The matter of which upstream signals regulate ARF expression has also been explored in T-ALL, and given the similarly high level of co-occurrence with NOTCH1 activating mutations, the possible relationship between ARF and NOTCH1 has been tested using null Arf Gfp/Gfp thymocytes transduced with the ICN1+-CFP form. The gene discussed is NOTCH1; the disease is acute lymphoblastic leukemia.