title: Bicoid--morphogen function revisited.
abstract: Bicoid (Bcd) functions as a morphogen during Drosophila development. Accordingly, bcd mRNA is maternally localized to the anterior pole of the embryo, and Bcd forms an anterior/posterior gradient, which functions in a concentration dependent fashion. Thus, nuclei receiving identical amounts of Bcd should express the same target genes. However, we found that ectopic, uniform expression of Bcd causes anterior gene expression in the posterior with mirror image polarity, indicating that one or several additional factors must provide positional information. Recently, we have shown that one of these factors is Capicua (Cic), a ubiquitous maternal repressor that is down-regulated at the embryonic termini by maternal Torso, a key component of the maternal terminal system. Cic acts on Bcd dependent enhancer elements by repression and thereby controls the posterior limit of Bcd target gene expression. Based on these new findings, we propose that spatial control of gene expression in the anterior region of the embryo is not solely the result of Bcd morphogen action. Rather, it relies on a "morphogenic network" that integrates the terminal system and Bcd activities, providing both polarity and spatial information to the prospective head region of the developing embryo.
authors.affiliation: Max Planck Institut für biophysikalische Chemie, Abteilung Molekulare Entwicklungsbiologie, Göttingen, Germany. uloehr@gwdg.de
authors.forename: Ulrike
authors.initials: U
authors.lastname: Löhr
authors.forename: Ho-Ryun
authors.initials: HR
authors.lastname: Chung
authors.forename: Mathias
authors.initials: M
authors.lastname: Beller
authors.forename: Herbert
authors.initials: H
authors.lastname: Jäckle
mesh_terms: D000818:Animals; D004330:Drosophila / Q000196:embryology* / Q000378:metabolism; D029721:Drosophila Proteins / Q000378:metabolism*; D005260:Female; D024002:HMGB Proteins / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism*; D009024:Morphogenesis; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D024002:HMGB Proteins; D018398:Homeodomain Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; C404284:cic protein, Drosophila; D020794:Receptor Protein-Tyrosine Kinases; C080148:tor protein, Drosophila
references.citation: Development. 2006 Feb;133(3):385-94
references.pmid: 16410409
references.citation: Mech Dev. 1996 May;56(1-2):3-15
references.pmid: 8798143
references.citation: EMBO J. 2003 May 1;22(9):1947-52
references.pmid: 12727862
references.citation: Development. 1990 Aug;109(4):811-20
references.pmid: 2226200
references.citation: Cell. 1988 Jul 1;54(1):83-93
references.pmid: 3383244
references.citation: Cell. 2004 Jan 23;116(2):143-52
references.pmid: 14744427
references.citation: EMBO J. 2007 Feb 7;26(3):668-77
references.pmid: 17255944
references.citation: Curr Biol. 2010 Mar 9;20(5):446-51
references.pmid: 20171100
references.citation: Curr Biol. 2008 Jun 24;18(12):915-9
references.pmid: 18571412
references.citation: Genes Dev. 1995 Dec 15;9(24):3163-76
references.pmid: 8543159
references.citation: EMBO J. 1988 Jun;7(6):1749-56
references.pmid: 2901954
references.citation: Mech Dev. 2002 Aug;116(1-2):75-83
references.pmid: 12128207
references.citation: Nature. 1995 Jul 20;376(6537):253-6
references.pmid: 7617036
references.citation: Proc Natl Acad Sci U S A. 2009 Mar 10;106(10):3823-8
references.pmid: 19237583
references.citation: Cell. 1988 Jul 1;54(1):95-104
references.pmid: 3383245
references.citation: Development. 2000 Jan;127(2):279-89
references.pmid: 10603346
references.citation: Nature. 1989 Jan 12;337(6203):138-43
references.pmid: 2911348
references.citation: Proc Natl Acad Sci U S A. 2005 Sep 13;102(37):13176-81
references.pmid: 16150708
references.citation: Dev Dyn. 2008 Mar;237(3):554-64
references.pmid: 18264999
references.citation: Hum Mol Genet. 2006 Jul 1;15(13):2125-37
references.pmid: 16717057
references.citation: Development. 2009 Feb;136(4):605-14
references.pmid: 19168676
references.citation: Proc Natl Acad Sci U S A. 2005 Apr 5;102(14):4960-5
references.pmid: 15793007
references.citation: Development. 1997 Oct;124(19):3827-34
references.pmid: 9367438
references.citation: Nature. 1996 Feb 22;379(6567):746-9
references.pmid: 8602224
references.citation: Nature. 2001 Oct 25;413(6858):797-803
references.pmid: 11677596
references.citation: Cell. 1993 Jul 30;74(2):347-55
references.pmid: 8343961
references.citation: Genes Dev. 2000 Jan 15;14(2):224-31
references.pmid: 10652276
references.citation: Proc Natl Acad Sci U S A. 2009 Dec 22;106(51):21695-700
references.pmid: 19959668
references.citation: Cell. 2007 Jul 13;130(1):141-52
references.pmid: 17632061
references.citation: Nature. 2008 Jan 31;451(7178):535-40
references.pmid: 18172436