title: The Wnt antagonists Frzb-1 and Crescent locally regulate basement membrane dissolution in the developing primary mouth.
abstract: The primary mouth forms from ectoderm and endoderm at the extreme anterior of the embryo, a conserved mesoderm-free region. In Xenopus, a very early step in primary mouth formation is loss of the basement membrane between the ectoderm and endoderm. In an unbiased microarray screen, we defined genes encoding the sFRPs Frzb-1 and Crescent as transiently and locally expressed in the primary mouth anlage. Using antisense oligonucleotides and ;face transplants', we show that frzb-1 and crescent expression is specifically required in the primary mouth region at the time this organ begins to form. Several assays indicate that Frzb-1 and Crescent modulate primary mouth formation by suppressing Wnt signaling, which is likely to be mediated by beta-catenin. First, a similar phenotype (no primary mouth) is seen after loss of Frzb-1/Crescent function to that seen after temporally and spatially restricted overexpression of Wnt-8. Second, overexpression of either Frzb-1 or Dkk-1 results in an enlarged primary mouth anlage. Third, overexpression of Dkk-1 can restore a primary mouth to embryos in which Frzb-1/Crescent expression has been inhibited. We show that Frzb-1/Crescent function locally promotes basement membrane dissolution in the primary mouth primordium. Consistently, Frzb-1 overexpression decreases RNA levels of the essential basement membrane genes fibronectin and laminin, whereas Wnt-8 overexpression increases the levels of these RNAs. These data are the first to connect Wnt signaling and basement membrane integrity during primary mouth development, and suggest a general paradigm for the regulation of basement membrane remodeling.
authors.affiliation: Whitehead institute for Biomedical Research, Cambridge, MA 02102, USA.
authors.forename: Amanda J G
authors.initials: AJ
authors.lastname: Dickinson
authors.forename: Hazel L
authors.initials: HL
authors.lastname: Sive
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001485:Basement Membrane / Q000196:embryology; D018507:Gene Expression Regulation, Developmental; D006023:Glycoproteins / Q000235:genetics / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D009055:Mouth / Q000196:embryology*; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D012313:RNA / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D051153:Wnt Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D029867:Xenopus Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics / Q000502:physiology; D000099274:Frizzled-Related Proteins
chemical_list: D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D012313:RNA; D051153:Wnt Proteins; D029867:Xenopus Proteins; D000099274:Frizzled-Related Proteins; C491629:frzb2 protein, Xenopus; C495248:wnt8a protein, Xenopus