Prenatal transportation stress alters genome-wide DNA methylation in suckling Brahman bull calves1,2

The objective of this experiment was to identify genome-wide differential methylation of DNA in young prenatally stressed (PNS) bull calves. Mature Brahman cows (n = 48) were transported for 2-h periods at 60 ± 5, 80 ± 5, 100 ± 5, 120 ± 5, and 140 ± 5 d of gestation or maintained as nontransported Controls (n = 48). Methylation of DNA from white blood cells from a subset of 28-d-old intact male offspring (n = 7 PNS; n = 7 Control) was assessed via reduced representation bisulfite sequencing. Samples from PNS bulls contained 16,128 CG, 226 CHG, and 391 CHH (C = cytosine; G = guanine; H = either adenine, thymine, or cytosine) sites that were differentially methylated compared to samples from Controls. Of the CG sites, 7,407 were hypermethylated (at least 10% more methylated than Controls; P ≤ 0.05) and 8,721 were hypomethylated (at least 10% less methylated than Controls; P ≤ 0.05). Increased DNA methylation in gene promoter regions typically results in decreased transcriptional activity of the region. Therefore, differentially methylated CG sites located within promoter regions (n = 1,205) were used to predict (using Ingenuity Pathway Analysis software) alterations to canonical pathways in PNS compared with Control bull calves. In PNS bull calves, 113 pathways were altered (P ≤ 0.05) compared to Controls. Among these were pathways related to behavior, stress response, metabolism, immune function, and cell signaling. Genome-wide differential DNA methylation and predicted alterations to pathways in PNS compared with Control bull calves suggest epigenetic programming of biological systems in utero.