ROLE OF CAMP-DEPENDENT PROTEIN-KINASE IN CONTROLLING AGGREGATION AND POSTAGGREGATIVE DEVELOPMENT IN DICTYOSTELIUM

We have examined the role of cAMP-dependent protein kinase (PKA) in co ntrolling aggregation and postaggregative development in Dictyostelium . We previously showed that cells in which the gene encoding the PKA c atalytic subunit has been disrupted (pkacat(-) cells) are unable to ag gregate [S. K. O. Mann and R. A. Firtel (1991). A developmentally regu lated, putative serine/threonine protein kinase is essential for devel opment in Dictyostelium. Mech. Der. 35, 89-102]. We show that pkacat(- ) cells are unable to activate adenylyl cyclase in response to cAMP st imulation due to the inability to express the aggregation-stage, G-pro tein-stimulated adenylyl cyclase (ACA). Constitutive expression of ACA from an actin promoter results in a high level of Mn2+-stimulated ade nylyl cyclase activity and restores chemoattractant- and GTP gamma S-s timulated adenylyl cyclase activity but not the ability to aggregate. Similarly, expression of the constitutively active, non-G protein-coup led adenylyl cyclase ACG in pkacat(-) cells also does not restore the ability to aggregate, although ACG can complement cells in which the A CA gene has been disrupted. These results indicate that pkacat(-) cell s lack multiple, essential aggregation-stage functions. As the mound f orms, high, continuous levels of extracellular cAMP functioning throug h the cAMP serpentine receptors activate a transcriptional cascade tha t leads to cell-type differentiation and morphogenesis. The first step is the induction and activation of the transcription factor GBF and d ownstream postaggregative genes, followed by the induction of prestalk - and prespore-specific genes. We show that pkacat(-) cells induce pos taggregative gene expression in response to exogenous cAMP, but the le vel of induction of some of these genes, including GBF, is reduced. SP 60 (a prespore-specific gene) is not induced and ecmA (a prestalk-spec ific gene) is induced to very low levels. Expressing GBF constitutivel y in pkacat(-) cells restores ecmA expression to a moderate level, but SP60 is not detectably induced. Overexpression of PKAcat from the Act in 15 (Act15) ecmA prestalk, and the PKAcat promoters in pkacat(-) cel ls results in significant aberrant spatial patterning of prestalk and prespore cells, as determined by lacZ reporter studies. Our studies id entify new, essential regulatory roles for PKA in mediating multicellu lar development. (C) 1997 Academic Press.