Cyclic AMP and Ca 2+ as regulators of zygote formation in the cellular slime mold Dictyostelium mucoroides

Abstract

Abstract To analyze the mechanism of the sexual process (macrocyst formation) in the cellular slime mold Dictyostelium mucoroides7(Dm7), the effects of 3′,5′–cyclic adenosine monophosphate (cAMP), conditioned medium (CM) factors, and various ions including Ca 2+ on zygote formation were examined. The application of cAMP was found to inhibit the sexual cell fusion. In addition, the activity of fusion inhibitor(s) contained in CM was heat stable and lost by phosphodiesterase (PDE)–treatment, thus indicating that cAMP is the inhibitor, being in contrast to ethylene as a fusion activator. Pulse experiments using two cAMP analogues, 2′–deoxy–cAMP and 8–bromo–cAMP suggested that the signal transduction system through the cell surface cAMP receptor is of particular importance for regulation of the sexual fusion process. Among several ions having effects on zygote formation, Ca2+ seemed to be necessary both for the acquisition of fusion competence and for cell fusion itself. In the presence of Ca 2+, K + and Na + had the opposite effects on zygote formation; K + was stimulative, while Na2+ inhibitory. The significance of these findings is discussed in relation to the regulatory mechanism of zygote formation.