Diofenolan induces male offspring production through binding to the juvenile hormone receptor in Daphnia magna

Juvenile hormone (JH) and JH agonists have been reported to induce male offspring production in various daphnid species including Daphnia magna. We recently established a short-term in vivo screening assay to detect chemicals having male offspring induction activity in adult D. magna. Diofenolan has been developed as a JH agonist for insect pest control, but its male offspring induction activity in daphnids has not been investigated yet. In this study, we found that the insect growth regulator (IGR) diofenolan exhibited a potent male offspring induction activity at low ng/L to μg/L concentrations, as demonstrated by the short-term in vivo screening assay and the recently developed TG211 ANNEX 7 test protocol. A two-hybrid assay performed using the D. magna JH receptor confirmed that diofenolan had a strong JH activity. Global whole body transcriptome analysis of D. magna exposed to 10 ng/L diofenolan showed an up-regulation of JH-responsive genes and modulation of several genes involved in the ecdysone receptor signaling pathway. These results clearly demonstrate that diofenolan has strong JH activity and male offspring induction activity, and that a combination of modified standardized regulatory testing protocols and rapid in vitro and in vivo screening assays are able to identify potential endocrine disruptors in D. magna. The observation that diofenolan modulates multiple endocrine signaling pathways in D. magna suggests that further investigation of potential interference with growth, development and reproduction is warranted.