The Role of the Cyclic Nucleotide Phosphodiesterase of Dictyostelium discoideum during Growth, Aggregation, and Morphogenesis: Overexpression and Localization Studies with the Separate Promoters of the pde

cAMP acts as a primary signal and is regulated by a secreted cyclic nucleotide phosphodiesterase (PDE) throughout development in Dictyostelium discoideum. Expression of the PDE gene ( pde) is controlled by promoters specific to vegetative growth (prV), aggregation (prA), or late development (prL). Promoter-containing regions were individually fused to the pde coding sequence. After transformation multiple copies of each construct led to overexpression of PDE mRNA and enzyme activity with the temporal profile expected of each promoter. Overexpression of PDE from prV and prA altered the timing of aggregation compared to control transformants, but the final morphology was normal. Control transformants showed delayed aggregation compared to nontransformed cells. Cells that overexpressed PDE from prL aggregated like the control transformants, but no fruiting bodies were formed. Individual promoter regions were fused to the β-galactosidase gene ( lacZ). Cells that expressed prA- lacZ were dispersed throughout aggregation fields and mounds. Cells that expressed prL- lacZ were first seen distributed homogeneously throughout tight and tipped mounds. In slugs most of these cells are localized in the anterior region. During culmination, cells that expressed the prL- lacZ construct became incorporated into the stalk and were seen in the upper and lower cups surrounding the spore mass.