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

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 long-lived 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

Some Like It Fat: Comparative Ultrastructure of the Embryo in Two Demosponges of the Genus Mycale (Order Poecilosclerida) from Antarctica and the Caribbean

0000-0002-7993-1523© 2015 Riesgo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License [4.0], which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

Memory effects in the electron glass

We investigate theoretically the slow nonexponential relaxation dynamics and associated memory effects of glasses far from equilibrium, which are arguably the most important characteristics of the glass phase. We focus on the electron glass which offers an advantageous starting point compared to other glassy systems both theoretically and experimentally: the model used here is discrete, and experimentally it offers new ways to address these effects by changing a simple experimental parameter —the gate voltage. The full nonlinearized self-consistent model of the dynamics of the occupation numbers in the system successfully recovers the general behavior found in experiments. Our numerical analysis is consistent with both the expected logarithmic relaxation and our understanding of how increasing disorder or interaction slows down the relaxation process, thus yielding a consistent picture of the electron glass, and shedding light on the understanding of glassy behavior in general. We also present a novel finite-size domino effect where the connection to the leads affects the relaxation process of the electron glass in mesoscopic systems. This effect speeds up the relaxation process, and may even reverse the expected effect of interaction; stronger interaction then leading to a faster relaxation

Eliciting environmental preferences of Ghanaians in the laboratory: an incentive-compatible experiment

2010 - In press

Eliciting environmental preferences of Ghanaians: An experimental approach

JENA ECONOMIC RESEARCH PAPER