# Self-organized mechano-chemical dynamics in amoeboid locomotion of Physarum fragments

## TL;DR

This study investigates the complex mechano-chemical dynamics driving amoeboid locomotion in Physarum fragments, revealing how flow, contractility, and chemical signaling coordinate to produce diverse migratory behaviors.

## Contribution

It provides the first detailed experimental quantification of intracellular flows, traction stresses, and calcium signaling in Physarum fragments, linking these to migration patterns and proposing a convection-diffusion model for calcium transport.

## Key findings

- Symmetric flow patterns slow migration.
- Asymmetric patterns correlate with faster movement.
- Calcium transport via convection influences contractile wave organization.

## Abstract

The aim of this work is to quantify the spatio-temporal dynamics of flow-driven amoeboid locomotion in small ($\sim$100 $\mu$m) fragments of the true slime mold \phys {\it polycephalum}. In this model organism, cellular contraction drives intracellular flows, and these flows transport the chemical signals that regulate contraction in the first place. As a consequence of these non-linear interactions, a diversity of migratory behaviors can be observed in migrating \phys fragments. To study these dynamics, we measure the spatio-temporal distributions of the velocities of the endoplasm and ectoplasm of each migrating fragment, the traction stresses it generates on the substratum, and the concentration of free intracellular calcium. Using these unprecedented experimental data, we classify migrating \phys fragments according to their dynamics, finding that they often exhibit spontaneously coordinated waves of flow, contractility and chemical signaling. We show that \phys fragments exhibiting symmetric spatio-temporal patterns of endoplasmic flow migrate significantly slower than fragments with asymmetric patterns. In addition, our joint measurements of ectoplasm velocity and traction stress at the substratum suggest that forward motion of the ectoplasm is enabled by a succession of stick-slip transitions, which we conjecture are also organized in the form of waves. Combining our experiments with a simplified convection-diffusion model, we show that the convective transport of calcium ions may be key for establishing and maintaining the spatio-temporal patterns of calcium concentration that regulate the generation of contractile forces.