DEVELOPMENTAL BIOLOGY 130,464-470 (1988) Reduced CAMP Secretion in Dictyostelium discoidem Mutant HB3

Extracellular CAMP induces the intracellular synthesis and subsequent secretion of CAMP in Dictgostelium dkcoi-deum (relay). CAMP relay was strongly diminished in mutant HB3 which shows abnormal development by making very small fruiting bodies. Extracellular CAMP binds to receptors on the surface of mutant cells and induces the rapid activation of adenylate cyclase. Intracellular CAMP rises to a concentration as high as that in wild-type cells but only a very small amount of CAMP is secreted. CAMP secretion in wild-type cells tarts immediately after CAMP production, and is proportional to the intracellular CAMP concentration. Inthe mutant cells CAMP secretion starts a few minutes after CAMP production; by that time most of the intracellular CAMP is already degraded by phosphodiesterase and little CAMP is available for secretion. We conclude that mutant HB3 has a defect in the mechanism by which Dictgoste-lium cells ecrete CAMP. o 1988 Academic Prey, 1~