Methylation profile of bovine gene coding region in relation to three germ layers.

Previous studies have shown that octamer-binding transcription factor 4 (Oct4) plays a significant role in early embryonic development of mammalian animals, and different expression levels induce multi-lineage differentiation which are regulated by DNA methylation. To explore the relationship between the methylation pattern of gene exon 1 and embryonic development, in this work, five different tissues (heart, liver, lung, cerebrum and cerebellum) from three germ layers were chosen from low age (50-60 d) and advanced age (60-70 d) of fetal cattle and the differences between tissues or ages were analyzed, respectively. The result showed that the DNA methylation level of gene exon 1 was significant different (<0.01) between any two of three germ layers in low age (<60 d), but kept steady of advanced age (>0.05) (>60 d), suggesting that 60-d post coital was an important boundary for embryonic development. In addition, in ectoderm (cerebrum and cerebellum), there was no significant methylation difference of gene exon 1 between low age and advanced age (>0.05), but the result of endoderm (liver and lung) and mesoderm (heart) were on the contrary (<0.01), which indicated the development of ectoderm was earlier than endoderm and mesoderm. The methylation differences from the 3rd, 5th and 9th CpG-dinucleotide loci of gene exon 1 were significantly different between each two of three germ layers (<0.05), indicating that these three loci may have important influence on bovine embryonic development. This study showed that bovine germ layers differentiation was significantly related to the DNA methylation status of gene exon 1. This work firstly identified the DNA methylation profile of bovine gene exon 1 and its association with germ layers development in fetus and adult of cattle. Moreover, the work also provided epigenetic information for further studying bovine embryonic development and cellular reprogramming.