Placental expression of erythropoietin mRNA, protein and receptor in sheep

In ovine placentae at 100 days gestation, we localized the expression of er ythropoietin (EPO) mRNA by in situ hybridization and determined the cellula r localization of EPO protein and EPO receptor protein by fluorescence immu nohistochemistry. Erythropoietin mRNA was observed in maternal tissue at th e apical tips of the fetal cytotrophoblastic villi at their interface with the maternal caruncle and was absent from both the centrally located fetal- maternal tissue and the more peripherally located maternal caruncle. An EPO -protein-associated fluorescent signal was observed in the same interface r egion as the EPO mRNA hybridization signal. An intense fluorescent signal a ssociated with EPO receptor protein was observed in the epical fetal-matern al interface region with a lower density signal dispersed throughout the re mainder of the interdigitating fetal-maternal tissue. The predominant cells in the apical fetal-maternal interface were identified as binucleate cells by immunohistochemistry. Thus the localization of the binucleate cells was the same as that for the EPO mRNA and the EPO protein, whereas the EPO rec eptor had a more generalized distribution. Since the binucleate cells are h ormone producing cells, we speculate that the binucleate cells are the sour ce of the EPO that is present in ovine placenta. (C) 2001 Harcourt Publishe rs Ltd.