Fig. 4.
The homeobox gene Six1 is essential for the development of MLL-AF9-driven AML but not normal adult hematopoiesis. (a) Experimental approach for evaluating the role of SIX1 in normal hematopoiesis of adult mice. (b) Tmx induction results in excision of the Six1 locus. Genomic DNA was extracted from whole blood of mice induced with Tmx or Veh for 8 wks. (c-k) Loss of Six1 does not affect mouse normal adult hematopoiesis as measured using contents of RBC (c), WBC (d) and platelets (e) from whole blood; and percentage of BM cells that are LT-HSC (f), LSK (g), GMP (h), MEP (i), CMP (j) and CLP (k) at week 8 after Tmx induction. n = 4 per group. (l) Experimental approach for evaluating the role of SIX1 in MLL-AF9-dependent leukemogenesis. (m) Significant reduction of Six1 mRNA levels and CFU counts were observed in Tmx-exposed MLL-AF9-transformed Six1-fl/fl;Scl-creERT LICs compared to WT controls. n = 3 per group. (n) Six1 null LICs proliferate more slowly compared to WT control cells. BrdU incorporation was used for the measurement of proliferation at the indicated time points. n = 3 per group. (o) Six1 null AML mice exhibit decreased LICs in total YFP+ leukemic cells of BM than WT controls. n = 4 per group. (p) Abundance of circulating YFP+ leukemic cells is decreased in mice transplanted with Six1 null LICs (n = 8) compared to WT controls (n = 6). (q) Loss of Six1 in LICs (n = 8) slows disease progression in animals engrafted with AML LICs as compared with WT controls (n = 6). Log-Rank test is used for statistical analysis. In c-k and m-p, data is expressed as mean ± S.D. Error bars represent indicated numbers of biological replicates. ** P < .01. * P < .05. ns: not significant. [Student's t-test].