Becoming multicellular by aggregation;: The morphogenesis of the social amoebae Dicyostelium discoideum

The organisation and form of most organisms is generated during their embryonic development and involves precise spatial and temporal control of cell division, cell death, cell differentiation and cell movement. Differential cell movement is a particularly important mechanism in the generation of form. Arguably the best understood mechanism of directed movement is chemotaxis. Chemotaxis plays a major role in the starvation induced multicellular development of the social amoebae Dictyostelium. Upon starvation up to 10(5) individual amoebae aggregate to form a fruiting body. In this paper we review the evidence that the movement of the cells during all stages of Dictyostelium development is controlled by propagating waves of cAMP which control the chemotactic movement of the cells. We analyse the complex interactions between cell-cell signalling resulting in cAMP waves of various geometries and cell movement which results in a redistribution of the signalling sources and therefore changes the geometry of the waves. We proceed to show how the morphogenesis, including aggregation stream and mound formation, slug formation and migration, of this relatively simple organism is beginning to be understood at the level of rules for cell behaviour, which can be tested experimentally and theoretically by model calculations.