Cul4A deletion is lethal. (A) Mutant (■) and controls (□) were induced with pIpC (n = 7 and n = 4, respectively) and monitored daily. Results from 3 independent experiments were combined. Percentage of the total surviving is graphed versus days after the initiation of induction. (B) Mutant and control mice were induced with pIpC. Four days after induction, sections from spleen, tibia for bone marrow, and duodenum were prepared. For each tissue, mutant and control images are shown at the same magnification. An Olympus BX41 microscope (Center Valley, PA) with Plan N 4×/0.10, Plan 10×/0.25, and Plan N 20×/0.40 objectives were used. Images were captured with a SPOT Insight 2MP Firewire Color Mosaic camera (Diagnostic Instruments, Sterling Heights, MI) and Spot Imaging software. Student t test was used for all statistical analyses. Mean and standard error of the mean are reported. Cul4A^flox/flox without Mx-Cre mice were controls in all experiments. In addition, wild-type mice with Mx-Cre were also controls for experiments for Figures 2–3 and Table 1 (N.J., unpublished results, April-May 2006). For these experiments, following pIpC induction, viability, changes in peripheral blood counts, and bone marrow total cellularity were the same in both control strains, and bone marrow progenitor frequency was slightly higher in wild-type Mx-Cre mice, indicating that Cre expression alone does not contribute to the lethality and hematopoietic failure resulting from Cul4Adeletion.