Retinoic acid exposure of the mouse on embryonic day 9 selectively spares derivatives of the frontonasal neural crest.

Retinoic acid is known to perturb craniofacial development and can be used to understand processes controlling early embryonic development of the face. The effects of retinoic acid on mouse craniofacial development were studied by administration of a single dose (25-200 mg/ kg) of all-trans retinoic acid (RA) to timed pregnant C57BL6/J mice at gestational days (gd) 8.25, 9, or 10. RA exposure on gd 8.25 or gd 10 resulted in craniofacial defects in fetuses but gd 9 exposure revealed a differential effect of RA depending upon whether tissues were derived from branchial arch or frontonasal neural crest. Embryos exposed to RA at gd 9 showed a dose-dependent effect of RA on branchial arch derived tissues; first arch derivatives were most severely affected with the mandible and zygoma becoming severely dysplastic at the highest dose of RA (200 mg/kg). However, RA exposure on gd 9 completely spared frontonasal neural crest-derived tissues. Paired premaxillae nasal and frontal bones as well as the cartilaginous nasoethmoid region and nasal capsule containing the osseous vomer showed no statistical difference from those of control animals. These studies showed a temporal and differential sensitivity to RA and may suggest a developmental heterogeneity of the cephalic neural crest cells destined to participate in formation of craniofacial structures.