title: Evidence for non-axial A/P patterning in the nonneural ectoderm of Xenopus and zebrafish pregastrula embryos.
abstract: Recent studies in early Xenopus and zebrafish embryos have demonstrated that posteriorizing, non-axial signals arising from outside the organizer (or shield) contribute to A/P patterning of the neural axis, in contradiction to the classical Spemann model in which such signals were proposed to be solely organizer derived. Our studies on the early expression of the transcription factors GATA-2 and 3 in both Xenopus and zebrafish nonneural ectoderm lend support to the existence of such non-axial signaling in the A/P axis. Thus we find that the earliest expression of GATA-2 and 3 is located in nonneural ectoderm and is strongly patterned in a graded manner along the A/P axis, being high anteriorly and absent from the most posterior regions. This results by early neurula stages in three broad zones: an anterior region which is positive for both GATA-2 and 3, a middle region which is positive for GATA-2 alone and a posterior region in which neither gene is expressed. These regions correspond to head, trunk and tail ectoderm and may represent the beginnings of functional segmentation of nonneural ectoderm, as suggested in the concept of the 'ectomere'. We find that A/P patterning of GATA expression in nonneural ectoderm may occur as early as late blastula/early gastrula stages. We investigate which posteriorizing signals might contribute to such distinct non axial ectodermal patterning in the A/P axis and provide evidence that both FGF and a Wnt family member contribute towards the final A/P pattern of GATA expression in nonneural ectoderm.
authors.affiliation: Developmental Biology Research Centre, King's College London, The Randall Institute, United Kingdom.
authors.forename: E M
authors.initials: EM
authors.lastname: Read
authors.forename: A R
authors.initials: AR
authors.lastname: Rodaway
authors.forename: B
authors.initials: B
authors.lastname: Neave
authors.forename: N
authors.initials: N
authors.lastname: Brandon
authors.forename: N
authors.initials: N
authors.lastname: Holder
authors.forename: R K
authors.initials: RK
authors.lastname: Patient
authors.forename: M E
authors.initials: ME
authors.lastname: Walmsley
mesh_terms: D000818:Animals; D001755:Blastocyst; D019521:Body Patterning / Q000235:genetics*; D055415:Bone Morphogenetic Protein 4; D052004:Bone Morphogenetic Protein Receptors; D019485:Bone Morphogenetic Proteins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics*; D004475:Ectoderm / Q000502:physiology*; D004627:Embryonic Induction; D005346:Fibroblast Growth Factors / Q000502:physiology; D050989:GATA2 Transcription Factor; D050990:GATA3 Transcription Factor; D005775:Gastrula; D018507:Gene Expression Regulation, Developmental; D008648:Mesoderm; D011506:Proteins / Q000502:physiology; D012313:RNA / Q000032:analysis / Q000494:pharmacology; D011956:Receptors, Cell Surface; D017468:Receptors, Fibroblast Growth Factor; D017978:Receptors, Growth Factor; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014212:Tretinoin / Q000494:pharmacology; D051153:Wnt Proteins; D060508:Wnt3 Protein; D014981:Xenopus; D029867:Xenopus Proteins; D015027:Zebrafish; D029961:Zebrafish Proteins
chemical_list: D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D050989:GATA2 Transcription Factor; C494714:GATA2 protein, Xenopus; D050990:GATA3 Transcription Factor; C494746:GATA3 protein, Xenopus; D011506:Proteins; D011956:Receptors, Cell Surface; D017468:Receptors, Fibroblast Growth Factor; D017978:Receptors, Growth Factor; D015534:Trans-Activators; D014157:Transcription Factors; D051153:Wnt Proteins; D060508:Wnt3 Protein; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C525812:bmp4 protein, Xenopus; C525813:bmp4 protein, zebrafish; C494747:gata3 protein, zebrafish; D014212:Tretinoin; D005346:Fibroblast Growth Factors; D012313:RNA; D052004:Bone Morphogenetic Protein Receptors