Transgenic mice carrying the erythropoietin gene promoter linked to lacZ express the reporter in proximal convoluted tubule cells after hypoxia

Results on the localization of erythropoietin (Epo) synthesis in renal cells have been contradictory, implicating either interstitial or tubular cells. We fused the lacZ gene to a 7-kb DNA fragment of the mouse Epo gene encompassing a portion of the first intron, the first exon, and a 6-kb sequence of the 5'-flanking region. Transgenic mice carrying this construct show a low level of specific expression of the lacZ gene in proximal convoluted tubule (PCT) cells. Without hypoxia, no significant expression was detected in the liver. Hypoxia induced a large degree of lacZ expression, mainly in kidney PCT cells and to a lesser degree in liver. However, anemia induced lacZ expression in both kidney and liver. These findings indicate that, under these conditions, Epo is expressed in tubular cells, specifically PCT cells.