Regulation of the developmental modes in Dictyostelium mucoroides by cAMP and ethylene.

The cellular slime mold Dictyostelium mucoroides-7 (Dm7) and a mutant (MF1) derived from it exhibit clear dimorphism in development depending upon environmental conditions: macrocyst formation occurs during the sexual cycle, and sorocarp formation during the asexual process. As previously reported, exposure of cells to ethylene gas is favorable to macrocyst formation, while exogenously added 3',5'-cyclic adenosine monophosphate (cAMP) induces sorocarp formation. The significance of ethylene and cAMP for the mechanism involved in selection of the developmental pathways was further confirmed by determining the amounts of these substances in macrocyst- or sorocarp-forming cells. Aminooxy-acetic acid (AOA), an inhibitor of ethylene synthesis, was found to switch development of Dm7 and MF1 cells from macrocyst to sorocarp formation by decreasing ethylene production. The cAMP content was shown to be always higher in cells destined for sorocarp formation than in those destined for macrocyst formation, particularly at the aggregation stage. All of the results obtained strongly suggested that the amounts of cAMP and ethylene present, and possibly the ratio between them, may be of great importance for determining which mode of development will be realized.