Induced Pluripotent Stem Cells: Generation Strategy and Epigenetic Mystery behind Reprogramming

Figure 1

Base methylation at DNA levels. Cytosine (C) is methylated to methylcytosine (5-mC) by methyltransferases (DNMTs), and the 5-mC is oxidized or hydroxylated by ten-eleven translocation proteins (TETs) to 5-hydroxymethylcytosine (5-hmC). And the 5-hmC is believed to be mediator for demethylation 5-mC to C through serial steps: 5-mC is further oxidized by TETs to generate 5-formal C (5-fC) and 5-carboxy-C (5-caC), and finally 5-fC and 5-caC are converted to regular C catalyzed by thymidine DNA glycosylase (TDG). Methylation of adenosine at 6 position (6mA) has been also detected in the genomes of mammalian, Chlamydomonas, Drosophila, and C. elegance cells. TETs or TET analogues are responsible for generation of the 6mA.