COP1 cooperates with Trib1 to induce ACL. Mice were transplanted with BM cells infected with retroviral vectors containing MigR1 (GFP⁺) control, COP1 (GFP⁺), CSmut (GFP⁺), and Trib1 and examined several months after BMT. (A) Myeloid leukemia-free survival curves of transplanted mice. Results are derived from 3 independent transfer experiments. The P value between Trib1 and COP1/Trib1 mice was calculated with log-rank test. P < .05. (B) May-Grunwald Giemsa–stained peripheral blood (PB) smears and cytospins of BM cells. (C) The counts of leukocytes (WBC) and hemoglobin (HGB). (D) Spleen weights of individual mice. Data presented in C and D are averages of 5 independent experiments shown as means ± SD. (E) Fluorescence-activated cell sorter analysis of BM and spleen cells for immature (Mac-1⁺Gr-1^lo) and differentiated (Mac-1⁺Gr-1^hi) granulocytes. The population of GFP-positive cells in BM and spleen is shown in the upper panels. (F) Total RNA extracted from GFP-positive BM cells was analyzed by quantitative RT-PCR using a pair of primers specific to COP1, Trib1, and GAPDH.