Distinct roles for Fgf, Wnt and retinoic acid in posteriorizing the neural ectoderm.
Early neural patterning in vertebrates involves signals that inhibit anterior (A) and promote posterior (P) positional values within the nascent neural plate. In this study, we have investigated the contributions of, and interactions between, retinoic acid (RA), Fgf and Wnt signals in the promotion of posterior fates in the ectoderm. We analyze expression and function of cyp26/P450RAI, a gene that encodes retinoic acid 4-hydroxylase, as a tool for investigating these events. Cyp26 is first expressed in the presumptive anterior neural ectoderm and the blastoderm margin at the late blastula. When the posterior neural gene hoxb1b is expressed during gastrulation, it shows a strikingly complementary pattern to cyp26. Using these two genes, as well as otx2 and meis3 as anterior and posterior markers, we show that Fgf and Wnt signals suppress expression of anterior genes, including cyp26. Overexpression of cyp26 suppresses posterior genes, suggesting that the anterior expression of cyp26 is important for restricting the expression of posterior genes. Consistent with this, knock-down of cyp26 by morpholino oligonucleotides leads to the anterior expansion of posterior genes. We further show that Fgf- and Wnt-dependent activation of posterior genes is mediated by RA, whereas suppression of anterior genes does not depend on RA signaling. Fgf and Wnt signals suppress cyp26 expression, while Cyp26 suppresses the RA signal. Thus, cyp26 has an important role in linking the Fgf, Wnt and RA signals to regulate AP patterning of the neural ectoderm in the late blastula to gastrula embryo in zebrafish.
Department of Anatomy and Developmental Biology, University College London, Gower St, London WC1E 6BT, UK. t.kudoh@ucl.ac.uk
Tetsuhiro
T
Kudoh
Stephen W
SW
Wilson
Igor B
IB
Dawid
D000818:Animals; D001756:Blastoderm / Q000502:physiology; D036703:Blastula / Q000502:physiology; D019521:Body Patterning / Q000187:drug effects / Q000502:physiology*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004475:Ectoderm / Q000502:physiology*; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000502:physiology; D005346:Fibroblast Growth Factors / Q000502:physiology*; D005775:Gastrula / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018021:Lithium Chloride / Q000494:pharmacology; D009420:Nervous System / Q000196:embryology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D000072516:Retinoic Acid 4-Hydroxylase; D014158:Transcription, Genetic; D014212:Tretinoin / Q000494:pharmacology / Q000502:physiology*; D051153:Wnt Proteins; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins
D011518:Proto-Oncogene Proteins; D051153:Wnt Proteins; D029961:Zebrafish Proteins; C094522:wnt8b protein, zebrafish; D014212:Tretinoin; D005346:Fibroblast Growth Factors; D003577:Cytochrome P-450 Enzyme System; D000072516:Retinoic Acid 4-Hydroxylase; D011505:Protein-Tyrosine Kinases; D018021:Lithium Chloride