Characterization of Tg LT-HSCs conditionally expressing MLL-ENL. (A) Schematic representation of human MLL-ENL (MLL: thick; ENL: thin) transcript and the corresponding region of the endogenous transcript of mouse Mll. Mll and the total MLL-ENL/Mll transcripts were analyzed by QRT-PCR using common primers (horizontal arrows) with either Mll- or MLL/Mll-TaqMan probes. (B-C) Expression level of Mll (B) and relative ratio of total MLL(-ENL)/Mll to Mll transcripts (C), quantified by QRT-PCR. Tg LT-HSCs (CD34[⁻]), ST-HSCs (CD34[⁺]), and MPs retrovirally transduced with mock or CreER were harvested at the first replating in myeloid immortalization assays. (D) Expression levels of Hoxa9, Meis1, Evi1, and MLL-ENL by QRT-PCR in the immortalization assays. Tg LT-HSCs (CD34[⁻]) and ST-HSCs (CD34[⁺]) retrovirally transduced with CreER were harvested at the end of each round, and the first round, of plating, respectively. (E-F) Colony replating assays of subpopulations in the immortalized cells constituting colonies of CreER-transduced Tg LT-HSCs after the third round of plating, sorted on the basis of the immunophenotype (E). (G) Immunophenotype of the cells derived from the c-Kit⁺Sca-1⁺Gr-1^– subpopulation of the immortalized Tg cells, harvested at the first replating. The bar graphs show the mean ± SD of 3 independent experiments.