Pattern Formation in Dictyostelium

INTRODUCTION Upon starvation, amoebae of the cellular slime mold Dictyostelium undergo a program of development in which individual cells aggregate to form a multicellular slug and, subsequently, a fruiting body consisting of stalk cells and spores (Loomis 1982). Terminal differentiation of stalk cells and spores is preceded by formation of prestalk and prespore cells in the slug stage. Dictyostelium has attracted considerable interest in recent years as a model system for studies of cell differentiation. In this paper we focus on the control of prestalk and prespore formation and the organization of the slug stage in which the prestalk/prespore decision occurs. Pattern of Prestalk and Prespore Cells Dictyostelium amoebae aggregate chemotactically to form an initially homogeneous multicellular mass. This mass then transforms into an elongated “slug,” which migrates over the substratum for varying periods of time depending on environmental conditions (Newell et al. 1969; Schindler and Sussman 1977). Prestalk and prespore cells first appear in the slug stage where they form a characteristic spatial pattern: prestalk cells in the anterior third of the slug and prespore cells in the posterior two-thirds. Prestalk and prespore cells differ histologically (Bonner et al. 1955), in buoyant density (Tsang and Bradbury 1981; Ratner and Borth 1983), cell-surface glycoproteins (West and McMahon 1979), metabolic activity (Bonner et al. 1984), expression of specific antigens (Krefft et al. 1983; Tasaka et al. 1983), specific polypeptides (Alton and Brenner 1979; Ratner and Borth 1982; Morrissey et al. 1984), and specific genes (see Chisholm et al., this volume). Some...