Directional memory arises from long-lived cytoskeletal asymmetries in polarized chemotactic cells

Abstract

Chemotaxis, the directional migration of cells in a chemical gradient, is robust to fluctuations associated with low chemical concentrations and dynamically changing gradients as well as high saturating chemical concentrations. Although a number of reports have identified cellular behavior consistent with a directional memory that could account for behavior in these complex environments, the quantitative and molecular details of such a memory process remain unknown. Using microfluidics to confine cellular motion to a 1D channel and control chemoattractant exposure, we observed directional memory in chemotactic neutrophil-like cells. We modeled this directional memory as a long-lived intracellular asymmetry that decays slower than observed membrane phospholipid signaling. Measurements of intracellular dynamics revealed that moesin at the cell rear is a longlived element that when inhibited, results in a reduction of memory. Inhibition of ROCK (Rho-associated protein kinase), downstream of RhoA (Ras homolog gene family, member A), stabilized moesin and directional memory while depolymerization of microtubules (MTs) disoriented moesin deposition and also reduced directional memory. Our study reveals that long-lived polarized cytoskeletal structures, specifically moesin, actomyosin, and MTs, provide a directional memory in neutrophil-like cells even as they respond on short time scales to external chemical cues. . In particular, chemical cues activate signaling at the cell surface and are integrated within the cell cytoplasm to give rise to a polarization in the direction of the local gradient. Although these processes have been the subject of detailed experimental study and theoretical and computational modeling, the mechanisms by which this orientation is achieved and maintained in the face of environmental noise remains incomplete.Although migration might be thought of as being very sensitive to the variations in the external environment, instead, we see robust migration in a variety of fluctuating environments. These observations all point to the existence of a directional memory in chemotactic cells-a biochemical pathway that stores information about cellular orientation and prevents the loss of orientation in the face of fluctuations, transient loss of polarization, or saturation of the receptors. For example, recent work has demonstrated memory-based behavior in Dictyostelium amoebae under fluctuating waves of chemoattractant (6, 7), although the authors do not identify potential molecular elements that store this information.Here, we use microchannel-based microfluidic devices to observe cell polarization and movement in confined mammalian neutrophil-like cells. Cells in this environment exhibit a strong bias to repolarize in the previous direction of motion after a period of depolarization. This memory is time-dependent and decays when the cell is unstimulated. To describe these results, we construct a minimal phenomenological model coupling membrane and cytoskeletal polarization lifetimes and show that thi...

A dual-docking microfluidic cell migration assay (D2-Chip) for testing neutrophil chemotaxis and the memory effect

“…Although the 1D cell migration system has the advantage for measuring the memory effect 44,63 , we chose the 2D cell migration system in this study to avoid the cell confinement effect in the 1D system, which can be difficult to decouple from chemotaxis. Our results are in general agreement with other relevant studies, which all reported retarded adjustment of cell migration upon change of the gradient condition 8,32,[36][37][38][39][40] . Our results further demonstrated that such chemotactic memory is chemoattractant gradient dependent.…”

“…We recently showed that chemotactic memory can be reflected by the chemotaxis history dependent chemotaxis-toflowtaxis transition in spatially-varying gradient fields using a microfluidic device 33 . Similarly, a recent study further suggested that cells can initiate and maintain chemotactic migration in response to chemoattractant waves and demonstrated the importance of localized cytoskeleton structure for preserving chemotactic memory 37 . However, a common drawback of these previous studies is the lack of spatial control of cell positions in their respective experimental systems, and the conclusion was often drawn based on the average of individual cell measurements with significant background variations.…”

“…Experimental and modeling efforts in this direction go back a long way in the field of cell migration research 8,15,[32][33][34][35][36][37][38][39][40] . Sensitive morphological, orientation and migratory response of neutrophils to temporal variations of chemoattractant fields, which depends on the cell's previous chemoattractant exposure, were consistently reported 21,32,37 . Furthermore, retarded adjustment of chemotactic migration in response to spatial changes of chemoattractant gradients was clearly demonstrated 8,33 .…”

Emergent memory in cell signaling: Persistent adaptive dynamics in cascades can arise from the diversity of relaxation time-scales

“…Another well-known example of eukaryotic cellular memory is observed during chemotactic migration along the gradient of a chemical signal [40,41]. The directionality of migration is known to persist for a certain duration, even if the chemical gradient is altered or becomes static.…”

“…The directionality of migration is known to persist for a certain duration, even if the chemical gradient is altered or becomes static. Studies show that the protein Moesin contributes to the long-lived rigidity of the cytoskeleton assembly that subsequently leads to the directional memory in polarized migrating cells [41]. However, the intra-cellular processes that underlie the persistent activity of Moesin in the absence of a gradient mediated signal are still largely unknown.…”