title: The prechordal region lacks neural inducing ability, but can confer anterior character to more posterior neuroepithelium.
abstract: The avian equivalent of Spemann's organizer, Hensen's node, begins to lose its ability to induce a nervous system from area opaca epiblast cells at stage 4+, immediately after the full primitive streak stage. From this stage, the node is no longer able to induce regions of the nervous system anterior to the hindbrain. Stage 4+ is marked by the emergence from the node of a group of cells, the prechordal mesendoderm. Here we have investigated whether the prechordal region possesses the lost functions of the organizer, using quail-chick chimaeras to distinguish graft- and host-derived cells, together with several region-specific molecular markers. We find that the prechordal region does not have neural inducing ability, as it is unable to divert extraembryonic epiblast cells to a neural fate. However, it can confer more anterior character to prospective hindbrain cells of the host, making them acquire expression of the forebrain markers tailless and Otx-2. It can also rescue the expression of Krox-20 and Otx-2 from nervous system induced by an older (stage 5) node in extraembryonic epiblast. We show that these properties reflect a true change of fate of cells rather than recruitment from other regions. The competence of neuroectoderm to respond to anteriorizing signals declines by stages 7-9, but both posteriorizing signals and the ability of neuroectoderm to respond to them persist after this stage.
authors.affiliation: Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
authors.forename: A C
authors.initials: AC
authors.lastname: Foley
authors.forename: K G
authors.initials: KG
authors.lastname: Storey
authors.forename: C D
authors.initials: CD
authors.lastname: Stern
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology*; D016380:Brain Tissue Transplantation; D002642:Chick Embryo; D002678:Chimera; D004268:DNA-Binding Proteins / Q000235:genetics; D029721:Drosophila Proteins; D051767:Early Growth Response Protein 2; D004627:Embryonic Induction / Q000502:physiology*; D004707:Endoderm; D005775:Gastrula; D018398:Homeodomain Proteins; D008648:Mesoderm; D009419:Nerve Tissue Proteins / Q000235:genetics; D051857:Otx Transcription Factors; D016548:Prosencephalon / Q000196:embryology*; D011784:Quail / Q000196:embryology; D012333:RNA, Messenger / Q000032:analysis; D012097:Repressor Proteins / Q000235:genetics; D012249:Rhombencephalon / Q000196:embryology*; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D051767:Early Growth Response Protein 2; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D051857:Otx Transcription Factors; D012333:RNA, Messenger; D012097:Repressor Proteins; C074090:TLL protein, Drosophila; D015534:Trans-Activators; D014157:Transcription Factors