Previously, we generated a knock-in mouse model of ETV6-RUNX1 ALL, in which expression of the fusion gene is driven from the endogenous Etv6 promoter, and is linked to expression of the Sleeping Beauty (SB) transposase allowing the identification of transposon gene mutations that co-operate with Etv6-RUNX1 in leukemia development [7]. The gene discussed is RUNX1; the disease is acute lymphoblastic leukemia.