Cyclic AMP inhibits dedifferentiation in the cellular slime mold Dictyostelium discoideum

When aggregating amoebas of the cellular slime mold Dictyostelium discoideum are disaggregated and morphogenesis is reinitiated, the amoebas will reaggregate in less than 1/10th the original time. When aggregating amoebas are disaggregated and resuspended either in full nutrient medium or in buffered salts solution containing dextrose, they retain this developmentally acquired capacity to rapidly reaggregate for approximately 1 hr and then lose it completely in a synchronous and discrete step which we have referred to as the "erasure event." In this report, it is demonstrated that micromolar concentrations of cAMP completely block this transition from the developmental to vegetative state, and that other cyclic nucleotides also inhibit it, but they do so at 20-fold higher concentrations. Neither the hydrolysis products of cAMP nor the vegetative chemoattractant folic acid inhibit dedifferentiation at concentrations as high as 10(-3) M, demonstrating a specificity for cyclic nucleotides and cAMP in particular. The addition of cAMP at any time during the lag period preceding the erasure event inhibits it and addition immediately after the erasure event reverses it. Since cAMP may inhibit the transition from the developmental to vegetative state intracellularly or extracellularly, we have also examined the intracellular concentration of cAMP and the levels of cAMP binding sites on the cell surface during the erasure process. Evidence is presented that the majority of cAMP binding sites on the cell surface are not necessary for the inhibition of erasure by cAMP. The results of these latter studies are discussed in terms of alternative models for the involvement of cAMP in the transition from the developing to vegetative state.