Practice question

ACA establishes positive feedback loop of cAMP signaling that organizes collective movement. Mutants lacking functional ACA fail to synthesize pulses, therefore no extracellular cAMP wave propagates, cells do not polarize, stream, or form mounds, and developmental program arrests early. Intracellular cAMP remains low, preventing induction of early genes like discoidin and contact site A. Phenotype includes lack of aggregation territory, no slug formation despite starvation. Normal aggregation patterns require ACA-mediated relay; excessive aggregation would require increased cyclase activity, while normal culmination occurs only if aggregation succeeded, demonstrating ACA indispensability at initiation of multicellular development.