title: Otx2 can activate the isthmic organizer genetic network in the Xenopus embryo.
abstract: Development and differentiation of the vertebrate caudal midbrain and anterior hindbrain are dependent on the isthmic organizer signals at the midbrain/hindbrain boundary (MHB). The future MHB forms at the boundary between the Otx2 and Gbx2 expression domains. Recent studies in mice and chick suggested that the apposition of Otx2- and Gbx2-expressing cells is instrumental for the positioning and early induction of the MHB genetic cascade. We show that Otx2 and Gbx2 perform different roles in this process. We find that ectopically expressed Otx2 on its own can induce a substantial part of the MHB genetic network, namely En2, Wnt1, Pax-2, Fgf8 and Gbx2, in a concentration-dependent manner. This induction does not require protein synthesis and ends during neurulation. In contrast, Gbx2 is a negative regulator of Otx2 and the MHB genes. Based on the temporal patterns of expression of the genes involved, we propose that Otx2 might be the early inducer of the isthmic organizer genetic network while Gbx2 restricts Otx2 expression along the anterior-posterior axis and establishes an Otx2 gradient.
authors.affiliation: Department of Cellular Biochemistry and Human Genetics, Hebrew University-Hadassah Medical School, P.O. Box 12272, Jerusalem 91120, Israel.
authors.forename: Ella
authors.initials: E
authors.lastname: Tour
authors.forename: Graciela
authors.initials: G
authors.lastname: Pillemer
authors.forename: Yosef
authors.initials: Y
authors.lastname: Gruenbaum
authors.forename: Abraham
authors.initials: A
authors.lastname: Fainsod
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000235:genetics; D004475:Ectoderm / Q000166:cytology; D004627:Embryonic Induction; D018628:Gene Dosage; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics; D017403:In Situ Hybridization; D007763:Lac Operon; D008636:Mesencephalon / Q000196:embryology; D009419:Nerve Tissue Proteins / Q000235:genetics*; D020897:Organizers, Embryonic; D051857:Otx Transcription Factors; D012249:Rhombencephalon / Q000196:embryology; D015534:Trans-Activators / Q000235:genetics*; D029867:Xenopus Proteins; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics*; D000099266:Engrailed 2 Protein
chemical_list: D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D051857:Otx Transcription Factors; D015534:Trans-Activators; D029867:Xenopus Proteins; D000099266:Engrailed 2 Protein; C513180:Gbx2 protein, Xenopus; C497661:Otx2 protein, Xenopus