Estrogen Signaling Inhibits the Expression of anti-Müllerian hormone (amh) and gonadal-soma-derived factor (gsdf) during the Critical Time of Sexual Fate Determination in Zebrafish

The mechanism of fish gonadal sex differentiation is complex and regulated by multiple factors. It has been widely known that proper steroidogenesis in Leydig cells and sex-related genes in Sertoli cells play important roles in gonadal sex differentiation. In teleosts, the precise interaction of these signals during the sexual fate determination remains elusive, especially their effect on the bi-potential gonad during the critical stage of sexual fate determination. Recently, all-testis phenotypes have been observed in thecyp17a1-deficient zebrafish and common carp, as well as incyp19a1a-deficient zebrafish. By matingcyp17a1-deficient fish with transgenic zebrafishTg(piwil1:EGFP-nanos3UTR), germ cells in the gonads were labelled with enhanced green fluorescent protein (EGFP). We classified thecyp17a1-deficient zebrafish and their control siblings into primordial germ cell (PGC)-rich and -less groups according to the fluorescence area of the EGFP labelling. Intriguingly, the EGFP-labelled bi-potential gonads incyp17a1+/+ fish from the PGC-rich group were significantly larger than those of thecyp17a1−/− fish at 23 days post-fertilization (dpf). Based on the transcriptome analysis, we observed that thecyp17a1-deficient fish of the PGC-rich group displayed a significantly upregulated expression ofamhandgsdfcompared to that of control fish. Likewise, the upregulated expressions ofamhandgsdfwere observed incyp19a1a-deficient fish as examined at 23 dpf. This upregulation ofamhandgsdfcould be repressed by treatment with an exogenous supplement of estradiol. Moreover, tamoxifen, an effective antagonist of both estrogen receptor α and β (ERα and Erβ), upregulates the expression ofamhandgsdfin wild-type (WT) fish. Using thecyp17a1- andcyp19a1a-deficient zebrafish, we provide evidence to show that the upregulated expression ofamhandgsdfdue to the compromised estrogen signaling probably determines their sexual fate towards testis differentiation. Collectively, our data suggest that estrogen signaling inhibits the expression ofamhandgsdfduring the critical time of sexual fate determination, which may broaden the scope of sex steroid hormones in regulating gonadal sex differentiation in fish.