Development of B-ALL–like disease in the absence of Bcl-xL. (A) Macroscopic phenotype of Bcl-x–deficient B-ALL mouse 17 days after induction. Enlarged lymph nodes are denoted by black arrows and spleen by the yellow arrow. (B) Top panel: lymphoblasts from diseased mice are B220^dim. Bone marrow cells were isolated from wild-type (purple), B-ALL (green), and Bcl-x–deficient B-ALL (red) and stained for expression of B220. Bottom panels: lymphoblasts from Bcl-x–deficient B-ALL mice are arrested at a pre–B-cell stage of development. Bone marrow cells stained for coexpression of B220 and CD19, CD43, and BP-1. (C) Wright-Giemsa staining of peripheral blood (PB; top panel) 14 days after induction and lymph node (LN) cells (bottom panel). Mitotic figures are denoted by black arrows. (D) DNA isolated from tissues of tissues from Bcl-x–deficient B-ALL mice was subjected to 3-primer PCR to determine efficiency of recombination of Bcl-x f/f alleles. DNA was isolated from bone marrow (BM; lanes 1 and 2), lymph node (LN; lanes 3 and 4), pleural effusion (PE; lanes 5 and 6), and spleen (SPL; lanes 7 and 8). Arrows indicate floxed and recombined alleles. Lane 9 represents no recombination. Vertical bars indicate repositioned lanes. (E) Result of Western blot analysis from pleural effusion of B-ALL (lanes 1-3) and Bcl-x–deficient B-ALL (lanes 4-6) mice. Lysates were immunoblotted against c-abl– (loading control, also recognizes BCR/ABL oncoproteins), Bcl-x–, and actin-specific antibodies.