Fig. 1: atRA induces NTDs in rat embryos ex vivo.

Abnormalities were observed in the craniocerebral and sacrococcygeal regions of atRA-treated embryonic rats. a Representative photos of normal and NTD embryos under a stereological microscope. Compared to the normal embryo, the NTD embryo exhibited distinct exencephaly (arrowhead), spina bifida (arrowhead), and craniofacial deformity (asterisk). b Magnified side view of the brains of normal (upper) and exencephalic (lower, arrowhead) embryos. c Magnified view from the back of the brain of normal (upper) and exencephalic (lower, arrowheads) embryos. d Magnified side view of the lumbosacral regions: the closed neural tube from a normal embryo (upper) and a defective neural tube from an embryo with spina bifida (lower). e Magnified view from the back of the lumbosacral region. The spinal neural tube of the normal embryo was smooth and continuous (upper) whereas the spinal neural tube of the spina bifida embryo was disturbed and not completely closed (lower, arrowheads). f The yolk sacs of normal and atRA-treated malformed embryos. A well-formed extensive blood vessel network with blood circulation (arrowhead) was observed in the yolk sac of the normal embryo. An under-developed blood vessel network (arrowhead) was observed in the yolk sac of the atRA-treated embryo. g A representative atRA-treated embryo with delayed formation of the heart chamber, detachment of the epicardium, and branchial arch malformations (asterisk). h A representative atRA-treated embryo with body-axis dysplasia (asterisk). i The relationship between the atRA dose and embryo dysmorphology. Epic epicardium, fb forebrain, hb hindbrain, hl hind lim, H heart, mb midbrain, ot otic vesicle, op optic vesicle. Scale bars: 500 μm.