Maternal behavior could either inhibit de novo methylation or stimulate demethylation. To address this question, we67 performed a simple developmental study of the methylation pattern of GR exon 17 promoter from embryonic day 20 to day 90 (a fully, sexually mature adult rat). High- and low-LG mothers differ in the frequency of pup LG only during the first week of life. Importantly, this period corresponds to the appearance of the difference in DNA methylation in the offspring in studies using NaBis mapping to precisely map the methylation status of the cytosines within the exon 17 GR promoter over multiple developmental time points. This analysis demonstrates that just 1 day before birth, on embryonic day 20, the entire exon 17 region is completely unmethylated in both groups. Strikingly, 1 day following birth (postnatal day 1) the exon 17 GR promoter is de novo methylated in both groups. The 5' and 3' CpG sites of the exon 17 GR NGFIA response element in the offspring of both high- and low-LG mothers, which exhibit differential methylation later in life, are de novo methylated
