title: Retinoic acid-mediated patterning of the pre-pancreatic endoderm in Xenopus operates via direct and indirect mechanisms.
abstract: Early patterning of the endoderm as a prerequisite for pancreas specification involves retinoic acid (RA) as a critical signalling molecule in gastrula stage Xenopus embryos. In extension of our previous studies, we made systematic use of early embryonic endodermal and mesodermal explants. We find RA to be sufficient to induce pancreas-specific gene expression in dorsal but not ventral endoderm. The differential expression of retinoic acid receptors (RARs) in gastrula stage endoderm is important for the distinct responsiveness of dorsal versus ventral explants. Furthermore, BMP signalling, that is repressed dorsally, prevents the formation of pancreatic precursor cells in the ventral endoderm of gastrula stage Xenopus embryos. An additional requirement for mesoderm suggests the production of one or more further pancreas inducing signals by this tissue. Finally, recombination of manipulated early embryonic explants, and also inhibition of RA activity in whole embryos, reveal that RA signalling, as it is relevant for pancreas development, operates simultaneously on both mesodermal and endodermal germ layers.
authors.affiliation: Department of Developmental Biochemistry, University of Goettingen, Justus-von-Liebig Weg 11, 37077 Goettingen, Germany.
authors.forename: Fong Cheng
authors.initials: FC
authors.lastname: Pan
authors.forename: Yonglong
authors.initials: Y
authors.lastname: Chen
authors.forename: Elke
authors.initials: E
authors.lastname: Bayha
authors.forename: Tomas
authors.initials: T
authors.lastname: Pieler
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology; D004707:Endoderm / Q000502:physiology*; D010179:Pancreas / Q000196:embryology* / Q000502:physiology; D015398:Signal Transduction; D014212:Tretinoin / Q000494:pharmacology*; D014982:Xenopus laevis / Q000196:embryology* / Q000502:physiology
chemical_list: D014212:Tretinoin