The DNA methylation system can be affected by exposure to high doses of organochlorine pesticides, methylmercury chloride or polychlorinated

biphenyls. Zama et Uzumcu reported an alterated methylation pattern in livers collected from rats treated in utero and postnatally with these chemicals. Pyrosequencing methylation analysis revealed that the high-dose groups generally decreased the methylation of CpG sites in the promoter of the tumor suppressor gene p16(INK4a) Target Selective Inhibitor Library cell assay (Desaulniers et al., 2009). Some pesticides belong to the environmental endocrine disruptors (EDs) family, synthetic chemicals that resemble natural hormones and are known to cause epigenetic perturbations (McLachlan et al., 2006). Among them methoxychlor (MXC), an organochlorine insecticide, has been reported to affect the male reproductive system (Stouder and Paoloni-Giacobino, 2011). Gestational exposure to MXC disrupts the female offspring reproductive system in adulthood, re-programming the expression of a suite of hypothalamic genes that control reproductive function. Rats treated with MXC had a different methylation pattern of two paternally imprinted (H19 and Meg3 (Gtl2)) and three maternally imprinted (Mest (Peg1), Snrpn, and Peg3)

genes (Stouder and Paoloni-Giacobino, 2011). Previous studies showed that fetal/neonatal exposure to MXC caused adult ovarian dysfunction due to altered expression of mTOR inhibitor key ovarian genes including Edoxaban estrogen receptor (ER)-beta, which was down-regulated, whereas ER-alpha was unaffected (Zama and Uzumcu, 2009). Thus, early life exposure to endocrine disruptors has

lifelong effects on neuroendocrine gene expression and DNA methylation, together with causing the reproductive dysfunctions. The research conducted by Stouder and Paoloni-Giacobino (2011) evaluates the possible deleterious effects of MXC on imprinted genes. MXC treatment of pregnant mice altered the methylation pattern of all the imprinted genes tested. MXC effects were transgenerational but disappeared gradually from F1 to F3. MXC did not affect imprinting in the somatic cells, suggesting that its effects are restricted to gamete development. Further investigations must be carried out in order to understand if other epigenetic modifications can explain the transgenerational effects of MXC (Stouder and Paoloni-Giacobino, 2011). Another chemical belonging to the EDs family is vinclozolin, a dicarboximide fungicides, which has been implicated in causing imprinting alterations in mouse embryos (Kang et al., 2011). To screen for possible epigenetic perturbations caused by EDs at imprinted loci, Kang et al. treated pregnant mice with di-(2-ethylhexyl)-phthalate (DEHP), bisphenol A (BPA), vinclozolin (VZ), or control oil vehicle. After isolating RNA from the placenta, yolk sac, amnion, head, body, heart, liver, lung, stomach, and intestines of embryos they measured the allele-specific expression of 38 imprinted transcripts.