Genetic and epigenetic regulation of major histocompatibility complex class I gene expression in bovine trophoblast cells

Problem The regulatory mechanisms governing differential expression of classical major histocompatibility complex ( MHC ) class I ( MHC ‐Ia ) and non‐classical MHC class I ( MHC ‐Ib ) genes are poorly understood. Method of study Quantitative reverse transcription‐ polymerase chain reaction ( PCR ) was used to compare the abundance of MHC ‐I transcripts and related transcription factors in peripheral blood mononuclear cells ( PBMC ) and placental trophoblast cells ( PTC ). Methylation of MHC ‐I CpG islands was detected by bisulfite treatment and next‐generation sequencing. Demethylation of PBMC and PTC with 5′‐aza‐deoxycytidine was used to assess the role of methylation in gene regulation. Results MHC ‐I expression was higher in PBMC than PTC and was correlated with expression of IRF 1 , class II MHC transactivator ( CIITA ), and STAT 1 . The MHC ‐Ia genes and Bo LA ‐ NC 1 were devoid of CpG methylation in PBMC and PTC . In contrast, CpG sites in the gene body of Bo LA ‐ NC 2 , ‐ NC 3, and ‐ NC 4 were highly methylated in PBMC but largely unmethylated in normal PTC and moderately methylated in somatic cell nuclear transfer PTC . In PBMC , demethylation resulted in upregulation of MHC ‐Ib by 2.8‐ to 6‐fold, whereas MHC ‐Ia transcripts were elevated less than 2‐fold. Conclusion DNA methylation regulates bovine MHC ‐Ib expression and is likely responsible for the different relative levels of MHC ‐Ib to MHC ‐Ia transcripts in PBMC and PTC .