Zhang Weimin, Zhang Yong, Zhang Lihong, Zhao Huihong, Li Xin, Huang He, Lin Haoran
Institute of Aquatic Economic Animals, School of Life Sciences, Zhongshan (Sun Yat-Sen) University, Guangzhou, P.R.China
Mol Reprod Dev. 2007 Jun;74(6):665-73. doi: 10.1002/mrd.20642.
The orange-spotted grouper Epinephelus coioides is a protogynous hermaphroditic fish, but the physiological basis of its sex change remains largely unknown. In the present study, the 2-year-old orange-spotted grouper was induced to change sex precociously by oral administration of 17alpha-methyltestosterone (MT, 50 mg/Kg diet, twice a day at daily ration of 5% bodyweight) for 60 days. The serum testosterone levels were significantly elevated after MT treatment for 20 and 40 days as compared to control, but the levels of serum estradiol (E(2)) remained unchanged. The expression of P450aromA in the gonad significantly decreased after MT treatment for 20, 40, and 60 days. Accordingly, the enzyme activity of gonadal aromatase was also lower. The expression of FSHbeta subunit in the pituitary was significantly decreased after MT treatment for 20 days, but returned to the control levels after 40 and 60 days; however, the expression of LHbeta subunit was not altered significantly by MT treatment. The expression of FTZ-F1 in the gonad also decreased significantly in response to MT treatment for 40 and 60 days, but its expression in the pituitary was not altered significantly. Interestingly, when tested in vitro on ovarian fragments, MT had no direct effect on the expression of P450aromA and FTZ-F1 as well as the activity of gonadal aromatase, suggesting that the inhibition of gonadal P450aromatase and FTZ-F1 by MT may be mediated at upper levels of the brain-pituitary-gonadal axis. Taken together, these results indicated that FSH, P450aromA, FTZ-F1, and serum testosterone are associated with the MT-induced sex change of the orange-spotted grouper, but the cause-effect relationship between these factors and sex change in this species remains to be characterized.
点带石斑鱼（Epinephelus coioides）是一种雌性先熟的雌雄同体鱼类，但其性别转变的生理基础仍 largely unknown。在本研究中，对2龄点带石斑鱼通过口服17α-甲基睾酮（MT，50毫克/千克饲料，每天两次，日投喂量为鱼体重的5%）诱导其早熟性转变60天。与对照组相比，MT处理20天和40天后血清睾酮水平显著升高，但血清雌二醇（E2）水平保持不变。MT处理20天、40天和60天后，性腺中P450aromA的表达显著降低。相应地，性腺芳香化酶的酶活性也较低。MT处理20天后垂体中FSHβ亚基的表达显著降低，但40天和60天后恢复到对照水平；然而，MT处理对LHβ亚基的表达没有显著改变。MT处理40天和60天后，性腺中FTZ-F1的表达也显著降低，但其在垂体中的表达没有显著改变。有趣的是，在体外对卵巢片段进行测试时，MT对P450aromA和FTZ-F1的表达以及性腺芳香化酶的活性没有直接影响，这表明MT对性腺P450芳香化酶和FTZ-F1的抑制可能是在脑-垂体-性腺轴的上游水平介导的。综上所述，这些结果表明FSH、P450aromA、FTZ-F1和血清睾酮与MT诱导的点带石斑鱼性别转变有关，但这些因素与该物种性别转变之间的因果关系仍有待确定。
