title: Mutual antagonism between dickkopf1 and dickkopf2 regulates Wnt/beta-catenin signalling.
abstract: Wnts are secreted glycoproteins implicated in diverse processes during embryonic patterning in metazoans. They signal through seven-transmembrane receptors of the Frizzled (Fz) family [1] to stabilise beta-catenin [2]. Wnts are antagonised by several extracellular inhibitors including the product of the dickkopf1 (dkk1) gene, which was identified in Xenopus embryos and is a member of a multigene family. The dkk1 gene acts upstream of the Wnt pathway component dishevelled but its mechanism of action is unknown [3]. Although the function of Dkk1 as a Wnt inhibitor in vertebrates is well established [3-6], the effect of other Dkks on the Wnt/beta-catenin pathway is unclear. Here, we report that a related family member, Dkk2, activates rather than inhibits the Wnt/beta-catenin signalling pathway in Xenopus embryos. Dkk2 strongly synergised with Wnt receptors of the Fz family to induce Wnt signalling responses. The study identifies Dkk2 as a secreted molecule that is able to activate Wnt/beta-catenin signalling. The results suggest that a coordinated interplay between inhibiting dkk1 and activating dkk2 can modulate Fz signalling.
authors.affiliation: Division of Molecular Embryology, Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Wu
authors.forename: A
authors.initials: A
authors.lastname: Glinka
authors.forename: H
authors.initials: H
authors.lastname: Delius
authors.forename: C
authors.initials: C
authors.lastname: Niehrs
mesh_terms: D000818:Animals; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D051157:Frizzled Receptors; D005786:Gene Expression Regulation / Q000502:physiology; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008845:Microinjections; D009024:Morphogenesis; D011506:Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators; D051153:Wnt Proteins; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology / Q000502:physiology; D029961:Zebrafish Proteins; D051176:beta Catenin
chemical_list: C495266:CTNNB1 protein, Xenopus; C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D003598:Cytoskeletal Proteins; C501126:DKK1 protein, human; C498622:DKK2 protein, human; C501127:Dkk1 protein, mouse; C498623:Dkk2 protein, Xenopus; C405060:Dkk2 protein, mouse; D051157:Frizzled Receptors; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins; D012333:RNA, Messenger; C093133:SIA1 protein, Xenopus; D015534:Trans-Activators; D051153:Wnt Proteins; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; D051176:beta Catenin; C110182:dkk1 protein, Xenopus; C501128:dkk1b protein, zebrafish; C094521:wnt8a protein, zebrafish