[Analysis of retinoic acid effects on craniofacial development in quail embryo]

Craniofacial deformities caused by retinoic acid (RA) treatment are well known, but its mechanisms remain to be elucidated. In order to study RA-induced deformities during craniofacial morphogenesis, several different stages and regions of quail embryo in ovo were examined. It was found that the RA injection to the subgerminal space in early-stage (H.H. stage 8) affects specifically craniofacial morphogenesis. Superficially, the acrania and the exencephalia are the most remarkable deformities. Bone and cartilage staining has revealed the hypoplasia of maxilla in high frequencies. Histochemical analyses have demonstrated abnormal development and growth of the central nervous system (CNS). The expression of the Nau gene, a marker of post-mitotic neuroblasts, was also examined by in situ hybridization. Strong expression of the Nau gene in normal embryo was observed in the mantle zone in CNS in the E5 embryo. In contrast, Nau negative nervous tissues were often observed in the RA-treated E5 quail embryo, which indicates abnormal proliferation and differentiation of the neuroblasts in the CNS.