title: Switching the in vivo specificity of a minimal Hox-responsive element.
abstract: The homeodomain proteins encoded by the Hox complex genes do not bind DNA with high specificity. In vitro, Hox specificity can be increased by binding to DNA cooperatively with the homeodomain protein extradenticle or its vertebrate homologs, the pbx proteins (together, the PBC family). Here we show that a two basepair change in a Hox-PBC binding site switches the Hox-dependent expression pattern generated in vivo, from labial to Deformed. The change in vivo correlates with an altered Hox binding specificity in vitro. Further, we identify similar Deformed-PBC binding sites in the Deformed and Hoxb-4 genes and show that they generate Deformed or Hoxb-4 expression patterns in Drosophila and mouse embryos, respectively. These results suggest a model in which Hox-PBC binding sites play an instructive role in Hox specificity by promoting the formation of different Hox-PBC heterodimers in vivo. Thus, the choice of Hox partner, and therefore Hox target genes, depends on subtle differences between Hox-PBC binding sites.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Center for Neurobiology and Behavior, Columbia University, New York, NY 10032, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Chan
authors.forename: H D
authors.initials: HD
authors.lastname: Ryoo
authors.forename: A
authors.initials: A
authors.lastname: Gould
authors.forename: R
authors.initials: R
authors.lastname: Krumlauf
authors.forename: R S
authors.initials: RS
authors.lastname: Mann
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001665:Binding Sites / Q000235:genetics; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004330:Drosophila / Q000196:embryology / Q000235:genetics; D029721:Drosophila Proteins; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D005801:Genes, Homeobox / Q000235:genetics*; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C066676:Dfd protein, Drosophila; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; C513262:Hoxb4 protein, mouse; D019476:Insect Proteins; D014157:Transcription Factors; C083405:exd protein, Drosophila; C059843:lab protein, Drosophila; D004247:DNA