Coordination of Kinesin Motors Pulling on Fluid Membranes

AbstractIntracellular transport relies on the action of motor proteins, which work collectively to either carry small vesicles or pull membranes tubes along cytoskeletal filaments. Although the individual properties of kinesin-1 motors have been extensively studied, little is known on how several motors coordinate their action and spatially organize on the microtubule when pulling on fluid membranes. Here we address these questions by studying, both experimentally and numerically, the growth of membrane tubes pulled by molecular motors. Our in vitro setup allows us to simultaneously control the parameters monitoring tube growth and measure its characteristics. We perform numerical simulations of membrane tube growth, using the experimentally measured values of all parameters, and analyze the growth properties of the tube considering various motor cooperation schemes. The comparison of the numerical results and the experimental data shows that motors use simultaneously several protofilaments of a microtubule to pull a single tube, as motors moving along a single protofilament cannot generate the forces required for tube extraction. In our experimental conditions, we estimate the average number of motors pulling the tube to be approximately nine, distributed over three contiguous protofilaments. Our results also indicate that the motors pulling the tube do not step synchronously

Black adzes in the Early Neolithic of Belgium: Contribution of the Raman microspectrometry and petrography in characterization and sourcing

Early Neolithic (Linear Pottery Culture) adzes originate from settlements and workshops accompany the neolithization of Belgium. They are made from a wide range of extraregional lithic raw materials such as metamorphic green rocks (amphibolite) and black volcanic rocks (“basalt’) beside more local or regional raw material as flints, light-coloured (sedimentary and lightly metamorphic) quartzites, black lydites (Cambrian nodular phtanite of Céroux-Mousty and Lower Namurian banded phtanites) and dark grey Lower Namurian silicified sandstones previously called “Micaceous sandstones of Horion-Hozémont’. The discovery of the workshop of Noirfontaine near the city of Liège in the 1970s and 1980s provides exceptional assemblage available for updating analytical studies. This research focuses on the multi-scale characterization, the discrimination and sourcing both Cambrian and Namurian black sedimentary rocks rich in secondary silica composing Early Neolithic adzes found in Belgium. Their black colour results from finely dispersed organic matter, but the absence of palynomorphs does not allow a biostratigraphic ascription. Additional petrographical analyses (Optical Petrography, Scanning Electron Microscope), X-ray diffraction, chemical analyses (Energy Dispersive Spectroscopy) and measuring the degree of graphitization of the organic matter through Raman microspectrometry have been decisive in identifying the geological and geographical provenances by comparing the acquired results with geological reference samples collected in the field or through reference collections. Cambrian lydites are coming from a very restricted area and were preferred to other more local rock sources

Intermediate filaments control collective migration by restricting traction forces and sustaining cell-cell contacts

Mesenchymal cell migration relies on the coordinated regulation of the actin and microtubule networks that participate in polarized cell protrusion, adhesion, and contraction. During collective migration, most of the traction forces are generated by the acto-myosin network linked to focal adhesions at the front of leader cells, which transmit these pulling forces to the followers. Here, using an in vitro wound healing assay to induce polarization and collective directed migration of primary astrocytes, we show that the intermediate filament (IF) network composed of vimentin, glial fibrillary acidic protein, and nestin contributes to directed collective movement by controlling the distribution of forces in the migrating cell monolayer. Together with the cytoskeletal linker plectin, these IFs control the organization and dynamics of the acto-myosin network, promoting the actin-driven treadmilling of adherens junctions, thereby facilitating the polarization of leader cells. Independently of their effect on adherens junctions, IFs influence the dynamics and localization of focal adhesions and limit their mechanical coupling to the acto-myosin network. We thus conclude that IFs promote collective directed migration in astrocytes by restricting the generation of traction forces to the front of leader cells, preventing aberrant tractions in the followers, and by contributing to the maintenance of lateral cell-cell interactions

Rain-Use-Efficiency: What it Tells us about the Conflicting Sahel Greening and Sahelian Paradox

Rain Use Efficiency (RUE), defined as Aboveground Net Primary Production (ANPP) divided by rainfall, is increasingly used to diagnose land degradation. Yet, the outcome of RUE monitoring has been much debated since opposite results were found about land degradation in the Sahel region. The debate is fueled by methodological issues, especially when using satellite remote sensing data to estimate ANPP, and by differences in the ecological interpretation. An alternative method which solves part of these issues relies on the residuals of ANPP regressed against rainfall (“ANPP residuals”). In this paper, we use long-term field observations of herbaceous vegetation mass collected in the Gourma region in Mali together with remote sensing data (GIMMS-3g Normalized Difference Vegetation Index) to estimate ANPP, RUE, and the ANPP residuals, over the period 1984–2010. The residuals as well as RUE do not reveal any trend over time over the Gourma region, implying that vegetation is resilient over that period, when data are aggregated at the Gourma scale. We find no conflict between field-derived and satellite-derived results in terms of trends. The nature (linearity) of the ANPP/rainfall relationship is investigated and is found to have no impact on the RUE and residuals interpretation. However, at odds with a stable RUE, an increased run-off coefficient has been observed in the area over the same period, pointing towards land degradation. The divergence of these two indicators of ecosystem resilience (stable RUE) and land degradation (increasing run-off coefficient) is referred to as the “second Sahelian paradox”. When shallow soils and deep soils are examined separately, high resilience is diagnosed on the deep soil sites. However, some of the shallow soils show signs of degradation, being characterized by decreasing vegetation cover and increasing run-off coefficient. Such results show that contrasted changes may co-exist within a region where a strong overall re-greening pattern is observed, highlighting that both the scale of observations and the scale of the processes have to be considered when performing assessments of vegetation changes and land degradation

Exome sequencing identifies germline variants in DIS3 in familial multiple myeloma

[Excerpt] Multiple myeloma (MM) is the third most common hematological malignancy, after Non-Hodgkin Lymphoma and Leukemia. MM is generally preceded by Monoclonal Gammopathy of Undetermined Significance (MGUS) [1], and epidemiological studies have identified older age, male gender, family history, and MGUS as risk factors for developing MM [2]. The somatic mutational landscape of sporadic MM has been increasingly investigated, aiming to identify recurrent genetic events involved in myelomagenesis. Whole exome and whole genome sequencing studies have shown that MM is a genetically heterogeneous disease that evolves through accumulation of both clonal and subclonal driver mutations [3] and identified recurrently somatically mutated genes, including KRAS, NRAS, FAM46C, TP53, DIS3, BRAF, TRAF3, CYLD, RB1 and PRDM1 [3,4,5]. Despite the fact that family-based studies have provided data consistent with an inherited genetic susceptibility to MM compatible with Mendelian transmission [6], the molecular basis of inherited MM predisposition is only partly understood. Genome-Wide Association (GWAS) studies have identified and validated 23 loci significantly associated with an increased risk of developing MM that explain ~16% of heritability [7] and only a subset of familial cases are thought to have a polygenic background [8]. Recent studies have identified rare germline variants predisposing to MM in KDM1A [9], ARID1A and USP45 [10], and the implementation of next-generation sequencing technology will allow the characterization of more such rare variants. [...]French National Cancer Institute (INCA) and the Fondation Française pour la Recherche contre le Myélome et les Gammapathies (FFMRG), the Intergroupe Francophone du Myélome (IFM), NCI R01 NCI CA167824 and a generous donation from Matthew Bell. This work was supported in part through the computational resources and staff expertise provided by Scientific Computing at the Icahn School of Medicine at Mount Sinai. Research reported in this paper was supported by the Office of Research Infrastructure of the National Institutes of Health under award number S10OD018522. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. The authors thank the Association des Malades du Myélome Multiple (AF3M) for their continued support and participation. Where authors are identified as personnel of the International Agency for Research on Cancer / World Health Organization, the authors alone are responsible for the views expressed in this article and they do not necessarily represent the decisions, policy or views of the International Agency for Research on Cancer / World Health Organizatio

Système biomimétique d'intermédiaires de transport tubulaires : Etude quantitative

Les tubes de membrane sont omniprésents dans les cellules vivantes eucaryotes. Ce sont des structures très dynamiques qui permettent en particulier la communication entre les différents compartiments de la cellule. Pour comprendre les mécanismes impliqués dans le trafic intracellulaire, il paraît essentiel d'isoler le rôle des différents constituants impliques. Dans ce but, un système minimal qui permet de mimer in vitro les différentes étapes d'extraction, de croissance et d'arrêt des tubes de membrane avec des éléments purifies ou artificiels (kinesines, microtubules, vésicules géantes unilamellaires) a été utilise. La comparaison des résultats expérimentaux avec ceux obtenus par une analyse théorique du système a ainsi permis de caractériser de fa¸con complète ces différentes étapes. Nous avons notamment montre l'existence d'un seuil de formation de tubes qui dépend essentiellement de deux paramètres non locaux supramoléculaires : la tension de membrane et la quantité de kinesines 'a la surface des vésicules. Lorsque le tube est forme, nous avons évalue le nombre de moteurs qui le tirent et montre qu'ils s'accumulent de fa¸con dynamique au bout du tube. De la mesure de la longueur caractéristique d'accumulation, nous avons déduit un paramètre moléculaire : le taux d'attachement des kinesines sur un microtubule dans une géométrie proche de celle observée in vivo. Enfin, nous avons mis en évidence un phénomène d'oscillations liées au comportement collectif de moteurs processifs pour des tubes très longs. Ce système, bien que simplifie, permet d'apporter une nouvelle approche du trafic intracellulaire, en proposant des mécanismes physiques qui sont souvent masques, dans les cellules, par des mécanismes moleculaires.Les tubes de membrane sont omniprésents dans les cellules vivantes eucaryotes. Ce sont des structures très dynamiques qui permettent en particulier la communication entre les différents compartiments de la cellule. Pour comprendre les mécanismes impliqués dans le trafic intracellulaire, il paraît essentiel d'isoler le rôle des différents constituants impliques. Dans ce but, un système minimal qui permet de mimer in vitro les différentes étapes d'extraction, de croissance et d'arrêt des tubes de membrane avec des éléments purifies ou artificiels (kinesines, microtubules, vésicules géantes unilamellaires) a été utilise. La comparaison des résultats expérimentaux avec ceux obtenus par une analyse théorique du système a ainsi permis de caractériser de fa¸con complète ces différentes étapes. Nous avons notamment montre l'existence d'un seuil de formation de tubes qui dépend essentiellement de deux paramètres non locaux supramoléculaires : la tension de membrane et la quantité de kin'esines 'a la surface des vésicules. Lorsque le tube est forme, nous avons évalue le nombre de moteurs qui le tirent et montre qu'ils s'accumulent de fa¸con dynamique au bout du tube. De la mesure de la longueur caractéristique d'accumulation, nous avons déduit un paramètre moléculaire : le taux d'attachement des kin'esines sur un microtubule dans une géométrie proche de celle observée in vivo. Enfin, nous avons mis en évidence un phénomène d'oscillations liées au comportement collectif de moteurs processifs pour des tubes très longs. Ce système, bien que simplifie, permet d'apporter une nouvelle approche du trafic intracellulaire, en proposant des mécanismes physiques qui sont souvent masques, dans les cellules, par des mécanismes mol'eculaires

Système biomimétique d'intermédiaires de transport tubulaires (étude quantitative)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Cell Cycle Intermediate filaments join the action

International audienceCell polarity reflects the morphological, structural and functional organization of the cell along a so-called polarity axis. The cell ability to polarize in response to its microenvironment is a prerequisite for most cell behaviors including division [...

Intermediate filaments in cell migration and invasion: the unusual suspects

International audienceCell migration is a multistep process which relies on the coordination of cytoskeletal structures in space and time. While the roles of actin and microtubules have been investigated in great details, the lack of inhibitors and visualizing tools and the large number of proteins forming intermediate filaments (IFs) have delayed the characterization of IF functions during migration. However, a large body of evidence has progressively pointed to changes in IF composition as an important parameter in the regulation of cell migratory properties both during development and tumor invasion. More recent in-depth analyses show that IFs are dynamically reorganized to participate, together with microfilaments and microtubules, to the key steps leading to cell migration

Cell Cycle Intermediate filaments join the action

International audienceCell polarity reflects the morphological, structural and functional organization of the cell along a so-called polarity axis. The cell ability to polarize in response to its microenvironment is a prerequisite for most cell behaviors including division [...