Anemia of EPAS1^–/– mice accompanied by depressed erythropoietin mRNA levels. (A) Hematocrit levels for EPAS1^+/+ (□) or EPAS1^–/– (▪) mice (n = 11 per genotype). Statistically meaningful difference in means between the hematocrits of EPAS1^+/+ and EPAS1^–/– mice is indicated with an asterisk (1-tailed t test with P < .001). (B) Kidney weight–to–body weight ratios (KW/BW) for EPAS1^+/+ (□) or EPAS1^–/– (▪) mice (n = 7 per genotype). Statistically meaningful difference between the KW/BW of EPAS1^+/+ and EPAS1^–/– mice is indicated with an asterisk (1-tailed t test with P < .005). (C) Real-time RT-PCR quantification of erythropoietin (Epo) mRNA levels in EPAS1^+/+ (□) or EPAS1^–/– (▪) kidney for mice maintained at room air (RA) or after exposure to short-term intermittent hypoxia (STIH) (n = 4 per genotype per treatment group). Statistically meaningful differences in means between the erythropoietin mRNA levels of EPAS1^+/+ and EPAS1^–/– mice maintained at RA (1-tailed t test with P < .001) or after STIH exposure (1-tailed t test with P < .001) are indicated with an asterisk. Values are expressed as the mean plus or minus standard error of the mean.