P3Pro-Cre–mediated inactivation of Hif-2α results in severe Epo-deficient anemia. (A) Shown are RBC and Hct values in 2- to 5-month-old P3Pro mutant mice (n = 26) compared with wild-type (Wt) littermate controls of the same age (n = 21). Diamonds represent control mice, P3Pro mutants are depicted by squares. (B) Serum Epo levels in 2-month-old mutants (n = 6) compared with Wt littermates (n = 5). (C) Relative Epo mRNA levels in kidneys from mutant and control animals (n = 9) as determined by real-time PCR analysis. (D) P3Pro mutant kidneys are hypoxic. (Top) Western blot analysis of Hif-1α in kidney extracts from mutant and Wt mice. Nuclear protein extracts from the liver of a Vhlh-deficient mouse were used as positive control (+co). Ponceau S staining is shown to demonstrate equal protein loading. (Bottom) mRNA levels of HIF target gene Phd3 in kidney (n = 6). Wt refers to Cre-negative littermates. Bars represent mean values ± SEMs; **P < .01, ***P < .001.