Possible role of contact following in the generation of coherent motion of Dictyostelium cells

After aggregation by chemotaxis, cells of the cellular slime mold Dictyostelium discoideum form a multicellular structure and show coherent motion such as vortices. Here, we present a mathematical model to explain both aggregation and coherent motion of cells in two-dimensional space. The model incorporates chemotactic response of cells and the cell's property, called "contact following", to follow the other cells with which they are in contact. Analytical study and computer simulation using the model show that with contact following, cells form circular clusters within which cell rotation occurs. Unidirectional cell motion in a long belt of cells is another type of solution of the model. Besides, contact following has an effect to accelerate cell cluster merging. By considering the mechanism of cell movement, possible explanations of contact following are proposed.