Growth retardation of APEX2-null mice. (A) No APEX2 protein was detected in the Apex2 KO mouse. Whole-cell extracts of thymocytes from wild-type (WT) and Apex2 KO mice were prepared. APEX2 protein in extracts was detected by Western blotting using anti-APEX2 antibody as indicated by an arrowhead. (B) Photograph of an F₆ 15-week-old APEX2-null male mouse (KO) and its wild-type littermate (WT). Body weights of the KO and WT mice were 19.9 g and 27.2 g, respectively. (C) Mean values ± standard deviation (SD) of body weights of male mice with each genotype at an age of 0 days (F₁₀ mice, 7 WT and 12 KO), 4 weeks (F₉ mice, 10 WT and 13 KO), and 2 years (F₃ mice, 12 WT and 7 KO) are shown. Open columns indicate WT; solid columns, KO mice. ^**P < .01. No asterisk indicates not statistically significant (P > .05). (D) Growth curves of APEX2-null males and their wild-type littermates. Each symbol tracks the growth of an individual mouse. Littermates with different genotypes are indicated with the same symbol. Open symbols indicate WT; closed symbols, KO mice.