TAL1 and leukemia: However, knock-down of Bmi1 (non-candidate control gene) did not alter the colony forming ability of Reg1Δ/Δ CD34− HSCs, suggesting that aberrant proliferation of these CD34− HSCs is induced by excessive expression of Gata2 and Tal1. In addition, we investigated the effect of shRNA-induced knockdown of Gata2 and Tal1 for leukemia development in vivo.