The cellular basis of movement of the migrating grex of the slime mould Dictyostelium Discoideum

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Abstract
Previous work has failed to suggest a mechanism for grex movement, which takes account of both the movement and contact interaction of grex cells, and properties of the whole grex. Here, some observations on the movement of grex cells under different conditions are reported. From these, it seems that the production of pseudopods by grex cells depends upon mechanical factors of their environment and that movement depends on pseudopods being able to form stable adhesion with the surfaces of other cells. Intercellular adhesions are stable to forces applied at right angles to the plane of adhesion, but a force parallel to the plane of adhesion causes the cell surfaces to slide past each other. It is suggested from observations on grex placed in aqueous media and paraffin oil that the slime sheath may play an important role in controlling the polarity of grex movement by restricting pseudopod formation in all directions except forwards. These suggestions are discussed briefly in relation to previous observations on grex movement.