cAMP induction of prespore and prestalk gene expression in Dictyostelium is mediated by the cell-surface cAMP receptor.

Abstract

Extracellular adenosine 3',5'-cyclic monophosphate (cAMP) is required for cell-type-specific gene expression in developing Dictyostelium discoideum. We have developed a microassay for the expression of these genes, using antibodies directed against their protein products. To characterize the transduction mechanism, we have used in this assay cAMP analogues that preferentially activate either the cellsurface cAMP receptor or the internal cAMP-dependent pro- The mechanism whereby the extracellular cAMP induces cell-type-specific gene expression is unknown. One possible mechanism is that cAMP binds to a cell-surface receptor, which then mediates the gene induction. A cAMP-dependent protein kinase has been shown to exist in Dictyostelium (18)(19)(20)(21)(22). A second possible mechanism would then be that cAMP enters the cells and directly activates this kinase. A third possibility would involve a yet unidentified cAMPbinding protein.As an approach to these questions, we have used cAMP analogues that preferentially activate either the cell-surface cAMP receptor or cAMP-dependent protein kinase in vitro. We have established a microassay by using antibodies made against regions of the protein products of several of these cAMP-regulated cell-type-specific genes. This assay allows us to examine the ability of the analogues to activate cell-type-specific gene expression in low-density cultures measured by an immunofluorescence assay and to examine questions concerning the differential expression of these genes. We find that cAMP analogues that activate the cell-surface receptor and have very limited ability to activate the cAMP-dependent protein kinase can induce cell-typespecific gene expression, while other analogues that activate cAMP-dependent protein kinase but not the cell-surface receptor are unable to cause cell-type-specific gene expression. These low-density cultures also allow the examination of the levels of cAMP necessary for cell-type-specific gene induction.

Activation of the prespore and spore cell pathway of Dictyostelium differentiation by cAMP-dependent protein kinase and evidence for its upstream regulation by ammonia.

“…Binding of cAMP triggers the activation of adenylate cyclase, guanylate cyclase and possibly phosphoinositidase C (reviewed by Janssens and Van Haastert, 1987;Firtel et al, 1989). Analysis of a mutant defective in the activation of adenylate cyclase, and of the effects of altering the cAMP induction regime, have suggested that elevation of the intracellular concentration of cAMP is not necessary for prestalk (Gomer et al, 1986;Oyama and Blumberg, 1986) or prespore cell differentiation (Oyama and Blumberg, 1986;Schaap et al, 1986). Similar methods have been used to rule out a role of intracellular cAMP in the expression of most early, non-cell type-specific genes (Mann et al, 1988) but repression of the expression of M4, an early gene of unknown function, has been shown to require elevation of the intracellular cAMP concentration (Kimmel and Saxe, 1986;Kimmel, 1987).…”

GSK3 is a multifunctional regulator ofDictyosteliumdevelopment

“…Extracellular cAMP acts, via an unknown intracellular signalling pathway, to induce prespore gene expression (Gomer et al, 1986;Kay et al, 1978). In the DH1-derived gskA-null strain, extracellular cAMP activates prespore gene expression very poorly, but in AX2G/gskAcells, cAMP is a potent activator.…”

Expression of a cAMP receptor gene of Dictyostelium and evidence for a multigene family.

“…Moreover, the duration of responses to cAMP differs between the early and later stages of development. Many cellular responses observed in early development adapt to a continous presence of cAMP, whereas cytodifferentiation and correlated changes in gene expression in later development require constant cAMP stimulation (Schaap and van Driel 1985;Gomer et al 1986;Haribabu and Dottin 1986;Oyama and Blumberg 1986;Kimmel 1987). It has not been clear whether these various receptor forms represent the interaction of identical proteins with distinct intracellular components or whether they represent related proteins encoded by different genes.…”