title: The boundary paradox in the Bithorax complex.
abstract: The parasegment-specific expression of the three Drosophila Bithorax complex homeotic genes is orchestrated by nine functionally autonomous regulatory domains. Functional autonomy depends upon special elements called boundaries or insulators that are located between each domain. The boundaries ensure the independent activity of each domain by blocking adventitious interactions with initiators, enhancers and silencers in the neighboring domains. However, this blocking activity poses a regulatory paradox--the Bithorax boundaries are also able to insulate promoters from regulatory interactions with enhancers and silencers and six of the nine Bithorax regulatory domains are separated from their target genes by at least one boundary element. Here we consider several mechanisms that have been suggested for how the Bithorax regulatory domains are able to bypass intervening boundary elements and direct the appropriate parasegment-specific temporal and spatial expression of their target gene.
authors.affiliation: Laboratory of Gene Expression Regulation in Development, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia.
authors.forename: Olga
authors.initials: O
authors.lastname: Kyrchanova
authors.affiliation: Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia; Nikolaev V.A. Sukhomlinsky National University, Department of Biology, Ukraine.
authors.forename: Vladic
authors.initials: V
authors.lastname: Mogila
authors.affiliation: Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Wolle
authors.affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK.
authors.forename: Jose Paolo
authors.initials: JP
authors.lastname: Magbanua
authors.affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK.
authors.forename: Robert
authors.initials: R
authors.lastname: White
authors.affiliation: Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia.
authors.forename: Pavel
authors.initials: P
authors.lastname: Georgiev
authors.affiliation: Laboratory of Gene Expression Regulation in Development, Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russia; Department of Molecular Biology, Princeton University, Princeton, NJ, USA. Electronic address: pschedl@princeton.edu.
authors.forename: Paul
authors.initials: P
authors.lastname: Schedl
mesh_terms: D000818:Animals; D002843:Chromatin / Q000235:genetics; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D005801:Genes, Homeobox / Q000235:genetics; D017344:Genes, Insect / Q000502:physiology; D038101:Insulator Elements / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics
chemical_list: D002843:Chromatin; D029721:Drosophila Proteins
keywords: Bithorax complex; Boundary bypass; Boundary element; Enhancer blocking; Insulator