title: The regional pattern of retinoic acid synthesis by RALDH2 is essential for the development of posterior pharyngeal arches and the enteric nervous system.
abstract: Targeted inactivation of the mouse retinaldehyde dehydrogenase 2 (RALDH2/ALDH1a2), the enzyme responsible for early embryonic retinoic acid synthesis, is embryonic lethal because of defects in early heart morphogenesis. Transient maternal RA supplementation from E7.5 to (at least) E8.5 rescues most of these defects, but the supplemented Raldh2(-/-) mutants die prenatally, from a lack of septation of the heart outflow tract (Niederreither, K., Vermot, J., Messaddeq, N., Schuhbaur, B., Chambon, P. and Dollé, P. (2001). Development 128, 1019-1031). We have investigated the developmental basis for this defect, and found that the RA-supplemented Raldh2(-/-) embryos exhibit impaired development of their posterior (3rd-6th) branchial arch region. While the development of the first and second arches and their derivatives, as well as the formation of the first branchial pouch, appear to proceed normally, more posterior pharyngeal pouches fail to form and the pharyngeal endoderm develops a rudimentary, pouch-like structure. All derivatives of the posterior branchial arches are affected. These include the aortic arches, pouch-derived organs (thymus, parathyroid gland) and post-otic neural crest cells, which fail to establish segmental migratory pathways and are misrouted caudally. Patterning and axonal outgrowth of the posterior (9th-12th) cranial nerves is also altered. Vagal crest deficiency in Raldh2(-/-) mutants leads to agenesis of the enteric ganglia, a condition reminiscent of human Hirschprung's disease. In addition, we provide evidence that: (i) wildtype Raldh2 expression is restricted to the posteriormost pharyngeal mesoderm; (ii) endogenous RA response occurs in both the pharyngeal endoderm and mesoderm, and extends more rostrally than Raldh2 expression up to the 2nd arch; (iii) RA target genes (Hoxa1, Hoxb1) are downregulated in both the pharyngeal endoderm and mesoderm of mutant embryos. Thus, RALDH2 plays a crucial role in producing RA required for pharyngeal development, and RA is one of the diffusible mesodermal signals that pattern the pharyngeal endoderm.
authors.affiliation: Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP/Collège de France, BP 10142, 67404 Illkirch Cedex, CU de Strasbourg, France.
authors.forename: Karen
authors.initials: K
authors.lastname: Niederreither
authors.forename: Julien
authors.initials: J
authors.lastname: Vermot
authors.forename: Isabelle
authors.initials: I
authors.lastname: Le Roux
authors.forename: Brigitte
authors.initials: B
authors.lastname: Schuhbaur
authors.forename: Pierre
authors.initials: P
authors.lastname: Chambon
authors.forename: Pascal
authors.initials: P
authors.lastname: Dollé
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001934:Branchial Region / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D002465:Cell Movement; D003391:Cranial Nerves / Q000002:abnormalities / Q000196:embryology; D004062:DiGeorge Syndrome / Q000209:etiology; D004707:Endoderm / Q000378:metabolism; D017615:Enteric Nervous System / Q000196:embryology* / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006627:Hirschsprung Disease / Q000209:etiology; D006801:Humans; D008431:Maternal-Fetal Exchange; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009432:Neural Crest / Q000166:cytology; D010641:Phenotype; D011247:Pregnancy; D012249:Rhombencephalon / Q000196:embryology; D015398:Signal Transduction; D014212:Tretinoin / Q000008:administration & dosage / Q000378:metabolism*; D014630:Vagus Nerve / Q000196:embryology
chemical_list: D014212:Tretinoin; D000445:Aldehyde Oxidoreductases; C470579:RALDH2 protein, mouse