CYCLIC AMP SIGNALS AND THE CONTROL OF CELL AGGREGATION IN DICTYOSTELIUM DISCOIDEUM

Abstract

This chapter discusses cyclic AMP signals and the control of cell aggregation in Dictyostelium discoideum. Aggregating cells of Dictyostelium discoideum are excitable. In many respects they behave like neurons, they autonomously generate periodic signals, transmitter release occurs possibly by exocytosis, and cyclic adenosine monophosphate (cAMP) receptors and phosphodiesterase at their surface are comparable to acetylcholine receptors and cholinesterase at a postsynaptic membrane. In dictyostelium discoideum, both cAMP and folic acid cause a chemotactic response; they stimulate cGMP and cAMP synthesis and accelerate cell differentiation. The efficiency of both agents is maximal when they are applied in repetitive pulses. Both cAMP and folic acid interact with the oscillating system that controls adenylyl cyclase activity and cAMP release. Transmembrane signal processing is mediated by cell surface receptors for cAMP and probably also for folic acid. The life time of the signals in the extracellular space is determined by soluble enzymes degrading folic acid and cAMP, the latter enzyme being regulated by a macromolecular inhibitor. More efficient in terminating cAMP signals during the aggregation phase is a cell-surface phosphodiesterase whose activity increases strongly between growth phase and aggregation competence.