title: Siamois is required for formation of Spemann's organizer.
abstract: Spemann's organizer develops in response to dorsal determinants that act via maternal components of the wnt pathway. The function of siamois, a wnt-inducible homeobox gene, in Spemann's organizer development was examined by fusion of defined transcriptional regulatory domains to the siamois homeodomain. Similar to native siamois, a VP16 activator fusion induced axis formation, indicating that siamois functions as a transcriptional activator in axis induction. Fusion of the engrailed repressor generated a dominant inhibitor that blocked axis induction by Xwnt8, beta-catenin, and siamois, and repressed wnt activation of the goosecoid promoter. Dorsal injection of the engrailed-siamois fusion resulted in complete inhibition of dorsal development and organizer gene expression, an effect rescued by siamois, but not by Xwnt8 or beta-catenin. Thus, as a zygotic mediator of maternal dorsal signals, siamois function is required for development of Spemann's organizer.
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA. kesslerd@mail.med.upenn.edu
authors.forename: D S
authors.initials: DS
authors.lastname: Kessler
mesh_terms: D000818:Animals; D019521:Body Patterning; D003598:Cytoskeletal Proteins; D004625:Embryo, Nonmammalian; D004627:Embryonic Induction; D018507:Gene Expression Regulation, Developmental; D011506:Proteins / Q000235:genetics; D014158:Transcription, Genetic; D051153:Wnt Proteins; D014981:Xenopus / Q000196:embryology; D029961:Zebrafish Proteins
chemical_list: D003598:Cytoskeletal Proteins; D011506:Proteins; D051153:Wnt Proteins; D029961:Zebrafish Proteins; C094521:wnt8a protein, zebrafish