RNA editing has become a generic term for a wide array of post-transcriptional processes that change the mature RNA sequence relative to the corresponding encoding genomic DNA matrix. This phenomenon, which is almost limited to eukaryotes with some exceptions, is characterized by nucleotide insertion, deletion, or substitution in various types of RNAs including mRNAs, tRNAs, miRNAs, and rRNAs , and is likely to contribute to RNA diversity. Until recently, this mechanism was considered relatively rare in vertebrates, mainly restricted to brain-specific substrates and repetitive regions of the genome, and limited to extensively validated ADAR-mediated adenosine to inosine (A-to-I) substitutions and APOBEC-mediated cytosine to uracil (C-to-U) changes.