Transgenerational Inheritance And Epigenetic Mechanism Of Cadmium-induced Wing Developmental Defects In Drosophila Melanogaster

Cadmium（Cd）is one of the common heavy metal pollutants,which is easy to accumulate in organisms and cause varying degrees of damage.Cd affects the growth,development,lifespan and reproduction of organisms by inducing oxidative stress and generating ROS,activating cell apoptosis,reducing ATP synthesis and changing mitochondrial permeability,etc.In addition,Cd exposure can also regulate the expression of related genes by inducing changes in epigenetic information such as DNA methylation,histone modification,or miRNA expression profiles,thereby affecting the traits and phenotypes of organisms.More and more evidences show that these epigenetic informations such as DNA methylation,histone modification,non-coding RNA,etc.can escape reprogramming and be transmitted through germline cells to the next generation who have not been directly exposed to the environment,thereby affecting the traits of the offspring,called trans-representative epigenetic.However,the transgenerational inheritance mechanism of epigenetic information is not clear,so this scientific field still needs further in-depth research.In this study,Drosophila melanogaster（Canton-S strain）were selected as the research object.The parent Drosophila（F0）was cultured from the egg on the Cd-containing medium,and subcultured to the F4 generation in the removal of stress conditions to explore the transgenerational inheritance effects of heavy metal Cd induced wing development defects in Drosophila and its epigenetic mechanism have been preliminarily studied.The results of the study are as follows:（1）Cd stress will cause Cd to accumulate in the larvae（F0）,but the Cd accumulated in the parent body cannot be effectively transmitted to the offspring of flies through the reproductive pathway.Compared with the control groups,Cd stress significantly delayed the pupal time and emergence time of Drosophila.And in the removal of stress conditions,the delayed effect of Cd on the developmental time of Drosophila can be transmitted to the offspring for two generations.Cd stress significantly reduced the levels of juvenile hormone and ecdysone in Drosophila.In the removal of stress conditions,this inhibitory effect can be transmitted for two or three generations.（2）Cd-stressed parents（F0）and de-stress offspring（F1-F4）have changed the wing veins of Drosophila,and the wing veins have been broken,merged,missing,and softened;the wing morphology has curled,incompleteness,shrinkage and nicks.And in the removal of stress conditions,significant phenotypic changes can still be observed up to the F4 generation.The statistical results of the wing defect rate show that the wing defect rate gradually decreases with the increase of the generation of Drosophila in the removal of stress conditions,and there is significant difference in the F4 generation,indicating that the effect of Cd on the wing phenotype can be transmitted for at least four generations.（3）After Cd stress,the expression of wing development-related genes shg,omb,F-actin,and Mekk1 in Drosophila（F0）was significantly reduced.And in the removal of stress conditions,the expression inhibition of shg and Mekkl can be transmitted for two generations in the three treatment groups;the expression inhibition of F-actin can be transmitted for two generations in the female treatment groups and the male treatment groups,but it can be transmitted for three generations in the male and female treatment groups;the expression inhibition of omb can be transmitted for two generations in the female treatment groups and can be transmitted for three generations in the male treatment groups and the male and female treatment groups.（4）After Cd stress,the level of H3K4me3 in the third instar larvae of the Drosophila is increased extremely,and the levels of H3K9me3 and H3K27me3 are reduced extremely.The expression of histone methylation-related genes dSet-1,ash1,Lsdl and DNA methylation-related genes dMBD2/3,dDnmt2 increased significantly after Cd stress,indicating that Cd treatment significantly affected the expression of histones methylation and DNA methylation genes in Drosophila.（5）After Cd stress,the level of H3K4me3 in the ovary and testis of the parent Drosophila（F0）increased significantly,and the level of H3K9me3 and H3K27me3 decreased significantly.In the removal of stress conditions,the effect of Cd on the level of H3K4me3 can be transmitted to the F1 generation in the ovary.Cd stress significantly promoted the expression of histone methyltransferase genes ash1,dSet-1 and demethylase gene Lsd1 in the ovary and testis.In the removal of stress conditions,the promotion effect of Cd on ash1 expression can be transmitted for two generations in the ovary and one generation in the testis.The promotion of dSet-1 expression can be transmitted for two generations in the testis and one generation in the ovary.And the promoting of Lsd1 expression can be transmitted for one generation in both the ovary and testis.（6）After Cd stress,the expression level of DNA methyltransferase gene dDnmt2 and methyl binding protein gene dMBD2/3 in the ovary and testis was significantly increased.In the removal of stress conditions,the promotion effect of Cd on dDnmt2 and dMBD2/3 expression can be transmitted for two generations in the ovary and one generation in the testis.In summary,the heavy metal Cd can induce wing development defects in Drosophila and shown as the transgenerational inheritance.It is speculated that Cd may regulate the expression of wing development-related genes by inducing changes in DNA methylation or histone methylation modification in the promoter regions of these genes,thereby affecting the phenotype of wings.And these changes in epigenetic information are transmitted to the offspring through germline cells,thereby mediating the transgenerational inheritance of wing development defects in Drosophila.In conclusion,this study initially explored the possible mechanism of the transgenerational inheritance of cadmium-induced wing development defects in Drosophila from the two epigenetic pathways of histone methylation modification and DNA methylation,which has laid a certain foundation in the transgenerational mechanism of epigenetic information.