Ontogeny of erythropoietin receptor mRNA expression in various tissues of the foetal and the neonatal pig

Erythropoietin receptor (EPOR) mRNA expression in liver, spleen, bone marrow and testes of foetal and neonatal pigs was analysed using a real-time RT-PCR assay. The results showed that early in the foetal life, EPOR expression is greatest in the liver. Later in foetal life, the spleen has the greatest expression of EPOR, whereas at 2 weeks after birth, the main expression of EPOR is found in the bone marrow. These findings contradict our earlier hypothesis that erythropoietin (EPO) acting in a paracrine fashion can account for an extensive erythropoiesis at birth, a point of time when plasma EPO concentrations are low. Results presented in the present paper suggest that the spleen or, alternatively, the bone marrow is able to respond to very low concentrations of circulating EPO around the time of birth. The testes were found to express significant amounts of EPOR. Since EPO mRNA has previously been found in the testes, a paracrine function of EPO may exist in this organ.