Chemotaxis in shallow gradients is mediated independently of PtdIns 3-kinase by biased choices between random protrusions

Abstract

Current models of eukaryotic chemotaxis propose that directional sensing causes localized generation of new pseudopods. However, quantitative analysis of pseudopod generation suggests a fundamentally different mechanism for chemotaxis in shallow gradients: first, pseudopods in multiple cell types are usually generated when existing ones bifurcate and are rarely made de novo; second, in Dictyostelium cells in shallow chemoattractant gradients, pseudopods are made at the same rate whether cells are moving up or down gradients. The location and direction of new pseudopods are random within the range allowed by bifurcation and are not oriented by chemoattractants. Thus, pseudopod generation is controlled independently of chemotactic signalling. Third, directional sensing is mediated by maintaining the most accurate existing pseudopod, rather than through the generation of new ones. Finally, the phosphatidylinositol 3-kinase (PI(3)K) inhibitor LY294002 affects the frequency of pseudopod generation, but not the accuracy of selection, suggesting that PI(3)K regulates the underlying mechanism of cell movement, rather than control of direction.

Migration of cells in a social context

“…Contrary to previous work (22,(24)(25)(26)29), these cells form neither 2D sheets nor 3D structures, nor are they highly polarized, and their single-cell migratory behavior is established (13,14,16). The microfluidic cell culture platform hosts independent and isolated culture conditions in each of the isolated 96 polymethylsiloxane (PDMS) chambers (34-nL volume) that mimic physiological conditions more plausibly than traditional cell-culture environments in which concentrations of, for instance, secreted signaling molecules are diluted into large volumes of surrounding fluid.…”

“…Furthermore, striking social effects such as highly sensitive collective responses in a number of sensing systems [e.g., quorum sensing (31,32) and onset of collective behavior in Dictyostelium discoideum (33)] mediated by increased levels of cell-secreted signals in higher cell density indicate that mechanical links are not necessary for collective behavior. At the subcellular level, many types of nonswimming motile cells involved in multicellular biology [e.g., fibroblasts, Dictyostelium, and neutrophils (13,14,(16)(17)(18)] have been found to transmit traction force to the substrate by intracellularly polymerizing their cytoskeletons in dynamically formed membrane protrusions known as pseudopodia. However, whether the social context changes this, mechanisms by which the social context manifests itself, and the implications of being close to neighboring cells all remain unexplored.…”

“…In addition to its aesthetic qualities, social cell migration is involved in embryonic development (7), wound healing (8), and immune response (9), and unregulated migration leads to disease, including cancer metastasis (10). Previous work on single-cell migration has focused on isolated (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) or strongly polarized and aligning (21, 22) cell types, mostly using population-averaged bulk assays (23) or simple observations in a social context (2, 3). However, strongly cross-correlated cell motion and collective substrate deformation has been found to arise in mechanically interlinked cells transmitting forces through both cell-cell linkages and the substrate (24-29).…”

High Resolution Tracking of Cell Membrane Dynamics in Moving Cells: an Electrifying Approach

“…Obvious problems with this approach are, firstly, that cells affected in critical components of their motile machinery may be completely immobile, useless for quantifying morphology, and, secondly, that differences in phenotypes may be very subtle because of common redundancy of regulatory pathways. Manually screening hundreds of cells for subtle differences is massively time consuming [2]. The need for automated approaches for reproducibly extracting quantitative data from image sequences is therefore plainly apparent [11,26].…”

Integrins in Cell Migration

“…The mechanisms that regulate the decision to disassemble or to elongate and grow are not understood. However, these mechanisms are likely the regulators of the directed migration of mesenchymal cells and may also contribute to directional decision-making during pseudopod selection by amoeboid cells migrating in vitro (Andrew and Insall 2007) and in vivo (Cvejic et al 2008;Yoo et al 2010).…”