Cul4A deletion leads to an increase in cells with DNA damage. Mutant mice (■) and controls (□) were induced and bone marrow LDMNCs were harvested and cultured in vitro as described for Figure 4. At 2 to 4 days after induction, cells were collected and analyzed for DNA damage by comet assay. The asterisk denotes a statistically significant difference (P = .01). A representative result of 3 independent experiments is shown. Inset images are of representative cells with ethidium bromide–stained DNA; a cell exhibiting no DNA damage (left) and one with damaged DNA (right).