Aggregation and the Streamer F mutation
Dictyostelium demonstrates a dramatic synergy of development and cell motility when subjected to starvation. Cells begin secreting what is normally an intracellular messenger - cyclic AMP (cAMP). In addition, they begin to express G protein coupled receptors for cAMP. When these receptors bind cAMP, they stimulate chemotaxis towards higher extracellular concentrations of cAMP and also increased synthesis and secretion of cAMP. The net result is movement of the cells towards common centers, which eventually form fruiting bodies consisting of a stalk with a sorus (which contains spores) at the top.
Chemotactic Responses to a Micropipet
Dictyostelium cells are chemotactic to a number of chemicals. During growth phase, they orient in gradients of folate, which may aid in finding food bacteria. During aggregation, they secrete cAMP(!) and, in addition, are chemotactic towards the secreted cAMP. The result of this positive feedback loop is the aggregation process that is characteristic of Dictyostelium when starved. All the movies below are of starved Dictyostelium cells responding to a micropipet filled with cAMP.