摘要:
鱼类金属硫蛋白(metallothionein, MT)mRNA作为生物标志物已越来越多地应用到水环境重金属污染的监测中,然而重金属胁迫下鱼类MT mRNA表达是否具有性别差异性特征目前尚无相关报道。以海洋模式鱼类-黑点青鳉(Oryzias melastigma)为实验鱼类,首次克隆了其MT基因全长cDNA序列,分析了黑点青鳉MT基因和氨基酸序列特征,然后进一步研究了水体中镉暴露后雌、雄性黑点青鳉肝脏中MT mRNA表达的差异性。结果显示,黑点青鳉MT基因cDNA全长为385 bp,编码60个氨基酸,预测编码的多肽分子量为5 990 Da,含有脊椎动物MT基因特征性序列结构cys-x-cys、cys-x-x-cys和cys-x-cys-cys。镉胁迫下雌、雄性黑点青鳉肝脏MT mRNA表达结果显示,在0.8,4.0和8.0 μg·L-1环境浓度的镉暴露1~7 d条件下,与对照组相比,雄性黑点青鳉在所有的不同暴露浓度和不同暴露时间的实验组中肝脏MT mRNA几乎均被显著性诱导表达;而雌性黑点青鳉只在较高暴露浓度和较长暴露时间的实验组中才被显著性诱导表达,并且MT mRNA的表达水平比雄性低得多。上述研究结果表明,在相同的镉胁迫条件下,雄性黑点青鳉肝脏MT mRNA的表达比雌性更敏感;以黑点青鳉MT mRNA作为生物标志物监测海洋环境重金属污染生物效应状况时,应选择更敏感的雄性黑点青鳉作为监测鱼类。利用生物标志物监测水环境污染物生物效应时,监测动物的性别差异是一个应当考虑的重要因素。
Abstract:
Although fish metallothionein (MT) mRNA as a biomarker has been widely used for monitoring heavy metal pollution in aquatic environment, there were no reports on the gender difference from fish hepatic MT mRNA expression under heavy metal exposure. In present study the full-length cDNA sequence of MT gene was isolated for the first time from medaka (Oryzias melastigma), a marine model fish, and MT gene and amino acid sequences were characterized. Then the gender difference of hepatic MT mRNA expression was studied between male and female medaka after exposure to environmentally relevant concentrations of Cd (0.8, 4.0 and 8.0 μg·L-1). The results indicate that hepatic MT cDNA of the medaka contains 385 bp, coding 60 amino acids with a predicted molecular weight 5 990 Da and containing the specific sequences of MT gene in vertebrates such as cys-x-cys, cys-x-x-cys and cys-x-cys-cys. After exposure to different concentrations of Cd for 1-7 d, hepatic MT mRNA expressions of all male medaka were almost significantly increased when compared with the control group, while the hepatic MT mRNA expressions of female medaka were significantly induced only by higher Cd concentrations with longer exposure time, and the induced levels were much lower than that of the male. By comparison of the gender difference of hepatic MT mRNA expression in the present study it is clear that male medaka is much more sensitive than the female, thus it is better to select the male medaka as a sentinel fish. The results indicate that gender difference is an important factor to be considered when using biomarkers for monitoring the biological effects of aquatic pollutants.
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