Abstract
BackgroundEarly sex differentiation genes of zebrafish remain an unsolved mystery due to the difficulty to distinguish the sex of juvenile zebrafish. However, aromatase inhibitors (AIs) could direct juvenile zebrafish sex differentiation to male and even induce ovary-to-testis reversal in adult zebrafish.ResultsIn order to determine the transcriptomic changes of sex differentiation in juvenile zebrafish and early sex-reversal in adult zebrafish, we sequenced the transcriptomes of juvenile and adult zebrafish treated with AI exemestane (EM) for 32 days, when juvenile zebrafish sex differentiation finished. EM treatment in females up-regulated the expression of genes involved in estrogen metabolic process, female gamete generation and oogenesis, including gsdf, macf1a and paqr5a, while down-regulated the expression of vitellogenin (vtg) genes, including vtg6, vtg2, vtg4, and vtg7 due to the lower level of Estradiol (E2). Furthermore, EM-juveniles showed up-regulation in genes related to cell death and apoptosis, such as bcl2l16 and anax1c, while the control-juveniles exhibited up-regulation of genes involved in positive regulation of reproductive process and oocyte differentiation such as zar1 and zpcx. Moreover, EM-females showed higher enrichment than control females in genes involved in VEGF signaling pathway, glycosaminoglycan degradation, hedgehog signaling pathway, GnRH signaling pathway and steroid hormone biosynthesis.ConclusionsOur study shows anti-masculinization in EM-treated adult females but not in EM-treated juveniles. This may be responsible for the lower sex plasticity in adults than juveniles.
Highlights
Sex differentiation genes of zebrafish remain an unsolved mystery due to the difficulty to distinguish the sex of juvenile zebrafish
Presence of atretic follicles in adult female zebrafish after 32-day EM treatment The effectiveness of EM was pre-tested through measuring vtg1 expression levels of the samples after EM treatment by Quantitative real-time PCR (qRT-PCR) [17]
We found that the gonads of adult female zebrafish was testis instead of ovary (Additional file 3), indicating the femaleto-male sex reversal induced by our EM treatment
Summary
Sex differentiation genes of zebrafish remain an unsolved mystery due to the difficulty to distinguish the sex of juvenile zebrafish. Aromatase inhibitors (AIs) could direct juvenile zebrafish sex differentiation to male and even induce ovary-to-testis reversal in adult zebrafish. Zebrafish is an important model species for biomedical research, its early sex differentiation genes are still unclear. As the sex of zebrafish cannot be clearly determined by morphology until 3 months post fertilization as adults, the early sex differentiation genes cannot be identified directly by comparison of genes between juvenile females and males [4]. Estrogen and androgen are important to female and male differentiation, respectively. Aromatase inhibitors (AIs) can induce male differentiation by decreasing estrogen levels [7] while increasing androgen levels in a wide variety of fish species [8, 9]. Early sex differentiation genes can be identified through a comparison of juvenile
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