Cross-induction of cell types in Dictyostelium: evidence that DIF-1 is made by prespore cells.
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 (IC(50) 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.
Kay
R R
RR
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK. rrk@mrc-lmb.cam.ac.uk
Thompson
C R
CR
D000818:Animals; D002454:Cell Differentiation; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology / Q000201:enzymology / Q000254:growth & development*; D005656:Fungal Proteins; D015971:Gene Expression Regulation, Enzymologic; D006588:Hexanones / Q000378:metabolism*; D008190:Lyases / Q000302:isolation & purification; D008745:Methylation; D008780:Methyltransferases / Q000235:genetics / Q000302:isolation & purification; D010088:Oxidoreductases; D015398:Signal Transduction; D014018:Tissue Distribution
C075859:DIF-1 3(5)-dechlorinase; D005656:Fungal Proteins; D006588:Hexanones; C053433:1-((3,5-dichloro)-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone; D000242:Cyclic AMP; D010088:Oxidoreductases; D008780:Methyltransferases; C096006:omtA protein, Aspergillus; D008190:Lyases