Although it is possible to examine CTCF mutations in cancer cells to determinetheir functional outcome, this setting is not ideal because the latter have many othergenetic and epigenetic alterations that would confound a clean analysis of their impact.To circumvent these issues, we made use of a small-molecule auxin inducible degron (AID)mouse ESC (mESC) system 4,8. The gene discussed is AICDA; the disease is cancer.