Notice of Retraction: Pattern of malformations in Xenopus tropicalis embryos induced by retinoic acids and phenotype-based teratogenic index

Retinoic acids (RAs) are known to regulate important processes in vertebrates, and some contaminants can disrupt the RA signal and lead to adverse effects. Frog embryos show the potential for an ideal model used for screening the chemicals with RA activity. In this paper, we exposed Xenopus tropicalis embryos to two RAs (all-trans-RA and 9-cis-RA) and LGD1069, a selective ligand of retinoid X receptor. After 48 h of exposure, three agents induced a variety of similar malformations. The most obvious alterations were abnormal eyes, reduced brain, bent axis and hypopigmentaion. The 48 h EC50 of all-trans-RA, 9-cis-RA and LGD1069 was 3.38 μg/L, 2.25 μg/L and 6.74 μg/L, respectively. The pattern of malformations was consistent with those induced by RAs in X. laevis, and the teratogenic degree could be evaluated using the percent of teratogenicity (POT) and the index of anterior-posterior degree (IAD). When the malformations were severe, the power of POT was reduced, but IAD was still valid. In addition, IAD provided useful clues for mechanistic studies. These results suggest that RAs are strong teratogens to X. tropicalis embryos, and that RXR is also the target of RA activity chemicals. Our results indicate that a phenotype-based assay can be developed to screen RA activity chemicals using X. tropicalis embryos.