title: Retinoic acid is a key regulatory switch determining the difference between lung and thyroid fates in Xenopus laevis.
abstract: BACKGROUND
  The lung and thyroid are derived from the anterior endoderm. Retinoic acid and Fgf signalling are known to be essential for development of the lung in mouse but little is known on how the lung and thyroid are specified in Xenopus.
  
  
  RESULTS
  If either retinoic acid or Fgf signalling is inhibited, there is no differentiation of the lung as assayed by expression of sftpb. There is no change in expression of thyroid gland markers when retinoic acid signalling is blocked after gastrulation and when Fgf signalling is inhibited there is a short window of time where pax2 expression is inhibited but expression of other markers is unaffected. If exogenous retinoic acid is given to the embryo between embryonic stages 20 and 26, the presumptive thyroid expresses sftpb and sftpc, specific markers of lung differentiation and expression of key thyroid transcription factors is lost. When the presumptive thyroid is transplanted into the posterior embryo, it also expresses sftpb, although pax2 expression is not blocked.
  
  
  CONCLUSIONS
  After gastrulation, retinoic acid is required for lung but not thyroid differentiation in Xenopus while Fgf signalling is needed for lung but only for early expression of pax2 in the thyroid. Exposure to retinoic acid can cause the presumptive thyroid to switch to a lung developmental program.
authors.affiliation: Children's Health Research Institute, London, Ontario, Canada.
authors.forename: Jean H
authors.initials: JH
authors.lastname: Wang
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Deimling
authors.forename: Nicole E
authors.initials: NE
authors.lastname: D'Alessandro
authors.forename: Lin
authors.initials: L
authors.lastname: Zhao
authors.forename: Fred
authors.initials: F
authors.lastname: Possmayer
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Drysdale
mesh_terms: D000818:Animals; D019521:Body Patterning; D004625:Embryo, Nonmammalian; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008168:Lung / Q000196:embryology*; D013961:Thyroid Gland / Q000196:embryology*; D014212:Tretinoin / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics* / Q000378:metabolism
chemical_list: D014212:Tretinoin; D005346:Fibroblast Growth Factors