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Role of cAMP-Dependent Protein Kinase in Controlling Aggregation and Postaggregative Development inDictyostelium

1997; Elsevier BV; Volume: 183; Issue: 2 Linguagem: Inglês

10.1006/dbio.1996.8499

1095-564X

Sandra K.O. Mann, Jason Brown, Celia P. Briscoe, Carole A. Parent, Geoffrey S. Pitt, Peter N. Devreotes, Richard Firtel,

Reproductive Biology and Fertility

We have examined the role of cAMP-dependent protein kinase (PKA) in controlling aggregation and postaggregative development inDictyostelium.We previously showed that cells in which the gene encoding the PKA catalytic subunit has been disrupted (pkacat−cells) are unable to aggregate [S. K. O. Mann and R. A. Firtel (1991). A developmentally regulated, putative serine/threonine protein kinase is essential for development inDictyostelium. Mech. Dev.35, 89–102]. We show thatpkacat−cells are unable to activate adenylyl cyclase in response to cAMP stimulation due to the inability to express the aggregation-stage, G-protein-stimulated adenylyl cyclase (ACA). Constitutive expression of ACA from an actin promoter results in a high level of Mn2+-stimulated adenylyl cyclase activity and restores chemoattractant- and GTPγS-stimulated adenylyl cyclase activity but not the ability to aggregate. Similarly, expression of the constitutively active, non-G protein-coupled adenylyl cyclase ACG inpkacat−cells also does not restore the ability to aggregate, although ACG can complement cells in which theACAgene has been disrupted. These results indicate thatpkacat−cells lack multiple, essential aggregation-stage functions. As the mound forms, high, continuous levels of extracellular cAMP functioning through the cAMP serpentine receptors activate a transcriptional cascade that leads to cell-type differentiation and morphogenesis. The first step is the induction and activation of the transcription factor GBF and downstream postaggregative genes, followed by the induction of prestalk- and prespore-specific genes. We show thatpkacat−cells induce postaggregative gene expression in response to exogenous cAMP, but the level of induction of some of these genes, includingGBF,is reduced.SP60(a prespore-specific gene) is not induced andecmA(a prestalk-specific gene) is induced to very low levels. Expressing GBF constitutively inpkacat−cells restoresecmAexpression to a moderate level, butSP60is not detectably induced. Overexpression of PKAcat from the Actin 15 (Act15), ecmAprestalk, and thePKAcatpromoters inpkacat−cells results in significant aberrant spatial patterning of prestalk and prespore cells, as determined bylacZ reporter studies. Our studies identify new, essential regulatory roles for PKA in mediating multicellular development.