Discrete Modeling of Amoeboid Locomotion and Chemotaxis in Dictyostelium discoideum by Tracking Pseudopodium Growth Direction

Zahra Eidi

doi:10.1038/s41598-017-12656-1

Abstract

Dictyostelium discoideum amoeba is a well-established model organism for studying the crawling locomotion of eukaryotic cells. These amoebae extend pseudopodium - a temporary actin-based protrusion of their body membrane to probe the medium and crawl through it. Experiments show highly-ordered patterns in the growth direction of these pseudopodia, which results in persistence cell motility. Here, we propose a discrete model for studying and investigating the cell locomotion based on the experimental evidences. According to our model, Dictyostelium selects its pseudopodium growth direction based on a second-order Markov chain process, in the absence of external cues. Consequently, compared to a random walk process, our model indicates stronger growth in the mean-square displacement of cells, which is consistent with empirical findings. In the presence of external chemical stimulants, cells tend to align with the gradient of chemoattractant molecules. To quantify this tendency, we define a coupling coefficient between the pseudopodium extension direction and the gradient of an external stimulant, which depends on the local stimulant concentration and its gradient. Additionally, we generalize the model to weak-coupling regime by utilizing perturbation methods.

Highlights

In order to probe the medium and move in the environment, the amoeba cells grow pseudopodium, a temporary actin-based protrusion of their membrane
Complex dynamics with anomalous diffusion has been reported for the spontaneous movement of Dictyostelium discoideum[19,20]
A few points regarding the wild type of cell movements are observed9: 1. Pseudopodia are extended perpendicular to the surface curvature at the place where they emerge[27]

Summary

Introduction

In order to probe the medium and move in the environment, the amoeba cells grow pseudopodium, a temporary actin-based protrusion of their membrane. Based on the experiments the cell extends pseudopodia in two types: (1) splitting on certain angles with respect to the existing pseudopodium, (2) growing protrusions occasionally at the rear side of the cell, called de novo[7]. The amoeba is propelled by growing successively splitting pseudopodia in a particular direction, while a random reorientation is generated by extending de novo pseudopodium[8,9,10]. The studies cover experimental and theoretical modeling of cell movement both in the absence and presence of external chemoattractants. The aim of the present work is to make a simple discrete model based on the experimental observations for Dictyostelium migration, first in a uniform environment and in the presence of external signaling. The pseudopodia do not bend towards the gradient and still are extended perpendicular to the local cell surface curvature[10]

Objectives

Methods

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Conclusion