Development and gene expression analysis of gonad during 17 alpha-methyltestosterone-induced sex reversal in mandarin fish (Siniperca chuatsi)

Mandarin fish (Siniperca chuatsi) is one of the most important commercial fish in aquaculture in the world. As females grow faster than males, the cultivation of all-female mandarin fish has great economic value and commercial prospects. However, little is known about the molecular mechanism of the early gonad development and sex reversal of mandarin fish. In this study, histological methods and transcriptome sequencing techniques were used to study the early gonadal development and gene expression pattern of genetically female (XX) mandarin fish during MT-induced masculinization. The histological results showed that the labile period of sex differentiation of XX mandarin fish was before 36 dpf and MT treatment before this period could induce complete sex reversal. The transcriptome results showed that the expression levels of a few female-related genes were down-regulated by MT during the morphological differentiation stage to cytological differentiation stage of XX gonad, such as cyp19a1a, foxl2, foxl3, hsd17b1, figla, gdf9, bmp15 and beta-catenin, suggesting that the changes of these genes may determine the direction of sex differentiation in mandarin fish. In addition, MT also activated the expression of some male-related genes, such as dmrt1, hsd17b3, hsd11b2, cyp11a1, cyp11b, amh, amhr2, sox9 and gsdf. Some of these genes were activated during spermatogenesis stage, suggesting that the up-regulation of these male-related genes may be the result of sex differentiation rather than the cause. The qRT-PCR results of eight randomly selected differentially expressed genes were basically consistent with the transcriptome results, which proved that the transcriptome data were reliable. These results indicated that the expression of genes related to estrogen synthesis in early development stage may play a decisive role in the direction of sex differentiation in mandarin fish.