“…Erythropoietin (Epo) is a glycoprotein hormone produced by the kidney and liver in the adult human which regulates red cell production (Fisher, 1993). Since the human, monkey, mouse and sheep Epo gene have all been cloned ( Jacobs et al, 1985;Lacombe et al, 1988b;Lin et al, 1985;McDonald et al, 1986;Shoemaker & Mitsock, 1986;Fu et al, 1993), cDNA probes for these species have been developed to localize Epo mRNA. Most previous studies involving the localization of Epo mRNA in the kidneys of mice and rats using in situ hybridization and/or transgenic technology have suggested that peritubular interstitial cells as the source of Epo (Bachmann et al, 1993;Koury et al, 1988Koury et al, , 1989Lacombe et al, 1988a;Schuster et al, 1992;Semenza et al, 1991a;Maxwell et al, 1993); however, two studies have reported that tubular epithelial cells are the source of Epo (Loya et al, 1994;Maxwell et al, 1990).…”