Pivotal Runx1 target genes during pre-B-cell progression and ALL induction. (A) RNA was isolated from B-cell progenitors isolated using the FACS scheme depicted in Figure 1E. To confirm the development stage of the isolated cell compartments, Igll gene transcript levels (encoding λ5 sLCs) and Vκ-Jκ rearranged transcripts of the Igl-κ (encoding LCs) locus were determined by qualitative reverse transcriptase-polymerase chain reaction. Subsequently, the relative gene expression levels of Lck, Blk, and Hck were determined, using Hprt transcript levels as control. (B) Plotted are the gene expression data for IKZF3 and SPIB for BCP-ALL patient samples [hyperdiploid (HD; n = 40), t(1;19) (E2A/PBX1; n = 36), t(12;21) (ETV6/RUNX1; n = 58), and t(9;22) (BCR/ABL, n = 122)]⁵¹  evaluated by the Leukemia Gene Atlas (www.leukemia-gene-atlas.org). Statistical significance was calculated with the Welch’s t test; ***P < .001; *P < .05. (C) Schematic model of key transcription events regulated by Runx1 during pre-B-cell progression. Green arrows denote interactions leading to up-regulation of gene transcription by Runx1 or products of the indicated gene, whereas yellow lines denote interactions leading to transcription repression of the indicated genes. Gray arrow denotes a possible feedback mechanism in which the product of the indicated gene may alter Runx1 activity by phosphorylation (P). ETV6-RUNX1 expression would repress SPIB and IKZF3 transcription, thereby blocking pre-B-cell progression, an important event in leukemogenesis.