Fig. (1) Schematic illustration of whole embryo culture and treatments. E11.0 SD-rat embryos were explanted and cultured for 48 h. They were separated into two experimental groups: (1) pre-treatment of 100 µM folic acid for 18h, followed by 20 µM 13-cis-RA for 24h (FA-RA), (2) treatment of 20 µM 13-cis-RA alone for 24h (RA). After the culture, midfacial morphogenesis was investigated with morphologic scoring system by light stereomicroscope. The midfacial processes of the embryos were also frontally sectioned for TUNEL assay, and PCNA staining.