用质量浓度为10 mg/kg的17α-甲基睾丸酮(MT)、芳香化酶抑制剂来曲唑(LE)分别对尼罗罗非鱼进行腹腔注射,在注射后12、24、48h和7、14、21 d检测P450arom、1 1β-HSD2、P450scc基因表达量.结果表明,3个基因表达量均先下调,而后回升.注射MT后,最先受到抑制的是P450scc基因,其次是P450arom和11β-HSD2基因.11β-HSD2基因的表达量在注射后7、14、21 d时均与对照组存在显著差异(P＜0.05),其中14 d时的表达量降至最低；P450scc基因的表达量在注射后12、24、48h与对照组存在显著差异(P＜0.05),其中24h时表达量降至最低；P450arom 基因至48h时表达量降至最低,与对照组存在显著差异(P＜0.05).注射LE后,P450arom和P450scc基因的表达较11β-HSD2基因先受到抑制.11β-HSD2基因的表达量在注射后48h,7d、14 d时均与对照组存在显著差异(P＜0.05),其中7d时降至最低；P450scc基因和P450arom基因的表达量均在注射后48h时表达量降至最低,且与对照组存在显著差异(P＜0.05).实验结果表明,MT可能是通过调节P450scc基因水平来降低P450arom的表达量,而LE则通过直接调节P450arom基因的表达进而影响罗非鱼类的性别形成.%Exogenous sex-steroid hormones and Letrozole(LE) ,a potently synthetic nonsteroidal aromatase inhibitor( AI) interfere in the committed step of the endogenous estrogens synthesis. In the present study, the efficacy of 17a-Methyltestosterone( MT)and Letrozole( LE)on gonad steroidogenic enzyme gene expression was evaluated in Nile tilapia(Oreochmmis niloticus). The genetically female tilapia were treated with 17a-Methyltestosterone and Letrozole (at a dose of 10 mg/kg). Expressions of cytochrome P450 aromatase (P450arom) ,1 l(3-hydroxysteroid dehydrogenase type 2(1 1β-HSD2)and cytochrome P450 cholesterol-side-chain-cleavage (P450scc)were examined in the gonads after injection treatment for 12 hours,24 hours,48 hours,7 days, 14 days and 21 days,respectively. The results showed that the levels of P4,50arom ,llβ-HSD2 and P450scc mRNA were decreased rapidly compared to the untreated group firstly, and then the mRNA levels of the three genes increased to the levels of pre-treatment. In the MT-treated group, the mRNA levels of P450scc were first decreased, followed by P450awm and β-HSD2. While in the LE-treated group, the mRNA levels of P45()arom and P450scc were firsted decreased, followed by 11β-H5D2. These results indicated that exogenous androgen or aromatase inhibitor treatment suppresses the expressions of key steroidogenic enzyme genes including P450arom,llβ-HSD2 and P4SCC in the female tilapia. Furthermore, it shows that MT may indirectly inhibit the expression of P450arom, while LE directly inhibits the expression of P450arom, and further influences the sex-inversion of fish. The present study suggests that besides steroid hormones,nonsteroidal compounds,such as aromatase inhibitors,have potential for production of monosex population in tilapia.
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