Vacuolar H+-ATPase and weak base action in Dictyostelium

Amoebae of Dictyostelium discoideum release ammonia during development, and the accumulation of this weak base is believed to be responsible for inhibiting fruiting-body formation and switching aggregates into migrating slugs. Exposure to weak bases can also inhibit aggregation and cell-type specific gene expression. The pathway by which weak bases influence development is not understood. We show here that the development of a set of mutants defective in acidification of intracellular acidic compartments is abnormally sensitive to inhibition by weak bases. Moreover even in the absence of added weak bases these mutants are delayed in aggregation and have a protracted migratory phase. The same behaviour is observed in transformants harbouring an antisense construct for one of the vacuolar H+-ATPase subunits. These results support the idea that weak bases exert their effects by inhibiting acidification of an intracellular acidic compartment.