Figure 2.

 Roles of intracellular and secreted cyclic adenosine monophosphate (cAMP) during Dictyostelium discoideum development. The transition from growth to aggregation requires release of protein kinase (PKA) from translational repression. At this stage, PKA triggers a basal level of expression of genes required for aggregation, such as cAR1, PdsA and ACA, which enable the cells to synthesize and secrete cAMP pulses. In addition to inducing chemotaxis and cell aggregation, the cAMP pulses further upregulate the expression of aggregation genes. After aggregation, ACG is translationally upregulated in the posterior region of the emerging slug. ACG synthesizes cAMP that acts both on cARs and PKA to induce prespore gene expression. The prespore cells produce differentiation inducing factor (DIF) and DIF‐like factors that cause prestalk cell differentiation in combination with cAMP acting on cARs. Later, extracellular cAMP (cAMP_ex) becomes an inhibitor of stalk cell differentiation. During fruiting body formation intracellular cAMP (cAMP_in) acting on PKA is essential for terminal maturation of spores and stalk cells. In the spores, active PKA blocks the transition from dormancy to germination.