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. 2011;6(11):e27532.
doi: 10.1371/journal.pone.0027532. Epub 2011 Nov 9.

Amoeboid cells use protrusions for walking, gliding and swimming

Peter J M Van Haastert  1
Affiliations

Amoeboid cells use protrusions for walking, gliding and swimming

Peter J M Van Haastert. PLoS One. 2011.

Abstract

Amoeboid cells crawl using pseudopods, which are convex extensions of the cell surface. In many laboratory experiments, cells move on a smooth substrate, but in the wild cells may experience obstacles of other cells or dead material, or may even move in liquid. To understand how cells cope with heterogeneous environments we have investigated the pseudopod life cycle of wild type and mutant cells moving on a substrate and when suspended in liquid. We show that the same pseudopod cycle can provide three types of movement that we address as walking, gliding and swimming. In walking, the extending pseudopod will adhere firmly to the substrate, which allows cells to generate forces to bypass obstacles. Mutant cells with compromised adhesion can move much faster than wild type cells on a smooth substrate (gliding), but cannot move effectively against obstacles that provide resistance. In a liquid, when swimming, the extending pseudopods convert to side-bumps that move rapidly to the rear of the cells. Calculations suggest that these bumps provide sufficient drag force to mediate the observed forward swimming of the cell.

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Conflict of interest statement

Competing Interests: The author has declared that no competing interests exist.

Figures

Figure 1
Figure 1. Side bumps on walking cells.
A. Presented is the root-mean-square speed relative to the substrate of the tip of 20 pseudopods.. B. Images of wild-type walking cells. C. Images of tail-attached wild-type cells. D. Images of gliding gbpD-null cells. In the three cases the frames are static and the dots are placed at fixed positions; the arrows point to moving bumps. Numbers indicate time in seconds.
Figure 2
Figure 2. Swimming cells.
The trajectory of 8 tail-attached cells was followed after detachment from the surface. A. Tracks of 2 swimming cells at 20 s interval; * indicate the start. B. Speed of the same 2 cells. C. Mean square displacement formula image of 8 swimming cells. The parameters of the equation for a persistent random walk in three dimensions formula image were fitted to the data points; the line presents the optimal fit with speed S = 3 µm/min and persistence time P = 1.3 min.
Figure 3
Figure 3. Gliding cells.
A. Adhesion of wild type and gbpD-null cells, expressed as the fraction of cells that detach from a plastic surface after shaking in buffer for 1 hour . B. Speed of wild-type and mutant cells on a solid support and under a block of agar.
Figure 4
Figure 4. Model of gliding, walking and swimming.
All cells extend pseudopods at a frequency of ∼4 per minute. In gliding cells, pseudopods are large and all contribute to forward moving; side bumps are rare. In walking cells, pseudopods are smaller and only ∼75% of pseudopods contribute to forward movement; these pseudopods convert to side-bumps that are stationary relative to the substrate. In swimming cells, pseudopods are small and convert to side-bumps that move to the rear of the cell. On average walking and swimming cells have ∼3 side-bumps (see table S1)
See this image and copyright information in PMC

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