Dietary aromatase inhibitor treatment converts XY gsdf homozygous mutants to sub-fertile male in Nile tilapia (Oreochromis niloticus)

Abstract

Gonadal soma-derived factor (gsdf) belongs to the TGF-β superfamily and is critical for sex determination and differentiation in fish. XY gsdf−/− Nile tilapia (Oreochromis niloticus) show male-to-female sex reversal 1 month after hatching (mah) and are infertile at the adult age; however, the functions of gsdf in spermatogenesis in fish are unclear. Herein, XY gsdf−/− Nile tilapia were converted to males with testis by feeding 200 μg/g letrozole (LE), an aromatase inhibitor, from 1 to 4 mah. The testis somatic index of XY gsdf−/− LE fish was significantly lower than that of XY gsdf+/+ LE fish at 6 mah. The artificial fertilization ratio of XY gsdf−/− LE fish sperm (53.22 ± 4.35%) was significantly lower than that of XY gsdf+/+ LE fish (86.33 ± 1.53%), indicating that XY gsdf−/− LE male fish were sub-fertile. Testes of LE XY gsdf−/− and gsdf+/+ fish at 6 mah were used for a transcriptome analysis. Compared with the testis of XY gsdf+/+ LE fish, 1426 and 1654 genes were up-regulated and down-regulated in the testis of XY gsdf−/− LE individuals, respectively. A KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis revealed that the differentially expressed genes (DEGs) were engaged in 21 pathways, including cancer, cell growth and death, and endocrine system pathways. Genes related to steroidogenesis and meiosis, such as cyp19a1a, foxl2, and cyp17a1, were significantly up-regulated, whereas sycp3, dmc1, and aldh1a1 were significantly down-regulated in the testis. In addition, a serum steroid hormone analysis showed that 17β-estradiol and 11-ketotestosterone levels of XY gsdf−/− LE fish were significantly higher and lower than those of XY gsdf+/+ LE fish. These findings demonstrated that endocrine system disruption in XY gsdf−/− LE might explain the decrease in fertility. This research establishes the groundwork for future research on the function of gsdf in spermatogenesis in fish.