title: A localized differentiation-inducing-factor sink in the front of the Dictyostelium slug.
abstract: Differentiation-inducing factor 1 [DIF-1; 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)-hexan-1-one] induces stalk cell differentiation during Dictyostelium development. It is present as a gradient in the multicellular slug, its lowest concentration being in the anterior. Here we demonstrate the existence of a localized sink for DIF-1, also in the anterior of the slug, which could be responsible for generating the DIF-1 gradient. DIF-1 is metabolized extensively by developing cells, initially by a mono-dechlorination. We used an enzyme assay for DIF-1 dechlorinase to examine its distribution in the slug. DIF-1 dechlorinase activity is 30-fold higher in prestalk cells (largely anterior) compared with prespore cells (posterior) when these are separated from each other on Percoll density gradients. Dissection experiments showed that DIF-1 dechlorinase is 25-fold enriched in the anterior 13% of the slug compared with the rest. These experiments also showed that DIF-1 dechlorinase is more anterior-enriched than the standard prestalk markers, the ecmA and ecmB mRNAs. When cut from a slug, both prestalk and prespore fragments regulate to restore the missing cell type. Prespore fragments rapidly regain (by 30 min) a DIF-1 sink in their anteriors, and prestalk fragments restore a posterior zone with low DIF-1 dechlorinase by 4 hr after cutting. The reappearance of the DIF-1 sink in the anterior of prespore fragments is accomplished without detectable cell sorting and may, therefore, be in response to positional signals. Finally, a localized sink may provide a general way of producing a gradient of a signal substance in a developing embryo.
authors.affiliation: Medical Research Council Laboratory of Molecular Biology, Cambridge, England.
authors.forename: R R
authors.initials: RR
authors.lastname: Kay
authors.forename: S
authors.initials: S
authors.lastname: Large
authors.forename: D
authors.initials: D
authors.lastname: Traynor
authors.forename: O
authors.initials: O
authors.lastname: Nayler
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D004023:Dictyostelium / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D006588:Hexanones / Q000378:metabolism*; D008190:Lyases / Q000032:analysis*; D010088:Oxidoreductases; D012333:RNA, Messenger / Q000032:analysis; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: C075859:DIF-1 3(5)-dechlorinase; D006588:Hexanones; D012333:RNA, Messenger; C053433:1-((3,5-dichloro)-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone; D010088:Oxidoreductases; D008190:Lyases