Examination of the testes of Pole4-deficient neonatal mice revealed a marked reduction in the number of promyelocytic leukemia zinc-finger (PLZF)-positive cells per tubules compared to controls (6.8 ± 2.2 versus 4.1 ± 1.9), suggesting that the subfertility of Pole4 mutant is likely due to germ cell attrition (Figure 1E, bottom). This evidence concerns the gene POLE4 and leukemia.