How amoeboids self-organize into a fruiting body: Multicellular coordination in Dictyostelium discoideum

When individual amoebae of the cellular slime mold Dictyostelium discoideum are starving, they aggregate to form a multicellular migrating slug, which moves toward a region suitable for culmination. The culmination of the mor phogenesis involves complex cell movements that transform a mound of cells into a globule of spores on a slender stalk. The movement has been likened to a "reverse fountain," whereby prestalk cells in the upper part form a st alk that moves downwards and anchors to the substratum. while prespore cell s in the lower part move upwards to form the spore head. So far, however, n o satisfactory explanation has been produced for this process. Using a comp uter simulation that we developed, we now demonstrate that the processes th at are essential during the earlier stages of the morphogenesis are in fact sufficient to produce the dynamics of the culmination stage. These process es are cAMP signaling, differential adhesion, cell differentiation, and pro duction of extracellular matrix. Our model clarifies the processes that gen erate the observed cell movements. More specifically, we show that periodic upward movements, caused by chemotactic motion, are essential for successf ul culmination, because the pressure waves they induce squeeze the stalk do wnwards through the cell mass. The mechanisms revealed by our model have a number of self-organizing and self-correcting properties and can account fo r many previously unconnected and unexplained experimental observations.