Abstract

Fugu (Takifugu rubripes) is a commercially important fish in aquaculture in China, Japan, and Korea. Male fugu are highly prized compared to females because the mature testes are regarded as a delicacy, thus all-male populations are preferred in aquaculture. However, the molecular mechanisms underlying sex differentiation in fugu remain largely unclear. Progestins, which are mediated by the progesterone receptor, can initiate spermatogenesis or ovarian differentiation in teleosts. To explore the effect of progestin blockage on fugu sex differentiation, the antiprogestin mifepristone (RU486) (500 μg/g of feed) was administrated to fugu larvae from 30 to 90 days after hatching (dah). Histological analysis revealed that RU486 treatment resulted in complete masculinization (100 %) of the XX fugu population at both 120 (RU486 withdrawal 30 days) and 150 (RU486 withdrawal 60 days) dah, and RU486-treated XX gonads developed testes-like structure. Gonadal transcriptomic analysis at 90 dah identified 3595 genes that were differentially expressed (DEGs) between the control and treated groups. Among them, the expression of steroid hormone biosynthesis-related genes (e.g., cyp11c1, cyp19a1a, and hsd17b1) and other key genes (e.g., gsdf, dmrt1, and foxl2) were altered in the gonads of RU486-treated groups. Most of the DEGs were enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to sex differentiation, such as neuroactive ligand-receptor interaction, ovarian steroidogenesis, and steroid hormone biosynthesis pathways. The expression of cyp19a1a, foxl2, cyp11c1, gsdf, dmrt3, and dmrt1 at 50, 70, and 90 dah was further assessed. The expression levels of gsdf, dmrt1, and cyp11c1 were increased, and the expression levels of cyp19a1a and foxl2 were decreased in the gonads of XX larvae in RU486 treated groups. These results demonstrated for the first time that RU486 induced masculinization in XX fugu and provided a theoretical basis for further studies of the regulatory role of progestins in sex differentiation in teleosts.