17α-甲基睾酮对斑马鱼肝脏vtg基因mRNA表达的影响
2016-11-01刘少贞吕文琪吕小也
刘少贞,吕文琪,吕小也
(山西农业大学动物科技学院,山西 太谷 030801)
17α-甲基睾酮对斑马鱼肝脏vtg基因mRNA表达的影响
刘少贞,吕文琪,吕小也
(山西农业大学动物科技学院,山西 太谷 030801)
为评价17α-甲基睾酮(17α-methyltestosterone,MT)对斑马鱼肝脏vtg基因mRNA表达的影响,利用MT处理斑马鱼雌、雄鱼7 d,采用实时定量PCR(qRT-PCR)检测雌、雄鱼肝脏中vtg基因mRNA的表达量。结果显示,MT处理雌鱼7 d,25 ng/L处理组肝脏vtg基因的表达量显著降低(P<0.05),50 ng/L和100 ng/L的MT处理组肝脏vtg基因mRNA表达量极显著降低 (P<0.01);MT处理雄鱼7 d,25 ng/L处理组肝脏vtg基因mRNA表达量与对照组相比差异不显著 (P>0.05),50 ng/L的MT处理组肝脏vtg基因mRNA表达量显著升高 (P<0.05),100 ng/L的MT处理组肝脏vtg基因mRNA表达量极显著升高(P<0.01)。斑马鱼肝脏vtg基因对MT比较敏感,可以作为监测环境中MT的生物标志物。
17α-甲基睾酮;斑马鱼;肝脏;vtg
环境中的雄激素主要有3个来源:造纸厂生产过程中会产生雄激素,随着造纸厂污水的排放从而进入环境中;污水处理厂会产生一定量的雄激素;农业活动中会有一定量的雄激素排放到环境中[1]。17α-甲基睾酮(17α-methyltestosterone,MT)是天然雄激素睾酮的17-α位甲基衍生物,也是一种重要的环境内分泌干扰物。研究表明,MT能够显著降低底鱂雄鱼体内的睾酮(T)和11-酮基睾酮(11-KT)的含量,并能够显著提高底鱂雌鱼卵巢中芳香化酶基因的表达[1]。雌鱼对MT的敏感程度显著高于雄鱼[2]。MT在鱼类体内会被芳香化成 17α-甲雌二醇,从而发挥雌激素功能[3]。因此,暴露在含有MT环境中的雌鱼,其卵巢中雌激素的分泌量会降低[4]。雄激素在体内的作用机理尚未明确,但由雄激素受体AR介导的外源性激素作用途径被多数学者认可[5]。卵黄蛋白原(vitellogenin,VTG)是卵黄蛋白的前体,其生成是通过下丘脑—垂体—性腺(hypothalamicpituitary-gonadal,HPG)轴激活雌激素受体来实现的[6]。在雄鱼和幼鱼中,VTG的生产可以作为生物标志物来检测环境中的雌激素[7]。该研究利用MT暴露斑马鱼,采用qRT-PCR的方法检测了肝脏vtg基因mRNA表达的变化情况,旨在为阐明MT在斑马鱼体内的作用机理提供理论基础。
1 材料与方法
1.1 实验动物 斑马鱼成鱼,购自山西省太谷县东苑水族同一批繁殖的4月龄斑马鱼,在实验室暂养2周后进行暴露试验。
1.2 主要仪器和药品 17α-甲基睾酮(Sigma),Trizol Reagent、RACE 试 剂 盒 (Invitrogen),Revert AidTMFirst Strand cDNA Synthesis Kit(Fermentas),6×Loading Buffer、Taq DNA 聚合酶(Sigma),dNTP mix、DNA Marker Ladder (DL 2 000)、SYBR Premix Ex TaqTMⅡ(TaKaRa)。
微量移液器(Eppendorf),VORTEX-6 漩涡混合器 (上海川翔生物科技有限公司),超低温冰箱Fouma 700 SERIES(Thermo),紫外分光光度计(NanoPhotometer),冷冻低温离心机(Pimor),PCR扩增仪(Bio-Rad),实时荧光定量PCR仪。
1.3 MT处理斑马鱼 斑马鱼成鱼在实验室内暂养2周后进行暴露试验,MT暴露分为3个浓度处理组,分别为 25、50、100 ng/L,按 0.001%(V/V)的浓度分别溶解在无水乙醇中,对照组用0.001%(V/V)无水乙醇水溶液处理,MT暴露时间为7 d。每个试验组和对照组各15尾鱼,雌、雄鱼分开暴露。每天定时、定量饲喂饲料。试验组和对照组的8个鱼缸中水的体积均为30 L,采用半静水暴露方法[8],每天定时更换一半体积的水及相应的暴露物质。光照周期为 14 h/10 h(明/暗),水温控制在(25±2)℃。
1.4 总RNA的提取、检测和反转录 测量MT暴露后斑马鱼的生物学指标,然后进行解剖,取其性腺和肝脏。应用Trizol一步法进行总RNA的提取,利用1%的琼脂糖凝胶电泳检测其完整性。反转录按照Revert AidTMFirst Strand cDNA Synthesis Kit(Fermentas,Canada)试剂盒的说明书进行操作。
1.5 qRT-PCR 采用实时荧光定量PCR(qRTPCR)技术检测雌、雄斑马鱼暴露MT 7 d后肝脏中vtg 基因的 mRNA 表达量[9]。
1.6 数据分析 采用 2-ΔΔCt对获得的 qRT-PCR试验数据进行处理。试验结果以Mean±SD表示。运用SPSS统计学分析软件中的单因素方差分析 (Oneway ANOVA)和最小显著差异法(LSD)进行显著性分析,P<0.05时认为差异显著,P<0.01时认为差异极显著。
图1 MT暴露7 d后斑马鱼肝脏vtg基因mRNA表达量的变化情况
2 结果与分析
该研究利用qRT-PCR方法检测了斑马鱼雌、雄鱼MT暴露7 d后,其肝脏中vtg基因mRNA的表达变化情况。结果表明,与对照组相比,25、50、100 ng/L的MT暴露7 d后,雌鱼肝脏中vtg基因的mRNA 表达均被显著抑制(P<0.05 或 P<0.01),尤其是50 ng/L的MT,其对雌鱼肝脏中vtg基因mRNA的表达抑制作用最为显著(P<0.01,见图1A);对于斑马鱼雄鱼,50 ng/L的MT暴露7 d后,雄鱼肝脏vtg基因的 mRNA表达量显著升高 (P<0.05),100 ng/L的MT暴露7 d后,雄鱼肝脏vtg基因mRNA的表达量极显著升高(P<0.01),而25 ng/L的MT暴露7 d后,雄鱼肝脏vtg基因的mRNA表达未受到显著影响(P>0.05,见图 1B)。
3 讨论
该试验研究了MT处理斑马鱼成鱼7 d后雌、雄鱼肝脏vtg基因mRNA表达量的变化情况,结果表明,利用50 ng/L或100 ng/L的MT处理7 d后,可引起斑马鱼雄鱼肝脏中vtg基因mRNA的表达量显著升高(P<0.05或 P<0.01),提示雄激素可能参与雄鱼肝脏VTG的合成。研究表明,利用4.5 ng/L的MT暴露斑马鱼雄鱼7 d后,其肝脏VTG的含量显著升高[10]。 高浓度的 MT 暴露(0.2~200 μg/L)同样可以使黑头软口鲦雄鱼体内的VTG含量显著升高[3,11]。 有学者推测,MT 之所以可以使鱼类体内的VTG含量升高,可能是由于MT被芳香化成了甲雌二醇(ME2),随后,ME2作为雌激素通过肝脏中的雌激素受体使得vtg基因的表达升高[3]。在该研究中,利用25~100 ng/L的MT暴露7 d后,雌鱼肝脏中vtg基因mRNA的表达量显著下调 (P<0.05或P<0.01),该结果与大多数已经报道的相关研究结果一致。Seki等[12]将日本青鱂幼鱼从孵化开始一直暴露于 MT(0.35~9.98 ng/L)中直至孵化后 60 d,结果表明,雌鱼体内的VTG水平受到显著抑制。利用MT处理罗非鱼雌鱼后,其肝脏中vtg基因的mRNA表达水平和VTG的水平均下降[13]。斑马鱼幼鱼暴露于100、260、500 ng/L的MT后,雌鱼体内的VTG含量显著降低[14]。 Korsgaard[15]研究表明,100 ng/L的MT能够显著降低绵鳚雌鱼体内的VTG水平。但是,也有学者研究发现,利用MT(0.2 mg/L和2 mg/L)暴露黑头软口鲦雌鱼21 d,其体内VTG含量呈升高趋势[11],推测这可能是由于种间差异造成的VTG/vtg对MT有不同的响应。综上所述,50 ng/L的MT对斑马鱼雌鱼肝脏vtg基因mRNA的表达产生最为显著的影响,可以作为检测环境中MT的生物标志物。
[1]RUTHERFORD R,LISTER A,HEWITT L M,et al.Effects of model aromatizable (17α-methyltestosterone)and nonaromatizable(5α-dihydrotestosterone) androgens on the adult mummichog (Fundulus heteroclitus) in a short-term reproductive endocrine bioassay[J].Comp Biochem Physiol C Toxicol Pharmacol,2015,170:8-18.
[2]SHARPE L,MACLATCHYD,COURTENAYS,etal.Effects of a model androgen (methyltestosterone) and a model anti-androgen (cyproterone acetate)on reproductive endpoints in a short-term adult mummichog(Fundulus heteroclitus)bioassay [J].Aquat Toxicol,2004,67 (3):203-215.
[3]HORNUNG M,JENSEN K,KORTE J,et al.Mechanistic basis for estrogenic effects in fathead minnow(Pimephales promelas)followingexposuretotheandrogen 17α -methyltestosterone:conversion of 17α -methyltestosterone to 17α-methylestradiol [J].Aquat Toxicol,2004,66(1):15-23.
[4]LI G L,LIU X C,LIN H R.Effects of aromatizable and nonaromatizable androgens on the sex inversion of redspotted grouper (Epinephelus akaara) [J].Fish Physiol Biochem,2006,32(1):25-33.
[5]MARTYNIUK C J,DENSLOW N D.Exploring androgenrelated pathways in teleost fish using transcriptomics and proteomics[J].Integr Comp Biol,2012,52(5):695-704.
[6]ANKLEY G T,JENSEN K M,DURHAN E J,et al.Effects of two fungicides with multiple modes of action on reproductive endocrine function in the fathead minnow(Pimephales promelas)[J].Toxicol Sci,2005,86 (2):300-308.
[7]HUTCHINSON T H,ANKLEY G T,SEGNER H,et al.Screening and testing for endocrine disruption in fishbiomarkers as signposts not traffic lights,in risk assessment [J].Environ Health Perspect, 2006,114(Suppl 1):106-114.
[8]LIU S,WANG L,QIN F,et al.Gonadal development and transcript profiling of steroidogenic enzymes in response to 17α-methyltestosterone in the rare minnow Gobiocypris rarus[J].J Steroid Biochem,2014,14:223-232.
[9]ZHANG W,SHENG N,WANG M,et al.Zebrafish reproductive toxicity induced by chronic perfluorononanoate exposure[J].Aquat Toxicol,2016,175:269-276.
[10]ANDERSEN L,GOTO-KAZETO R,TRANT J M,et al.Short-term exposure to low concentrations of the synthetic androgen methyltestosterone affects vitellogenin and steroid levels in adult male zebrafish(Danio rerio)[J].Aquat Toxicol,2006,76(3/4):343-352.
[11]ANKLEY G T,JENSEN K M,KAHLM D,etal.Description and evaluation of a short-term reproductive test with the fathead minnow (Pimephales promelas)[J].Environ Toxicol Chem,2001,20(6):1276-1290.
[12]SEKI M,YOKOTA H,MATSUBARA H,et al.Fish full life-cycle testing for androgen methyltestosterone on medaka(Oryzias latipes) [J].Environ Toxicol Chem,2004,23(3):774-781.
[13]LAZIER C B,LANGLEY S,RAMSEY N B,etal.Androgen inhibition of vitellogenin gene expression in tilapia(Oreochromis niloticus)[J].Gen Comp Endocrinol,1996,104(3):321-329.
[14]ÖRN S,HOLBECH H,MADSEN T H,et al.Gonad development and vitellogenin production in zebrafish(Danio rerio)exposed to ethinylestradiol and methyl testosterone[J].Aquat Toxicol,2003,65 (4):397-411.
[15]KORSGAARD B.Effects of the model androgen methyltestosterone on vitellogenin in male and female eelpout,Zoarces viviparus(L) [J].Mar Environ Res,2006,62(Suppl):S205-S210.
Effect of 17α-methyltestosterone(MT)on mRNA Expression of vtg Gene in Liver of Brachydanio rerio
LIU Shao-zhen,LÜ Wen-qi,LÜ Xiao-ye
(College of Animal Science and Veterinary Medicine,Shanxi Agricultural University,Taigu 030801,China)
This study aimed to evaluate the effect of 17α-methyltestosterone(MT) on mRNA expression of vtg gene in liver of Brachydanio rerio.The male and female Brachydanio rerio were treated with different concentrations of MT for 7 days,and qRTPCR assay were used to determine the mRNA expression of vtg gene in their livers.For female Brachydanio rerio,the mRNA expression of vtg gene in 25 ng/L MT treatment group was significantly reduced after 7 days (P<0.05),and that in 50 and 100 ng/L MT treatment group was extremely significantly reduced(P<0.01).For male Brachydanio rerio,there were no significant differences in the mRNA expression of vtg gene between 25 ng/L MT treatment group and control group after 7 days (P>0.05).However,the mRNA expression of vtg gene in 50 and 100 ng/L MT treatment groups was significantly and extremely significantly increased (P<0.05 and P<0.01),respectively.The results suggest that the vtg gene in liver of Brachydanio rerio is sensitive to MT,and it is potential to serve as a biomarker for MT monitoring in environment.
17α-methyltestosterone;Brachydanio rerio;liver;vtg
X171.5
A文章顺序编号:1672-5190(2016)05-0009-03
2016-05-03
项目来源:山西农业大学引进人才博士科研启动费项目(2014YJ08)。
刘少贞(1983—),女,讲师,博士,主要研究方向为环境毒理学。
(责任编辑:赵俊利)