Modelling Dictyostelium discoideum Morphogenesis

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Abstract

Morphogenesis of the social amoebae Dictyostelium discoideum results from the aggregation of individual cells to form a multicellular hemispherical cell mass, the mound. In the mound the cells differentiate into several cell types. These cell types arise initially in random location in the mound, but then sort out from one another to form a slug. In the slug these cell types are arranged in a simple axial pattern. The slug can migrate and under suitable conditions transforms into a fruiting body consisting of a stalk supporting a mass of spores. It is well established that cells aggregate in response to propagating waves of the chemoattractant cAMP. There is increasingly good experimental evidence that the later stages of morphogenesis are also controlled by cAMP wave propagation and Chemotaxis. Here we present a hydrodynamic model to describe Dictyostelium development from early aggregation up to migrating slug. We consider the population of cells as an excitable medium, which supports propagation of waves of the chemoattractant cAMP. To model the chemotactic cell movement we consider the masses of moving cells as a fluid flow. The morphogenesis of this multicellular organism is basically modelled as shape changes occurring in a drop of liquid with a free surface. At the mound stage this liquid consists of two randomly mixed component fluids corresponding to two cell types. Cell sorting can be effectively modelled as the separation of the component fluids driven by differential Chemotaxis. Finally, our model calculations show that migration of the slug can result from chemotactic flows inside the slug.