Effects Of Cadmium On The Early Development Of Mouse Embryos

In recent years,environmental health problems caused by cadmium pollution have attracted increasing attention with the development of heavy industry.Long-term excessive intake of cadmium can not only cause damage to various tissues and organs including bones,liver and kidneys,but also damage the reproductive system,such as affecting spermatogenesis,reducing the quality of oocytes,and changing the ultrastructure of the placenta.However,the harm of environmental cadmium exposure to early embryos is not completely clear.In this study,mice were as model to study the effect of cadmium exposure on early embryonic development.1 Effects of cadmium on the development of mice oocytes and early embryosOur previous studies have shown that pregnant mice drinking cadmium-containing water can interfere the normal meiotic maturation process of oocytes and early embryonic development.In order to further study whether cadmium affects oocytes and embryos by destroying the microenvironment of the reproductive system,or directly acts on the oocytes and early embryos themselves to exert toxic effects,we studied the effects of cadmium during vitro culture environment.After superovulation of female mice,the oocytes were collected and were cultured in vitro with 10,25 and 50 μM cadmium.The results showed that with the increase of cadmium concentration,the proportion of immature oocytes(MI)increased,the proportion of mature oocytes(MⅡ)decreased,and there was a significant difference compared with the control group at 50 μM cadmium concentration.The results suggest that cadmium exposure does not inhibit the resume of oocyte meiosis,but disturbs with the normal completion of the first meiosis.This result is consistent with our previous studies in vivo.We further collected the fertilized eggs and cultured in vitro with 5 μM and 10 μM cadmium.The results suggest that compared with the control group,with the increase of cadmium concentration and culture time,the growth speed of early embryos slowed down,the blastocyst development rate reduced and the embryos death rate increased.The results suggest that cadmium exposure can cause damage to early embryos and reduce their developmental quality.In conclusion,cadmium can directly act on oocytes and early embryos themselves to exert toxic effects,interfere with the meiotic maturation process of oocytes and damage early embryonic development.2 Effects of cadmium on the DNA damage and oxidative stress of mice early embryosTo further study the mechanism of cadmium damage the early embryonic development,we examined the effect of cadmium on DNA damage and repair levels during early embryonic development in vivo.Pregnant mice were free to drink cadmium-containing water(64 mg/L)for 2 days and collected embryos.The expression level and lacation of DNA damage marker protein(y-H2AX)in early embryos was detected by immunofluorescence;the expression level of gene related to DNA damage and repair was detected by qRT-PCR.The results showed that,compared with the control group,the relative fluorescence intensity of γ-H2AX in the cadmium-treated group was significantly increased,and the mRNA levels of PARP1,RAD51 and XRCC6 was significantly decreased in the cadmium-treated group,but the mRNA levels of ATM,BRCA1 and PRKDC were not significantly changed between two groups.The results indicate that cadmium exposure can cause DNA damage and inhibit the expression of some DNA repair genes in early embryos of mice,this may be the reason of why cadmium can influence the development of early embryos.It has shown that there is a close relationship between DNA damage and oxidative stress caused by ROS.We further examined the effect of cadmium on ROS levels during early embryonic development in vivo and the relationship with mitochondrial function.The results showed that compared with the control group,the ROS level in the cadmium-treated group was significantly increased,and the mitochondrial oxidative activity was also significantly enhanced,indicating that cadmium exposure can lead to oxidative stress,and mitochondrial function will be enhanced response it in early embryos.3 Effects of cadmium on histone modification of mice early embryosDuring early embryonic development after fertilization,epigenetic modifications change violently to eliminate differences between parents and establish epigenetic information for progeny.In order to investigate whether cadmium can cause abnormal epigenetic modifications of early embryos,pregnant mice were free to drink cadmium-containing water(64 mg/L)for 2 days and collected the embryos in vivo.The immunofluorescence experiments were used to detected H3K4me2,H3K9me2,H4K8ac and H4K12ac level,histone deacetylase HDAC1 expression level was detected to reflect effects of cadmium on early embryo epigenetic modification.The results showed that the cadmium treatment lead to a significant reduction in the level of H4K8ac and H4K12ac in early embryos,but H3K4me2 and H3K9me2 levels were not significantly changed.Immunofluorescence results showed that HDAC1 protein co-localized with chromatin in mitotic division interphase,and cadmium treatment significantly increased the expression level of HDAC1.The results indicated that cadmium may reduce the histone acetylation level by up-regulating the expression of HDAC1,but cadmium has no significant effect on histone methylation levels.The abnormality of histone acetylation mediated by HDAC1 may be one of the reasons why cadmium can influence the development of early embryos.In summary,cadmium can interfere with the meiotic maturation process of oocytes,and damage early embryonic development by the abnormalities of ROS,mitochondrial function,DNA damage and histone acetylation modification.