title: Two distinct mechanisms for differential positioning of gene expression borders involving the Drosophila gap protein giant.
abstract: We have combined genetic experiments and a targeted misexpression approach to examine the role of the gap gene giant (gt) in patterning anterior regions of the Drosophila embryo. Our results suggest that gt functions in the repression of three target genes, the gap genes Krüppel (Kr) and hunchback (hb), and the pair-rule gene even-skipped (eve). The anterior border of Kr, which lies 4-5 nucleus diameters posterior to nuclei that express gt mRNA, is set by a threshold repression mechanism involving very low levels of gt protein. In contrast, gt activity is required, but not sufficient for formation of the anterior border of eve stripe 2, which lies adjacent to nuclei that express gt mRNA. We propose that gt's role in forming this border is to potentiate repressive interaction(s) mediated by other factor(s) that are also localized to anterior regions of the early embryo. Finally, gt is required for repression of zygotic hb expression in more anterior regions of the embryo. The differential responses of these target genes to gt repression are critical for the correct positioning and maintenance of segmentation stripes, and normal anterior development.
authors.affiliation: Department of Biology, New York University, New York, NY 10003, USA.
authors.forename: X
authors.initials: X
authors.lastname: Wu
authors.forename: R
authors.initials: R
authors.lastname: Vakani
authors.forename: S
authors.initials: S
authors.lastname: Small
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins; D001483:Base Sequence; D019521:Body Patterning / Q000235:genetics; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D004330:Drosophila / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism; D029721:Drosophila Proteins; D018507:Gene Expression Regulation, Developmental; D018390:Gene Targeting; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000235:genetics; D017403:In Situ Hybridization; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors; D009154:Mutation; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins; D014157:Transcription Factors / Q000235:genetics; D015053:Zygote / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D019476:Insect Proteins; C497244:Kr protein, Drosophila; D051741:Kruppel-Like Transcription Factors; D012333:RNA, Messenger; D012097:Repressor Proteins; D014157:Transcription Factors; C052837:eve protein, Drosophila; C061245:hb protein, Drosophila; D004247:DNA