TET1 and cancer: CRISPR-based demethylation editors subsequently emerged that involved protein fusions with dCas9 and the catalytic domain of TET1 (TET1CD), and these dCas9-TET1 systems both demethylated target DNA and activated gene expression in cancer cell lines, mouse embryonic stem cells, mouse cortical neurons, and in vivo in mice [272,282–284].