Effects Of Heavy Metal Cadmium On The Expression Of Metallothionein In Drosophila

Cadmium (Cd), one of the major heavy metal pollutants in the environment, was world-widely recognized as carcinogenic heavy metals with high toxicity and strong accumulation, and can accumulate in organisms by enrichment. Numerous studies have shown that cadmium can cause oxidative damage, cell apoptosis, and organism tissue necrosis as well as suppressing normal growth and development of organisms. When creatures are under the stress of heavy metal, the body itself will also produce the corresponding mechanisms to reduce the damage caused by heavy metal and excrete harmful metal out of body to maintain body’s homeostasis. Metallothionein (MT) is non-enzyme protein produced by body itself to adjust the steady state of metal ions and reduce the toxicity when under the threat of heavy metal. It has the same function of detoxication as HMT-1(Heavy metal tolerance factor1). Insects are the most widely distributed animal groups in nature which are highly susceptible to such environmental factors as heavy metals.Drosophila melanogaster, which belongs to Drosophila, fruit fly, diptera, insecta, arthropoda, is one of important model organisms in biology research. On the basis of previous researches, the present study chooses Drosophila melanogaster Canton-S strain as experiment material, applies Real-Time PCR. method, and tests expression differences of Drosophila metallothionein genes including MtnB, MtnC, MtnD, MtnE and metal tolerance factor gene Hmt-1mRNA, and tests the change of metallothionein content under the stress of cadmium by using the method of cadmium saturation. The related responsive reaction of Drosophila under the stress of heavy metal cadmium is studied from physiological and molecular level. The thesis is divided into three parts:Firstly, in order to study Drosophila melanogaster’ the sensitivity to heavy metal cadmium, evaluate cadmium toxicity in the body, and provide a basis for experimental concentration in subsequent trials, the study is carried out by the method of chronic toxication of cadmium, feeding flies with different concentration of cadmium, and sum up the death number of Drosophila melanogaster and calculate fruit flies median lethal concentration10d later after cadmium treatment. The results show that after different concentrations of cadmium treatment, the obvious physiological effects happen on the male and female fruit flies, which could shorten fruit flies’life. After the determination of cadmium stresses flies10d, its median lethal concentration was52.0mg/L, providing the basis for the later research on flies detoxification mechanism under the stress of cadmium.Secondly, in order to study the influence of heavy metal cadmium with different concentration on fruit flies and related gene expression of metallothionein in reproduction system, the study applies Real-Time PCR method to study expression differences of related gene expression of metallothionein MtnB, MtnC, MtnD, MtnE and expression differences of metal tolerance factor1gene after cadmium treatment of different mass concentration (6.5mg/L,13.0mg/L,26.0mg/L,52.0mg/L) and discusses the influence of heavy metal cadmium on related gene expression in the reproduction system, removal reproductive system and overall fruit flies. The results show that the cadmium exposure caused related gene expression of metallothionein to rise in expression of mRNA level and be obviously dose-dependent. And there is a sharp difference in expression of fruit flies metallothionein gene in the different organizations compared with control group, at the same time, within a certain range, Hmt-1gene expression will rise with the concentration of the heavy metal cadmium, and there is the dose-dependent effect.Thirdly, in order to study the content change of fruit flies metallothionein under cadmium stress, and to provide the basis for study on the flies’own detoxification mechanism under cadmium stress, this study adopts the cadmium saturation method to test content change of fruit flies metallothionein under cadmium stress in different mass concentrations (6.5mg/L,13.0mg/L,26.0mg/L,52.0mg/L). The results show that metallothionein content rises significantly after male and female fruit flies are treated under cadmium stress. Besides, compared with the control group, there is extremely significant difference and a dose-dependence. The results show that when the bodies are under cadmium stress, metallothionein content in flies’body can be used as a kind of evaluation standard for toxicity effect.To sum up, the heavy metal cadmium in the environment can lead to Drosophila melanogaster s excessive accumulation of growth, and shorten life span of Drosophila melanogaster. The stress of heavy metal cadmium leads to an increase in mRNA, the related gene of metallothionein, in female and male Drosophila melanogaster, which shows that Drosophila melanogaster can protect its body by responsive physiology phenomenon such as expression of metallothionein and metal tolerance factors. The study lays a experimental foundation for the research on the toxic effect produced by flies and their mechanism under the stress of heavy metal cadmium, provides an important experimental and theoretical basis for the research on detoxification mechanism of organism, and supplies experimental basis for the assessment of heavy metal pollutants and study on the molecular mechanisms causing human disease.