Pharmacological evidence that stalk cell differentiation involves increases in the intracellular Ca(2+) and H(+) concentrations in Dictyostelium discoideum

Differentiation-inducing factors (DIFs) are required for stalk cell formation in Dictyostelium discoideum. In the present study, in order to support our hypothesis that DIFs may function via increases in [Ca(2+)](c) and [H(+)](c), we investigated the combined effects of 5,5-dimethyl-2,4-oxazolidinedione (DMO, a [H(+)](c)-increasing agent), thapsigargin (Tg) and BHQ ([Ca(2+)](c)-increasing agents) on in vitro stalk cell formation in several strains. DMO, in combination with Tg or BHQ, induced stalk cell formation in a DIF-deficient mutant HM44. Although the rates of stalk cell induction by the drugs were low in the presence of cerulenin (an inhibitor of endogenous DIF production) in HM44 and V12M2 (a wild-type strain), the drugs succeeded in inducing sufficient stalk cell formation when a small amount of DIF-1 was supplied. Furthermore, co-addition of DMO, BHQ and a small amount of DIF-1 also induced sufficient stalk cell formation in AX-4 (an axenic strain) and HM1030 (dmtA(-)) but not in CT15 (dimA(-)). The drugs suppressed spore formation and promoted stalk cell formation in both HM18 (a sporogenous mutant) and 8-bromo-cAMP-stimulated V12M2. The present results suggest that DIFs function, at least in part, via increases in [Ca(2+)](c) and [H(+)](c) in D. discoideum.