Renal EPO mRNA transcription and HIF-1 expression after hypoxia. (A) Photograph of 2% agarose gel stained for EPO transcript coamplified with 18S rRNA to control for RNA loading and efficiency of RT-PCR (top panel). Bottom panel of densitometry data for EPO gene expression after normalization to 18S rRNA shows attenuated response in KO mice. Values are expressed as mean ± SEM for 6 mice at each time point (*P < .05). (B) Effect of hypoxia on nuclear HIF-1α accumulation. Nuclear extracts of kidneys of Wt and KO mice after hypoxia were probed with antibody against HIF-1α. The blots were stripped and probed with antibody against HIF-1β. Data are representative of 4 animals at each time point. By densitometry, nuclear HIF-1α was significantly greater in Wt mice at 2 hours but not at 6 hours of hypoxia.