Effect of neuronal induction on NSE, Tau, and Oct4 promoter methylation in bone marrow mesenchymal stem cells.

Cell differentiation involves widespread epigenetic reprogramming, including modulation of DNA methylation patterns. The differentiation potential differences in DNA methylation patterns might function in pluripotency restriction, while tissue-specific differences might work in lineage restriction. To investigate the effects of neuronal induction on promoter methylation pattern in rat bone marrow mesenchymal stem cells (MSCs), we used bisulfite sequencing to analyze the methylation status of the promoter regions in neuron-specific enolase (NSE), microtubule-associated protein Tau, and Oct4 genes in MSCs pre- and post-chemical induction. Neurocytes from the newborn rat brains were used as control. Data showed that NSE and Tau were abundantly expressed in the brain cells and MSC-derived neurocyte-like cells as well but not in the MSCs. However, both NSE promoter (-214~+57 bp) and Tau promoter (-239~+131 bp) were hypomethylated (<4 % CpG methylation). Oct4 was expressed in MSCs, and the Oct4 promoter (-293~-85 bp) was hypermethylated (>79 % CpG methylation). Interestingly, it was found that the methylation of the locus -113 bp upstream of Oct4 transcription start site was specifically enhanced in the process of MSCs' neuronal differentiation. Further experiments in hepatocytes derived from MSCs and hepar tissue proved that the -113 bp locus methylation increased also in non-neurogenic lineages. Tfsitescan prediction showed that AP-2-alpha/gamma and Sp1 might regulate Oct4 transcription upon MSC differentiation by binding the -113 bp locus. So, we conclude that promoter methylation modifies pluripotency-specific gene, rather than regulates the expression of neural-specific genes when MSCs differentiate into neurocyte-like cells.