Vinculin controls talin engagement with the actomyosin machinery

The link between extracellular-matrix-bound integrins and intracellular F-actin is essential for cell spreading and migration. Here, we demonstrate how the actin-binding proteins talin and vinculin cooperate to provide this link. By expressing structure-based talin mutants in talin null cells, we show that while the C-terminal actin-binding site (ABS3) in talin is required for adhesion complex assembly, the central ABS2 is essential for focal adhesion (FA) maturation. Thus, although ABS2 mutants support cell spreading, the cells lack FAs, fail to polarize and exert reduced force on the surrounding matrix. ABS2 is inhibited by the preceding mechanosensitive vinculin-binding R3 domain, and deletion of R2R3 or expression of constitutively active vinculin generates stable force-independent FAs, although cell polarity is compromised. Our data suggest a model whereby force acting on integrin-talin complexes via ABS3 promotes R3 unfolding and vinculin binding, activating ABS2 and locking talin into an actin-binding configuration that stabilizes FAs

Gene Expression Profiles of the NCI-60 Human Tumor Cell Lines Define Molecular Interaction Networks Governing Cell Migration Processes

Although there is extensive information on gene expression and molecular interactions in various cell types, integrating those data in a functionally coherent manner remains challenging. This study explores the premise that genes whose expression at the mRNA level is correlated over diverse cell lines are likely to function together in a network of molecular interactions. We previously derived expression-correlated gene clusters from the database of the NCI-60 human tumor cell lines and associated each cluster with function categories of the Gene Ontology (GO) database. From a cluster rich in genes associated with GO categories related to cell migration, we extracted 15 genes that were highly cross-correlated; prominent among them were RRAS, AXL, ADAM9, FN14, and integrin-beta1. We then used those 15 genes as bait to identify other correlated genes in the NCI-60 database. A survey of current literature disclosed, not only that many of the expression-correlated genes engaged in molecular interactions related to migration, invasion, and metastasis, but that highly cross-correlated subsets of those genes engaged in specific cell migration processes. We assembled this information in molecular interaction maps (MIMs) that depict networks governing 3 cell migration processes: degradation of extracellular matrix, production of transient focal complexes at the leading edge of the cell, and retraction of the rear part of the cell. Also depicted are interactions controlling the release and effects of calcium ions, which may regulate migration in a spaciotemporal manner in the cell. The MIMs and associated text comprise a detailed and integrated summary of what is currently known or surmised about the role of the expression cross-correlated genes in molecular networks governing those processes

Interactions among white spruce tannins, Bacillus thuringiensis subsp kurstaki, and spruce budworm (Lepidoptera : Tortricidae), on larval survival, growth, and development

The interactions among white spruce, Picea glauca (Moench) Voss, purified acetone tannin extracts (hydrolyzable and condensed tannin), Bacillus thuringiensis subsp. kurstaki CrylA(c) delta-endotoxin strain HD-73 (Btk), and spruce budworm, Chotistoneura fumiferana (Clemens) (Lepidoptera: Tortricidae) on larval survival, growth, and development were investigated over the whole larval feeding period by using artificial diet supplemented with three concentrations of Btk toxins per milliliter of diet (0, 0.021, and 1.72 mu g/ml) and three concentrations of foliar tannin extract (0, 8, and 15% dry mass basis). At high Btk concentration, tannin antagonized Btk potency against spruce budworm by lowering Btk-related larval mortality from 83 to 43%. At moderate Btk concentration tannin did not affect Btk potency. Host tree tannins antagonized not only the lethal effects of Btk toxin but also sublethal Btk-related impacts in terms of larval development, pupal weight, relative consumption rate, and growth rate. When alone in the diet, tannin negatively affected larval survival, growth, and development. Maximum potency of tannins against spruce budworm larvae (60% mortality) was reached at dietary concentrations corresponding to what is found in the plant (8% dry mass). The addition of Btk toxin in food containing tannin reduced percentage of larval mortality by one-third, indicating that Btk toxin can antagonize tannin potency against the insect. Development of Btk transgenic spruce trees should consider the antagonistic effect the toxin may have on the resistance conferred by tannins that have evolved naturally in spruce trees

Sensibilité du pin maritime Pinus pinaster Ait, installé dans des conditions stationnelles différentes, aux attaques de la pyrale du tronc, Dioryctria sylvestrella Ratz (Lepidoptera, Pyralidae). Relations avec quelques caractéristiques de croissance

Pour évaluer l'impact des caractéristiques de croissance du pin maritime semé dans des conditions stationnelles différentes dans le massif des Landes (France), divers critères reflétant leurs croissances différentielles ont été mesurés dans 15 placettes et corrélés à l'intensité des attaques de Dioryctria sylvestrella. Les arbres localisés dans les placettes les plus productives sont les plus attaqués. Dans une parcelle donnée, les tiges présentant la croissance radiale la plus forte sont préférentiellement attaquées. Par suite, les auteurs suggèrent que la présence d'un liber dénudé et d'un fin rhytidome faciliterait la ponte de la femelle comme la pénétration des larves, la qualité et la quantité du liber facilitant plutôt leur développement.Sensitivity of Maritime Pine (Pinus pinaster Ait) to attack by the Pine moth, Dioryctria sylvestrella Ratz (Lepidoptera, Pyralidae) in a range of site conditions. Relationships to certain growth characteristics. In order to evaluate the differential susceptibility of Pinus pinaster Ait growing in 13-21-yr-old stands where the soil conditions and water content vary gradually with the attacks of the Pine moth Dioryctria sylvestrella (Ratz), several types of measurement were made (basal area, height of the 100 largest trees/ha, etc) and correlated with the intensity of attacks. It appears that the highest productivity stands are the most infected. In a given stand, the trees with the best radial growth are attacked first. It is suggested that the larval penetration in the inner bark is aided by any naked surface of the tree (linked wounds or cut branches) as well as the presence of a thin bark; the quality and quantity of the inner bark facilitates larval growth

Combining AFM and Acoustic Probes to Reveal Changes in the Elastic Stiffness Tensor of Living Cells

AbstractKnowledge of how the elastic stiffness of a cell affects its communication with its environment is of fundamental importance for the understanding of tissue integrity in health and disease. For stiffness measurements, it has been customary to quote a single parameter quantity, e.g., Young’s modulus, rather than the minimum of two terms of the stiffness tensor required by elasticity theory. In this study, we use two independent methods (acoustic microscopy and atomic force microscopy nanoindentation) to characterize the elastic properties of a cell and thus determine two independent elastic constants. This allows us to explore in detail how the mechanical properties of cells change in response to signaling pathways that are known to regulate the cell’s cytoskeleton. In particular, we demonstrate that altering the tensioning of actin filaments in NIH3T3 cells has a strong influence on the cell's shear modulus but leaves its bulk modulus unchanged. In contrast, altering the polymerization state of actin filaments influences bulk and shear modulus in a similar manner. In addition, we can use the data to directly determine the Poisson ratio of a cell and show that in all cases studied, it is less than, but very close to, 0.5 in value

Influence d'un stress hydrique sur la dynamique des élements minéraux dans la sève xylèmique d'un peuplement d'Epicea. Conséquences sur l'apparition des carences minérales des peuplements d'Epicea dépérissants

National audienc

Dynamique des éléments minéraux dans la sève xylémique d'épicéas de 30 ans

Le flux hydrique circulant dans les troncs d'un perchis d'épicéa des Vosges a été directement mesuré par des sondes de fluxmètre radial au cours d'une saison de végétation. Parallèlement, les sèves xylémiques de branches et de troncs ont été extraites sur des échantillons prélevés à intervalle régulier, respectivement par pression sur les parties feuillées et par déplacement par une colonne d'eau. Ces sèves ont été analysées par ICP pour les principaux éléments minéraux (Ca, K, P, Mg, Si, Mn). Les flux d'éléments minéraux calculés par produit des flux hydriques par les concentrations ont été comparés au prélèvement en éléments minéraux, préalablement évalué par une étude classique de minéralomasse. La variation saisonnière des concentrations dans la sève de la base du tronc diffère suivant les éléments. Les teneurs en Ca, Mg, K et P sont maximales lors du débourrement (K) ou en début de croissance des pousses puis se stabilisent durant l'été pour raugmenter en fin de saison. Outre un pic lors de l'allongement des pousses, Si semble s'élever parallèlement à la progression de la sécheresse édaphique estivale. La variation saisonnière des concentrations de la sève de branche est moins marquée, mais similaire à celle observée pour les troncs. Les teneurs en éléments minéraux de la sève du haut du tronc et du houppier sont toujours très supérieures à celles de la base du tronc. Les flux de Ca et Mg dans la sève de la base du tronc sont d'importance comparable à ceux du prélèvement brut du peuplement estimé à partir de l'étude des biomasses. Ceux de P et K lui sont très supérieurs à la base du tronc. Ces résultats sont interprétés comme traduisant l'existence d'un pool mobile d'éléments minéraux dans l'arbre, particulièrement important dans les parties métaboliquement très actives comme le houppier et les racines.Mineral element dynamics in the xylem sap of 30-year old spruce. Xylem sap fluxes and mineral contents in branches and boles of a 30-yr-old spruce stand were monitored during the 1990 growing period. On average, four trees were felled fortnightly. Three portions of the bottom of each felled trunk and four branches per tree from the third and fourth whorl were sampled before sunrise. Sap extractions were carried out immediatly after felling. Bole xylem sap was displaced by the pressure of a 1-metre high column of water applied to the end of each portion sampled, whereas twig sap was extracted by applying slight air pressure (+1 MPa over potential) in a Schollander bomb. Xylem sap rise was recorded continuously in four trees with a heating probe device (fig 2). Sap water fluxes were multiplied by sap mineral contents in order to calculate the flux of mineral elements rising annually in the xylem tissues. This flux was compared to the mineral content and annual uptake of the stand, previously evaluated by a biomass and mineral content inventory (Le Goaster et al, 1991; Dambrine et al, 1991). Sap element content was found to have a systematically higher concentration in the crown compared to the bottom of the trunk (fig 3). Seasonal variations in the mineral concentrations of bole xylem sap depend on the element: Ca, Mg, K and P peak during or after bud break, then decrease and remain low and steady during summer with a final increase at the end of the growing period. Si seems to increase with drought (fig 4). Seasonal variations of branch xylem sap contents show a less pronounced pattern (fig 6). Concentrations of Ca, P and K peak at the beginning of shoot or needle growth, after the peak of bole sap concentrations. Mg content does not change greatly whereas Si increases in parallel with the drought. The ratio between branch and bole sap concentrations (fig 6) is highest for Ca and Mg, which are available to the trees in very limited amounts. Annual fluxes of Ca and Mg in bole xylem sap were found to be lower than (Ca) or of the same order of magnitude (Mg) as the gross uptake of the stand, assessed by a biomass and mineral content inventory (table IV). This discrepency between the Ca flux in sap and gross Ca uptake could be partly due to uncertainties in gross uptake evaluation. Conversely, fluxes of K and P in bole xylem sap are far higher than the gross uptake. Fluxes of all elements in branch xylem sap are higher (Ca, Si) or far higher (Mg, P, K) than the gross uptake. For P and K, fluxes are of the same order of magnitude as the total content of the stands crown (table V). These results strongly suggest the existence of a mobile pool of mineral elements, cycling continuously in the tree, and particularly in the crown. This is in agreement with previous investigations showing that root and branch sap concentrations were higher than those from the bole (table VI)