title: A direct screen for secreted proteins in Xenopus embryos identifies distinct activities for the Wnt antagonists Crescent and Frzb-1.
abstract: To determine the spectrum of secreted proteins that are present in the extracellular space of early Xenopus embryos, a direct secretion screen was performed. Surprisingly, 24% of previously identified bona fide secretory proteins corresponded to four secreted Wnt antagonists of the same family: frzb-1, sizzled, sfrp-2 and crescent. sfrp-2 and crescent are novel components of the growing cocktail of growth factor antagonists secreted by Spemann organizer cells in Xenopus. Crescent is first expressed at blastula, defining a deep endodermal region that may be homologous to the avian hypoblast. Unlike other members of this family of inhibitors, microinjection of crescent mRNA causes the development of cyclopic embryos, even though the amount of anterior neural tissue is normal. In crescent-injected embryos, studies with specific markers indicate that morphogenetic movements of the anterior midline are abnormal, resulting in a more posterior location of prechordal plate and ventral forebrain markers with respect to the developing eye field. The results are discussed in light of recent findings in zebrafish and Xenopus that suggest that Wnt signaling through non-canonical (non-beta-catenin dependent) pathways plays a pivotal role in the regulation of morphogenetic movements.
authors.affiliation: Department of Biological Chemistry, Howard Hughes Medical Institute, University of California, Los Angeles 90095-1662, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: Pera
authors.forename: E M
authors.initials: EM
authors.lastname: De Robertis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019521:Body Patterning / Q000235:genetics; D002490:Central Nervous System / Q000196:embryology; D003001:Cloning, Molecular; D005110:Extracellular Space / Q000378:metabolism; D005124:Eye Abnormalities / Q000196:embryology / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D047908:Intracellular Signaling Peptides and Proteins; D008845:Microinjections; D008969:Molecular Sequence Data; D010802:Phylogeny; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000008:administration & dosage / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D051153:Wnt Proteins; D014981:Xenopus / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins; D000099274:Frizzled-Related Proteins
chemical_list: D006023:Glycoproteins; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D012333:RNA, Messenger; D051153:Wnt Proteins; D029867:Xenopus Proteins; D000099274:Frizzled-Related Proteins; C491629:frzb2 protein, Xenopus; C512785:wnt11b protein, Xenopus