Retinoic acid-induced thymic abnormalities in the mouse are associated with altered pharyngeal morphology, thymocyte maturation defects, and altered expression of Hoxa3 and Pax1

Teratology. 1998 Dec;58(6):263-75. doi: 10.1002/(SICI)1096-9926(199812)58:6<263::AID-TERA8>3.0.CO;2-A.


Exogenous retinoic acid is teratogenic in animals and man, causing a spectrum of abnormalities termed retinoic acid embryopathy. Using a mouse model of retinoic acid embryopathy, our results show that exposure to all-trans retinoic acid (RA) on gestational day (gd) 9 results in thymic ectopia, hypoplasia, and thymocyte maturational defects. Immunohistochemical and flow cytometric analyses showed aberrant expression of stromal and thymocyte markers, and abnormalities in thymocyte development. RNA in situ hybridization for the transcription factors Hoxa3 and Pax1 was used to investigate the basis of this defect. Hoxa3 and Pax1 have been shown to be required for normal thymus development, and are normally expressed in the cells of the third pharyngeal pouch and third and fourth pharyngeal arches, involved in thymus organogenesis RA-exposed embryos showed an increased level of Hoxa3 expression in the neural tube and caudal pharyngeal arches as soon as 6 hr after exposure. The Pax1 expression pattern, in conjunction with analysis of the external pharyngeal morphology, showed that the development and structure of the third pharyngeal pouch and cleft were disrupted, resulting in a reduced third pharyngeal arch and/or fusion of the third and fourth arches. Changes in the expression of cellular retinoic acid binding protein (CRABP) and in the morphology of the cranial ganglia were consistent with altered neural crest cell migration from the caudal hindbrain after RA exposure. Together, our findings suggest that the teratogenic effects of RA on thymus development include changes in both the cranial neural crest and pharyngeal endoderm that contribute to thymus development. Further, the observed defects in thymus development may be mediated by RA-induced alterations in the expression of Hoxa3.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Branchial Region / abnormalities
  • Branchial Region / metabolism
  • DNA-Binding Proteins / metabolism*
  • Flow Cytometry
  • Gene Expression Regulation, Developmental
  • Homeodomain Proteins*
  • Immunohistochemistry
  • In Situ Hybridization
  • Mice
  • Mice, Inbred C57BL
  • Neural Crest / abnormalities
  • Neural Crest / metabolism
  • Paired Box Transcription Factors
  • Rhombencephalon / drug effects
  • Rhombencephalon / embryology
  • Teratogens / toxicity*
  • Thymus Gland / abnormalities*
  • Thymus Gland / embryology
  • Transcription Factors / metabolism*
  • Tretinoin / metabolism
  • Tretinoin / toxicity*


  • DNA-Binding Proteins
  • HOX3A protein, Felis catus
  • Homeodomain Proteins
  • Paired Box Transcription Factors
  • Teratogens
  • Transcription Factors
  • PAX1 transcription factor
  • Tretinoin