The cellular basis of Dictyostelium morphogenesis

One of the central aims of the study of development is to understand how distinct cellular behaviours, for example, division, differentiation, apoptosis, and movement, are coordinated in space and in time to result in reproducible pattern formation and morphogenesis. Coordination of these cellular behaviours requires extensive communication between cells of different types and between the cells and their environment. The social amoeba Dictyostelium discoideum, a simple genetically tractable organism situated at the threshold of single and multicellular organisms in the evolutionary tree of life, is well suited for the study of these interactions because its genome has been sequenced and it is amenable to experimental manipulation through targeted gene disruption and replacement (Kreppel, Fey et al. 2004; Eichinger, Pachebat et al. 2005). Dictyostelium cells normally live as single cells in the leaf litter of the soil where they feed on bacteria and divide by binary fission. Under starvation conditions, up to several hundred thousand cells aggregate chemotactically to form a multicellular structure the slug, that directed by light and temperature gradients migrates to the surface of the soil to form a fruiting body. The fruiting body is composed of a stalk supporting a mass of spores. The spores are a dormant stage which after dispersal may germinate to release amoebae, thus closing the life cycle (Fig. 1). We describe here key aspects of the signalling mechanisms coordinating cellular behaviours responsible for pattern formation and morphogenesis.