Second, loss of ASH1L in the MLL-AF9-transformed cells largely impaired the colony formation in vitro and delayed the leukemia development in the recipient mice transplanted with leukemic cells (Figures 2 and 3), suggesting ASH1L facilitates the maintenance of MLL-AF9-transformed cells in vitro and leukemia progression in vivo. The gene discussed is MLLT3; the disease is leukemia.