Gene expression and DNA methylation status of chicken primordial germ cells

DNA methylation reprogramming of primordial germ cells (PGCs) in mammals establishes monoallelic expression of imprinting genes, maintains retrotransposons in an inactive state, inactivates one of the two X chromosomes, and suppresses gene expression. However, the roles of DNA methylation in chickens PGCs are unknown. In this study, we found a 1.5-fold or greater difference in the expression of 261 transcripts when comparing PGCs and chicken embryonic fibroblasts (CEFs) using an Affymetrix GeneChip Chicken Genome Array. In addition, we analyzed the methylation patterns of the regions ~5-kb upstream of 261 sorted genes, 51 of which were imprinting homologous loci and 49 of which were X-linked homologous loci in chicken using the MeDIP Array by Roche NimbleGen. Seven hypomethylated and five hypermethylated regions within the 5-kb upstream regions of 261 genes were found in PGCs when compared with CEFs. These differentially methylated regions were restrictively matched to differentially expressed genes in PGCs. We also detected 203 differentially methylated regions within imprinting and X-linked homologous regions between male PGCs and female PGCs. These differentially methylated regions may be directly or indirectly associated with gene expression during early embryonic development, and the epigenetic difference could be evolutionally conserved between mammals and birds.