title: Cytoplasmic acidification facilitates but does not mediate DIF-induced prestalk gene expression in Dictyostelium discoideum.
abstract: Stalk cell differentiation in Dictyostelium can be induced by the differentiation-inducing factor, DIF, or by conditions that decrease intracellular pH (pHi). We have investigated whether cytoplasmic acidification acts directly to induce expression of pDd56 and pDd63, two DIF-regulated genes, specifically expressed in prestalk cells. The weak base methylamine, which increases pHi, inhibits DIF-induced transcription. The weak acid 5,5-dimethyl-2,4-oxazolidinedione (DMO), which decreases pHi, stimulates DIF-induction of the two prestalk genes. After relatively long incubation periods, DMO also induces a low level of prestalk gene expression in the absence of added DIF. However, unlike DIF-mediated induction, the apparent DMO-mediated induction decreases to undetectable levels when the cell density is reduced from 10(7) to 10(5) cells/ml. This indicates that DMO does not itself induce gene expression, but acts to enhance the effects of an autonomously secreted stalk-inducing factor, presumably DIF. These results suggest that the effects of DIF on gene expression are regulated by intracellular pH, but do not support a role for protons as direct intermediates in the DIF signal transduction pathway.
authors.affiliation: Cell Biology and Genetics Unit, Zoological Laboratory, Leiden University, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Wang
authors.forename: J H
authors.initials: JH
authors.lastname: Roelfsema
authors.forename: J G
authors.initials: JG
authors.lastname: Williams
authors.forename: P
authors.initials: P
authors.lastname: Schaap
mesh_terms: D000242:Cyclic AMP / Q000502:physiology; D004023:Dictyostelium / Q000378:metabolism*; D004114:Dimethadione / Q000494:pharmacology; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects*; D006588:Hexanones / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008744:Methylamines / Q000494:pharmacology; D010422:Pentanones / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects
chemical_list: D006588:Hexanones; D008744:Methylamines; D010422:Pentanones; D012333:RNA, Messenger; C053433:1-((3,5-dichloro)-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone; C055365:1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl-)-1-pentanone; C055364:1-(3-chloro-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone; D004114:Dimethadione; C027451:methylamine; D000242:Cyclic AMP