Adenylyl Cyclase Localization Regulates Streaming during Chemotaxis

AbstractWe studied the role of the adenylyl cyclase ACA in Dictyostelium discoideum chemotaxis and streaming. In this process, cells orient themselves in a head to tail fashion as they are migrating to form aggregates. We show that cells lacking ACA are capable of moving up a chemoattractant gradient, but are unable to stream. Imaging of ACA-YFP reveals plasma membrane labeling highly enriched at the uropod of polarized cells. This localization requires the actin cytoskeleton but is independent of the regulator CRAC and the effector PKA. A constitutively active mutant of ACA shows dramatically reduced uropod enrichment and has severe streaming defects. We propose that the asymmetric distribution of ACA provides a compartment from which cAMP is secreted to locally act as a chemoattractant, thereby providing a unique mechanism to amplify chemical gradients. This could represent a general mechanism that cells use to amplify chemotactic responses

PI 3-Kinases and PTEN How Opposites Chemoattract

AbstractPhosphatidylinositol lipids, such as PI(4,5)P2 and PI(3,4,5)P3, are key mediators in diverse intracellular signaling pathways. Two recent reports examine how the metabolism of these lipids by phosphatidylinositol 3-kinases and the PTEN 3-phosphoinositide phosphatase may coordinate G protein coupled signaling pathways during eukaryotic chemotaxis

Cell Shape Dynamics: From Waves to Migration

We observe and quantify wave-like characteristics of amoeboid migration. Using the amoeba Dictyostelium discoideum, a model system for the study of chemotaxis, we demonstrate that cell shape changes in a wave-like manner. Cells have regions of high boundary curvature that propagate from the leading edge toward the back, usually along alternating sides of the cell. Curvature waves are easily seen in cells that do not adhere to a surface, such as cells that are electrostatically repelled from surfaces or cells that extend over the edge of micro-fabricated cliffs. Without surface contact, curvature waves travel from the leading edge to the back of a cell at ∼35 µm/min. Non-adherent myosin II null cells do not exhibit these curvature waves. At the leading edge of adherent cells, curvature waves are associated with protrusive activity. Like regions of high curvature, protrusive activity travels along the boundary in a wave-like manner. Upon contact with a surface, the protrusions stop moving relative to the surface, and the boundary shape thus reflects the history of protrusive motion. The wave-like character of protrusions provides a plausible mechanism for the zig-zagging of pseudopods and for the ability of cells both to swim in viscous fluids and to navigate complex three dimensional topography

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

Des pistes pour améliorer les compétences en lecture des élèves

La dernière enquête pancanadienne sur les compétences en lecture des élèves du secondaire dresse un portrait peu flatteur des élèves québécois par comparaison avec leurs pairs de l’Ontario, de l’Alberta ou de la Colombie-Britannique. Profitant de la diffusion de ces résultats accablants, la ministre de l’Éducation, du Loisir et du Sport a annoncé un certain nombre de mesures visant à rectifier le tir en matière d’enseignement de la lecture, répondant ainsi en partie à des revendications portées depuis quelque temps par les instances syndicales. Les mesures annoncées concernent la révision des orientations du programme du préscolaire et du primaire pour les premiers apprentissages, l’ajout d’une épreuve d’évaluation à la fin du deuxième cycle du primaire ainsi qu’un engagement à débloquer des fonds non négligeables pour des recherches relatives à la question de l’acquisition de la compétence en lecture

LTB4 Is a Signal-Relay Molecule during Neutrophil Chemotaxis

SummaryNeutrophil recruitment to inflammation sites purportedly depends on sequential waves of chemoattractants. Current models propose that leukotriene B4 (LTB4), a secondary chemoattractant secreted by neutrophils in response to primary chemoattractants such as formyl peptides, is important in initiating the inflammation process. In this study we demonstrate that LTB4 plays a central role in neutrophil activation and migration to formyl peptides. We show that LTB4 production dramatically amplifies formyl peptide-mediated neutrophil polarization and chemotaxis by regulating specific signaling pathways acting upstream of actin polymerization and MyoII phosphorylation. Importantly, by analyzing the migration of neutrophils isolated from wild-type mice and mice lacking the formyl peptide receptor 1, we demonstrate that LTB4 acts as a signal to relay information from cell to cell over long distances. Together, our findings imply that LTB4 is a signal-relay molecule that exquisitely regulates neutrophil chemotaxis to formyl peptides, which are produced at the core of inflammation sites

The Ionomics of Lettuce Infected by Xanthomonas campestris pv. vitians

Bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vitians (Xcv) places a major constraint on lettuce production worldwide. The most sustainable strategy known to date for controlling BLS is the use of resistant cultivars. The nutrient elemental signature (ionome) of ten lettuce cultivars with three levels of resistance was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine which nutrient balances are linked to resistance to BLS, and to assess the effect of Xcv infection on the ionome. The elemental concentrations were preprocessed with isometric log-ratios to define nutrient balances. Using this approach, 4 out of 11 univariate nutrient balances were found to significantly influence the resistance of lettuce cultivars to BLS (P < 0.05). These significant balances were the overall nutritional status balancing all measured nutrients with their complementary in the dry mass, as well as balances [Mn | Zn,Cu], [Zn | Cu], and [S,N | P]. Moreover, the infection of lettuce cultivars mostly affected the lettuce ionome on the [N,S | P] balance, where infection tended to lean the balance toward the N,S part relatively to P. This study shows that nutrient uptake in lettuce can be affected by BLS infection and that nutrient status influences resistance to BLS infection

Adenylyl cyclase mRNA localizes to the posterior of polarized DICTYOSTELIUM cells during chemotaxis

In Dictyostelium discoideum, vesicular transport of the adenylyl cyclase A (ACA) to the posterior of polarized cells is essential to relay exogenous 3′,5′-cyclic adenosine monophosphate (cAMP) signals during chemotaxis and for the collective migration of cells in head-to-tail arrangements called streams. Using fluorescence in situ hybridization (FISH), we discovered that the ACA mRNA is asymmetrically distributed at the posterior of polarized cells. Using both standard estimators and Monte Carlo simulation methods, we found that the ACA mRNA enrichment depends on the position of the cell within a stream, with the posterior localization of ACA mRNA being strongest for cells at the end of a stream. By monitoring the recovery of ACA-YFP after cycloheximide (CHX) treatment, we observed that ACA mRNA and newly synthesized ACA-YFP first emerge as fluorescent punctae that later accumulate to the posterior of cells. We also found that the ACA mRNA localization requires 3′ ACA cis-acting elements. Together, our findings suggest that the asymmetric distribution of ACA mRNA allows the local translation and accumulation of ACA protein at the posterior of cells. These data represent a novel functional role for localized translation in the relay of chemotactic signal during chemotaxis.https://doi.org/10.1186/s12860-017-0139-