Chemoselective labeling and site-specific mapping of 5-formylcytosine as a cellular nucleic acid modification.

DNA methylation has a profound impact on the regulation of gene expression in normal cell development, and aberrant methylation has been recognized as a key factor in the pathogenesis of human diseases such as cancer. The discovery of modified nucleobases arising from 5-methylcytosine (5mC) through consecutive oxidation to give 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) has stimulated intense research efforts regarding the biological functions of these epigenetic marks. This Review focuses on the sensitive detection and quantitation of 5fC in DNA and RNA by chemoselective labeling, which aims at discriminating between 5fC and its thymine counterpart 5-formyluracil (5fU), and summarizes single-base resolution sequencing methods for locus-specific mapping of 5mC and its oxidized derivatives.