Anterior repression of a Drosophila stripe enhancer requires three position-specific mechanisms.
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.
Andrioli
Luiz Paulo Moura
LP
Department of Biology, New York University, 1009 Main Building, 100 Washington Square East, New York 10003-6688, USA.
Vasisht
Vikram
V
Theodosopoulou
Ekaterina
E
Oberstein
Adam
A
Small
Stephen
S
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
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