended on the in cubation time. In general, the optimum temperature and pH decreased with increasing periods of incubation.

    12. The effect of exogenous messengers on the amino acid incorporation was studied. Untreated ribosomes could hardly be stimulated by such messen gers.

    13. Two methods were developed for the elimination of endogenous messen gers from 80 S ribosomes. According to the first method 80 S ribosomes were preincubated at pH 8.6 in a complete, but unlabeled, incubation mixture for 3 hours. Then the ribosomes were pelleted at 105,000 x g and incubated in a complete labeled incubation mixture. The second method consisted of dialysis against 10 -4M Mg 2+in standard buffer during 14 hours. During this dialysis the ribosomes unfolded to 60 S particles. The dissociation of 70 S ribosomes into 50 S and 35 S subunits proved to result in the elimination of endogenous messengers from these ribosomes.

    14. Preincubated and dialyzed 80 S and 70 S ribosomes could be programmed by poly U as an exogenous messenger. Incorporation continued at a constant rate for over 2 hours. The optimal Mg 2+concentrations were I11 mM for the 80 S and 18 mM for the 70 S ribosomes, respectively. At these concentrations, a stimulation of 10-40 times was obtained. Again, the 70 S ribosomes were about 2.5 times as active as the 80 S ribosomes. The activities were 30-45 μμmoles phenylalanine per mg per hour for the 80 S ribosomes and 70-140 μμmoles for the 70 S ribosomes.

    15. Viral RNAs did not stimulate to an appreciable extent the amino acid incorporation by either type of ribosomes. Initiation factors such as leucovorin were added, but none of these showed any effect. Some fractions, isolated from the supernatant of ribosomes centrifuged at 105,000 x g however, showed a small effect on the over-all incorporation. It was concluded that in our system some special initiation factor(s) may be missing and that it might be possible to isolate from the supernatant fractions such a factor or factors.

    Properties of 70 S en 80 S ribosomes from tobacco leaves = Eigenschappen van 70 S en 80 S ribosomen uit tabaksbladeren
    Brouwer, D. - \ 1970
    Wageningen : Veenman - 101
    nicotiana - tabak - motiliteit - cellen - trilharen - flagellen - nucleïnezuren - plantkunde - nicotiana - tobacco - motility - cells - cilia - flagella - nucleic acids - botany
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