Actin Flows Mediate a Universal Coupling between Cell Speed and Cell Persistence

Cell movement has essential functions in development, immunity, and cancer. Various cell migration patterns have been reported, but no general rule has emerged so far. Here, we show on the basis of experimental data in vitro and in vivo that cell persistence, which quantifies the straightness of trajectories, is robustly coupled to cell migration speed. We suggest that this universal coupling constitutes a generic law of cell migration, which originates in the advection of polarity cues by an actin cytoskeleton undergoing flows at the cellular scale. Our analysis relies on a theoretical model that we validate by measuring the persistence of cells upon modulation of actin flow speeds and upon optogenetic manipulation of the binding of an actin regulator to actin filaments. Beyond the quantitative prediction of the coupling, the model yields a generic phase diagram of cellular trajectories, which recapitulates the full range of observed migration patterns

Innate control of actin nucleation determines two distinct migration behaviours in dendritic cells

Dendritic cell (DC) migration in peripheral tissues serves two main functions: antigen sampling by immature DCs, and chemokine-guided migration towards lymphatic vessels (LVs) on maturation. These migratory events determine the efficiency of the adaptive immune response. Their regulation by the core cell locomotion machinery has not been determined. Here, we show that the migration of immature DCs depends on two main actin pools: a RhoA mDial-dependent actin pool located at their rear, which facilitates forward locomotion; and a Cdc42 Arp2/3-dependent actin pool present at their front, which limits migration but promotes antigen capture. Following TLR4 MyD88-induced maturation, Arp2/3-dependent actin enrichment at the cell front is markedly reduced. Consequently, mature DCs switch to a faster and more persistent mDial-dependent locomotion mode that facilitates chemotactic migration to LVs and lymph nodes. Thus, the differential use of actin-nucleating machineries optimizes the migration of immature and mature DCs according to their specific function

Essai de lutte intégrée contre la prolifération de Cissus quadrangularis L. (Vitaceae) dans le Parc National des Iles de la Madeleine (Sénégal)

Objectif : contribuer à mettre en place une lutte intégrée contre la prolifération de Cissus quadrangularis L. dans le Parc National des Iles de la Madeleine (PNIM) au Sénégal.Méthodologie et résultats : Des essais de contrôle biologique et physique ont été testés. La lutte biologique a été basée sur la collecte et l’élevage en laboratoire de chenilles capables de dégrader les tiges et les feuilles de C. quadrangularis. Quant à la lutte physique, elle a consisté à arracher les individus de l’espèce et à suivre la capacité de régénération des résidus de la plante après différents traitements. Les résultats obtenus ont montré qu’une lutte biologique est envisageable à travers la chenille de   Hippotion celerio, phytophage de C. quadrangularis. Aussi, les tests de contrôle physique ont montré que l’arrachage manue  semblerait être efficace quand les fragments de la plante sont éliminés par  incinération hors du parc.Conclusion et application: La combinaison de ces deux méthodes pourrait permettre de réduire et de limiter la superficie d’occupation de C. quadrangularis dans le PNIM.Mots clés: Cissus quadrangularis, plante proliférante, Parc National des Iles de la Madeleine, lutte physique, lutte biologique, Hippotion celerio.Introduction: Help put up a integrated fight against the proliferation of Cissus quadrangularis L. in the National Park des Iles de la Madeleine (NPIM) in Senegal.Methodology and results: of trying to biological and physical control. Biological control has been based on collecting and raising caterpillars capable of degrading the stems and leaves of the concern species. As for the physical struggle, it was to snatch individuals of C. quadrangularis and follow the regenerative capacity of the plant residues after different treatments. The results have shown that biological control is possible through the caterpillar of Hippotion celerio, phytophage of C. quadrangularis. Also, physical control tests have shown that manual eradication would seem to be effective when the fragments of the plant are disposed of by incineration out of the park.Conclusion and application: The combination of these two methods could reduce and limit the occupancy area and possible spread of C. quadrangularis in NPIM.Keywords: Cissus quadrangularis, Alien plants, National Park des Iles de la Madeleine, physical control, biological control, Hippotion celerio

Numerical simulation of Richards equation in partially saturated porous media: Under-relaxation and mass balance

10.1007/s10706-007-9126-7Geotechnical and Geological Engineering255525-541GGEN