Effects of the chorion on the developmental toxicity of organophosphate esters in zebrafish embryos

Many toxicological studies have utilized zebrafish embryos to investigate the developmental toxicity of organophosphate esters (OPEs). However, in respect of the presence or absence of the chorion, a consistent experimental methodology has yet to be developed. In this study, we used a fixed exposure scheme to compare the developmental toxicities of six major OPEs in chorionated and dechorionated zebrafish embryos. Removal of the chorion increased sensitivity to OPEs: we found higher incidence of mortality and malformation in dechorionated embryos. In a behavioral assay, the locomotive activity of zebrafish larvae was consistently inhibited by OPEs except tris (1-chloropropyl) phosphate regardless of chorion presence. However, at the molecular level, the expression of ZHE1 and mmp9 was affected by the presence of the chorion in zebrafish embryos exposed to tributyl phosphate and triphenyl phosphate (TPHP), respectively. Furthermore, in zebrafish embryos exposed to TPHP, the increased expression of miR-137 and miR-141 was abolished by the presence of the chorion. Our results demonstrate for the first time that the presence of the chorion influences phenotypic morbidity, organismal behavior, and gene expression in zebrafish embryos exposed to chemicals; thus, we suggest that dechorionation is desirable for exploring the toxicity mechanisms that underlie effects of chemical exposure.