title: Retinoic acid synthesis and hindbrain patterning in the mouse embryo.
abstract: Targeted disruption of the murine retinaldehyde dehydrogenase 2 (Raldh2) gene precludes embryonic retinoic acid (RA) synthesis, leading to midgestational lethality (Niederreither, K., Subbarayan, V., Dolle, P. and Chambon, P. (1999). Nature Genet. 21, 444-448). We describe here the effects of this RA deficiency on the development of the hindbrain and associated neural crest. Morphological segmentation is impaired throughout the hindbrain of Raldh2-/- embryos, but its caudal portion becomes preferentially reduced in size during development. Specification of the midbrain region and of the rostralmost rhombomeres is apparently normal in the absence of RA synthesis. In contrast, marked alterations are seen throughout the caudal hindbrain of mutant embryos. Instead of being expressed in two alternate rhombomeres (r3 and r5), Krox20 is expressed in a single broad domain, correlating with an abnormal expansion of the r2-r3 marker Meis2. Instead of forming a defined r4, Hoxb1- and Wnt8A-expressing cells are scattered throughout the caudal hindbrain, whereas r5/r8 markers such as kreisler or group 3/4 Hox genes are undetectable or markedly downregulated. Lack of alternate Eph receptor gene expression could explain the failure to establish rhombomere boundaries. Increased apoptosis and altered migratory pathways of the posterior rhombencephalic neural crest cells are associated with impaired branchial arch morphogenesis in mutant embryos. We conclude that RA produced by the embryo is required to generate posterior cell fates in the developing mouse hindbrain, its absence leading to an abnormal r3 (and, to a lesser extent, r4) identity of the caudal hindbrain cells.
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP/Collège de France, CU de Strasbourg.
authors.forename: K
authors.initials: K
authors.lastname: Niederreither
authors.forename: J
authors.initials: J
authors.lastname: Vermot
authors.forename: B
authors.initials: B
authors.lastname: Schuhbaur
authors.forename: P
authors.initials: P
authors.lastname: Chambon
authors.forename: P
authors.initials: P
authors.lastname: Dollé
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000818:Animals; D030161:Avian Proteins; D019521:Body Patterning / Q000502:physiology*; D016923:Cell Death; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000235:genetics; D051767:Early Growth Response Protein 2; D036383:Ephrin-A2; D036385:Ephrin-A4; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics; D051258:MafB Transcription Factor; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D009432:Neural Crest; D009474:Neurons / Q000166:cytology; D015513:Oncogene Proteins; D010641:Phenotype; D050697:Retinal Dehydrogenase; D012249:Rhombencephalon / Q000196:embryology*; D014157:Transcription Factors / Q000235:genetics; D014212:Tretinoin
chemical_list: D030161:Avian Proteins; D004268:DNA-Binding Proteins; D051767:Early Growth Response Protein 2; C497327:Egr2 protein, mouse; D036383:Ephrin-A2; D036385:Ephrin-A4; C101121:HOXB1 homeodomain protein; D018398:Homeodomain Proteins; C400681:Hox3 protein, Ciona intestinalis; D051258:MafB Transcription Factor; C490406:Mafb protein, mouse; D008565:Membrane Proteins; D015513:Oncogene Proteins; D014157:Transcription Factors; D014212:Tretinoin; D000445:Aldehyde Oxidoreductases; D050697:Retinal Dehydrogenase