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. Author manuscript; available in PMC: 2013 Jan 25.
Published in final edited form as: Methods Enzymol. 2012;512:93–105. doi: 10.1016/B978-0-12-391940-3.00005-6

Figure 5.1.

Figure 5.1

Proposed models of Tet-initiated DNA demethylation pathways. DNA methylation (5mC) is established and maintained by DNA methyltransferases (Dnmt). In mammals, 5mC can be oxidized by the Tet proteins to generate 5hmC, 5fC, and 5caC. These 5mC derivatives, specifically 5fC and 5caC, can be actively removed through base excision repair initiated by the glycosylase TDG or can be passively removed through replication-dependent dilution during preimplantation development. 5hmC may also be deaminated by AID/APOBEC into 5hmU, which can be removed by TDG or SMUG1. In addition, a putative decarboxylase may directly convert 5caC to C.