性类固醇激素对胡子鲇性分化的影响

EFFECTS OF SEX STEROID HORMONES ON SEX DIFFERENTIATION OF CLARIAS FUSCUS

研究采用组织学和荧光实时定量PCR方法,检测17α-甲基睾酮(17α-MT)和17β-雌二醇(17β-E2)对胡子鲇(Clarias fuscus)性腺组织学、性别比率以及性分化前后脑型芳香化酶基因(Cyp19a1b)和翼状螺旋/叉头转录因子2(Foxl2)基因表达的影响。结果表明:在出膜后2—30日龄,17α-MT(50、100和200μg/L)浸浴、17β-E2(100、200和300μg/g)投喂处理对成活率无显著影响,但中、高剂量(100和200μg/L)17α-MT显著抑制卵巢发育,促进精巢发育,卵巢腔出现时间分别推迟4d和6d,初级卵母细胞出现时间分别推迟8d和9d,而初级精母细胞出现时间则分别提前3d和5d,且雄性率分别达70%和76%,显著高于50μg/L组和对照组(P<0.05)。相反,中、高剂量17β-E2(200和300μg/g)处理使卵巢腔出现时间分别提前2d和3d,初级卵母细胞出现时间分别提前1d和3d,初级精母细胞出现时间分别推迟3d和7d,而雌性率分别达74%和78%,显著高于100μg/g组和对照组(P<0.05)。此外,在性腺分化期,17α-MT促进Cyp19a1b但抑制Foxl2的表达,而17β-E2促进Cyp19a1b和Foxl2的表达。结果显示Cyp19a1b不是引起胡子鲇性分化的直接因素,但可能通过"下丘脑垂体性腺轴"对胡子鲇性分化过程产生间接影响;而Foxl2直接参与胡子鲇的性分化,即17α-MT和17β-E2分别通过抑制和促进Foxl2的表达来影响雌激素的生物合成,从而调控胡子鲇性分化的方向。

Clarias fuscus, a common freshwater fish in China, was selected as our experiment material. Two-day juve- nile C. fuscus was divided into two groups. They were immersed in different doses of 17α-methyltestosterone （50, 100, and 200 μg/L 17α-MT） or fed with 17β-estradiol （100, 200, and 300μg/g 17β-E2） for 30 days. Effects of 17α-MT and 17β-E2 on survival rate, sex ratio, gonad histology, and Foxl2 and Cypl9alb expressions were examined by mor- phologic observation, histology and Real time fluorescent quantitative PCR during its period of sex differentiation （2--30d after hatching）. The results showed that 17α-MT and 17β-E2 had no influence on survival rate but affected sex ratio and the time of gonadal differentiation. Doses of 17α-MT at 100 and 200μg/L produced more males （70% and 76%, respectively） than 50 μg/L 17α-MT （54%） did （P〈0.05）, but no significant difference in sex ratio was observed between the 50 μg/L 17α-MT treated group and the control group （56%）. In addition, the former accelerated the occurrence of primary spermocytes for three and five days, but deferred that of ovarian cavity for four and six days, and primary oo- cytes for eight and nine days, respectively. In contrast, doses of 17β-E2 at 200 and 300 μg/g produced more males （74% and 78%, respectively） than the control group （P〈0.05）, but no significant difference in sex ratio was observed between the 100 μg/g 17β-E2 treated group （66%） and the control group （56%）. Dose of 17β-E2 at 200 and 300 μg/g accelerated the occurrence of ovarian cavity for two and three days, and primary oocytes for one and three days, respectively, but deferred that of primary spermatocytes for three and seven days. The expressions of Foxl2 and Cyplgalb showed that dose of 200 μg/L 17α-MT increased the expression of Cyplgalb but inhibited that of Foxl2. However, dose of 300μg/g 17β-E2 increased the expression both of Cypl9alb and Foxl2. The results suggested that Foxl2 but not Cyplgalb in- volved in mediating sex differentiation directly in C. fuscus, and 17α-MT inhibited but 17β-E2 promoted the expressions of Fox/2 to influence the estrogen biosynthesis, which controlled the sex differentiation. However, Cypl9alb played an indirect role on sex differentiation by acting on the hypothalamic-pituitary-gonadal axis.