title: The dynamic expression pattern of frzb-1 suggests multiple roles in chick development.
abstract: The Wnt family of secreted proteins has been shown to have multiple roles in embryonic development. Wnt signals are thought to be propagated by binding to the cysteine-rich extracellular domain (CRD) of Frizzled, a seven-transmembrane-domain cell surface receptor. Secreted Frizzled-related proteins (generally denoted Frzb or Sfrp) possess a domain with a high degree of sequence identity and structural similarity with the CRD of Frizzled. Current data indicate that the cysteine-rich domain of secreted Frzb proteins can bind Wnt proteins, suggesting the possibility that Frzbs compete with membrane-bound Frizzled for Wnt binding and consequently act as competitive inhibitors of Wnt signaling. In order to gain a better understanding of the potential roles of Frzb-1 in chick development, we utilized the polymerase chain reaction to isolate a partial cDNA of the chick orthologue of frzb-1, cfrzb-1, and compared its expression pattern to that of Wnt-1, Wnt-3a, Wnt-5a, Wnt-7a, and Wnt-8c. Whole-mount in situ hybridizations have revealed three major phases of expression for cfrzb-1 in the developing chick. The earliest expression of cfrzb-1 is in cells fated to become neural ectoderm in streak-stage embryos. Expression of cfrzb-1 in the neural ectoderm continues up through stage 8. After stage 8, cfrzb-1 expression is gradually attenuated in the closing neural tube of the trunk and is concomitantly up-regulated in neural crest cells. Finally, cfrzb-1 appears in the condensing mesenchyme of the bones in both the limb and the trunk in stage 25+ embryos. Comparative analysis of the cfrzb-1 and the Wnt gene expression patterns suggests possible interactions between cFrzb-1 and all of the Wnt family members examined.
authors.affiliation: Department of Biology, San Francisco State University, 1600 Holloway Avenue, San Francisco, California, 94132, USA.
authors.forename: M
authors.initials: M
authors.lastname: Baranski
authors.forename: E
authors.initials: E
authors.lastname: Berdougo
authors.forename: J S
authors.initials: JS
authors.lastname: Sandler
authors.forename: D K
authors.initials: DK
authors.lastname: Darnell
authors.forename: L W
authors.initials: LW
authors.lastname: Burrus
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001842:Bone and Bones / Q000196:embryology / Q000378:metabolism; D002642:Chick Embryo; D017931:DNA Primers; D018076:DNA, Complementary; D047108:Embryonic Development; D051157:Frizzled Receptors; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D011506:Proteins / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D051157:Frizzled Receptors; D011506:Proteins