Requirements for the adenylyl cyclases in the development of Dictyostelium

It has been suggested that all intracellular signaling by cAMP during devel opment of Dictyostelium is mediated by the cAMP-dependent protein kinase, P KA, since cells carrying null mutations in the acaA gene that encodes adeny lyl cyclase can develop so as to form fruiting bodies under some conditions if PKA is made constitutive by overexpressing the catalytic subunit. Howev er, a second adenylyl cyclase encoded by acrA has recently been found that functions in a cell autonomous fashion during late development. We have fou nd that expression of a modified acaA gene rescues acrA(-) mutant cells ind icating that the only role played by ACR is to produce cAMP. To determine w hether cells lacking both adenylyl cyclase genes can develop when PKA is co nstitutive we disrupted acrA in a acaA(-) PKA-C-over strain. When developed at high cell densities, acrA(-) acaA(-) PKA-C-over cells form mounds, expr ess cell type-specific genes at reduced levels and secrete cellulose coats but do not form fruiting bodies or significant numbers of viable spores. Th us, it appears that synthesis of cAMT is required for spore differentiation in Dictyostelium even if PKA activity is high.