Effect of prenatal transportation stress on DNA methylation in Brahman heifers

Abstract

Prenatal stress in beef cattle has the potential to result in unexpected, long-term phenotypic changes to an animal's performance. One possible explanation for this phenomenon is stress-induced epigenetic alterations of the genome (e.g., methylation or histone modifications). The objective of this experiment was to identify differential DNA methylation patterns in prenatally stressed (PNS) Brahman females compared to control animals. Pregnant Brahman cows (n = 48) were transported for 2-h periods at 60 ± 5, 80 ± 5, 100 ± 5, 120 ± 5, and 140 ± 5 d. A non-transported group (n = 48) was maintained as a control (Control). Methylation of leukocyte DNA from 28-d old heifer calves born following the PNS exposure (Control n = 8, PNS n = 6) was assessed by reduced representation sodium bisulfite sequencing. Mean methylation ratios at locations across the genome in PNS and Control females were compared using Fisher's Exact t-tests. There were 16,377 CG sites, 309 CHG, and 612 CHH (C= cytosine; G= guanine; H = adenine, cytosine or thymine) sites that were differentially methylated in PNS females compared to the Control (P ≤ 0.05). Differentially methylated regions located in promoters of genes were analyzed to identify genetic pathways and biological functions potentially influenced by the alterations. Important pathways (P ≤ 0.05) included those involved in cell signaling, neurological development, cellular development, immune response, and metabolism. Alterations in expression of genes in pathways such as the “Axonal Guidance Signaling”, “Corticotrophin Releasing Hormone Signaling” and the Neurotrophin/TRK Signaling” pathways could change animal phenotypes.