Phenylthiourea disrupts thyroid function in developing zebrafish

Abstract

Thyroid hormone (T4) can be detected in thyroid follicles in wild-type zebrafish larvae from 3 days of development, when the thyroid has differentiated. In contrast, embryos or larvae treated with goitrogens (substances such as methimazole, potassium percholorate, and 6-n-propyl-2-thiouracil) are devoid of thyroid hormone immunoreactivity. Phenythiourea (PTurea; also commonly known as PTU) is widely used in zebrafish research to suppress pigmentation in developing embryos/fry. PTurea contains a thiocarbamide group that is responsible for goitrogenic activity in methimazole and 6-n-propyl-2-thiouracil. In the present study, we show that commonly used doses of 0.003% PTurea abolish T4 immunoreactivity of the thyroid follicles of zebrafish larvae. As development of the thyroid gland is not affected, these data suggest that PTurea blocks thyroid hormone production. Like other goitrogens, PTurea causes delayed hatching, retardation and malformation of embryos or larvae with increasing doses. At doses of 0.003% PTurea, however, toxic side effects seem to be at a minimum, and the maternal contribution of the hormone might compensate for compromised thyroid function during the first days of development.

Altered Behavioral Performance and Live Imaging of Circuit-Specific Neural Deficiencies in a Zebrafish Model for Psychomotor Retardation

“…In contrast, the expression levels of klf9 , nrgna and HPT-axis-related genes were not changed in 3 dpf mct8 −/− zebrafish embryos; nevertheless, apparent neurological and behavioral deficiencies were found. A possible explanation to the lack of gene alteration in mct8 −/− zebrafish could be the relatively early developmental stage at which the embryos were sampled, when the negative TH feedback loop was still not apparent [18] and endogenous TH production was limited [75]. This unchanged TH status during the early stages of embryonic development might also be the case in MCT8-deficient mammals.…”

Alterations along the Hypothalamic-Pituitary-Thyroid Axis of the Zebrafish (Danio rerio) after Exposure to Propylthiouracil

“…In lower vertebrates such as fish and amphibians, and also in birds, thyroid follicle cells do not merge with the ultimobranchial bodies, which are instead located elsewhere in the body [57–59]. In zebrafish, the first follicle differentiates around 55 hours postfertilization (hpf), and T4-production can be revealed at around 72 hpf [35, 60]. This thyroid follicle formed first corresponds to the most anterior follicle in the adult fish, and new follicles are added more caudally [60].…”

Phenothiourea Sensitizes Zebrafish Cranial Neural Crest and Extraocular Muscle Development to Changes in Retinoic Acid and IGF Signaling

“…PTU at a concentration of 0.003% was previously shown to cause mild teratogenesis and delayed hatching [3], with a dose-dependent response leading to severe malformations and death at higher concentrations [9]. Given the interaction between PTU, retinoic acid and IGF1R in the regulation of craniofacial development, we decided to test whether PTU itself had toxic effects on the neural crest in two well-established transgenic strains, Tg( fli1::EGFP ) or Tg( sox10::EGFP ).…”

“…Previous studies demonstrated that treatment with 0.003% PTU starting at 6 hpf decreased thyroxine (T4) in thyroid follicles of the nasopharynx of 5 days post fertilization (dpf) embryos [9]. The role of thyroid hormone on neural crest development is not well defined, despite the expression of thyroid receptor (TR) αA and αB early in the developing neural crest [23].…”

“…In fact, Karlsson and colleagues found that PTU at a concentration of 70 µM that is added to the media at the 28 somitic stage minimizes mortality and teratogenic effects, but still maintains transparency. Furthermore, PTU at a concentration of 0.003% has been reported to inhibit thyroid function similar to methimazole and potassium percholorate, which are well-known goitrogens [5], [9]. It is unknown whether the toxic effects of PTU are through inhibition of thyroid hormone.…”