ACTIVATION OF THE PRESPORE AND SPORE CELL PATHWAY OF DICTYOSTELIUM DIFFERENTIATION BY CAMP-DEPENDENT PROTEIN-KINASE AND EVIDENCE FOR ITS UPSTREAM REGULATION BY AMMONIA

Expression of a dominant inhibitor of the Dictyostelium cAMP-dependent protein kinase in prespore cells blocks their differentiation into sp ore cells. The resultant structures comprise a normal stalk supporting a bolus of cells that fail to express a sporulation-specific gene and that show greatly reduced levels of expression of several prespore-sp ecific genes. The latter result suggests that in addition to activatin g spore formation, the cAMP-dependent protein kinase may play a role i n initial prespore cell differentiation. Development of the strain exp ressing the dominant inhibitor is hypersensitive to the inhibitory eff ects of ammonia, the molecule that is believed to repress entry into c ulmination during normal development. This result supports a model whe reby a decrease in ambient ammonia concentration at culmination acts t o elevate intracellular cAMP and hence induce terminal differentiation .