AUTHOR=Yuan Zhen , Shen Xufang , Yan Hongwei , Jiang Jieming , Liu Binwei , Zhang Lei , Wu Yumeng , Liu Ying , Liu Qi 

TITLE=Effects of the Thyroid Endocrine System on Gonadal Sex Ratios and Sex-Related Gene Expression in the Pufferfish Takifugu rubripes

JOURNAL=Frontiers in Endocrinology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2021.674954

DOI=10.3389/fendo.2021.674954

ISSN=1664-2392

ABSTRACT=<p>To examine the effect and mechanism of thyroid hormone on gonadal sex differentiation, <italic>Takifugu rubripes</italic> larvae were treated with goitrogen (methimazole, MET, 1000 μg/g), and thyroxine (T4, 2nM) from 25 to 80 days after hatching (dah). Gonadal histology and sex ratios of fish were then determined at 80 dah. MET treatment induced masculinization, but T4 treatment did not induce feminization in <italic>T. rubripes</italic> larvae. Transcriptomic analysis of gonads at 80 dah was then conducted. Among the large number of differentially expressed genes between the groups, the expression of <italic>foxl2</italic>, <italic>cyp19a1a</italic>, and <italic>dmrt1</italic> was altered. The expression of <italic>foxl2</italic>, <italic>cyp19a1a</italic>, <italic>dmrt1</italic> and <italic>gsdf</italic> at 25, 40, 55 days after treatment (dat) was further analyzed by qPCR. MET treatment suppressed the expression of <italic>foxl2</italic> and <italic>cyp19a1a</italic>, and induced the expression of <italic>dmrt1</italic> in genetic females (<italic>p</italic> &lt; 0.05). Additionally, T4 treatment induced an increase in the expression of <italic>cyp19a1a</italic> in genetic XY gonads only at 25 dat. However, the increase in <italic>cyp19a1a</italic> expression did not continue to 40 and 55 dat. This may explain why feminization of larvae was not found in the T4-treated group. Thus, the present study provides the first evidence that MET treatment causes masculinization in teleost fish. The effects of MET-induced masculinization in <italic>T. rubripes</italic> may act primarily <italic>via</italic> suppression of the expression of <italic>foxl2</italic> and <italic>cyp19a1a</italic>, and stimulation of the expression of <italic>dmrt1</italic>. Moreover, the effects of higher concentrations of T4 or different concentrations of T3, on sex differentiation require further testing.</p>