Effect of Retinoic Acid on Palate Formation during Rat Embryogenesis

Cheng, Meang Sub; Yoo, Byoung Ki; Park, Hyoung Woo; Kim, Myoung Hee

Abstract

In order to understand the effect of retinoic acid (RA) on the craniofacial pattern formation during embryogenesis, we injected RA intraperitoneally into the pregnant female rat on day 11 post coitum (p.c.) and then embryos of day 13 to day 17 p.c. were isolated consequently. The overall morphology and the differential gene expression patterns were analyzed by the microscopic and (DD) RT-PCR methods, respectively. For the morphological study, the retardation of craniofacial region, the shortage of crown rump length and limbs were analyzed in the RA-treated embryos. In the RA-treated embryos of day 17, it was observed that the palatogenesis was completely finished just like in the normal embryos. However, the cleft plate was observed in 36 out of 52 total samples with the distance of cleft palate being 0.80+/-0.36 mm in average. The temporal expression pattern of Hox genes through RT-PCR revealed that the expression of Hoxa7 reached its peak on day 13 then slowly declined in the normal embryos. Whereas in the RA-treated embryos, the expression peak was observed on day 15, then declined subsequently. With the Hoxc8 gene, its expression was low in all stages until the day 16 of normal embryogenesis. On the other hand, Hoxc8 gene expression was detected slightly early on day 15 in the RA-treated embryos. In the study of Bcl-2 family genes, uniformly strong expression of anti-apoptotic and pro-apoptotic genes was observed from day 13 to day 17 of normal embryos, whereas anti-apoptotic gene expressions were decreased after day 16 in the RAtreated embryos. Additionally, a dramatic decline of pro-apoptotic gene expression was observed from day 13 to day 15 of the RA-treated embryos. Therefore, we believe that RA is a potential factor that is actively involved in the cleft palate formation. Moreover, it is profoundly linked with the regulation of Hox and Bcl-2 family gene expression pattern that leads to the embryonic malformation.