title: Anterior repression of a Drosophila stripe enhancer requires three position-specific mechanisms.
abstract: The striped expression pattern of the pair-rule gene even skipped (eve) is established by five stripe-specific enhancers, each of which responds in a unique way to gradients of positional information in the early Drosophila embryo. The enhancer for eve stripe 2 (eve 2) is directly activated by the morphogens Bicoid (Bcd) and Hunchback (Hb). As these proteins are distributed throughout the anterior half of the embryo, formation of a single stripe requires that enhancer activation is prevented in all nuclei anterior to the stripe 2 position. The gap gene giant (gt) is involved in a repression mechanism that sets the anterior stripe border, but genetic removal of gt (or deletion of Gt-binding sites) causes stripe expansion only in the anterior subregion that lies adjacent to the stripe border. We identify a well-conserved sequence repeat, (GTTT)(4), which is required for repression in a more anterior subregion. This site is bound specifically by Sloppy-paired 1 (Slp1), which is expressed in a gap gene-like anterior domain. Ectopic Slp1 activity is sufficient for repression of stripe 2 of the endogenous eve gene, but is not required, suggesting that it is redundant with other anterior factors. Further genetic analysis suggests that the (GTTT)(4)-mediated mechanism is independent of the Gt-mediated mechanism that sets the anterior stripe border, and suggests that a third mechanism, downregulation of Bcd activity by Torso, prevents activation near the anterior tip. Thus, three distinct mechanisms are required for anterior repression of a single eve enhancer, each in a specific position. Ectopic Slp1 also represses eve stripes 1 and 3 to varying degrees, and the eve 1 and eve 3+7 enhancers each contain GTTT repeats similar to the site in the eve 2 enhancer. These results suggest a common mechanism for preventing anterior activation of three different eve enhancers.
authors.affiliation: Department of Biology, New York University, 1009 Main Building, 100 Washington Square East, New York 10003-6688, USA.
authors.forename: Luiz Paulo Moura
authors.initials: LP
authors.lastname: Andrioli
authors.forename: Vikram
authors.initials: V
authors.lastname: Vasisht
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Theodosopoulou
authors.forename: Adam
authors.initials: A
authors.lastname: Oberstein
authors.forename: Stephen
authors.initials: S
authors.lastname: Small
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001426:Bacterial Proteins; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics; D002874:Chromosome Mapping; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004330:Drosophila / Q000196:embryology* / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics; D019476:Insect Proteins / Q000235:genetics; D007763:Lac Operon; D008969:Molecular Sequence Data; D009154:Mutation; D012689:Sequence Homology, Nucleic Acid; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C056478:bcd protein, Drosophila; C052837:eve protein, Drosophila; C061245:hb protein, Drosophila; C074838:slp1 protein, Drosophila; D004247:DNA