title: The role of binding site cluster strength in Bicoid-dependent patterning in Drosophila.
abstract: The maternal morphogen Bicoid (Bcd) is distributed in an embryonic gradient that is critical for patterning the anterior-posterior (AP) body plan in Drosophila. Previous work identified several target genes that respond directly to Bcd-dependent activation. Positioning of these targets along the AP axis is thought to be controlled by cis-regulatory modules (CRMs) that contain clusters of Bcd-binding sites of different "strengths." Here we use a combination of Bcd-site cluster analysis and evolutionary conservation to predict Bcd-dependent CRMs. We tested 14 predicted CRMs by in vivo reporter gene assays; 11 show Bcd-dependent activation, which brings the total number of known Bcd target elements to 21. Some CRMs drive expression patterns that are restricted to the most anterior part of the embryo, whereas others extend into middle and posterior regions. However, we do not detect a strong correlation between AP position of target gene expression and the strength of Bcd site clusters alone. Rather, we find that binding sites for other activators, including Hunchback and Caudal correlate with CRM expression in middle and posterior body regions. Also, many Bcd-dependent CRMs contain clusters of sites for the gap protein Kruppel, which may limit the posterior extent of activation by the Bcd gradient. We propose that the key design principle in AP patterning is the differential integration of positive and negative transcriptional information at the level of individual CRMs for each target gene.
authors.affiliation: Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Ochoa-Espinosa
authors.forename: Gozde
authors.initials: G
authors.lastname: Yucel
authors.forename: Leah
authors.initials: L
authors.lastname: Kaplan
authors.forename: Adam
authors.initials: A
authors.lastname: Pare
authors.forename: Noel
authors.initials: N
authors.lastname: Pura
authors.forename: Adam
authors.initials: A
authors.lastname: Oberstein
authors.forename: Dmitri
authors.initials: D
authors.lastname: Papatsenko
authors.forename: Stephen
authors.initials: S
authors.lastname: Small
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D019521:Body Patterning / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004330:Drosophila / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins; D018507:Gene Expression Regulation, Developmental; D017344:Genes, Insect; D005816:Genetic Complementation Test; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D005810:Multigene Family; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; D004247:DNA