The Fab-8 boundary defines the distal limit of the bithorax complex iab-7 domain and insulates iab-7 from initiation elements and a PRE in the adjacent iab-8 domain

• Published in: Development (Cambridge) Vol. 127; no. 4; pp. 779 - 790
• Main Authors: Barges, S, Mihaly, J, Galloni, M, Hagstrom, K, Müller, M, Shanower, G, Schedl, P, Gyurkovics, H, Karch, F
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists Limited 01.02.2000; Company of Biologists
• Subjects: Abdominal-B (Abd-B) gene; Abdominal-B gene; Animals; Animals, Genetically Modified; Body Patterning; Body Patterning - genetics; Chromatin; Chromatin - genetics; Development Biology; Drosophila; Drosophila - embryology; Drosophila - genetics; Drosophila - growth & development; Enhancer Elements (Genetics); Enhancer Elements, Genetic; Female; Gene Expression Regulation, Developmental; Genes, Homeobox; Genes, Insect; Genes, Regulator; Genes, Reporter; Lac Operon; Life Sciences; Male; Mutation
• ISSN: 0950-1991; 1477-9129
• DOI: 10.1242/dev.127.4.779

The Drosophila bithorax complex Abdominal-B (Abd-B) gene specifies parasegmental identity at the posterior end of the fly. The specific pattern of Abd-B expression in each parasegment (PS) determines its identity and, in PS10-13, Abd-B expression is controlled by four parasegment-specific cis-regulatory domains, iab-5 to iab-8, respectively. In order to properly determine parasegmental identity, these four cis-regulatory domains must function autonomously during both the initiation and maintenance phases of BX-C regulation. The studies reported here demonstrate that the (centromere) distal end of iab-7 domain is delimited by the Fab-8 boundary. Initiators that specify PS12 identity are located on the proximal iab-7 side of Fab-8, while initiators that specify PS13 identity are located on the distal side of Fab-8, in iab-8. We use transgene assays to demonstrate that Fab-8 has enhancer blocking activity and that it can insulate reporter constructs from the regulatory action of the iab-7 and iab-8 initiators. We also show that the Fab-8 boundary defines the realm of action of a nearby iab-8 Polycomb Response Element, preventing this element from ectopically silencing the adjacent domain. Finally, we demonstrate that the insulating activity of the Fab-8 boundary in BX-C is absolutely essential for the proper specification of parasegmental identity by the iab-7 and iab-8 cis-regulatory domains. Fab-8 together with the previously identified Fab-7 boundary delimit the first genetically defined higher order domain in a multicellular eukaryote.