| Heavy metal refering to the density is more than5g-cm-3metal elements, including cadmium,chromium, mercury, lead, copper, zinc, silver, tin. In recent years, heavy metal pollution has aroused people’s concern. Cadmium (Cd) is one of the important heavy metal pollutants, which has been classified as the most important agricultural environmental pollutants by the U.S. Committee on Agriculture, and is recognized as one of the carcinogenic heavy metal with the features of high toxicity and widely distribution. It can be released into the environment by waste gas, waste water, waste residue and massively accumulate in plant. Human can absorb into the body through the food chain and seriously endanger human health. Former studies have indicated that cadmium can cause oxidative damage of the organisms; its toxic effect also reflected in the epigenetic changes involving in genomic DNA methylation levels, promoter methylation status and methyltransferase activity.The Canton-S Drosophila melanogaster strain was used among our experiments for all analyses. Firstly, we suggest using the fruit fly(Drosophila melanogaster) to study the lifespan and its fertility after different concentrations of cadmium (7.5mg/L,15.0mg/L,30.0mg/L,60.0mg/L) being treated by survival tests and statistical method; Secondly, Real-Time PCR was used to study the effects of different concentrations cadmium on the expression of CuZn-SOD, Mn-SOD, CAT and dDnmt2, dMBD2/3in parental and filial flies at the molecular level. In addition, Real-time PCR was used to characterize dDnmt2and dMBD2/3expression during different development stages in D.melanogaster (0～3h embryo,6～9h embryo,12～18h embryo,18～21h embryo, third instar larvae, pupae, female flies, male flies). The results were as follows:1. Cadmium produced obvious physiological effects on flies. All cadmium treatments shortened the average lifespan, middle lifespan, maximum lifespan in female and male parental Drosophila significantly (P<0.05), with the maximum dose group (60.0mg/L) shortening the life span by7to8times. At the same time, the first generation untreated also appeared phenomenon of shortening life. The results showed that all cadmium treatments tended to shorten the average lifespan, middle lifespan, maximum lifespan in female and male filial Drosophila significantly (P<0.05), with the maximum dose (60.0mg/L) shortening the lifespan by1to1.5times. Therefore, cadmium caused apoptosis in Drosophila and resulted in aging, and the influence of cadmium on the lifespan and fertility in Drosophila can be at least passed on to the first generation.2. Then, the fertility of parental Drosophila being treated with cadmium and filial Drosophila untreated were analyzed separately. Male and female fruit flies both exposed to cadmium after five days, cadmium treatments reduced the number of Drosophila produced offspring (Statistics for ten days) and more distinctly with the increase of cadmium concentration, the concentrations of15.0mg/L,30.0mg/L and60.0mg/L reached a significant level compared with the control (P﹤0.05), indicating that high concentrations of cadmium exposure can significantly reduce the number of hatching in flies, and cadmium can lead to the weakening of Drosophila fertility.3. Real-time PCR was used to study the expression of CuZn-SOD, Mn-SOD, CAT in parental Drosophila after being treated with cadmium and the untreated filial Drosophila. The results showed that cadmium treatments tended to decrease the expression of CuZn-SOD, Mn-SOD, CAT gene with increasing cadmium concentration, with treatment of60.0mg/L cadmium showing the best significant effects (P﹤0.05). The expression of CuZn-SOD, Mn-SOD, CAT in the untreated filial Drosophila tended to decrease with increasing concentration. Thus, it can be seen that the effects of different dosages of cadmium on CuZn-SOD, Mn-SOD, CAT in Drosophila were inactive. Meanwhile, those effects were inheritable to the first finial generation at least, in advance it resulted in fruit flies aging through causing oxidative damage.4. Real-time PCR was used to characterize the expression of dDnmt2and dMBD2/3during different developmental stages of D.melanogaster. The results showed that dDnmt2and dMBD2/3express at all developmental stages (0～3h,6～9h,12～15h,18～21h embryo, larva, pupa, female and male adult) with the highest expression in6-9h and0-3h embryo (P﹤0.05), obviously decreasing in12-15h and18～21h embryo, larva, pupa and adult. The expression of dDnmt2and dMBD2/3were, consisting with DNA methylation of dynamic changes in all developmental stages in D.melanogaste.5. Real-time PCR was used to study the expression of dDnmt2, dMBD2/3in parental Drosophila after being treated with cadmium and the untreated filial Drosophila. The results showed that cadmium treatments tended to increase the expression of dDnmt2, dMBD2/3compared with the control. On the contrary, low dosage cadmium treatment (7.5mg/L) tended to increase the expression dDnmt2, dMBD2/3significantly (P<0.05), moreover, those effects have been appeared in untreated filial Drosophila. Thus cadmium can induced epigenetic changes to fruit flies, and these changes may have inherited to filial Drosophila. |
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