Reversibility of Thyroid Hormone System–Disrupting Effects on Eye and Thyroid Follicle Development in Zebrafish (Danio rerio) Embryos

摘要

Early vertebrate development is partially regulated by thyroid hormones (THs). Environmental pollutants thatinteract with the TH system (TH system–disrupting chemicals THSDCs) can have massively disrupting effects on this essentialphase. Eye development of fish is directly regulated by THs and can, therefore, be used as a thyroid‐related endpointin endocrine disruptor testing. To evaluate the effects of THSDC‐induced eye malformations during early development,zebrafish (Danio rerio) embryos were exposed for 5 days postfertilization (dpf) to either propylthiouracil, a TH synthesisinhibitor, or tetrabromobisphenol A, which interacts with TH receptors. Subsequently, one half of the embryos were exposedfurther to the THSDCs until 8 dpf, while the other half of the embryos were raised in clean water for 3 days to check forreversibility of effects. Continued THSDC exposure altered eye size and pigmentation and induced changes in the cellularstructure of the retina. This correlated with morphological alterations of thyroid follicles as revealed by use of a transgeniczebrafish line. Interestingly, effects were partly reversible after a recovery period as short as 3 days. Results are consistentwith changes in TH levels measured in different tissues of the embryos, for example, in the eyes. The results show that eyedevelopment in zebrafish embryos is very sensitive to THSDC treatment but able to recover quickly from early exposure byeffective repair mechanisms.