The effect of cAMP on differentiation inducing factor (DIF)-mediated formation of stalk cells in low-cell-density monolayers of Dictyostelium discoideum

Abstract

Abstract The requirement for cyclic AMP (cAMP) for stalk-cell formation in low-density monolayers of Dictyoste-lium discoideum, is mediated through the cell-surface cAMP receptor. Stalk-cell formation is markedly inhibited by the cAMP relay inhibitor, caffeine. This inhibition is reversed by high concentrations of 8-Br-cAMP, a highly cell-perme-abie analog of cAMP. These results suggest that elevated intracellular concentrations of cAMP are necessary for stalk-cell formation. The induction of stalk-cell formation in monolayers can be divided into a cAMP-dependent period and a differentiation inducing factor (DIF)-dependent period [21]. Despite this clearcut separation of the cAMP and DIF induction periods, cAMP enhanced the effects of DIF at low DIF concentrations. Evidence is presented that this was not a direct cooperative effect. The effect of caffeine was inhibitory during both periods and was not reversed by a combination of DIF and cAMP. Ammonia inhibited stalk-cell formation at all stages of the differentiation process, but the inhibition engendered during the initial cAMP-induction period was reversed by a combination of DIF and cAMP.