A role for calcineurin in Dictyostelium discoideum development

We have used the immunosuppressants cyclosporin A and FK506 to investigate the involvement of the Ca2+/CaM-dependent protein phosphatase calcineurin in Dictyostelium discoideum development. We found that CsA had little effect on cell growth, or on the aggregation of developing amoebae, suggesting that calcineurin does not play a significant role at these stages of the D. discoideum life cycle. In contrast, when cells were allowed to differentiate under buffer in the presence of cAMP, addition of CsA and FK506 strongly inhibited stalk cell formation in the wild-type and spore formation in a sporogenous derivative of D. discoideum strain V12. These agents also reduced the expression of prestalk-and prespore-specific transcripts in both strains. These results indicate a requirement for calcineurin activity in both pathways of cell differentiation. In addition, time-course experiments suggest that calcineurin is required early in the differentiation processes, but that the maturation of the two cell types is resistant to calcineurin inhibition. We also found that CsA and FK506 were unable to affect spore formation in rapidly developing/sporogenous rdeC mutants of strain NC4, showing that constitutive cAMP-dependent protein kinase activity renders the spore pathway resistant to calcineurin inhibition.