Partially impaired transformation of B-cell progenitors from Pik3r1 null fetal liver by BCR-ABL but not v-ABL. Wild-type (WT) and Pik3r1 null (KO) fetal liver cells were infected with Ab-MuLV or pMIG-p190-BCR-ABL. Transformation by v-ABL (A) and BCR-ABL (B) was measured by counting colonies formed in soft agar or methylcellulose. Open symbols are from a single transformation assay done in cells from a mixed genetic background (129SvEv × C57BL6) at embryonic day 16.5, whereas the closed symbols were from 3 independent assays done in cells from a Balb/c background at E18.5. Horizontal bars depict averages: v-ABL WT, 67; v-ABL KO, 40; BCR-ABL WT, 20; and BCR-ABL KO, 8. Data analyzed by paired t test revealed no difference between v-ABL WT and KO (P = .46) but showed a significant decrease in transformation of KO by p190-BCR-ABL (P = .037).