Current technological advances in mapping new DNA modifications

The recent discovery of Tet (Ten eleven translocation) family of enzymes implicated in the chemical conversion of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxycytosine (5caC) has significantly enlarged the repertoire of known modifications present in the genomic DNA of higher eukaryotes. Considered as new epigenetic marks but also as DNA demethylation intermediates, intense research efforts have been directed towards deciphering of the biological function of Tet-driven DNA modifications. However, their low abundance in the mammalian genome, the relative similarity between their chemical structures and the predicted transient nature of 5fC and 5caC in genomic DNA make these modified DNA bases extremely challenging to study. The following review summarizes the techniques developed recently to quantify, profile and map 5hmC, 5fC and 5caC in a genomic context .