Collective cell migration requires vesicular trafficking for chemoattractant delivery at the trailing edge

Chemoattractant signaling induces the polarization and directed movement of cells secondary to the activation of multiple effector pathways. In addition, chemotactic signals can be amplified and relayed to proximal cells via the synthesis and secretion of additional chemoattractant. The mechanisms underlying such remarkable features remain ill defined. We show that the asymmetrical distribution of adenylyl cyclase (ACA) at the back of Dictyostelium discoideum cells, an essential determinant of their ability to migrate in a head-to-tail fashion, requires vesicular trafficking. This trafficking results in a local accumulation of ACA-containing intracellular vesicles and involves intact actin, microtubule networks, and de novo protein synthesis. We also show that migrating cells leave behind ACA-containing vesicles, likely secreted as multivesicular bodies and presumably involved in the formation of head-to-tail arrays of migrating cells. We propose that similar compartmentalization and shedding mechanisms exist in mammalian cells during embryogenesis, wound healing, neuron growth, and metastasis

Persistent holes in a fluid

We observe stable holes in a vertically oscillated 0.5 cm deep aqueous suspension of cornstarch for accelerations a above 10g. Holes appear only if a finite perturbation is applied to the layer. Holes are circular and approximately 0.5 cm wide, and can persist for more than 10^5 cycles. Above a = 17g the rim of the hole becomes unstable producing finger-like protrusions or hole division. At higher acceleration, the hole delocalizes, growing to cover the entire surface with erratic undulations. We find similar behavior in an aqueous suspension of glass microspheres.Comment: 4 pages, 6 figure

Shocks in supersonic sand

We measure time-averaged velocity, density, and temperature fields for steady granular flow past a wedge and calculate a speed of granular pressure disturbances (sound speed) equal to 10% of the flow speed. The flow is supersonic, forming shocks nearly identical to those in a supersonic gas. Molecular dynamics simulations of Newton's laws and Monte Carlo simulations of the Boltzmann equation yield fields in quantitative agreement with experiment. A numerical solution of Navier-Stokes-like equations agrees with a molecular dynamics simulation for experimental conditions excluding wall friction.Comment: 4 pages, 5 figure

Myosin II activity regulates vinculin recruitment to focal adhesions through FAK-mediated paxillin phosphorylation

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. The definitive version was published in Journal of Cell Biology 188 (2010): 877-890, doi:10.1083/jcb.200906012.Focal adhesions (FAs) are mechanosensitive adhesion and signaling complexes that grow and change composition in response to myosin II–mediated cytoskeletal tension in a process known as FA maturation. To understand tension-mediated FA maturation, we sought to identify proteins that are recruited to FAs in a myosin II–dependent manner and to examine the mechanism for their myosin II–sensitive FA association. We find that FA recruitment of both the cytoskeletal adapter protein vinculin and the tyrosine kinase FA kinase (FAK) are myosin II and extracellular matrix (ECM) stiffness dependent. Myosin II activity promotes FAK/Src-mediated phosphorylation of paxillin on tyrosines 31 and 118 and vinculin association with paxillin. We show that phosphomimic mutations of paxillin can specifically induce the recruitment of vinculin to adhesions independent of myosin II activity. These results reveal an important role for paxillin in adhesion mechanosensing via myosin II–mediated FAK phosphorylation of paxillin that promotes vinculin FA recruitment to reinforce the cytoskeletal ECM linkage and drive FA maturation.This work was supported by NHLBI (C.M. Waterman and A.M. Pasapera; and grant HL093156 to D.D. Schlaepfer) and the Burroughs Wellcome Fund (E. Rericha)

<i>Dictyostelium</i> Cells Migrate Similarly on Surfaces of Varying Chemical Composition

<div><p>During cell migration, cell-substrate binding is required for pseudopod anchoring to move the cell forward, yet the interactions with the substrate must be sufficiently weak to allow parts of the cell to de-adhere in a controlled manner during typical protrusion/retraction cycles. Mammalian cells actively control cell-substrate binding and respond to extracellular conditions with localized integrin-containing focal adhesions mediating mechanotransduction. We asked whether mechanotransduction also occurs during non-integrin mediated migration by examining the motion of the social amoeba <i>Dictyostelium discoideum</i>, which is thought to bind non-specifically to surfaces. We discovered that <i>Dictyostelium</i> cells are able to regulate forces generated by the actomyosin cortex to maintain optimal cell-surface contact area and adhesion on surfaces of various chemical composition and that individual cells migrate with similar speed and contact area on the different surfaces. In contrast, during collective migration, as observed in wound healing and metastasis, the balance between surface forces and protrusive forces is altered. We found that <i>Dictyostelium</i> collective migration dynamics are strongly affected when cells are plated on different surfaces. These results suggest that the presence of cell-cell contacts, which appear as <i>Dictyostelium</i> cells enter development, alter the mechanism cells use to migrate on surfaces of varying composition.</p></div

Cells migrate similarly on various substrates.

<p><b>A.</b> Quantification of average speed, relative contact area, absolute contact area, and polarization (see Material and Methods) for WT (AX3) cells on each surface. Time-lapse images were collected for 90 min and each cell was tracked for at least 5 min. Error bars indicate SD of three independent experiments, each with over 30 individual cells analyzed. All values were not statistically different (p>0.05; ANOVA). <b>B.</b> Quantification of temporal speed and relative contact area for WT (AX3) cells during migration on BSA and PLL coated surface. Speed and relative contact are averaged over all cells at corresponding time point. <b>C.</b> Comparison of average speed, relative contact area, absolute contact area, and polarization with the fluctuation of all these four measurements. *indicates statistical significance on speed fluctuation compared to the other three surfaces (p<0.05; ANOVA, Tukey test).</p

Cell-surface adhesion is actin-dependent.

<p><b>A.</b> Representative bright field (BF; left half of image) and IRM (right half of image) images of WT (AX3) cells on the 4 different surfaces. Scale bar = 35 µm. <b>B.</b> Quantification of average percent of cell in contact on each surface, for WT (AX3) cells and WT cells treated with 5 µM Latrunculin A. <b>C.</b> Representative BF and IRM images of WT (AX3) cells treated with Latrunculin A and plated on the 4 different surfaces. Scale bar = 35 µm. <b>D.</b> Quantification of average percent of cell in contact on BSA and PLL surfaces. WT cells were treated with different Latrunculin A concentrations, as indicated. For B and D, error bars indicate SEM of three independent experiments, each with over 30 individual cells analyzed. For B, *indicates statistical significance (p<0.05; ANOVA, Tukey test). For D, *indicates statistical significance compared to the control condition (*: p<0.05, T-test; **: p<0.005; T-test).</p