Actin cytoskeleton of chemotactic amoebae operates close to the onset of oscillations

Abstract

The rapid reorganization of the actin cytoskeleton in response to external stimuli is an essential property of many motile eukaryotic cells. Here, we report evidence that the actin machinery of chemotactic Dictyostelium cells operates close to an oscillatory instability. When averaging the actin response of many cells to a short pulse of the chemoattractant cAMP, we observed a transient accumulation of cortical actin reminiscent of a damped oscillation. At the single-cell level, however, the response dynamics ranged from short, strongly damped responses to slowly decaying, weakly damped oscillations. Furthermore, in a small subpopulation, we observed self-sustained oscillations in the cortical F-actin concentration. To substantiate that an oscillatory mechanism governs the actin dynamics in these cells, we systematically exposed a large number of cells to periodic pulse trains of different frequencies. Our results indicate a resonance peak at a stimulation period of around 20 s. We propose a delayed feedback model that explains our experimental findings based on a time-delay in the regulatory network of the actin system. To test the model, we performed stimulation experiments with cells that express GFP-tagged fusion proteins of Coronin and actin-interacting protein 1, as well as knockout mutants that lack Coronin and actin-interacting protein 1. These actin-binding proteins enhance the disassembly of actin filaments and thus allow us to estimate the delay time in the regulatory feedback loop. Based on this independent estimate, our model predicts an intrinsic period of 20 s, which agrees with the resonance observed in our periodic stimulation experiments.Dictyostelium discoideum | microfluidics | caged cAMP | delay-differential equation T he actin cytoskeleton provides the basis for shape dynamics and motility of eukaryotic cells. Essential biological processes like wound healing, embryonic morphogenesis, or cancer metastasis rely on the rapid rearrangement of the actin cytoskeleton in response to external chemical cues (1). Many of the underlying actin-driven processes have been investigated in cells of the social amoeba Dictyostelium discoideum. Under starvation, the singlecelled amoeba expresses a chemotactic signaling system to aggregate into a multicellular structure, mediated by the chemoattractant cAMP. The corresponding receptor signaling pathway and the downstream cytoskeletal machinery show remarkable similarities to motile cells of higher organisms, in particular neutrophils (2), making Dictyostelium one of the most popular models for eukaryotic cell motility and chemotaxis (3, 4).In earlier studies, it was observed that the actin system of chemotactic Dictyostelium cells shows a complex, nonmonotonic response when exposed to a sudden increase in the extracellular chemoattractant concentration (5-7). Between 5 and 10 s after the stimulus, a first maximum in the filamentous actin content is observed, followed by a second, less intense but prolonged maximum that starts about 30 s after the stimulus and...

Signaling in chemotactic amoebae remains spatially confined to stimulated membrane regions

“…The PIP 3 -rich domains move in conjunction with actin waves at their border and show the hallmarks of waves in an excitable system, such as mutual annihilation upon collision or spiral core formation Gerisch et al, 2011;Taniguchi et al, 2013;Gerhardt et al, 2014). Also, oscillatory dynamics has been observed (Westendorf et al, 2013;Huang et al, 2013). Prompted by these observations, recent modeling approaches rely on excitable dynamics to describe gradient sensing and chemotaxis (Xiong et al, 2010;Hecht et al, 2011;Neilson et al, 2011;Cooper et al, 2012;Huang et al, 2013;Knoch et al, 2014).…”

Effective Dynamics of Microorganisms That Interact with Their Own Trail

“…Chemically-mediated interactions between bacteria or eukaryotic cells [4,[19][20][21][22][23][24] as well as artificial active colloids [25][26][27] lead to a variety of collective phenomena including collapse, pattern formation, alignment and oscillations. Auto-chemotactic effects have been studied in the context of swimming bacteria [28,29] and Dictyostelium cells [30]. While much is known about the chemotactic machinery in bacteria [31,32] and eukaryotic cells [23], relatively little is known about trail-mediated interactions.…”

Intracellular photoactivation of caged cGMP induces myosin II and actin responses in motile cells

“…33 For extracellular stimulation of Dictyostelium cells with complex and rapidly switching signals, the light-induced release of such compounds was successfully demonstrated. 34,35 In the present work, we used the [7-(dimethylamino)coumarin-4-yl]methyl (DMACM) ester of 8-Br-cGMP, a photolabile cGMP analogue that is known to be membrane permeable, poorly hydrolyzed by phosphodiesterases, stably soluble in aqueous buffer solution, and rapidly released upon illumination. 30 Compared to the nitrobenzyl derivatives, optimal photocleavage of this compound is shifted to longer wavelengths (330-440 nm, l max 398 nm), reducing cell damage and photo-bleaching.…”