Cross-induction of cell types inDictyostelium: evidence that DIF-1 is made by prespore cells

Abstract

To investigate how cell type proportions are regulated during Dictyostelium development, we have attempted to find out which cell type produces DIF-1, a diffusible signal molecule inducing the differentiation of prestalk-O cells. DIF-1 is a chlorinated alkyl phenone that is synthesized from a C12 polyketide precursor by chlorination and methylation, with the final step catalysed by the dmtA methyltransferase. All our evidence points to the prespore cells as the major source of DIF-1. (1) dmtA mRNA and enzyme activity are greatly enriched in prespore compared with prestalk cells. The chlorinating activity is also somewhat prespore-enriched. (2) Expression of dmtA is induced by cyclic-AMP and this induction is inhibited by DIF-1. This regulatory behaviour is characteristic of prespore products. (3) Short-term labelling experiments, using the polyketide precursor, show that purified prespore cells produce DIF-1 at more than 20 times the rate of prestalk cells. (4) Although DIF-1 has little effect on its own synthesis in short-term labelling experiments, in long-term experiments, using 36Cl– as label, it is strongly inhibitory (IC50 about 5 nM), presumably because it represses expression of dmtA; this is again consistent with DIF-1 production by prespore cells. Inhibition takes about 1 hour to become effective. We propose that prespore cells cross-induce the differentiation of prestalk-O cells by making DIF-1, and that this is one of the regulatory loops that sets the proportion of prespore-to-prestalk cells in the aggregate.

Generating polyketide diversity in Dictyostelium : a Steely hybrid polyketide synthase produces alternate products at different developmental stages

“…DIF-1 is made by prespore cells during multicellular development, prior to fruiting body formation [29], but in contrast, CDF-1 accumulates in the stalk cells of the mature fruiting body, not in its spores [25]. The mRNAs for StlB and ChlA first accumulate when DIF-1 is made, then decline, before a strong increase late in development [20].…”

“…Deletion of the DmtA methyl transferase (strain HM1030) still permitted production of the late chlorinated compounds, indicating that it is not essential. A role in decorating these compounds cannot be totally excluded, even though dmtA is expressed in the spore region of the fruiting body [29], rather than the stalk where stlB and chlA are expressed. By contrast, no chlorinated compounds were detected in the absence of ChlA (strains HM1522 and HM1523), showing that it is the only relevant chlorinating enzyme.…”

Autophagy of the somatic stalk cells likely nurses the propagating spores of Dictyostelid social amoebas

“…For asexual aggregates it is well-documented that cells that enter starvation while late in the cell cycle (and are thus relatively large) or cells fed in glucose-rich versus glucose-poor media preferentially differentiate into spores compared to cells that have just divided ( Gomer & Firtel, 1987 ; Leach et al , 1973 ; Ohmori & Maeda, 1987 ; Weijer et al , 1984 ). The differentiating prespore cells then secrete compounds, such as DIF-1, that prevent other cells from differentiating as prespore cells, but to which they are less responsive ( Kay & Thompson, 2001 ; Thompson & Kay, 2000 ). In short, the larger well-fed cells are predisposed to propagate the organism and then coerce the leaner cells to give up their resources through autophagy.…”

Regulative differentiation as bifurcation of interacting cell population

“…Differentiation to prespore cells is induced by cAMP, and the cell state is maintained by a positive-feedback loop of prespore cell specific adenylyl cyclase G activity (Hopper et al, 1993;Williams, 2006;Alvarez-Curto et al, 2007). On the other hand, differentiation-inducing factor-1 (DIF-1) is necessary for the differentiation from a prespore-cell to a prestalk-cell (at least for the differentiation to pstO which is a subtype of the prestalk-cell) (Williams, 2006;Kay and Thompson, 2001). As an intercellular interaction, this DIF-1 is produced by prespore-cells, and are degraded by prestalk-cells.…”