title: Elements of the Drosophila bithorax complex that mediate repression by Polycomb group products.
abstract: The Polycomb (Pc) group genes encode repressors that restrict expression of homeotic genes to precise domains along the anterior-posterior (A-P) axis. We describe germ-line transformation constructs, containing portions of the bxd, iab-2, or iab-3 regulatory regions of the bithorax complex (BX-C), that are controlled by Pc group products in embryos. There are multiple BX-C elements that mediate Pc group control, which we call Pc group response elements (PREs), and they can work when removed from the normal BX-C context. These constructs are each regulated by the genes Polycomb (Pc), extra sex combs (esc), Enhancer of zeste (E[z]), polyhomeotic (ph), Polycomb-like (Pcl), Sex comb on midleg (Scm), Posterior sex combs (Psc), and Additional sex combs (Asx), consistent with multiple Pc group products acting together. Depending upon context, a PRE from the iab-3 region can restrict expression in different A-P positions. Thus, PREs are not specialized for particular parasegments, suggesting that Pc group products do not directly specify A-P boundaries of homeotic expression. Instead, the results support the idea that Pc group products provide stable memory or imprinting of boundaries which are initially specified by gap and pair-rule regulators.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: J
authors.initials: J
authors.lastname: Simon
authors.forename: A
authors.initials: A
authors.lastname: Chiang
authors.forename: W
authors.initials: W
authors.lastname: Bender
authors.forename: M J
authors.initials: MJ
authors.lastname: Shimell
authors.forename: M
authors.initials: M
authors.lastname: O'Connor
mesh_terms: D000818:Animals; D004252:DNA Mutational Analysis; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D005786:Gene Expression Regulation; D005801:Genes, Homeobox; D005809:Genes, Regulator; D009024:Morphogenesis