Gene expression profiling of key genes in hypothalamus-pituitary-gonad axis of rare minnow Gobiocypris rarus in response to EE2.

The 17α-ethinylestradiol (EE2), which could induce estrogenic effects, is found in different aquatic systems. The current study aimed to assess in vivo effects of short-term EE2 exposure on the transcriptional activity of genes in the brain and gonad tissues in order to characterize the mode of action of EE2 on the hypothalamus-pituitary-gonad axis in rare minnow (Gobiocypris rarus). The full length cDNAs of fshβ, lhβ, fshr and lhr were first characterized in G. rarus. The homology and phylogenetic analyses of the amino acid sequences revealed that these four genes share high identity in cyprinid fish. The tissue distribution analysis by qRT-PCR showed that fshβ and lhβ were mainly expressed in the brain and fshr and lhr were mainly expressed in gonads. Adult G. rarus was exposed to EE2 at 1, 5, 25 and 125 ng/L for 3 and 6 days and the expression of brain cyp19a1b, fshβ and lhβ, estrogen receptors (esr1, esr2a, and esr2b) and gonadal fshr, lhr and cyp19a1a were assessed. Cyp19a1b was significantly up-regulated in the brains of female exposed to EE2 at 1-125 ng/L for 6 days. The brain lhβ, but not fshβ was strongly suppressed in most EE2 exposure groups of both sexes. The brain esr2b was inhibited in both sexes exposed to EE2 at all of the four concentrations for 6 days. Esr2a was up-regulated in the females by 6-day EE2 treatment at 1 and 25 ng/L. The high responsiveness of brain lhβ and esr2s to EE2 and their significant correlation in both sexes suggested that the transcriptional activity of Esr2s could play key roles in modulation of lhβ expression via direct action on gonadotropic cells in response to EE2. In gonads, fshr was strongly inhibited by EE2 in males, while lhr was significantly stimulated by EE2 in females. Cyp19a1a was inhibited by EE2 in both sexes. The positive correlations of gene expressions of both fshr and lhr with cyp19a1a in testes suggest that the suppression of 17α-estradiol (E2) synthesis in testis by exogenous estrogen could mediate via both Fsh/Fshr and Lh/Lhr signaling in male G. rarus.