Generate paraffin-embedded section of wild-type CD1 mouse embryos and adult brain tissues as described previously25. Use brain tissue sections fixed with either 4% formaldehyde (FA) or 4% paraformaldehyde (PFA) for immunostaining method25. NOTE: The use of paraffin embedded tissue sections requires de-waxing prior to antibody labelling. Since the treatment with 2 - 4 M hydrochloric acid (HCl) employed in the protocol for DNA denaturing is not compatible with most antigen retrieval strategies, we recommend the use of either cryo- or microtome sections for co-detection of 5mC oxidation derivatives with protein markers.