TheDictyosteliumbZIP transcription factor DimB regulates prestalk-specific gene expression

Abstract

The ecmA gene is specifically expressed in prestalk cells and its transcription is induced by the chlorinated hexaphenone DIF-1. We have purified a novel bZIP transcription factor, DimB, by affinity chromatography on two spatially separated ecmA promoter fragments. Mutagenesis of the cap-site proximal DimB-binding site (the -510 site) greatly decreases ecmA expression in the pstO cells, which comprise the rear half of the prestalk zone, and also in the Anterior-Like Cells, which lie scattered throughout the prespore region. However, DimB is not essential for normal expression of the ecmA gene, instead it spatially limits its expression; ecmA is relatively highly expressed in the subset of prestalk cells that coats the prestalk zone, but in slugs of a DimB-null strain, ecmA is highly expressed throughout the prestalk zone. Because the -510 site is required for correct ecmA expression, we posit a separate activator protein that competes with DimB for binding to the -510 site. DimB rapidly accumulates in the nucleus when cells are exposed to DIF-1, and ChIP analysis shows that, in the presence of extracellular cAMP, DIF-1 causes DimB to associate with the ecmA promoter in vivo. Thus, DIF-1 regulates DimB activity to generate a gradient of ecmA expression in the prestalk zone of the slug.

Autophagic or necrotic cell death triggered by distinct motifs of the differentiation factor DIF-1

“…The choice between DIF-1-induced cell death types is a function of the state of these starved cells. In wild-type cells, ACD occurs, [16][17][18][19][20][21] and this requires the IP3R probably to ensure Ca2 þ flux from the ER to the cytosol. 18 When autophagy cannot take place because of an atg1 À mutation, NCD occurs.…”

“…When wild-type Dictyostelium cells were subjected to starvation and DIF-1, they underwent ACD, with emergence of paddle cells and IP3R-dependent and transcription factor-dependent vacuolization and death. [16][17][18][19][20][21] When cells mutated for the atg1 autophagy gene were similarly treated, they underwent NCD instead, with mitochondrial uncoupling causing perinuclear clustering, then lysosomal and plasma membrane alterations ( 22,23 ; Giusti et al, in preparation; Figure 1a). Remarkably, these two different types of death both required induction by DIF-1, in cells subjected to either starvation alone (wt cells, induced to undergo ACD), or starvation aggravated by inhibition of autophagy (atg1 À cells, induced to undergo NCD).…”

The Inositol 1,4,5-Trisphosphate Receptor Is Required to Signal Autophagic Cell Death

“…The iplA Ϫ mutation prevented cellulose shell synthesis around cells subjected to DIF, consistent with control by IP3R and Ca 2ϩ flux of the expression of genes governing cellulose synthesis. Moreover, addition of DIF triggered nuclear accumulation of DimA, and also of DimB, a second bZIP transcription factor, within a few minutes in AX2 and AX4 strains (Huang et al, 2006;Zhukovskaya et al, 2006). Interestingly, DimB was required for vacuolar cell death and repression of nonvacuolar cell death in response to DIF (Huang et al, 2006), like Atg1.…”

A necrotic cell death model in a protist

“…When added after a 4 h starvation period, DIF led within 2-3 min to the tyrosine phosphorylation of the STATc transcription factor, 21 thus detectably preventing the exit of STATc from the nucleus, 22 and induced changes in subcellular localization of the transcription factor DimB. 23,24 The relationship between DIF-induced rapid phosphorylation events and DIF-induced rapid uncoupling of oxidative phosphorylation is not known.…”