In vivo and in vitro inhibitory action of 17β-estradiol and environmental estrogen 4-nonylphenol on gonad-inhibiting hormone (GIH) expression in the eyestalks of Litopenaeus vannamei

The gonad-inhibiting hormone (GIH) belongs to a neuropeptide family synthesized and released in an X-organ sinus gland complex of crustacean eyestalks. GIH inhibits crustacean ovarian maturation by suppressing vitellogenin (Vtg) synthesis, whereas estrogen is responsible for the stimulation of vitellogenesis (not established). In this study, the effects of 17 beta-estradiol (E-2, 10(-6) M), estrogen receptor antagonist tamoxifen (TAM, 10(-6), 10(-7), and 10(-8) M), and the environmental estrogen nonylphenol (NP, 1 mu g/L and 100 mu g/L) on LvGIH expression in the eyestalks of shrimp were determined by quantitative real-time PCR. Results showed that LvGIH expression decreased significantly during the L. vannamei ovarian maturation cycle. E-2 and NP significantly reduced LvGIH transcripts in vivo, but TAM neutralized the inhibitory action of E-2 in a dose-dependent manner (P < 0.05). In addition, the LvGIH expression levels decreased significantly in a time-dependent manner (P < 0.05) when ovary fragments were cultured in vitro with E-2. The results of this study suggested that estrogen regulates GIH expression in L. vannamei eyestalks. E-2 promoted ovarian development not only by directly upregulating vitellogenesis in the hepatopancreas, but it was also capable of downregulating LvGIH expression, which indirectly resulted in the stimulation of L. vannamei vitellogenesis.