The erythropoietin gene is expressed strongly in the mammalian mesonephric kidney.

In the ovine fetus at 41 days of gestation (term is 150 days), there are two sets of kidneys, mesonephrol and metanephrol. We have examined the expression of the erythropoietin (Epo) gene in both types of kidneys by competitive reverse transcriptase-polymerase chain reaction and hybridization histochemistry and compared the expression to that of the 60-day fetal metanephros. At 41 days, the Epo gene was expressed in both mesonephros and metanephros, as well as in the fetal liver. The cells expressing the Epo gene in the mesonephros were interstitial cells in the vicinity of the proximal tubules.