Estrogen signaling counteracts androgen/Ar-mediated suppression of foxl2 expression and ovarian differentiation during sexual fate determination in zebrafish.

In teleosts, gonadal differentiation is a complex and precisely controlled process that requires a proper balance of androgen and estrogen signaling activities. However, the interaction between these steroid signals remains unclear, particularly during the critical stage that determines the sexual fate of the bipotential gonad in zebrafish. In the present study, we investigated the expression of cyp19a1a and foxl2, the amount of primordial germ cells (PGCs), and the status of ovarian differentiation, in response to 17β-estradiol (E2) and 11-ketotestosterone (11-KT) using the Tg(piwil1:EGFP-nanos3'UTR) zebrafish line. The expression of cyp19a1a, foxl2a, foxl2b and foxl2l was significantly higher in the PGC-rich group reared in control medium (CM) at 23 days post-fertilization (dpf) than in the PGC-less group. Treatment with E2 promoted ovarian differentiation in 83% of individuals and increased foxl2 expression. Conversely, 11-KT treatment caused testis-biased differentiation in 86% of individuals and decreased foxl2 and cyp19a1a expression at the same stage. Significant differences were observed when the number of PGCs labeled with green fluorescent protein (GFP) in E2- and 11-KT-treated fish were compared. Furthermore, the inhibitory effect of 11-KT on the expression of foxl2 and ovarian differentiation, which was Androgen receptor (Ar)-dependent, could be completely counteracted in wild-type (WT) fish when E2 was co-administered. In summary, our results showed that estrogen signaling is sufficient to counteract the effect of androgen/Ar signaling on upregulating foxl2 expression and promoting ovarian development and differentiation.