YelA, a putative Dictyostelium translational regulator, acts as antagonist of DIF-1 signaling to control cell-type proportioning.

DIF-1 (differentiation-inducing factor1) is a polyketide produced by Dictyostelium prespore cells which induces initially uncommitted cells to differentiate as prestalk cells. Exposure of cells to DIF-1 causes transitory hypo-phosphorylation of seven serine residues in YelA, a protein with a region of strong homology to the MIF4G domain of the eukaryotic initiation factor eIF4G. Based upon its domain architecture, which in one important aspect closely resembles that of Death-Associated Protein 5 (DAP5), we predict a role in stimulating internal ribosome entry-driven mRNA translation. The two paradigmatic DIF-1 inducible genes are ecmA (extracellular matrixA) and ecmB. In support of a YelA function in DIF-1 signaling, a YelA null strain showed greatly increased expression of ecmA and ecmB in response to DIF-1. Also, during normal development in the null strain, expression of the two genes is accelerated. This is particularly evident for ecmB, a marker of stalk tube and supporting structure differentiation. Mutants in DIF-1 bio-synthesis or signaling display a rudimentary or no basal disc and, conversely, YelA null mutants produce fruiting bodies with a highly enlarged basal disc that ectopically expresses a stalk tube-specific marker. Thus YelA acts as an antagonist of DIF-1 signaling, with a consequent effect on cell type proportioning and it is predicted to act as a translational regulator.

The Dictyostelium prestalk inducer differentiation-inducing factor-1 (DIF-1) triggers unexpectedly complex global phosphorylation changes.

Differentiation-inducing factor-1 (DIF-1) is a polyketide that induces Dictyostelium amoebae to differentiate as prestalk cells. We performed a global quantitative screen for phosphorylation changes that occur within the first minutes after addition of DIF-1, using a triple-label SILAC approach. This revealed a new world of DIF-1-controlled signaling, with changes in components of the MAPK and protein kinase B signaling pathways, components of the actinomyosin cytoskeletal signaling networks, and a broad range of small GTPases and their regulators. The results also provide evidence that the Ca(2+)/calmodulin-dependent phosphatase calcineurin plays a role in DIF-1 signaling to the DimB prestalk transcription factor. At the global level, DIF-1 causes a major shift in the phosphorylation/dephosphorylation equilibrium toward net dephosphorylation. Of interest, many of the sites that are dephosphorylated in response to DIF-1 are phosphorylated in response to extracellular cAMP signaling. This accords with studies that suggest an antagonism between the two inducers and also with the rapid dephosphorylation of the cAMP receptor that we observe in response to DIF-1 and with the known inhibitory effect of DIF-1 on chemotaxis to cAMP. All MS data are available via ProteomeXchange with identifier PXD001555.