Retinoic acid is a key regulatory switch determining the difference between lung and thyroid fates in Xenopus laevis.

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.