Figure 1. Decreased BCR-ABL–mediated (p190) colony transformation of both α-null and α/β-null progenitor B cells.

(A) Plating of p190-infected whole BM (5 × 10⁴ cells) from 3- to 6-week-old mice of the indicated genotypes, on M3630 (CFU–pre-B) medium. *P < 0.05 versus WT; ^#P < 0.01 versus β-null; ^†P < 0.001 versus β-null; 1-way ANOVA, n = 3–7 independent experiments; mean values ± SEM are shown. (B) Schematic flowchart depicting the clonogenic expansion and assessment of PI3K expression status in L-CFCs. CFU–pre-B colonies were scored at day 7 after infection, and single colonies were selected and transferred to liquid culture. Outgrowth of p190⁺ L-CFCs was then quantified (“expansion” was defined as reaching ≥1 × 10⁶ cells), followed by immunoblot assessment of Pik3r1 deletion and p55γ upregulation. Table 1 displays percentages of colonies meeting requirements for expansion, deletion of Pik3r1, and absence of p55γ upregulation. (C) monitoring class IA PI3K subunit expression in expanded L-CFCs. Representative immunoblot shows multiple clones of each genotype with variable loss of p85α and p55γ upregulation. p85α-specific antibody was used to distinguish p85α from p85β. White boxes represent clones that failed to delete p85α or upregulated p55γ. Black boxes represent clones that were used for in vitro and/or in vivo assays. (D) Immunoblot for class IA PI3K catalytic subunits in established L-CFCs. Representative blot for 3 independent clones.