Exposure of pregnant mice to chlorpyrifos-methyl alters embryonic H19 gene methylation patterns.

The aim of this study was to identify whether chlorpyrifos methyl (CPM) exposure during pregnancy leads to changes in the methylation patterns of H19 gene. CPM 4, 20, 100 mg/kg bw/day was administered to 4 pregnant mice per group between 7 and 12 days post coitum (d.p.c.). Pregnant mice were killed at 13 d.p.c. The genomic methylation in primordial germ cells (PGCs) and fetal organs (the liver, intestine, and placenta) was examined. Four polymorphism sites in the H19 alleles of maternal (C57BL/6J) and paternal (CAST/Ei) alleles were identified at nucleotide position 1407, 1485, 1566, and 1654. The methylation patterns of 17 CpG sites were analyzed. The methylation level in male and female PGCs was not altered by CPM treatment in the maternal allele H19. The methylation level of the paternal H19 allele was altered in only male PGCs in response to the CPM treatment. The methylation level at a binding site for the transcriptional regulator CTCF2 was higher than that at the CTCF1 binding site in all CPM-treated groups. In the placenta, the aggregate methylation level of H19 was 56.89%in control group. But, those levels were ranged from 47.7% to 49.89% after treatment with increasing doses of CPM. H19 gene from the liver and intestine of 13 d.p.c. fetuses treated with CPM was hypomethylated as compared with controls, although H19 mRNA expression was unaltered. In the placenta, H19 expression was slightly increased in the CPM-treated group, although not significantly. IGF2 expression levels were not significantly changed in the placenta. In conclusion, CPM exposure during pregnancy alters the methylation status of the H19 gene in PGCs and embryonic tissues. We infer that these alterations are likely related to changes in DNA demethylase activity.